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Report No. 237

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EFFECTS OF AGRICULTURAL WATER TABLE MANAGEMENT

ON DRAINAGE HATER QUALITY

R. 0. Evans* J. W. Gilliam** R, W. Skaggs*

Department o f Biological and Agricultural Engineering* and

Department o f Soil Science** College o f Agriculture and Life Sciences 4 North Carolina State University

March 7989

Water Resources Research lnslilule OF THE UNIVERSITY OF NORTH CAROLINA

UNC-WRRI-89-237

EFFECTS OF AGRICULTURAL WATER TABLE MANAGEMENT

ON DRAINAGE WATER QUALITY

by

* R. 0 . Evans J. W. Gi1lia"ls-k B. W. Skaggs*

* Department of Biological and Agricultural Engineering

and

Department of S o i l Science .k.k

College of Agriculture and Life Sciences North Carolina State University Raleigh, North Carolina 27695

The work on which this publication is based was supported in part by funds provided by The University of North Carolina Water Resources Research Institute. Additional support was provided by the North Carolina Agricultural Research Service and the North Carolina Agricultural Extension Service. were established with cost-share funds provided by the Resource Conservation Act, 1977 and administered by the Soil Conservation Service.

The water table management study sites

WRRT Project No. 70056/70081

ABSTRACT

The influence of controlled drainage, subirrigation and conventional drainage on drainage water quality was investigated at five field locations. Drainage simulations using the water management simulation model, DRAINMOD, were also used to evaluate water management alternatives that were not implemented at each site for field evaluation.

Drainage control was effective in reducing drainage outflow and the potential transport of nutrients to receiving surface waters. reduced drainage outflow at the field edge by approximately 40 percent as compared to conventional drainage practices. affected by the type of drainage system (surface vs subsurface drainage), although total outflow was slightly higher (2-5 percent) for good subsurface drainage as compared to surface drainage alternatives.

The control structures

The reduction in outflow was not

Drainage control had very little influence on nutrient concentrations in drainage outflow. Nitrate concentrations at the field edge tended to be slightly higher and TKN and TP concentrations slightly lower for good subsurface drainage compared to surface drainage alternatives. nitrate concentrations was observed among sites, but this also appeared to be related to the relative intensity of subsurface drainage present. concentrations increased as the saturated hydraulic conductivity increased. (Hydraulic conductivity is generally a good indication of the potential for subsurface drainage.)

Variation in

Nitrate

The dominant factor influencing total nutrient transport was the &mount that drainage outflow was reduced by controlled drainage practices. in nutrient transport was nearly outflow.

The reduction proportional to the reduction in drainage

There was no evidence that the reduction in drainage outflow contributed to an increase in nitrate transport to groundwater. Nitrate concentrations in shallow groundwater wells showed no response to different water table management strategies. water table dropped below 2 meters, nitrate concentrations increased to approximately 1 mg/L at the 3 to 4 meter depth. all water table management treatments. During periods when the water table was less than 2 meters deep, nitrate concentrations at the 3 to 4 meter depth were typically less than 0.3 mg/L. Reduction in nitrate/chloride ratios in time and with depth suggested that nitrates were reduced by denitrification upon reaching the saturated zone. Phosphorus concentrations in groundwater wells were nearly always less than 0.02 mg/L.

During the very dry summer and fall periods when the

This increase was observed on

From the results of this study, the total impact of drainage control on receiving streams is difficult to quantify. Clearly, water table management alternatives that reduce drainage outflow, also reduce total nutrient transport at the field edge as was determined in this study. Controlled drainage reduced the annual transport of tota'l nitrogen (NO3 and nW) by 7 kg/ha (46.5 % ) and total phosphorus by 0.19 kg/ha ( 4 4 a ) . hectares of cropland in North Carolina are artificially drained, this represents a potential reduction at the field's edge of nearly 7,000 metric tons N and 190 metric tons P annually. estuaries if all improved drainage systems used controlled drainage would be less than observed at the field edge in this study but still significant.

Considering that nearly 1 million

The reduction of N and P to streams and

ii

TABLE OF CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . X

SLi?.IMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii .

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

EXPERIMENTAL METHODS . . . . . . . . . . . . . . . . . . . . . . . . . 4

RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . 13

Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 Drainage and Runoff . . . . . . . . . . . . . . . . . . . . . . . 14

Seepage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Nutrient Concentrations in Shallow Groundwater Wells . . . . . . . 40

Nutrient Concentrations . . . . . . . . . . . . . . . . . . . . . 35

Water Table Management Simulations . . . . . . . . . . . . . . . . 45 Nutrient Transport . . . . . . . . . . . . . . . . . . . . . . . . 53 Vater Conservation . . . . . . . . . . . . . . . . . . . . . . . . 57

REFERENCES . 58

APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

A . Soil Properties and Site Descriptions . . . . . . . . . . . . 60 B . Daily Rainfall . . . . . . . . . . . . . . . . . . . . . . . . 7 5

C . Field Measured Water Table Depths . . . . . . . . . . . . . . 79

D . Nitrate and Nitrate/Chloride Ratios in Groundwater wells e . . 82

iii

LIST OF FIGURES

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure 10.

Figure 11.

Figure 12.

Figure 13.

Figure 14.

General location of water management sites for water quality evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . Location of Ferebee and Reid sites in Camden County. . . . . . Location of Cahoon site in Pamlico County. . . . . . . . . . . Schematic layout of treatments and instrumentation at the Cahoon site in Pamlico county. . . . . . . . . . . . . . . . . Schematic layout of treatments and instrumentation at Reid site in Camden county. . . . . . . . . . . . . . . . . . . . . Wendell Gilliam installed groundwater wells using a Giddings Probe (top), fall, 1985. Groundwater wells were installed to various depths ranging from 0.5 to 5.0 meters (bottom). Water level recorders were used to continuously monitor field water table depths. . . . . . . . . . . . . . . . . . . . . . . . . . Walter Lembke (top) assisted with the seepage measurements using piezometers and calcium chloride as a tracer January, 1986 during his sabbatical study leave from the University of Illinois. Drainage outflow quality was determined by collecting grab samples (center) for chemical analysis. Several combinations of water table management alternatives were evaluated such as subirrigation (bottom). . . . . . . . . Soil properties were measured at each site to evaluate the influence of soil properties on water table management effectiveness (top). Rainfall was measured with a weighing bucket raingauge and event recorder (center) and potential evaporation was measured with a standard screened evaporation pan. Drainage outflow was measured with stage recorders in the outlet ditches (bottom). . . . . . . . . . . . . . . . . . Daily drainage outflow volume at the Cahoon site, 1986. Values are combined surface and subsurface flow . . . . . . . . Daily drainage outflow volume at the Cahoon site, 1987. Values are combined surface and subsurface flow . . . . . . . . Daily drainage outflow volume at the Reid site, 1986. Values are combined surface and subsurface flow . . . . . . . . Daily drainage outflow volume at the Reid site, 1987. Values are combined surface and subsurface flow . . . . . . . . Outflow rate at the field edge, Reid Site, for a series of events from 2/15/86 to 3/13/86. . . . . . . . . . . . . . . . .

5

6

6

7

7

10

11

12

15

15

16

16

17

Field water table depth for a series of events from 2/15/86 to 3/13/86, Reid site. . . . . . . . . . . . . . . . . . . . . . . 17

iv

Figure 15. Outflow rate a t the f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 3/14/86 t o 4/01/86. . . . . . . . . . . . . . . . .

Figure 1 6 . F i e l d water t a b l e depth f o r a s e r i e s of events from 3/14/86 t o 4/01/86, Reid s i t e . . . . . . . . . . . . . . . . . . . . . . .

Figure 17. Outflow r a t e a t the f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 8/02/86 t o 8/16/86. . . . . . . . . . . . . . . . .

Figure 18. F i e ld water t a b l e depth f o r a s e r i e s of events from 8/02/86 t o 8/17/86, Reid s i te . . . . . . . . . . . . . . . . . . . . . . .

Figure 19. Outflow rate a t t he f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 8/17/86 t o 9/09/86. . . . . . . . . . . . . . . . .

Figure 20. F i e ld water t a b l e depth f o r a s e r i e s of events from 8/17/86 t o 9/09/86, Reid s i t e . . . . . . . . . . . . . . . . . . . . . . .

Figure 2 1 . Outflow r a t e a t the f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 12/11/86 t o 12/31/86. . . . . . . . . . . . . . . .

Figure 22 . F i e ld water t a b l e depth f o r a s e r i e s of events from 12/11/86 t o 1/01/87, Reid s i t e . . . . . . . . . . . . . . . . . . . . . .

Figure 23. Outflow r a t e a t t he f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 1/01/87 t o 1/27/87. . . . . . . . . . . . . . . . .

Figure 24. F i e ld water t a b l e depth f o r a s e r i e s of events from 1/01/87 t o 1/27/87, Reid s i te . . . . . . . . . . . . . . . . . . . . . . .

Figure 25. Outflow r a t e a t the f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 2/17/87 t o 3/08/87. . . . . . . . . . . . . . . . .

Figure 26 . F i e ld water t a b l e depth f o r a s e r i e s of events from 2/17/87 t o 3/08/87, Reid s i t e . . . . . . . . . . . . . . . . . . . . . . .

Figure 27. Outflow r a t e a t t he f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 3/09/87 t o 3/27/87. . . . . . . . . . . . . . . . .

Figure 28. F i e l d water t a b l e depth f o r a s e r i e s of events from 3/09/87 t o 3/27/87, Reid s i te . . . . . . . . . . . . . . . . . . . . . . .

Figure 29. Outflow r a t e a t t he f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 3/27/87 t o 5/01/87. . . . . . . . . . . . . . . . .

Figure 30. F i e ld water t a b l e depth f o r a s e r i e s of events from 3/27/87 t o 5/02/87, Reid s i t e . . . . . . . . . . . . . . . . . . . . . . .

Figure 31. Outflow r a t e a t t h e f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 11/29/87 t o 1/03/88 . . . . . . . . . . . . . . . .

Figure 32. F i e ld water t a b l e depth f o r a s e r i e s of events from 11/29/87 to 1/02/88, Reid s i t e . . . . . . . . . . . . . . . . . . . . . . .

19

1 9

20

20

2 1

2 1

22

22

24

24

25

25

26

26

27

27

29

29

V

Figure 33. Outflow rate at the field edge, Reid Site, for a series of events from 1/03/88 to 1/29/88. . . . . . . . . . . . . . . . . 30

Figure 34. Field water table depth for a series of events from 1/03/88 to 1/29/88, Reid site. . . . . . . . . . . . . . . . . . . . . . . 30

Figure 35, Outflow rate at the field edge, Cahoon site, for the period 8/19/86 to 8/27/86 . . . . . . . . . . . . . . . . . . , 31

Figure 36. Field water table depth for the period 8/09/86 to 8/27/86, Cahoon site . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 37. Outflow rate at the field edge, Cahoon site, for the period 3/01/87 to 3/08/87 . . . . . . , . . . . . . . , . . . e 32

Figure 38. Field water table depth for the period 2/26//87 to 3/11/87, Cahoon site. . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 39.

Figure 40.

Figure 41.

Figure 42.

Figure 43.

Figure 44.

Figure 45.

Figure 46.

Figure 47.

Figure 48.

Figure 49.

Cumulative measured outflow at the Cahoon site during the period 1/1/86 to 9/27/87. . . . . . . . . . . . . . . . . . . . 33

Cumulative measured outflow at the Reid site during the period 1/1/86 to 1/26/88. . . . . . . . . . . . . . . . . . . . . 33

Time variant nitrate concentration in drainage outflow at the Cahoon site during the period 1/1/86 to 9/27/87. . . . . . . . 36

Time variant total phosphorus concentration in drainage outflow at the Cahoon site during the period 1/1/86 to 9/27/87. - . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Nitrate and nitrate chloride ratios in shallow wells at Ferebee site, 3/86 to 3/88. Controlled tile drainage. Absent data implies that the well was dry. , . . . . . . . . . . . . . 41

Nitrate and nitrate chloride ratios in shallow wells at Ferebee site, 3/86 to 3/88. Controlled ditch drainage. Absent data implies that the well was dry. . . . . . . . . . . . . . . 41

Nitrate and nitrate chloride ratios in shallow wells at Williford site, 3/86 to 10/87. Controlled tile drainage Absent data implies that the well was dry. . . . . . . . . . . 42

Nitrate and nitrate chloride ratios in shallow wells at Williford site, 3/86 to 10/87. Controlled ditch drainage. Absent data implies that the well was dry. . . . . . . . . . . 42

Nitrate and nitrate chloride ratios at well depths 3 and 4, Ferebee site. Controlled tile drainage. Exploded scale. . . . 44

Nitrate and nitrate chloride ratios at well depths 3 and 4, Ferebee site. Controlled ditch drainage. Exploded scale. . . . 44

Nitrate and nitrate chloride ratios at well depths 2 and 4, Williford site. Controlled tile drainage. Exploded scale. . . 45

vi

Figure 50. Nitrate and nitrate chloride ratios at well depths 3 and 4, Williford site. Controlled ditch drainage. Exploded scale. . . 45

Figure 51. Observed and predicted water table depth, Cahoon site, 1986. Controlled tile drainage, 24 meter tile spacing. Horizontal observed line implies observation well bottomed out. Intermittent subirrigation days 120-180. . . . . . . . . . . . 46

Figure 52. Observed and predicted water table depth, Cahoon site, 1986. No controlled tile drainage, 24 meter tile spacing. Intermittent subirrigation days 120-180 with no drainage control during non-cropping season. . . . . . . . . . . . . . . 46

Figure 53. Observed and predicted water table depth, Reid site, 1986. Controlled tile drainage, 24 meter tile spacing. Horizontal observed line implies observation well bottomed out. L'ater level recorder not working days 65-100. . . . . . . . . . . . 47

Figure 54. Observed and predicted water table depth, Reid site, 1986. No control ditch drainage, 100 meter ditch spacing. Horizontal observed line implies observation well bottomed out. . . . . . 47

Figure 55. Observed and predicted cumulative outflow, Cahoon site, 1/1/86 to 9/27/87. No control tile drainage, tile spacing 24 meters. (Includes both surface and subsurface flow.). . . . . . 49

Figure 56. Observed and predicted cumulative outflow, Reid site, 1/1/86 to 12/31/87. No control ditch drainage, ditch spacing 100 meters. (Includes both surface and subsurface flow.). . . . . . 49

Figure 57. Observed and predicted cumulative outflow, Cahoon site, 1/1/86 to 9/27/87. Controlled tile drainage, tile spacing 24 meters. (Includes both surface and subsurface flow.). . . . . . 50

Figure 58. Observed and predicted cumulative outflow, Reid site, 1/1/86 to 12/31/87. Controlled tile drainage, tile spacing 24 meters. (Includes both surface and subsurface flow.) . . . . . . . . . 50

Figure 59. Observed and predicted cumulative outflow, Cahoon site, 1/1/86 to 9/27/87. Controlled ditch drainage, ditch spacing 80 meters. (Includes both surface and subsurface flow.) . . . . 51

Figure 60. Observed and predicted cumulative outflow, Reid site, 1/1/86 to 12/31/87. Controlled ditch drainage, ditch spacing 100 meters. (Includes both surface and subsurface flow.). . . . . . 51

LIST OF APPENDIX FIGURES

Figure A l . Instrumentation at Reid site in Camden County. . . . . . . . . 61 Figure A2. Instrumentation at Ferebee site in Camden County. . . . . . . . 63 Figure A3. Instrumentation at Cahoon site in Pamlico County. . . . . . . . 65

vii

Figure A4. Instrumentation at Williford site in Hyde County. . . . . . . . 67 Figure AS. Instrumentation at Stauldieun site in Beaufort County. . . . . 6 9

Figure A6. Drainable porosity (potential soil storage) vs water table depth, Cahoon site. . . . . . . . . . . . . . . . . . . . . . . 44

Figure A7. Drainable porosity (potential soil storage) vs water table depth, Reid site. . . . . . . . . . . . . . . . . . . . . . . . 7 4

Figure C1. Water table depths measured at Cahoon site, 11/25/85 to 3/27/87. Drain spacing 12 meters. . . . . . . . . . . . . . . . 7 9

Figure C2. Water table depths measured at Cahoon site, 11/25/85 to 3/27/87. Drain spacing 18 meters. . . . . . . . . . . . . . . . 7 9

Figure C3. Water table depths measured at Cahoon site, 11/25/85 to 3/27/87. Drain spacing 24 meters . . . . . . . . . . . . . . . 80

Figure C4. Water table depths measured at Cahoon site, 11/25/85 to 3/27/87. Ditch spacing 80 meters . . . . . . . . . . . . . . 80

Figure C5. Water table depths measured at Reid site, 1986. . . . . . . . 81 Figure C6. Water table depths measured at Reid site, 1987. . . . . . . . 81 Figure D1. Nitrate and nitrate chloride ratios in shallow groundwater

wells. Cahoon site-no control tile drainage. Absent data implies well vas dry. . . . . . . . . . . . . . . . . . . . . 82

Figure D2. Nitrate and nitrate chloride ratios in shallow groundwater wells. Cahoon site-controlled tile drainage. Absent data implies well was dry. . . . . . . . . . . . . . . . . . . . . 82

Figure D3. Nitrate and nitrate chloride ratios in shallow groundwater wells. Cahoon site-no control ditch drainage. Absent data implies well was dry. . . . . . . . . . . . . . . . . . . . . 83

Figure D4. Nitrate and nitrate chloride ratios in shallow groundwater wells. Cahoon site-controlled ditch drainage. Absent data implies well was dry. . . . . . . . . . . . . . . . . . . . . 83

Figure D5. Nitrate and nitrate chloride ratios in shallow groundwater wells. Reid site-controlled tile drainage. Absent data implies well was dry. . . . . . . . . . . . . . . . . . . . . 84

Figure D6. Nitrate and nitrate chloride ratios in shallow groundwater wells. Reid site-controlled ditch drainage, Absent data implies well was dry. . . . . . . . . . . . . . . . . . . . . 84

Figure 07. Nitrate and nitrate chloride ratios in shallow groundwater wells. Reid site-no control ditch drainage. Absent data implies well was dry. . . . . . . . . . . . . . . . . . . . . 85

viii

Figure D8. Nitrate and nitrate chloride ratios in shallow groundwater wells. Stauldieun site-controlled tile drainage. Absent data implies well was dry. . . . . . . . . . . . . . . . . . 85

Figure D9. Nitrate and nitrate chloride ratios in shallow groundwater wells at depths 3 and 4. Reid site-controlled tile drainage. Absent data implies well was dry. . . . . . . . . . . . . . . 86

Figure D10. Nitrate and nitrate chloride ratios in shallow groundwater wells at depths 3 and 4. Reid site-controlled ditch drainage. Absent data implies well was dry. . . . . . . . . . 86

Figure D11. Nitrate and nitrate chloride ratios in shallow groundwater wells at depths 2 and 4. Reid site-no control ditch drainage. Absent data implies well was dry. . . . . . . . . . 87

Figure D12. Nitrate and nitrate chloride ratios in shallow groundwater wells at depths 3 and 4. Stauldieun site-controlled tile drainage. Absent data implies well was dry. . . . . . . . . . 87

ix

LIST OF TABLES

Table 1 . Summary of treatments and instrumentation at all sites. . . . . Table 2. Rainfall at the study sites for the period 1-86 to 12-87. (cm) a

Table 3 . Average nutrient concentrations at all sites for the period 1-1-86 to 1-29-88. . . . . . . . . . . . . . . . . . . . . ~

Table 4. Comparison of observed and predicted cumulative drainage outflow for the Cahoon and Reid sites. (Total cumulative outflow through 12/31/87.). . . . . . . . . . . . . . . . .

Table 5 . Simulated drainage outflows for all water table management strategies at all sites, January 1, 1986 to December 31, 1987. .

Table 6. Predicted nutrient transport in drainage outflow for the period 1/1/86 to 12/31/87. . . , . . e . . . . . . . . . e - a

Table 7. Estimated annual transport of nitrogen and phosphorus in drainage outflow. . . . . . . . . e . . . . . . . . . . - e

APPENDIX TABLES

Table Al. Example of layout of ground water observations wells and field water table well at one sampling station, Reid Site. . . - . .

Table A2. Example of layout of ground water observations wells and field water table well at one sampling station, Ferebee Site . . . e

Table A 3 . Example of layout of ground water observations wells and field water table well at one sampling station, Cahoon Site. . . e a

Table A 4 . Example of layout of ground water observations wells and field water table well at one sampling station, Williford Site . . .

Table A5. Example of layout of ground water observations wells and field water table well at one sampling station, Stauldieun Site. . .

Table A6. Saturated hydraulic conductivity measured at study sites. . . - Table A7. Soil water characteristic curves for study sites. . . . . . . . Table B1. Daily rainfall at Reid site, 1986. . . . . , . . . . . . . . . a

Table B2. Daily rainfall at Reid site, 1987. . . . . . . , . . . . . . e

Table B3. Daily rainfall at Cahoon s i t e , 1986. . . . . . . . . . . . . . - Table B4. Daily rainfall at Cahoon site, 1987. . . . . . . . . . . . . . .

8

13

39

52

54

55

56

60

62

64

66

68

70

71

75

76

77

78

X

SUMMARY

Water table control is a rapidly growing management alternative being implemented by farmers in several states along the Atlantic Coast. the water control structures being installed, are funded in part by state incentive programs to improve agricultural drainage water quality. As the competition for cost-share funds increase, it is important that the moneys be spplied to attain the maximum possible water quality benefit. The primary objective of this study was to evaluate the influence of soil and site properties and water management strategies on drainage water quality.

Many of

Drainage water quality for several combinations of surface, subsurface and controlled drainage water management alternatives was evaluated. drainage was provided by open ditches, subsurface drainage was provided by underground drainage tubing, and controlled drainage was provided by placing flashboard riser type control structures in the outlet ditches. The study sites are located in four counties in Eastern North Carolina. All of the sites are typically poorly drained and require artificial drainage for efficient agricultural production.

Surface

A total of six water management strategies were investigated (surface drainage, controlled surface drainage, subsurface drainage, controlled subsurface drainage, subirrigation utilizing open ditches, and subirrigation utilizing underground tubing); however, not all strategies were implemented at each site. In fact, none of the five study sites included all six water management strategies; therefore, DRAINMOD was used to estimate drainage outflows for those alternatives that were not measured in the field. The overall conclusions in this study are based on the collective results of field measurements and DRAIhMOD simulations.

Drainage water quality was evaluated by collecting weekly grab samples from each site. Observation wells were installed at several location at each site to evaluate the quality of shallow groundwater. Water level recorders were installed at two sites to monitor field water table fluctuations in response to the different water table management strategies. installed in the outlet ditches and together with V-notch weirs provided a measure of the drainage outflow volume.

Stage recorders were

All evaluations in this study are based on field scale systems that were managed by the land owner, edge and do not necessarily reflect the impact on receiving streams or estuaries. For example, nutrient concentrations reaching receiving waters (streams or estuaries) at the field edge due to chemical transformations, deposition, or dilution along transport canals. translate to expected impacts on receiving streams. For example, any management strategy that results in either a reduction in peak outflow, total outflow, nutrient transport or nutrient concentration at the field edge should also represent a reduction to receiving waters; however, the magnitude of the reduction could be significantly different. In addition, the impacts on natural receiving waters that drain large areas may be further enhanced by applying additional management practices along the transport canals.

All results are based on observations at the field

would be expected to be different than values measured

However, general trends observed in this study should

xi

CONCLUSIONS

Drainage control was effective in reducing total drainage outflow at the field edge at all sites. Controlled drainage reduced total outflow by an average of 40 percent. The reduction in outflow was consistent for all soil types and water table management alternatives, provided the drainage outlet was controlled year around.

The influence of controlled drainage on peak outflow rates was variable and dependent on seasonal rainfall. There were clearly periods when drainage control either reduced or totally eliminated outflow at the field edge as compared to no control. This was most apparent during drainage events that occurred immediately after periods of below normal rainfall and would be an expected result during the late summer and fall period in most years, since short term drought conditions are prevalent in North Carolina during the summer. However, since saline estuaries are not believed to be as sensitive to fresh water inflow during this season, reduced peak outflows at the field edge resulting from controlled drainage may not always represent a benefit to saline estuaries.

There was also evidence that drainage control reduced peak outflow rates at the field edge during the spring period. during this study because rainfall during March, April and May was considerably below normal. During years of normal spring rainfall, controlled drainage would probably result in higher spring outflow rates as was observed during the winter months of January and February when rainfall was normal and ET was low. Vhile drainage control clearly reduced total drainage outflow at the field edge, we can not conclude from these results, that drainage control had or would have a positive effect on peak fresh water inflow to saline estuaries during the spring period when estuarine salinity is most critical. This is believed to be the case even when the water control structure is maintained during the winter period. the critical spring period may be reduced by watershed scale control practices along the entire reach of transport canals; however, this management strategy was not investigated in this study.

This situation probably occurred

Peak inflow rates to estuaries during

Nutrient concentrations in drainage outflow were only slightly affected by the water management strategy at any given site. Nitrate concentrations at the field edge tended to be slightly higher and TKN and TP concentrations slightly lower for good subsurface drainage compared to surface drainage alternatives. There were differences in nitrate concentrations among sites. concentrations increased as the saturated hydraulic conductivity increased. The reduction in nitrate concentrations as a function of management strategy was more visible on those soils which had the highest concentrations in the absence of a drainage control strategy. However, the influence of controlled drainage on concentration and subsequently nutrient transport, was overshaldowed by the tremendous influence of controlled drainage on total outflow.

Nitrate

The primary benefit resulting from controlled drainage management practices observed in this study was a significant reduction in total nutrient transport from the fields at all sites. The reduction in nutrient transport resulted primarily from the reduction in total outflow. Controlled drainage reduced total nitrogen transport by an average of 7 kgfia (46.5 %). Total nitrogen

xii

transport was approximately 30 percent higher on the tiled treatments (subsurface drainage) (both controlled and non-controlled) as compared to drainage using ditches (surface drainage). However, drainage control was equally effective in reducing the relative amount of nitrogen transport at all sites regardless of drainage intensity.

Total phosphorus transport was about 20 percent higher on the surface drainage treatments compared to the tiled treatments. However, drainage control did not appear to increase the relative magnitude of surface runoff (which would tend to increase phosphorus transport) compared to subsurface drainage. In fact, drainage control reduced total phosphorus transport by an average of 0.19 kg/ha (44 %) on both the surface and subsurface drainage treatments.

Results of the DRAINMOD simulations indicated drainage control would be effective in reducing drainage outflows and nutrient transport at all locations regardless of soil and site properties or drainage intensity. simulated results also showed that intensive management including weir adjustment and very selective pumping strategies would be necessary to enhance drainage water quality on subirrigated sites. showed that subirrigation could be managed on a practical basis and still reduce drainage outflow and nutrient transport relative to non-controlled water management alternatives.

The

Field results at one site

There was no evidence that the reduction in drainage outflow contributed to an increase in nitrate transport to groundwater. Nitrate concentrations in shallow wells to a depth of 4 meters did show minor fluctuations in nitrate concentration, however, the fluctuations were observed on all treatments both with and without drainage control. periods when the water table dropped below 2 meters, nitrate concentrations increased to approximately 1 mg/L at the 3 to 4 meter depth. when the water table was less than 2 meters deep, nitrate concentrations at the 3 to 4 meter depth were typically less than 0.3 mg/L. nitrate/chloride ratios in time and with depth, suggested that nitrates were reduced by denitrification upon reaching the saturated zone. concentrations in groundwater wells were always less than 0.02 mg/L.

During the very dry summer and fall

During periods

Reduction in

Phosphorus

xiii

ACLVOWLEDGMENTS

This r e p o r t is based on r e sea rch supported i n p a r t by funds provided by The Univers i ty of North Caro l ina Water Resources Research I n s t i t u t e . A s p e c i a l n o t e of apprec i a t ion i s expressed t o D r . David Moreau, D i rec to r of t h e I n s t i t u t e , D r . James S t e w a r t and Mrs. Linda Lambert f o r t h e i r a s s i s t a n c e and advice during t h e course of t h e study.

The water t a b l e management systems s tud ied were e s t a b l i s h e d wi th cost-share funds provided by t h e Resource Conservation Act (RCA) of 1977. A s p e c i a l n o t e of apprec i a t ion i s extended t o P e t e r Tidd, J i m Tatum and David Stockbridge, admin i s t r a to r s of t h e S o i l Conservation Serv ice RCA program. a l s o expressed t o Richard Gallo, Ass i s t an t S t a t e Conserva t ion is t (Water Resources),who administered t h e RCA program i n North Carolina. Spec ia l apprec i a t ion is expressed t o m a n e Hinson, D i s t r i c t Conserva t ion is t , SCS, who provided t e c h n i c a l a s s i s t a n c e and program d i r e c t i o n f o r t h e RCA program i n North Carolina. water management program was t h e impetus t h a t l ed t o t h e rap id acceptance and growth of water t a b l e management i n e a s t e r n North Carolina. Camden County Extension Direc tor ; Rodney Johnson, Camden County SCS Dis t r i c t Conserva t ion is t ; Fred May, Pamlico County Extension Direc tor and Andy Metts, Pamlico County SCS Dis t r ic t Conservat ionish provided suppor t and a s s i s t a n c e dur ing t h e c o u r s e - o f t h i s study.

Appreciation i s

Dwane's dedica ted e f f o r t dur ing t h e e a r l y years of t h e RCA

Gordon Sawyer,

A very s p e c i a l no te of g r a t i t u d e is expressed t o M r . Pe t e Reid, Mr. Ed Ferebee, Mr. Garland Cahoon, M r . Charles Wi l l i fo rd , M r . van S tau ld ieun and t h e i r famil ies f o r t h e tremendous cooperation which they showed throughout t h e du ra t ion of t h e f i e l d experiments. Without t h e u s e of t h e i r land and o t h e r resources , t h i s p r o j e c t would no t have been poss ib le .

W e would l i k e t o recognize t h e e f f o r t s of Tommy Cone, Don Keaton and Tony Jacobs f o r t h e i r t ireless e f f o r t t o c o l l e c t f i e l d da ta . Greg Hodges was pr imar i ly r e spons ib l e f o r developing t h e d i g i t i z i n g programs t o eva lua te t h e s t a g e and water l e v e l recorder data . F i n a l l y , w e would l i k e t o express s p e c i a l thanks t o Bertha Crabrree and Lydia Nelson who were r e spons ib l e f o r l abora to ry ana lyses .

x iv

INTRODUCTION

There is tremendous concern for the effects of agricultural drainage on water resources. There are many streams, rivers, lakes and estuaries along the East Coast with severe water quality problems. Agricultural drainage is one source of nutrients and sediment contributing to this problem. Under normal rainfall conditions, 60 percent of the total nitrogen and 27 percent of the total phosphorus delivered to the Chesapeake Bay is believed to originate from cropland (Magette and Weismiller, 1984).

Crops are grown on about 50 million ha of poorly-drained soils. This makes up about 22 percent of the nation's cropland, In states like North Carolina, Michigan and Ohio, over 40 percent of the cropland requires drainage. It is apparent that agricultural production is essential to these areas, but it is also obvious that future agricultural practices must be designed with water quality as a consideration.

Drainage waters present two particular problems to fresh waters and saline estuaries: 1 - a reduction in salt concentration due to fresh water dilution and 2 - contamination due to nutrients and sediment in the runoff. Development of poorly drained soils for agriculture tends to increase runoff and peak flows when the natural vegetation is removed, field surfaces graded and the soils are channelized to accommodate surface drainage. Skaggs et al. (1980) reported peak runoff rates at the field edge to be three to four times higher on developed land with primarily surface drainage as compared to similar undeveloped land. Bailey and Bree (1980) found that improved drainage due to channelization doubled peak flows as compared to unchannelized areas.

The increased runoff caused by the development of field systems has an influence on the quality and quantity of water reaching receiver waters; however, the impact at the receiving stream is not usually as great as the input at the field edge. flow to receiving streams that drain large areas compared to the peak flow at the field edge.

Konhya et al. (1988) reported a reduction in peak

Subsurface drainage systems tend to reduce peak flows from fields as compared to surface systems on similar soils. The influence of a good subsurface drainage system is to lower the water table and increase the potential for infiltration and soil storage at the time of a rainfall event thereby reducing surface runoff. Eggelsmann (1972) reported that subsurface drainage reduced peak flows by four times as compared to a conventionally surface drained site. Skaggs and Tabrizi (1982) found that improved subsurface drainage reduced surface runoff by three-fold. al. (1974), and McLean (1981).

Similar results have been reported by Burk et

Improved subsurface drainage will not only reduce the impact of increased freshwater flows into estuaries by reducing peak flow at the field edge, but it can also influence the nutrient loss as the concentration in subsurface flow is generally different from surface runoff. Surface runoff tends to be higher in phosphorus and organic nitrogen than subsurface runoff (Deal e t al., 1986; Evans et d., 1984; and Gilliam and Skaggs, 1985) while subsurface drainage tends to be higher in nitrate-nitrogen than surface runoff (Deal et al., 1986; Gast et al., 1978; Gambrel1 et al., 1975; Gilliam et al., 1979; and Gilliam

1

and Skaggs, 1985). Surface runoff also presents a greater potential for soil erosion and sediment transport (Jarrett and Hoover, 1979; Schwab and FOUSS, 1967 and Skaggs et al., 1982). poses the greatest detrimental effect to receiving waters. There are usually several water management alternatives that will satisfy the agricultural drainage requirements. basis of minimum total cost.

It is not clear which of the above situations

Selection between alternatives is normally made on the

The influence of controlled drainage and subirrigation on peak drainage outflow from fields is not as well documented. Previous studies have concentrated on one or two aspects of total water management such as surface and/or subsurface drainage. small, well defined systems maintained by the investigator. drainage has been reported to reduce flow at times during recharge periods when the water table is rising. by either controlled drainage or subirrigation may eventually reduce potential storage and infiltration during other periods when the water table is higher than would occur under conventional drainage. During these periods, water table management may actually increase the potential for higher peak flows similar to those which now occur for surface drainage systems. A critical management decision will be to select the water management strategy which restricts drainage during periods when receiving waters are most sensitive, especially if this is not entirely compatible with production requirements.

In addition, these studies have been confined to Controlled

However, maintaining high water table levels

Controlled drainage and subirrigation may also influence nutrient concentrations in outflow from fields by increasing in greater transport of phosphorus and sediment than with uncontrolled drainage. denitrification, thereby reducing nitrate transport from fields (Gilliam et al., 1978). Water management systems are intensively managed for production purposes from May through September in North Carolina. While this will provide the greatest benefit for water conservation and some benefit to drainage water quality, the greatest benefit for water quality requires intensive management during the winter period when flow volumes are normally high (Gilliam et al., 1978).

surface runoff resulting

However, higher water table levels increase the potential for

Previous studies by Deal et al. (1986), Gilliam et al. (1978), Gilliam and Skaggs, (1985) and Skaggs and Gilliam (1982) have concluded that a significant reduction in nitrate nitrogen entering surface waters could be achieved by controlled drainage practices. The result of this work led to the adoption of controlled drainage as a best management practice for artificially brained soils qualifying for cost share assistance under the North Carolina Agricultural Cost Share Program.

Recently, producer interest in total water management systems has grown rapidly. In North Carolina alone, more than 2000 control structures have been installed since 1983 to provide controlled drainage on nearly 50,000 ha. the 20 CAMA (Coastal Area Management Act) counties in eastern North Carolina, controlled drainage has accounted for over 80 percent of the cost share funds expended in those counties. This represents 60 to 80 new control structure installations per county annually. Other Atlantic Coast States including Delaware, Maryland and Virginia have recently incorporated control drainage into their cost share incentive programs to improve water quality in the Chesapeake and Back Bays.

In

2

The net effect of an integrated total water management program may be significantly different from the sum of the effects of the individual system components. Furthermore, the recent increase in water management systems will undoubtedly alter the characteristics of drainage water and have an effect on the rate and quality of water reaching environmentally sensitive areas.

The primary objective of this study was to evaluate the influence of controlled drainage and subirrigation on drainage water quality and to estimate the off-site environmental impacts of these water management practices for the Tidewater Region of North Carolina. Specifically, the costs of installing water control structures are presently cost-shared at a fixed rate of 75 percent through the North Carolina Agricultural Cost Share Program. We wished to determine if the water quality benefits resulting from these practices are influenced by the type of drainage system (surface drainage with open ditches vs subsurface drainage with underground drainage tubing), soil hydraulic properties (hydraulic conductivity, drainable porosity, etc.), or water management strategy (growing season control vs year around control). the water quality benefits of these water management practices are significantly affected by the above factors, then the effectiveness of the North Carolina Agricultural Cost share program could be enhanced by adjusting the future cost share rate proportionally to the potential water quality benefits. To quantify this objective, it was necessary to determine:

If

1. The drainage volume and time distribution of drainage water as a function of specific site characteristics, alternatives and management strategies being practiced.

water management

2. The quality of drainage water as a function of specific site characteristics, water management alternatives and management strategies being practiced.

3 . The fate of the non-drainage volume (seepage) and nutrient movement which develops as a result of the specific water management alternatives and management strategies.

Objectives 1 and 2 have also been addressed in previous work, however the earlier studies focused on the 'potential' benefits of drainage control to enhance drainage water quality. by the investigators in their attempt to identify management strategies that could improve drainage water quality. While these earlier studies concluded that controlled drainage could significantly reduce nitrate nitrogen entering surface waters, the magnitude of the benefit was very dependent on winter control. The earlier studies did not address the likelihood or willingness sf the farmer to incorporate this non-traditional winter management into his overall management scheme.

One unique feature of this study is that all field evaluations are based on field scale water management systems on privately owned farming operations. While recommendations were suggested, the farm manager made the final decision concerning management and maintenance of the systems on his farm. Consequently, our results reflect a more realistic estimate of the 'attainable' as opposed to 'potential' benefits of water table management and controlled drainage.

In most cases, management decisions were made

3

EXPERIMENTAL METHODS

Water table management alternatives were established on seven sites during 1983 and 84 by the Soil Conservation Service with cost share funds provided through the Resource Conservation Act (RCA) of 1977. These sites were established primarily to demonstrate to farmers the potential water conserving opportunities through water table management and to provide local SCS agents training and experience in designing, installing and managing water table management systems. By expanding the experimental framework, these sites presented an excellent opportunity for evaluating the environmental impact of water table management strategies for a wide range of soil and site conditions. Four of the seven RCA sites and one water table management site established independently by the farmer were selected to evaluate the impact of water table management on drainage water quality.

The water table management strategies implemented included several combinations of surface drainage and subsurface drainage/irrigation for different spacings of underground drainage tubing, conventionally spaced open ditches, and combination tubing and open ditches. These water management practices were established on five farms in four eastern North Carolina counties - Ferebee and Reid in Camden Co., Stauldieun in Beaufort Co,, Williford in Hyde Co. and Cahoon in Pamlico Co.

Field scale treatments of the water management alternatives being evaluated were provided at each site, although, the actual size of the experimental treatment varied from site to site. Thus, all outflow results are reported on a unit area basis. Wherever possible, conventional drainage practices were evaluated for comparison with the water table management alternatives.

Each of the sites are located near environmentally sensitive areas (Fig. 1). Two of the five sites, Cahoon and Reid, were instrumented for intensive monitoring of the water management techniques being implemented. The Cahoon site drains into the Neuse River through Dawson Creek (Fig. 2) and the Reid site drains into the Pasquotank River through South Canal (Fig. 3 ) . Although not shown, the Williford site drains directly into the Pamlico sound through a dug canal and the Stauldieun site drains into the Pungo River through Broad Creek. shown for the Cahoon site in Fig. 4 and for the Reid site in Fig. 5.

A schematic of the practices and instrumentation are

Table 1 summarizes the practices and instrumentation for all sites. particular water management practices implemented at each site were selected by the local farmer in conjunctton with recommendations provided by the local SCS District Conservationist. depending on which practices could be most cost effectively implemented in lieu of constraints imposed by the existing drainage system. were no exact replications of any water management practice at any two sites, We did not have the resources to incorporate any treatments that had not already been installed by the local farmer. the water quality benefits of those practices that were installed and project the benefits of the other practices that could not be implemented.

The

The practices varied from site to site

In fact, there

We simply attempted to quantify

This situation influenced the number of water management treatments that were available for field monitoring at each site. at the Cahoon site required only one flashboard riser water control structure on the lower end of the experimental ditch providing the drainage outlet for

For example, the original layout

4

Figure 1. General location of water management sites for water quality evaluation.

the drainage tubing treatment (refer to Fig. 4 ) and one additional water control structure on the main drainage outlet for all other fields. Due to a topogrzphy difference of approximately 60 cm from one end of the field to the other, the farmer decided to install additional water control structures after the first year of operation at the midway distance of each field ditch to provide more concise field water table control. except the tile drained field were still controlled by the control structure on the main drainage outlet. Each control structure would accommodate a 90' V-notch weir for measuring outflow. A water control structure was not installed on the lower end of the ditch treatment (no control ditch) and thus no mechanism was available to measure outflow volume on this treatment, even through grab samples could be collected from the ditch to evaluate drainage water quality. management practices could conveniently be instrumented at the other sites.

The lower half of all fields

Similar circumstances influenced which particular water

Prior to the installation of the RCA water management demonstration plots, the drainage system at each site was a conventional surface drainage system with open ditches spaced 100 m apart (except Cahoon site where ditch spacing was 80 m) and all fields had a 15 to 30 cm 'turtle back' crown in the center of each field to promote surface runoff. The fields selected for the installation of underground drainage tubing were precision land graded to provide a flat soil surface (the 'turtle back' crown was removed). Subsurface drain tubing was installed in one field at each site at 18, 24 and 30 m spacings. All

5

Figure 2 . Location of Reid and Ferebee sites i n Cmden County.

Figure 3 . Location of Cahoon s i t e in Pamlico county.

6

VAIN OUTLET

A /

V

DRAIN SPACING 24 m 00 DRAIN SPACING 24 m

i f DRAIN SPACING 18 m 11.11

I A I n n 0

SUBRIRGATDN w l N 0 WINTER CONTROL SUBTRRGATON w/WR(TER CONTROL RRIGAT)OX PLaAp

OD DITCH SPACING 80 m 0 0 DITCH SPACING B O m

/- ' MAIN OUTLET CANAL

FLASHBOARD REER CONTROL a STRUCTURE w l V NOTCH WEIR

0 WATER LEVEL RECORDER

0 GRWHDWATER WELLS

A DRAR(AGE WATER CRAB SAMPLES

Figure 4 , Schematic layout of treatments and instrumentation at the CaRoon site in Pamlico county.

Fl w

Figure 5.

I

0 - CONVEHTIONAl SURFACE DRAINAGE

SURFACE DRAINAGE W/COHTROllED OUTLET

d v

SLRFACE DRAINAGE WXX3NTRULED OUlLEl o m

0 GROUNDWATER WELLS

A DRAINAGE WATER GRAB SAMPLES

WATER CONTROL STIILICPURES a W/ V-NOTM WEIR

WATER LEVEL RECORDERS

Schematic layout of treatments and instrumentation at Reid site in Camden county.

7

Table 1. Summary of Treatments and Instrumentation at all sites.

Site Locat ion Size Drainage Data - -- --- _- _-=PI-- --=E=========

(county) (ha) Treatments Collected

Cahoon Pam( ice 15 1. ditch, uncontrolled drainage outflow 2. ditch controlled. water table elevation

Fer e bee Camden 32

Reid Camden 73

with subirrigation drainage water qual 3. t i 1 e, uncont roll ed groundwater quality 4. tile controlled,

with subirrigation

1. ditch controlled drainage water qual 2. tile controlled, groundwater quality

with subirrigation

1. ditch uncontrolled drainage outflow 2. ditch controlleg 3. tile controlled drainage water quality

water table elevation

grounduater quality

Stauldieun Beaufort 20 9 . tile Controlled, drainage water quality with subirrigation grounduater quality

Uilliford Hyde 20 1. ditch controlled drainage water quality 2. tile controlled, groundwater quality

Nith subirrigation

lateral drain lines were connected to a submain which outleted into the existing field ditch. The drainage outflows reported in this report from fields containing drainage tubing represent the composite outflow for all drainage tubing spacings in an experimental field. between outflows for the different spacings, although field water table levels for the different spacings were monitored.

We could not distinguish

Water table control was provided by placing flashboard riser type water control structures in the outlet ditches. Where the control structures were installed in lateral field ditches, the control structure was equipped with a ninety degree V-notch weir to measure drainage outflow. calibrated in the lab before installation. In some cases, water table control was provided by a control structure on the main outlet ditch which provided an outlet for more than one treatment. In these cases, outflow was not measured, however, grab samples were collected upstream from the main control Structure at a location where flow was contributed by a single field. water table control was provided year around with the control level managed at 60 cm below the average soil surface of each field. the option of occasionally adjusting the water control level as needed to respond to extreme climatic conditions.

The weirs were

In most cases,

However, each farmer had

Continuous monitoring of field and outlet ditch water levels, drainage volume and rainfall were performed on the Cahoon and Reid sites. descriptions, hydraulic conductivity and soil-water characteristic relationships, and drainage water quality were determined for all sites.

Soil profile

Stevens type F water level recorders were used to measure field and outlet ditch water levels. Hydraulic conductivity was measured in situ by the Auger Hole Method (van Beers, 1970) and soil water characteristic curves were determined in the lab from undisturbed soil cores by the Pressure Plate Method (Hillel, 1971). The drainage water quality was evaluated by collecting weekly grab samples from each site. to provide the best estimate of the quality of drainage water actually leaving each site. All water quality samples were frozen on the same day the sample was collected until chemical analysis could be performed. The Cahoon site was equipped with automatic samplers to take samples twice daily to evaluate time variant nutrient concentrations in drainage water. All water samples were analyzed for nitrogen (NO3-N, NH4 and TKN), phosphorus (OP and TP) chloride (C1-) and acidity (pH) by Standard Methods.

Rainfall was measured with tipping bucket rain gauges,

Samples were collected only at times when flow was occurring

Ground water observation wells were installed at several locations at each site to evaluate the quality of shallow groundwater and potential seepage. Samples were collected once each month from the tile depth (1 m) down to approximately 5 m at intervals based on the geomorphology of the sediments at each site. Typical sampling depths were .5-1 m, 1.5-2 m, 2.5-3 m and greater than 3 m. wells to the desired depths with open walls in the observation well to expose the desired zone to be sampled. analysis, the observation well was pumped to the bottom, then a sample taken as soon as the water level rose to the upper limit of the desired zone. Groundwater samples were collected monthly and analyzed for nitrogen (NO3 and N H 4 ) phosphorus (OP) chloride (Cl-) and acidity (pH),

Desired sample depths were controlled by installing observation

To collect the sample for water quality

The magnitude and direction of the seepage flux was estimated at the Reid site by monitoring the movement of a concentrated calcium chloride solution injected into the suspected lateral seepage zone at several locations in the field. A battery of observation wells were installed around a calcium chloride source well and the time variant hydraulic gradient and calcium chloride concentration measured.

Site instrumentation began in October, 1985 and instrumentation of all sites was completed by February, 1986. Figs. 6-9. Soil profile descriptions, site instrumentation, hydraulic conductivity and soil water characteristlc values for each site are shown fw Appendix A .

Example equipment installations are shown in

9

Figure 6. Wendell Gilliam installed groundwater wells using a Giddings Probe (top), fall, 1985. Groundwater wells were installed to various depths ranging from 0.5 t o 5.0 meters (bottom). Water level recorders were used to continuously monitor field water table depths.

Figure 7 , Walter Lembke (top) assisted with the seepage measurements using piezometers and calcium chloride as a tracer January, 1986 during

Drainage outflow quality was determined by collecting grab samples (center) for chemical analysis. Several combinations of water table management alternatives were evaluated such as subirrigation (bottom)

batical study leave from the University of Illinois.

11

Figure 8. ties were measured at each influence of soil properties on water table management effectiveness (top). recorder (center) and potential evaporation was measured with a standard screened evaporation pan. stage recorders and 90' V-notch weirs in the outlet ditches (bot).

Rainfall was measured with a weighing raingauge and event

Drainage outflow was measured with

12

RESULTS AND DISCUSSION

RAINFALL

Drainage studies are dependent on excessive rainfall to generate runoff events. As shown in Table 2, rainfall at the study sites was below normal for the entire study period. Rainfall was above normal only 6 of 21 months at the Cahoon site and 5 of 24 months at the Reid site. Drainage or runoff during periods of near normal rainfall is also dependent on seasonal rainfall trends. For example, during dry seasons, the soil's capacity to adsorb and retain rainfall is greater than normal up to the peak storage capacity where soil water depletion by evaporation becomes limiting. runoff will likely be below normal even for short periods of near normal

During dry seasons

rainfall. Such was the below normal during all seasonal rainfall was 1 was below normal due to shown in Appendix B.

case at both study sites where seasonal rainfall was periods except Jan-Mar, 1987 at the Reid site when cm above normal. Even during this wet period, runoff the extremely dry fall of 1986. Daily rainfall is

Table 2.

CAHOON (Pzmlico county) 1-86 thru 9-87 (183.72 cm or 75 % of normal)

Rainfall at the study sites for the period 1-86 to 12-87. (cm) E=__ E-----.-- - - _p____=--==_C---s__=.==== *

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR

NORMAL 10.19 10.08 9.19 7.57 11.20 13.03 17.15 16.08 14.61 8.61 7.82 9.37 134.90

1986 7.96 3.75 10.63 1.58 5.10 16.28 9.97 28.35 1.77 4.70 5.58 10.38 106.05 % of N 78 37 116 21 46 125 58 176 12 55 71 111 79

1987 4.01 6.29 9.98 3.75 3.19 7.68 11.61 24.80 6.36 - 77.67 % of N 39 62 109 50 28 59 68 154 44 71

--__Crc_I- -=---===E=======E==

REID (Camden county)' 1-86 thru 12-87 (154.97 cm or 62 % of normal)

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR

NORMAL 10.24 9.58 10.54 7.52 9.96 10.21 14.48 14.50 11.99 9.93 7.52 7.87 124.33

1986 7.96 3.81 3.24 2.47 .21 6.78 7.25 30.04 2.40 -67 3.99 8.52 77.34 % of N 78 40 31 33 2 66 50 207 20 7 53 108 62

1987 16.86 9.09 6.76 5.21 6.17 5.36 2.65 4.50 .03 3.67 7.87 9.46 77.63 % of N 165 95 64 69 62 52 18 31 0 37 105 120 62

* Values for January - June, 1986 taken from National Weather Service, New Bern #Value for January, 1986 taken from National Weather Service, Elizabeth City

13

DRAINAGE ARD RUNOFF

Annual drainage outflow hydrographs for the Cahoon site are shown in Figs. 9 and 10 and the Reid site are shown in Figs. 11 and 12. Long term hydrographs like the ones shown are not very informative for individual event because the time resolution is compressed for individual events and the individual treatment effects tend to overlap for the major drainage events. They do indicate the relative frequency of events and the peak daily outflow volumes for each treatment. in major outflow on all treatments. treatments clearly resulted in more frequent flows of longer duration but lower peak daily outflow rates than the controlled treatments.

The traditional association of surface drainage with ditches and subsurface drainage with underground drainage tubing is not appropriate for this study since our experimental setup did not allow us to differentiate between surface runoff and subsurface drainage. The outflows for all treatments contain combinations of both surface runoff and subsurface drainage. further discussions in this report will distinguish treatments as either controlled or no control tile or ditches.

There were only two events in 1986 and 1987 that resulted At both locations, the no control

Therefore

Individual event hydrographs for the Reid site are shown in Figs. 13, 15, 17, 19, 21, 23, 25, 27, 29, 31 and 33. In most cases, the time periods shown range from 14 to 31 days and include several rainfall events. These time periods were selected because they represent a break in outflow (a period of no flow on all treatments) or a major change in outflow rate. Field water table elevations corresponding to the same time periods are shown in Figs. 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 and 34. The field water table elevations are important to understanding the drainage outflow hydrographs.

The first event shown began 2/15/86 (Fig. 13) and was associated with 0.86 cm of rainfall on 1/15, 0.63 cm on 2/19, and 0.58 cm on 2/27 (Appendix Bl). Rainfall occurred on several occasions between 1/1/86 and 2/15/86 that resulted in outflow, however, this data is not shown, because the field water table levels had been elevated due to pumping to conduct the seepage study discussed later. considered to be representative of traditional management during the winter period and was neglected. field water table elevation appeared to have recovered to respond to climatic conditions by this event.

The outflow that occurred during the seepage study was not

The seepage study was completed 1/31/86 and the

All of the above rainfall events are relatively smaii, however, they are sufficient to maintain the field water table elevation on the no control ditch treatment approximately 60 cm above the bottom of the outlet ditch V-notch weir and thus provided outflow. The outflow rate is relatively small compared to some of the events shown later, and could be considered to represent base flow without surface runoff. The field water table response on the controlled treatments is about the same as the no control treatment, however, no measurable outflow occurred because the field water table elevation rarely rose above the outlet control level (Fig. 14). The field water table elevations began to decline on all three treatments approximately 3/1/86 in response to an increase in ET.

Similar conclusions can be drawn for the event which began on 3/14/86, Figs. 15 and 16. Again, outflow was observed on only the no control ditch

14

DAILY OUTFLOW AT CAHOON SITE, 1986

'T

1 31 61 91 121 151 181 211 241 271 301 331 361 JULIAN DAY

Figure 9. Daily drainage outflow volume at the Cahoon site, 1986. Values are combined surface and subsurface flow

DAILY OUTFLOW AT CAHOON SITE, 1987

- CONTROLLED TILE

NO CONTROL TILE

_- CONTROLLED DITCH

1 31 61 91 121 151 181 211 241 271 0 0 e

JULIAN DAY

Figure 10. Daily drainage outflow volume at the Cahoon site, 1987. Values are combined surface and subsurface flow

15

DAILY OUTFLOW AT THE FIELD EDGE REID SITE, 1 9 8 6

- CONTROLLED TILE D 1.4 A --. CONTROLLED DITCH

1.2

1 Y

0 'i' 0.8

F L 0.6 0

0.4

m 0.2

0

C

. . ' NO CONTROL DITCH

1 1

. . . . . . : ..._ .. , :. . ... , , I

t

1 31 61 91 121 151 181 211 241 271 301 331 361 JULIAN DAY

Figure 11. Daily drainage outflow volume a t the Reid s i t e , 1 9 8 6 . Values are combined surface and subsurface flow.

DAILY OUTFLOW AT THE FIELD EDGE REID SITE 1 9 8 7 TO JANUARY 27, 1988

- CONTROLLED TILE

--. CONTROLLED DITCH

. I . N O CONTROL DITCH

1 .a

D 1.6

A I 1.4 L Y 1.2

U T F 0.8

L 0 0.6 W

0.4

0 1

C

m 0.2

0

1987 JULIAN DAY 1 31 61 91 121 151 181 211 241 271 301 331 361 26

1988

Figure 1 2 . Daily drainage outflow volume a t the Reid s i t e , 1987. Values are combined surface and subsurface flow.

16

O U T F L O W RATE AT THE FIELD E D G E REID S I T E FOR A S E R I E S OF E V E N T S FROM 2/15/86 T O 3/13/86

0 U

F L 0 0.08 W

T 0.1

0.06

T E 0.Q4 -r

0.12 T

--

- -

--

m m

H r

/ 0.02

.. .. . . . . . . . . . .

.. ; -. . - . .

: . .. . . . .

I. . .. . * . - . -.

. .* ' . i . . : I i.. . . ; ; -. . . . .. 1 ..., -- * * - * . . :

* . . . - * . . _ _ _ _ *-\. _ - .

- CONTROLLED TILE

A T IO - - E R 2 0 - -

T 30--

CONTROLLED DITCH

NO CONTROL DITCH

- CONTROLLED TILE (59 em)

-_. CONTROLLED DITCH (64 cm)

... NO CONTROL TILE (1 14 cm) -. . -

17

treatment. The field water table elevations clearly rose in response to the 2.46 cm rainfall that occurred on 3/14, however, field water table levels on the control treatments were only slightly higher than the outlet control level and not high enough to result in measurable outflow. The field water table elevation on the no control ditch treatment rose to approximately 70 cm above the ditch outlet level which provided sufficient gradient for base flow (probably without surface runoff) as evidenced by the relatively low peak outflow rate.

No additional outflow was observed on any treatments at this site until 8/4/86 Figs. 17 and 18. rainfall event on 8/3 could not be observed because the water table was below the measurable depth of the field water level recorders; however, the water table rose to approximately 20 cm above the weir elevation on the no control ditch treatment but remained well below the control level on the controlled treatments. This event likely resulted in surface runoff based on the rapid increase and decrease in the outflow hydrograph for the no control ditch treatment. however, since the outlet ditches were dry at the time of the event, the surface runoff on the controlled treatments was likely retained in the outlet ditch by the control structures. ditch on the no control ditch treatment was not retained and thus resulted in outflow. The very brief response of the water table on both ditch treatments can only be explained as incidental rainfall or surface ponding that ran d o r n the side of the water table observation well, since the water table remained flat immediately after the field surface runoff, even though additional rainfall occurred on 8/8 (1.4 cm). The first clear measurable response of the water table (water table rise above the bottom of the observation wells) was associated with the events on 8/11, 8/12 and 8/13 (3.1, 0.8 and 0.7 cm of rainfall, respectively) where the water table started rising on all treatments (hour 280 in Fig. 18).

The first major outflow event at the Reid site began on 8/17/86 (Figs. 19 and 20) and was associated with rainfall events of 5.6 em on 8/17, 3.1 cm on 8/20, 2.5 em on 8/27 and 3.1 cm on 8/28. resulted in both surface runoff and subsurface drainage; however, it is not possible to determine this from our data for reasons discussed earlier. water table elevations rose well above the outlet control levels on all treatments and thus outflow was observed on all treatments. The field water table elevations were higher on the controlled treatments (controlled ditch slightly higher than controlled tile) than on the no control ditch which is what would be expected for this amount of rainfall and management strategies. Peak outflow rates for these rainfall events appeared to be slightly higher on the no control ditch treatment, however, it is not clear since the no control ditch field water table recorder malfunctioned from hour 24 to 192.

The actual water table depth at the start of the 6.73 em

In fact, surface runoff probably occurred on all three treatments,

Any surface runoff that reached the outlet

Some of these rainfall events may have

Field

Rainfall for September, October and November was significantly below normal (Appendix B1) and as a result, the field water table elevations declined to the lowest measurable depths during this period. considerable potentia2 soil storage (Fig. A6) for the events that began in December, 1986, Figs. 21 and 22. The first event (2.0 em rainfall on 12/11) elevated the field water table levels on all treatments, but only the no control ditch treatment rose above the weir level. flow was observed on this treatment for approximately 48 hours. rainfall on 12/24 (hour 336) also elevated the field water table levels, but

As a result, there was

As a result, very low base The 4.9 cm

18

OUTFLOW RATE AT THE FIELD EDGE REID SITE FOR A SERIES OF EVENTS FROM 3/14/86 TO 4/01/86

8.12 7

L 0 0.08 - - i W

0.06 - - i T E

m 0.04~- :

- CONTROLLED TILE

--. CONTROLLED DITCH

NO CONTROL DITCH

m I :

.. - - " . . . - .. . _ . . . . , . - - . ..I - . ._.

96 144 192 2 4 0 208 336 384 432

-.. .. .. .. .. .. . . .. . .-.-. .. .- . .. .

... . r

0 0 40

ELAPSED TIME SINCE START OF FIRST EVENT, H r

Figure 15. Outflow rate a t the f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 3/14/86 t o 4/01/86.

FIELD WATER TABLE DEPTH FOR SERIES OF EVENTS FROM 3 / 1 4 / 8 6 TO 4 / 0 1 / 8 6 , REID SITE

w 0 A T - CONTROLLED TILE (59 cm)

B L E 60

--. CONTROLLED DITCH (64 cm) n

96 144 192 240 288 336 384 432 m = I 120

0 48

ELAPSED TIME SINCE START OF FIRST EVENT, Hr

Figure 16. F i e l d water table depth for a series of events from 3/14/86 to 4/01/86, Reid site. Numbers in ( ) are weir depths.

19

OUTFLOW RATE AT THE FIELD EDGE REID SITE FOR A SERIES OF EVENTS FROM 8/02/86 TO 8/16/86

L

W 0 0.4 --

0.3 --

T E

m m

H r

0.2

/ 0.1

0

- CONTROLLED TILE

--. CONTROLLED DITCH

. . NO CONTROL DITCH

- - . . . . I . . .

-- . .

,--_ . . . '. . .._ '.-

Figure 1 7 . Outflow r s t e a t the f i e l d edge, Reid S i t e , for a s e r i e s of events from 8/02/86 t o 8/16/86.

FIELD WATER TABLE DEPTH FOR SERIES OF EVENTS FROM 8/02/86 TO 8/17/86, REID SITE

w 8 ,

- CONTROLLED TILE (59 cm)

--. CONTROLLED DITCH ( 6 4 cm)

... NO CONTROL DITCH (1 14 cm)

A

R

T 40

48 96 144 192 240 200 m 4 160

0

ELAPSED TIME SINCE START OF FIRST EVENT, Hr

Figure 18 . F i e l d water tab le depth f o r a s e r i e s of events from 8/02/86 t o 8/17/86, Reid site. Numbers in ( ) are weir depths.

2 0

0.7 - 0

T F L 0.5 - 0 W

R A T 8.3 E

m 0.2 m

0.6.

0.4

0.1 r

0

OUTFLB\Y RATE AT THE FIELD EDGE REID SITE FOR A SERIES OF EVENTS fROM 8/17/86 TO 9/09/86

- CONTROLLED TILE - .... R

0 48 96 144 192 240 268 336 364 A32 480 528 ELAPSED TIME SINCE START OF FIRST EVENT, Hr

Figure 19. Outflow rate at the f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 8/17/86 t o 9/09/86.

= r .. NO CONTROL DITCH ( 1 14 sm) pn 120

0 48 96 144 192 240 288 336 384 432 460 528

ELAPSED TIME SINCE START OF FIRST EVENT, H r

Figure 20. f i e l d water tab le depth for a s e r i e s of events from 8/17/86 t o 9 / Q 9 / 8 6 , Reid site. Numbers in ( ) are weir depths.

21

OUTFLO\Y RATE AT THE F I E L D E D G E R E I D SITE FOR A S E R I E S OF EVENTS F R O M 12/11/86 TO 12/31/86

0.06

0 U

F L 0 0.04 - *

W

0.05

0.03 - - T

. E 0.02 T

7’

-- . - COh’TROLLED TILE

--. CONTROLLED DITCH

NO CONTROL DITCH

m m

H r

/ 0.01 - -

... . ,

..... . . . . . . . . .

. . . . . . . . . . . . . . . . . . * . f . . . . . . . . . . - . . . .

... ........

.... ..... . . . . . . . . . . . . . .

Figure 21. Outflow rate a t the f i e l d edge, Reid S i t e , for a s e r i e s of esents from 12/11/66 t o 12/31/86.

F I E L D WATER TABLE DEPTH FOR S E R I E S OF EVENTS F2OM 12/11/86 TO 1/01/87, R E I D SITE

---- -_--- . _ _ -- _--_ ---- ~ -. . --- w o i A T I R

- CONTROLLED TILE (59 cm)

--. CONTROLLED DITCH (E4 cm) I

-. * T ... h‘0 CONTROL DITCH (114 cm) --> A ----.

120.- ,-/‘

c ,140-

0 48 96 144 192 240 268 336 384 432 460

ELAPSED TtME SINCE START OF FIRST EVENT, Hr

Figure 22. F i e l d water table depth for a s e r i e s of events from 12/11/66 to 1/01/87, Reid site. h’um5ers in ( ) are weir depths.

22

aga in the water t a b l e d i d not r i s e above the o u t l e t c o n t r o l l e v e l on e i t h e r of t he con t ro l l ed t r ea tmen t s , thus no outflow w a s observed. The f i e l d water t a b l e e l e v a t i o n on the no con t ro l d i t c h t reatment rose t o approximately 75 cm above t h e o u t l e t wei r e l e v a t i o n which r e s u l t e d i n outflow f o r t h i s t rea tment ,

The inf luence o f drainage con t ro l on outf low r a t e s during pe r iods of nea r normal r a i n f a l l (1/1/87 t o 3/08/87) are shown i n Figs . 23 and 25. Corresponding f i e l d water t a b l e e l eva t ions a r e shown During these even t s , peak outflow r a t e s were usua l ly t i l e , followed by t h e no c o n t r o l d i t c h and lowest on Some o f these events l i k e l y included su r face runoff , f i e l d water t a b l e rose t o the s o i l su r f ace (hour 1 2 , hour 228 i n F ig . 26) . During these even t s , drainage adverse e f f e c t on outf low when the f i e l d water t a b l e

i n F igs . 24 and 26. h ighe r on the con t ro l l ed t h e c o n t r o l l e d d i t c h . p a r t i c u l a r l y when the 432, 528 i n Fig. 24 and c o n t r o l had a s l i g h t ro se t o the su r face thus

r e s u l t i n g i n s u r f a c e runoff by promoting s l i g h t l y h igher outflow r a t e s compared t o t h e no c o n t r o l d i t c h t rea tment . I n genera l , however, outflow dura t ion (base flow) was usua l ly inve r se ly r e l a t e d t o peak outflow r a t e such t h a t t h e t o t a l outf low volume f o r events during t h i s w in te r per iod was about t h e same on a l l t rea tments .

During the 1987 s p r i n g per iod , Figs . 27 and 29, drainage c o n t r o l had both p o s i t i v e and nega t ive e f f e c t s on peak outflow r a t e s which seemed t o be r e l a t e d t o t h e amount of r a i n f a l l and the pe r iod between r a i n f a l l events . For example, t h e r a i n f a l l event on 3/12/87 of 0 .7 c m r e s u l t e d i n a h igher peak outf low ra te on t h e con t ro l l ed t i l e t rea tment , however, t h e dura t ion of flow was much s h o r t e r . The f i e l d water t a b l e e l eva t ion , F ig . 28, dec l ined a f t e r t h e r a i n f a l l event i n response t o both subsurface flow (base flow) and ET which usua l ly inc reases i n March. The f i e l d water table e l e v a t i o n had dropped t o nea r the c o n t r o l e l e v a t i o n on the con t ro l l ed t rea tments by the small r a i n f a l l events on 3/16 and 3/19 such t h a t t h e peak outflow r a t e s f o r t hese events were l e s s f o r the con t ro l l ed t rea tments than t h e no con t ro l d i t c h t rea tment .

S imi l a r r e s u l t s are seem f o r t he events shown i n Fig. 29. The r a i n f a l l event o f 1.4 em on 3/27 d i d no t r e s u l t i n any outflow on the c o n t r o l l e d t i l e t rea tment because t h e f i e l d water t a b l e j u s t rose t o about t he o u t l e t c o n t r o l e l e v a t i o n . outf low occurr ing on t h e con t ro l l ed d i t c h t reatment . 3/29 and 3/30 o f 0.6 c m r e s u l t e d i n h ighe r peak outflow on both the c o n t r o l l e d t rea tments compared t o t h e no c o n t r o l d i t c h t reatment as t h e f i e l d water t a b l e had a l ready r i s e n t o o r above the o u t l e t con t ro l e l e v a t i o n during the prev ious event (Fig. 30). By t h e r a i n f a l l event on 4/16 of 1 .4 cm, t h e f i e l d water table e l eva t ions on t h e con t ro l l ed t rea tments had dropped w e l l below t h e c o n t r o l e l e v a t i o n due t o ET and thus t h i s event d id n o t r e s u l t i n any outf low on these t rea tments while base flow w a s occur r ing on the no con t ro l d i t c h t rea tment f o r t h e e n t i r e per iod . I t should be poin ted o u t t h a t while t he v i s u a l impression o f t h e t reatment effects on outflows i n F igs . 27 and 29 appear s i g n i f i c a n t , t h e inf luence o f t hese events on r ece iv ing streams may n o t be ve ry d i f f e r e n t s i n c e t h e r e l a t i v e peak outflow ra tes f o r t hese events a re an o rde r of magnitude less than rhe outf low r a t e s dur ing t h e January and February pe r iod .

Outflow occurred on both d i t c h t reatments w i t h t he h ighes t peak The r a i n f a l l event on

The f i n a l two outf low per iods f o r t h e Reid s i t e are shown i n F igs . 31 and 33. R a i n f a l l from July through October, 1987, was s i g n i f i c a n t l y below normal (Appendix B 2 ) . R a i n f a l l dur ing November was s l i g h t l y above normal, bu t because

23

F 0.7 L W 0 :::I 0.6 NO CONTROL DITCH

OUTFLOW RATE AT THE FIELD EDGE REID SITE FOR A SERIES OF EVENTS FROM 1 / 0 1 / 8 7 TO 1 / 2 7 / 8 7

- - I -I -, , I ;. * a * . I * I

! I .

- CONTROLLED TILE n c

\:; I' I

FIELD WATER TABLE DEPTH FOR SERIES OF EVENTS FROM 1 / 0 1 / 8 7 TO 1 / 3 1 / 8 7 , REID SITE

Figure 24. Fie ld water t a b l e depth f o r a s e r i e s of events from 1/01/87 t o 1/31/87, Reid s i t e . Numbers i n ( ) a r e weir depths .

2 4

O U T F L O W RATE AT T H E FIELD E D G E REID S I T E F O R A S E R I E S O F E V E N T S FRQM 2 / 1 7 / 8 7 T O 3/08/87

0.9 7- I

- CONTROLLED TILE T F 0.7 - - CONTROLLED DITCH

NO CONTROL DITCH 0 0.6 W

- - = - ^ ^

0 40 Y b 144 192 240 208 336 304 432 ELAPSED TIME SINCE START O F FIRST EVENT, Hr

Figure 2 5 . Outf low rate a t the f i e l d edge, Reid S i t e , for a ser i e s of events from 2/17/87 t o 3/08/87.

FIELD WATER TABLE D E P T H F O R S E R I E S O F E V E N T S FROM 2/17/87 TO 3/08/87, REID S I T E

L \

'- . ._ 7

'\*

-. I

.r.

I .

'- -- - t - - CONTROLLED TILE (59 cm)

--1 CONTROLLED DITCH (64 cm) 70

NO CONTROL DITCH (1 14 cm) C

0 48 96 I 4 4 192 240 288 336 304 432 ELAPSED TIME SINCE START OF FIRST EVENT, H r

Figure 2 6 , Field water table depth for a s e r i e s of events from 2/17/87 to 3/08/87, Reid s i t e . Numbers i n ( ) are weir depths.

2 5

OlJTFLOW RATE AT THE FIELD EDGE REID SITE TOR A SERIES OF EVENTS FROM 3/09/87 TO 3/27/87

0.12 T

I 0 - CONTROLLED TILE

- - CONTROLLED DITCH L

NO CONTROL DITCH

- _

m

~

0 0 48 06 144 192 2 4 0 288 336 384 432

ELAPSED TIME SINCE START OF FIRST EVENT, H r

Figure 2 7 . Outflow r a t e a t t h e f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 3/09/87 t o 3/27/87.

FIELD \Z’ATER TABLE DEPTH FOR SERIES OF EVENTS FROM 3/09/87 TO 3/27/87, REID SITE

- _ _ _ _ I$’ or - - _ _ __ _.____________-

R 2 0 , , L

A I - CONTROLLED TILE (59 cm)

9 - - CONTROLLED DITCH (64 cm) 1 . -

NO CONTROL DITCH (1 14 cm> : ’\

. . ‘r . . . c

E

90

100 C

0 48 96 144 192 240 288 336 384 432

ELAPSED TIME S I N C E START OF FIRST EVENT, H r

Figure 28. F i e l d water table depth f o r a s e r i e s of events from 3/09/87 to 3/27/87, Reid s i t e . h’umbers i n ( ) a r e weir depths .

26

OUTFLOW RATE AT T H E FIELD E D G E REID S I T E F O R A S E R I E S O F E V E N T S FROM 3/27/87 TO 5/01/87

0 48 96 144 192 240 288 336 384 432 480 528 576 624 672 720 768 816 ELAPSED TIME S I N C E START OF FIRST EVENT, H r

Figure 29. Outflow r a t e a t t he f i e l d edge, Reid S i t e , f o r a s e r i e s of events from 3/27/87 t o 5/01/87.

FIELD WATER TABLE D E P T H F O R S E R I E S O F E V E N T S F R O M 3/27/87 T O 5/02/87, REID S I T E 9 o r - -

- CONTROLLED TILE (59 em)

CONTROLLED DITCH (64 em) E 204 R I ” T A B L E

D E P T

m c l 120 0 48 96 144 192 240 288 336 384 432 480 528 576 624 672 720 768 816

ELAPSED TIME S I N C E START OF FIRST EVENT, Hr

Figure 30. F i e l d water t a b l e depth f o r a s e r i e s of events from 3/27/87 t o 5/01/87, Reid s i te . Numbers i n ( ) a r e weir depths .

27

of the preceding dry period, no outflow was observed during this period although the water table was rising in response to the November rainfall. December, 1987, Figs. 31 and 32, the water table elevation on the no control ditch treatment had risen above the outlet weir elevation and thus, the rainfall during December resulted in outflow (probably base flow) on this treatment. In fact, the peak outflow rates increased with each subsequent rainfall event, even through the major rainfall events were about the same magnitude ( 2.3 cm on 12/11, 1.8 cm on 12/15, and 2.2 cm on 12/21). By the January, 1988 events, the field water table had risen to above the outlet weir elevation on both ditch treatments, and thus all rainfall events during this period resulted in outflow on these two treatments. The field water table elevation on the controlled tile treatment did not rise above the outlet control elevation until the last two events in January which resulted in the first outflow since April, 1987 on this treatment. There were no observed differences between the soil properties on these treatments to explain the relative differences in the rate of rise of the field water table elevation. The difference may be due to seepage (discussed later) resulting in a lower water table depth on the controlled tile treatment. However, since the field water table depth at the start of the event was below the measurable depth, there is no conclusive evidence to explain why the water table rose slower on the controlled tile treatment.

By

Similar trends were observed in outflow hydrographs for the Cahoon site and thus, for brevity, only two drainage outflow hydrographs are presented for the Cahoon site. A comparison of peak flows following a dry period is shown in Fig. 35, The rainfall associated with this drainage event was 12 em. The field water table recorders showed that the water table rose to the surface on the controlled ditch treatment but was no closer than 25 cm on the controlled tile treatment and 40 cm on the no control treatment, Fig. 36. This likely resulted in surface runoff on the controlled ditch treatment as evidenced by the higher peak outflow rate. the Cahoon site appeared to be related to the difference in water table depths (and thus in soil storage available for infiltrating rainfall) prior to the events. treatment prior to the rainfall event was approximately 75 cm. The field water table depth on the controlled ditch treatment was approximately 60 cm as compared to 85 cm on the no control tile treatment. rose to 15, 45 and 55 cm above the outlet weir level on the controlled tile, controlled ditch and no control tile, respectively, and was directly related to the relative difference in the peak outflow rates on each treatment.

As at the Reid site, the peak outflow rates at

For example, the field water table depth on the controlled tile

The field water table

Drainage hydrographs for the period 2/26 to 3/10, 1987 are shown in Fig. 3 7 , and field water table elevations for the same period are shown in Fig. 38. This represents a period of near normal rainfall and the resulting hydrographs are typical of winter drainage with higher peak outflows occurring on the controlled drainage treatments and longer duration flows occurring on the tiled treatments. higher during the winter period than during the drier fall period.

The peak outflow rates are also approximately 2 times

Individual. event hydrographs do not provide a clear distinction between total outflow volumes for the drainage treatments. water table management treatments is more easily seen by comparing cumulative outflows. Cumulative outflow hydrographs are shown in Figs. 39 and 40. While relative outflows varied from one event to the next, drainage control clearly reduced the total outflow on both the controlled ditch and tile treatments

The distinction between

2 8

OUTFLOW RATE AT THE FIELD EDGE REID SITE FOR A SERIES OF EVENTS FROM 17/29/87 TO 1 / 0 3 / 8 8

0.18 T

0.1

0.08

R

E

m m 0.04 - -

0.06

/ H 0.02 _.

r

0

T F 0.14 L 0 0.12 W

- -

--

--

:*...-. ....

- CONTROLLED TILE

CONTROLLED DITCH

. NO CONTRQL DITCH

... I 8 . , .

....... . . . . . . . . . . . . . . . .

._

.......

0 ' 0 48 96 144 192 240 280 336 384 432 480 528 576 624 672 720 768 616

ELAPSED TIME SINCE START OF FtRST EVENT, Hr

Figure 31. Outflow rate a t the f i e l d edge, Reid S i t e , for a s e r i e s O f events from 11/29/87 to 1/03/88.

ELAPSED TIME SINCE START OF FIRST EVENT. Hr

Figure 32. F ie ld water tab le depth for a series of events from 11/29/87 t o 1/02/88, Reid s i t e . Numbers i n ( ) are weir depths.

29

O U T F L O W RATE AT T H E FIELD E D G E REID F O R A S E R I E S OF E V E N T S F R O M 1/03/88 TO

. . . .

- CONTROLLED TILE

--. CONTROLLED DITCH

NO CONTROL DITCH

.. .., . *

SITE 7 / 2 9 / 8 8

.. ... .

Figure 33. Outflow rate a t the f i e l d edge, Reid S i t e , for a series of events from 1/03/88 to 1/29/88.

w A T

C m

FIELD WATER TABLE D E P T H F O R S E R I E S OF E V E N T S F R O M 1/03/88 TO 1/29/88, REID S I T E

0 -

10 - - - CONTROLLED TILE (59 cm)

--. CONTROLLED DITCH (64 cm) .

f . ;L.;

NO CONTROL DITCH (1 14 cm) 1 1.. 30

40

50

60

70

80

CIA

100 '"I v 0 48 96 144 192 240 288 336 304 432 480 528 576

ELAPSED TIME SINCE START OF FIRST EVENT, H r

Figure 3 4 . F i e l d water table depth for a series of events from 1/03/88 to 1/29/88, Reid s i te . Numbers in ( ) are weir depths.

3 0

OUTFLOW RATE AT THE FIELD EDGE CAHOON SITE AUGUST 19 TO 27, 1986

1.8-

u 1.6- RAINFALL 1 2 3 mm

?OTAL OUTFLOW (mm)

O

T

- CONTROLLED TILE (22.5)

- CONTROLLED DITCH (21.4)

NO CONTROL TILE (34.8)

- . . . .

- - 0 12 24 36 48 60 72 84 96 108 120 132 144 156 168 1 8 0 192

ELAPSED TIME SINCE START OF RAINFALL, Hr

Figure 35* Outflow ra te a t the f i e l d edge, Cahoon s i t e , f o r the period 8/19/86 t o 8/27/86.

FIELD WATER TABLE DEPTH, CAHOON SITE 8/09/86 TO 8/27/86

-

, I t t

- CONTROLLED TILE

-- CONTROLLED DITCH

. NO CONTROL TILE

I. ...- . .- .

“ I 120 221 223 225 227 229 231 233 235 237 239 241 243 245 247

JULIAN DAY

Figure 36. F i e l d water table depth for the period 8/09/86 t o 8/27/86, Cahoon s i te . August 19 is Jul ian day 231.

31

OUTFLOW RATE AT T H E r lELD E D G E CAHOON SITE h4ARCH 1 TO 8, 1987

i? " 3 - O T 7 W '4 2 .

A

m

RAINFALL 82.9 mm

TOTAL OUTFLOW (mm)

- CONTROLLED TILE (69.6)

- CONTROLLED DITCH (66.7)

(72.3)

. . . O J . ' ' . -+ - 0 12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192

ELAPSED TIME SINCE START OF RAItJFALL, Hr

Figure 37. Outflow ra te a t the f i e l d edge, Cahoon s i t e , for the period 3/01/87 t o 3/08/87.

FIELD WATER TABLE

- 0 W

- CONTROLLED TILE

- - COI4TFIOLLED DITCH

NO CONTROL TILE A

E SO--

. .. . . . .-.. . . , . , .... I . . .

.. ... 90 - -

C

Figure 38. F i e l d water table depth for the period 2/26//87 to 3/11/87, Cahoon s i t e . March 1 i s Jul ian day 60.

32

CUMULATIVE OUTFLOW CAHOON SITE, 1 /1/86 TO 9/27/87

u 40 L

T 32 I

E 24

A 36

v 28

0 20 - - u 16 - - T F 12-- L 8 . . 0 w 4 - -

0 -

C

; I

-- - CONTROLLED TtLE I

I /

-- I------------------ /- .-- -- ... CONTROLLED DITCH

- - * NO CONTROL DITCH /

i - - - -

-~ .....-... ... .. .. ..-...... . I

*-*

U M 44 T

- CONTROLLED TILE

. . CONTROLLED DITCH

--. NO CONTROL TILE

E 24

f------

Figure 39. Cumulative measured outflow a t the Cahoon s i t e during the period 1/1/86 to 9/27/87.

CUMULATIVE OUTFLOW REID SITE, 1/1/86 TO 1 / 2 6 / 8 8

C

33

relative to the uncontrolled water management treatments. the Cahoon site was 1 9 . 2 , 21 .6 and 43.9 cm for the controlled tile, controlled ditch and no control tile treatments. Thus, drainage control reduced outflow by approximately 50 percent at this site. Total outflow at the Reid site was 24.5 20.2 and 4 0 . 8 cm for the controlled tile, controlled ditch and no control ditch treatments. approximately 45 percent.

Total outflow at

Drainage control at this site reduced totah outflow by

The predominant difference between the Cahoon and Reid site is hydraulic conductivity. m/day compared to 18 .7 m/day at the Cahoon site. Cahoon site were approximately 4 times greater for the major events than peak drainage rates at the Reid site, but flow duration was at least twice as long at the Reid site such that the total flow was about the same at both sites. The difference in soil hydraulic properties such as hydraulic conductivity did not appear to influence the effect of controlled drainage on total outflow.

A s was discussed earlier (page 1) drainage waters present two particular problems to fresh waters and saline estuaries: 1 - a reduction in salt concentration due to fresh water dilution and 2 - contamination due to nutrients and sediment in the runoff. discussed in this section, it is difficult to relate the overall effect that controlled drainage has on peak outflow at the field edge and the subsequent effect the peak outflow has on the delivery of fresh water to saline estuaries. totally eliminated outflow at the field edge as compared to no control. was most apparent during drainage events that occurred immediately after periods of below normal rainfall and would be an expected result during the late sUmmer and fall period in most years since short term drought conditions are prevalent in North Carolina during the summer, However, since saline estuaries are not believed to be as sensitive to fresh water inflow during this season, reduced peak outflows at the field edge resulting from controlled drainage may not represent a benefit to saline estuaries.

Conductivity values measured at the Reid site were only 0 . 8 Peak outflow rates at the

Based on the drainage hydrographs

There were clearly periods when drainage control either reduced or This

There was also evidence that drainage control reduced peak outflow rates at the field edge during the spring period. in bare fields during March and April. from a bare field when the water table drops below about 60 cm (Anderson, 1985) and potential evapotranspiration is relatively high due to warming air temperatures. The influence of drainage control during this period is to retain more water in the soil profile compared to no drainage control which may increase soil evaporation. study because rainfall during March, April and May was considerably below normal. During years of normal spring rainfall, controlled drainage would probably result in higher spring outflow rates as was observed during the winter months of January and February.

Normally, tillage operations result Soil conditions may limit evaporation

This situation probably occurred during this

Based on these results, the influence of drainage control on peak outflows is clearly variable and very dependent on seasonal rainfall conditions. drainage control clearly reduced total drainage outflow at the field edge, we can not conclude from these results, that drainage control had or would have a positive effect on peak fresh water inflow to saline estuaries during the spring period when estuarine salinity is most critical. be the case even when the water control structure is maintained during the winter period.

While

This is believed to

3 4

One drainage control management strategy that was not been evaluated in this study, may provide a positive benefit to saline estuaries during the critical spring period. Continuous drainage control at a constant elevation will result in higher peak outflows at the field edge and spring rainfall than no control. the spring may be to provide drainage control only during and for a short period after rainfall events. To minimize surface runoff, the control elevation could be set at or near the soil surface. A s soon as all surface water had infiltrated, the control elevation could be lowered incrementally to its lowest possible level or until the next rainfall event occurred. This would allow the soil profile to drain gradually, but uniformly and also provide the maximum potential soil storage for the next rainfall event. management process would be very intensive and at the present, can not be evaluated with our existing models. the frequent adjustment required by this level of management would be acceptable to or practical for the farmer. However, this management strategy could be accomplished with the development of drainage control structures that adjusted automatically to rainfall conditions.

during normal winter A more desirable management strategy for

This

Furthermore, it is highly unlikely that

The major disadvantage of this proposed management strategy is that total drainage outflow would likely increase compared to conventional drainage control. As discussed in a later section of this report, an increase in total outflow would result in greater transport of nutrients to the receiving waters. This would be undesirable where the receiving surface water was a major stream, river or fresh water lake where the primary influence of agricultural drainage is an increased efflux of nitrogen and phosphorus. To evaluate the overall performance of more intensive management strategies like the one proposed will require further investigation.

hVTR1ENT CONCENTRATIONS

Nitrate concentrations in drainage outflow for the Cahoon site are shown in Fig. 41. Concentrations were fairly constant during 1986 with no apparent influence of the water management treatments. Beginning in January, 1987, nitrate concentrations started to decline from about 15 mg/l to less than 2 mg/l by October. This trend was observed on all treatments and the rate of decline was nearly the same for all treatments.

The Cahoon site was planted to continuous corn both years of this study. Nitrogen fertilization was reduced approximately 25 kgha from 1986 to 1987. Subirrigation is also practiced at this site on all treatments during the growing season. Therefore, drainage control was imposed on all treatments from May through July. Prior to the start of our study, Mr. Cahoon utilized drainage control only during the growing season. winter and spring of 1986 were not controlled on any treatment. outflow was subsurface, which-is likely considering the high conductivity of this soil, then high nitrate levels in the drainage outflow on all treatments would be expected. coupled with the possible loss of some nitrogen fertilizer by denftrificatfon during the subirrigation period may have significantly reduced the level of residual nitrate in the soil profile by the fall of 1987. groundwater wells were removed in March, 1987 to accommodate tillage operations. comparison.

Thus, outflows during the If most

The slight reduction in nitrogen fertilization in 1987

Unfortunately,

Thus groundwater nitrate concentrations were not available for

35

Z a

1 - 3

Q W Jtz c Q w

i=

--e

I

a n v ) b 0 0 z z

m

0 0 cr(

ma 1 0 k .d O h

N U

Q) k 3 tr

-rl E4

I

37

Total phosphorus concentrations for the Cahoon site are shown in Fig. 42. Phosphorus concentrations were more variable but show a gradual increase during the same period that nitrate concentrations were declining. suggest that surface runoff increased during this period, although total outflow was still probably dominated by subsurface flow. All water management treatments have the potential to provide both surface and subsurface drainage. Our experimental setup did not allow us to differentiate between the two. The predominant drainage event during the summer of 1987 resulted from 14 cm of rainfall on August 13, 1987 which could have resulted in significant surface runoff. was in the form of surface runoff when this site has such a high conductivity value which would be conducive to predominately subsurface drainage.

This would

However, it is unlikely that the majority of the drainage during 1987

Daily nutrient concentration values in drainage outflow for all sites is not presented. collected that nitrate concentrations in drainage outflow were generally independent of flow volume. Changes in concentration occurred gradually during the year with the highest nitrate concentrations observed in the late summer and early fall then decreasing gradually to their lowest levels by early spring. drainage outflow at the Cahoon site during 1987 was an exception to this trend.) Variation between events was believed to be due to the relative proportion of flow (surface or subsurface) in the event, however, as discussed earlier, we

However, it was concluded from the combination of all data

(As was shown above, the decline in nitrate concentration in

Phosphorus, NH4 and TKN showed no apparent fluctuation with time.

able to quantify this difference with the experimental setup used. esults have been reported by Deal et al. (1986), Evans et al. (1984)

and Gilliam et al. (1979). times total flow provides a good estimate of total nutrient mass transport in drainage water. in Table 3.

Since each drainage treatment contained combinations of both surface and subsurface drainage, the drainage treatment at any given site had only a minimum influence on drainage water concentrations of nitrate and phosphorus. Similar results have been reported by Gilliam et al. (1979); however, for this study period, this is believed to be attributable to the relatively low volume of drainage on all treatments. Had rainfall and drainage volumes been near normal, it is believed that the water table management treatment would have influenced nutrient concentrations in outflow. When comparing concentrations within sites, it would appear that minimizing drainage outflow by controlling the drainage outlet is more important than the actual type of system selected. However, when comparing concentrations between sites, it is apparent that nitrate concentrations are affected by the intensity of subsurface drainage. Based on the systems installed and the hydraulic conductivity at each site, the relative magnitude of subsurface drainage in this study was in the order of Cahoon > Stauldieun >> Ferebee = Reid = Williford.

This would suggest that average concentration

Average nutrient concentrations in drainage outflow are shown

SEEPAGE

There has been concern that controlled drainage practices that reduced drainage outflow might increase seepage and potential transport of nutrients to groundwater. Earlier studies by Gilliam et al. (1978) reported reduced drainage outflows due to controlled drainage, however, the reduced outflow could not be accounted for in a water balance. It was assumed that the

Table 3. Average Nutrient Concentrations at all Sites for the Period 1-1-86 to 1-29-88.

Nutrient Concentration OP TP C1- * Site Treatment Observations N03-N NH4-N TKN

(No) - - - - - - - - - - - - - - - - - (mg/L)--------------------- Cahoon' 1 27 11 * 10 .25 .70 .03 .15 24.63

2 95 11.03 .07 .73 .02 .12 26.84 3 17 7.28 .16 .48 .03 .16 26.21 4 16 9.82 1.13 2.16 * 09 .16 35.06

Fe r eb e e 1 5 3.82 .30 2.18 .04 .09 54.54 3 1 3.40 .20 2.90 .02 .08 52.50

Reid 1 16 4.20 .04 1.64 .02 .08 41.44 3 17 4.09 .03 1.44 .02 -06 36.88 4 28 3.87 .05 2.32 .06 .I5 32.74

Williford' 1 8 3.61 .09 .85 .Ol .02 47.54 3 4 3.10 .18 1.73 .02 .07 35.13

Stauldieun# 1 7 9.00 .01 1.40 .Ol .02 23.41

* Treatment 1 - controlled tile, 2 - no control tile, 3 = controlled ditch, 4 - no control ditch. *Outflow sample collection terminated 9/27/87.

reduced drainage outflow resulted in increased evapotranspiration, seepage or both. Attempts were made in this study to quantify experimentally any increased seepage that might be occurring. calcium chloride solution into source wells along a potential lateral seepage boundary at the Reid site was inconclusive. boundary, there was evidence of lateral seepage to the main collector canal, yet 30 m further along the same boundary, there was no evidence of a gradient. This situation may be fairly common due to variation in soil properties and stratification; however, this type of variation makes experimental evaluation extremely difficult. field ditch that had been backfilled. was no seepage gradient to the main collector canal, but rather that we were unable to detect the gradient either because of the lack of sensitivity of the methods used (static water level in piezometers) or that we failed to locate the seepage boundary within the 2 . 5 m zone evaluated. gradients are difficult to locate. Recent work by Glass (1988) suggest that leaching or seepage fractions are not uniform, but rather, are concentrated in fingers of preferential flow. Even during saturated flow conditions, the seepage fraction may be overlooked by failing to locate the fingers. This may have been the case in our field measurements.

The field water table recorders also indicated a potential loss of water by seepage. Referring to Figs. 26-30 in particular, the water table was receding faster on the controlled treatments at the Reid site, even when the field

The introduction of a concentrated

At one location along the

The gradient that was detected was traced back to a We do not intend to imply that there

Often, seepage

39

water table depth was below the outlet control elevation, than was the no control treatment. When the field water table elevation is above the outlet control elevation, the rate of decline of the water table could be affected by subsurface drainage, ET or both. But during periods when the no control water table was higher than the controlled water table elevations and the controlled water table elevations were below the outlet control elevation, the faster decline of the field water table depth on the controlled treatments can only be explained by seepage.

Fipps and Skaggs, (1986) have developed finite element methods to predict lateral seepage. Their results show that lateral seepage affects the outflow and water table level only at the first drain line adjacent to the seepage sink such as a main collector canal. The field water level recorders in our study at the Reid site were located between the second and third tile line from the main collector canal. Based on the work by Fipps, seepage to the main collector canal would not account for the the difference between outflows on the controlled vs no control treatments in this study. In addition, the main collector canal was dry during both the summer and fall of 1986 and 1987. The depth of the main canal is 2 . 3 m. Based on the water level in groundwater observation wells installed to monitor groundwater nutrient concentrations, (discussed in a later section) wells in the 1.8 to 2.7 m depth range were dry during this same period suggesting that the field water table level was in fact lower than the bottom of the main collector canal. This would suggest that there was no seepage to the collector canal during this time period. Thus, the difference between outflows for the controlled and non controlled water management treatments could only be accounted for as either lateral seepage below 2 meters to a remote sink, deep vertical seepage or increased evaporation on the controlled treatments. The scope of our study did not permit quantifying any of these.

NUTRIENT CONCENTRATIONS IN SHALLOW GROUNDWATER WELLS

k%ile controlled drainage may increase lateral or vertical seepage in some cases, there was no apparent evidence of conventional fertilizer nutrient accumulation in groundwater on these poorly drained soils. Comparison of nitrate/chloride ratios in time and with depth were used to qualify nitrate movement in seepage water. measured in shallow groundwater wells are shown in Figs. 43 -46 for two treatments at the Ferebee and Williford sites. Groundwater nitrate concentrations for all other sites are shown in Appendix D. Nitrate concentrations at the lower depth (2-3 m) at some sites were elevated immediately after well installation which was believed to be due to contamination during the installation. Groundwater wells installed at the tile depth (1-1.5 m) revealed nitrate levels consistent with those measured in drainage outflow.

ts was predominately subsurface drainage. the water table management treatments had any effect on the concentration of nitrate in the deeper groundwater wells at depths 3 and 4 . the benefits to receiving surface waters from reduced drainage outflow by controlled drainage practices is not at the expense of potential increases in nitrate concentrations in groundwater. wells at all sites.

Nitrate concentrations and nitrate/chloride ratios

This would indicate that drainage outflow on these There was no evidence that

This would suggest

This situation was observed in all

4 0

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW GROUNDWATER FEREBEE SITE, CONTROLLED TILE DRAINAGE

T N l o 0 3 8 N

m 1

Y L 2

0

0.2 T

0.18

0 0.16 3 D DEPTH 2 (1.0-1.7m) N 0.14 - 0 DEPTH 3 (2.0-2.7m)

B DEPTH 4 (3.0-3.5m) L 0.1

A c.06

t9 DEPTH 1 (.6-.9m)

c O*l2

0.01

0.04

0 0.01

8 86074 88105 88161 11117 17015 17046 87074 87105 171J5 67166 87191 17227 172511 17218 87315 8734s 88046 88074

JUUAN SAMPUNC DATE

Figure 4 3 . N i t r a t e and n i t r a t e ch lor ide r a t i o s i n shallow w e l l s a t Ferebee s i t e , 3 / 8 6 t o 3 / 8 8 . Controlled t i l e drainage. Absent da t a implies t h a t t he we l l was dry.

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS FEREBEE SITE, CONTROLLED DITCH DRAINAGE

18 11

14

3 12 N io m a

L 4 3 '

2 0

0.7 118 87311 1734l 88041 88071

N 0.6 0 0 DEPTH 1 (.6-.9m)

E3 DEPTH 2 (1.0-1.7~1) 3 ,, 0.5

c 0.4 0 O E P l H 3 (2.0-2.7m)

L S. DEPTH 4 (3.0-3.5m)

A

I 0 0.1

-

R OJ

1 Od

0 16074 88105 16188 11227 17015 87041 87074 17105 87135 1716.1 1715.1 17227 871% 17288 87315 87%) 18046 DO074

JUUAH SAMPUNC DATE

Figure 4 4 . Nitrate and n i t r a t e ch lor ide r a t i o s i n shallow w e l l s a t Ferebee s i t e , 3 / 8 6 t o 3 / 8 8 . Control led d i t c h drainage. Absent da t a implies t h a t t he we l l w a s dry.

41

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS WILLIFORD SITE, CONTROLLED TILE DRAINAGE

3 1.5 L l

0.5 0

16074 16105 16111 0.35 T

JL 1hZ511 8 S Z M

5 4.5

N 4

3 N 3

2.5

0 3.5

3 1.5 L l

0.5 0

16074 16105 16111 1hZ511 11SZM 17041 117074 117105 117115 117111 117111 117217 87158 671611 JL-% 17041 117074 -

117105 117115 117111 117111 117217 87158 671611

N 0.1 0

0.25 I3 DEPTH 1 (.5m) - DEPTH 2 (1.4-1.8m) c 0.2 L E DEPTH 4 (3.8-4.4m)

R

I

0.15

; 0.1

0 0.05

0 86074 86105 16106 1162511 8 h Z M 117048 17074 671W 117135 17186 171SI 17227 117151 172811

u .-.. 1

0 0.05

0 86074 86105 16106 1162511 8 h Z M 117048 17074 671W 117135 17186 171SI 17227 117151 172811

JUUAN SAMPUNG DATE

Figure 45 . Nitrate and nitrate chloride ratios in shallow wells at Villiford site, 3/86 to 10/87. that the well was dry.

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS WILLIFORD SITE, CONTROLLED DITCH DRAINAGE

Controlled tile drainage. Absent data implies

6

N 5 0 3 4 N

m 3

3' '1

0

T B DEPTH 1 (Sm)

DEPTH 2 (1.4-1.8~1)

0 DEPTH I (2.4-2.6m)

H DEPTH 4 (3.8-4.4m)

16074 111105 116116 116250 8 6 Z M 07041 07074 07105 I 7 1 U 87181 17111 07227 1725l 072611 JUUAN SAMPLING DATE

Figure 4 6 . Nitrate and nitrate chloride ratios in shallow wells at Williford site, 3/86 to 10/87. Controlled ditch drainage. Absent data implies that the well was dry.

4 2

Based on fluctuations in nitrate concentrations at depths 2-2.7 m and 3 - 3 . 5 m (Figs. 47-50) (exploded views), there was evidence of downward water and nitrate movement. drainage treatment, but apparently by rainfall or more specifically, lack of rainfall. During the dry summers and falls of 1986 and 1987, the water table obviously dropped below the depth of the wells at depth 3 (1.7-2.7m depending on site) because many wells at this depth were dry (dry wells are indicated by absence of nitrate concentration data). Rainfall percolating through the root zone to recharge the water table during or after dry periods, transported nitrates from the root zone to the water table depth. elevated nitrate concentrations in wells at depths 3 and 4 during recharge periods. However, there is no evidence that these nitrates accumulated in the groundwater. depths following periods of nitrate transport, any nitrate movement below the tile depth was apparently denitrified and showed no evidence of potential groundwater contamination. Previous studies by Gilliam et al. (1978) have shown that the redox potential of these soil types is well below the reduction threshold for denitrification at depths below 1 meter.

The relative magnitude of movement was not influenced by

This is indicated by

Based on the reduction in nitrate/chloride ratios at these

While commercial fertilizer nutrients showed no evidence of deteriorating groundwater quality, there may be potential problems associated with other agricultural chemicals such as pesticides that are not removed from the soil solution once leached below the root zone. This is not very likely since the natural mechanisms that cause soils to be poorly drained do not usually have significant vertical seepage. limited and this is an area that should be addressed in future studies.

However the data in this area is very

WATER MANAGEMENT SIMULATIONS

We did not instrument each site to measure drainage outflows. However, the utility of using DRAINMOD to simulate drainage outflows for different water table management treatments has been demonstrated (Skaggs 1980).

Several water table management strategies implemented at the Cahoon and Reid sites were simulated using DRAINMOD to compare with field measured water table depths and drainage outflows. verification of DRAINMOD. Neither our site instrumentation nor soil property measurements were intensive enough to provide this type of evaluation. Furthermore, DRAINMOD has been adequately tested and verified in earlier studies. The purpose of this comparison was to determine if DRAINMOD, in conjunction with the soil and site properties that were measured, could be used to approximate the drainage outflows observed in the field so that we could then expand our results to include management strategies that were not available for field evaluation at some sites.

This comparison was not intended as a

le simulated and measured water table depth curves for a controlled and

and Figs. 53 and 54 for the Reid site. The comparison between predicted easured water table depth is relatively good. Our field water level ders bottomed-out at approximately 1.2 m, thus during dry periods the

water table was below the measurable depth. DRAINMOD predicted water table depths approaching 2 m during some dry periods, but based on the dryness of the groundwater wells, the water table was probably below the simulated depth. Apparently the effective root depth was deeper that we estimated which would account for the fact that the actual water table depth was deeper than.

non controlled management strategy are shown in Figs. 51 and 52 for the Cahoon

4 3

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTHS 3 AND 4 FEREBEE SITE, CON TROLLED TILE DRAINAGE

m

9 l 0.5

a 86074 8L105 6 6 1 1 1 81217 87015 67041 67074 87105 87133 871L1 6 7 1 9 1 87117

N - 0.OK C L

0 04

A

0 ; o m

0

0 D E F l H 3 (2.0-2.7m)

I: DEPTH 4 (3.0-3.5m) Qa -<

86074 B a t 0 3 86111 88127 87015 87046 87074 87101 87tSS 171eI 17196 87217 87258 87281 1731# 8724s 88046 88074

JUUAN SAMPLING DATE

Figure 4 7 . h’itrate and n i t r a t e chloride ra t ios a t well depths 3 and 4 , Ferebee s i t e . Controlled t i l e drainage. Exploded s c a l e .

0.1

N 0 0.01 3 N - 0.08 C L R 0.04

A

0 : 0.01

0

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTHS 3 AND 4 FEREBEE SITE, CONTROLLED DITCH DRAINAGE

3

2.5

0 3 1 N

m 1.5

3 ’ 0.5

0

0 DEPTH 3 (2.0-2.7m) I DEPTH 4 (3.0-3.5m)

JUUAN SAUPUNC DATE

Figure 4 8 . h’itrate and n i t r a t e chloride r a t i o s a t well depths 3 and 4, Ferebee Controlled di tch drainage. Exploded s c a l e . s i t e .

4 4

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTHS 2 AND 4 WILLIFORD SITE, CONTROLLED TILE DRAINAGE

3

1.s

0 3 2 N

m 1.5

3 ' L 0 3

0 06074 81105 011118 0 6 U 8 0 6 l M 07046 07074 07105 07135 07168 071118 07217 0 7 1 s 071M

0 0.08

R 0.04

A

0

0

B DEPTH 2 (1.4-1.8rn)

5 DEPTH 4 (3.8-4.4m)

06074 88105 #Ell11 0 1 2 s @C?M 0704( 87074 07105 1 1 7 % ~ 87168 17,1111 07227 0 7 z s 8711)o JUUAN SAMPUNC DATE

Figure 4 9 . Nitrate and nitrate chloride ratios at well depths 2 and 4 , Williford site. Controlled tile drainage. Exploded scale.

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTHS 3 AND 4 WILLIFORD SITE, CONTROLLED DITCH DRAINAGE

n 1.5

0 3 1 N

m 1 .!I

3 ' L o 3

0

0.1 0 DEPTH 5 (2 .4 -2 .6~1)

DEPTH 4 (3 .8 -4 .4~1) N 0 0.01) 3 N

L R 0.04

A

0

- c O-O'

7 0.02

0 16074 161oI 161111 161% 112.80 17041 17074 1 7 1 w ' 7 1 s 17,111 17l(' ,7217 #,ayl '7288

JUUAN SAUPUNC DATE

Figure 50. Nitrate and nitrate chloride ratios at well depths 3 and 4, Williford site. Controlled ditch drainage. Exploded scale.

4 5

OBSERVED AND PREDICTED WATER TABLE DEPTH CAHOON SITE: CONTROLLED DRAINAGE, 80 FT TILE SPACING

O r -

Figure 51. Observed and p red ic t ed water t a b l e depth, Cahoon s i t e , 1986. Cont ro l led t i l e dra inage , 24 m t i l e spacing. Horizontal observed l i n e impl ies observat ion we l l bottomed o u t . I n t e r m i t t e n t s u b i r r i g a t i o n days 120-180.

WATER TABLE DEPTH CAHOON SITE, 1986 80 FT TILE SPACING SUBIRRIGATION WITH NO WINTER CONTROL

0

A -20 - observed T E -40 R

-60 A B

E -80

-100

P -120

1 331 361

Figure 52. Observed and p red ic t ed water t a b l e depth, Cahoon s i t e , 1986. No c o n t r o l l e d t i l e dra inage , 24 m t i l e spacing. I n t e r m i t t e n t s u b i r r i g a t i o n days 120-180 wi th no drainage c o n t r o l dur ing non- cropping season.

4 6

; 120--

140--

* 160--

C

4 7

: 2 , .. . . . .

- . . _ .

simulated. predicted water table depths during August. DRAINMOD predicted a rise in the water table depth sooner and higher than was measured in the field. between predicted and observed water table depths could probably be improved by increasing the effective root depth.

Also, this would explain the difference between the measured and

Agreement

The management strategy farmer in response to weather conditions. operating in the controlled or non controlled mode, the control changed several times during the growing season. management strategy, it was necessary to run several simulations for each treatment for each change in management strategy, then piece together the output so that the simulated management strategy would coincide with what was actually being practiced in the field. simulated vs observed values for Julian days 135 to 200 (Figs. 51 and 52) where the management strategy included several changes between no control, control and control with subirrigation.

at the Cahoon site during 1986 was adjusted by the Rather than a particular treatment

To accommodate this fluctuation in

This explains the variation in

Cumulative predicted and observed outflows are shown for the Cahoon site in Figs. 55, 57 and 59 and for the Reid site in Figs. 5 6 , 58 and 60. hThile there are differences between measured and predicted outflow values for individual events at both sites for the no control treatments, the total outflow for the two year study period agrees fairly well. outflow for the no control tile treatment (Cahoon site) and slightly under-predicted outflow for the no control ditch treatment (Reid site). DRAINMOD over-predicted outflow for all control treatments at both sites. This is likely due in part to more intensive management by the farmer during the growing season when he adjusted the control level and pumping frequency in response to prevailing weather conditions. For example, Mr. Cahoon would stop pumping in anticipation of forecast rainfall. table to recede due to ET providing more potential soil storage and consequently less drainage outflow should the rainfall develop as forecast. DRAINMOD does not account for this management flexibility. Referring to the water table hydrograph (Fig. 53), the field measured water table was obviously dropping on Julian day 160-170 when DRAINMOD predicted the water table would be rising in response to subirrigation. The pump was turned off during this period in the field, but could not be turned off in the simulation. The difference between measured and predicted outflow at the Reid site was due partly to the under-prediction of the water table depth during the extreme dry periods as discussed earlier.

DRAINMOD slightly over-predicted

This would allow the water

One of the primary objectives of this study was to evaluate the influence of water table management alternatives and management strategies on drainage outflow quantity and quality in response to different soil and site properties. water table management alternatives, DRAINMOD was used to estimate drainage outflows for those alternatives that were not measured in the field. As was shown above, DRAINMOD tended to over-predict outflow on the controlled drainage treatments compared to what we measured in the field. Our field measurements did not quantify seepage which could occur as a short circuit around the control structure, lateral seepage to surrounding uncontrolled fields or to a remote sink, or deep vertical seepage. As a result, our water balance did not close. After consideration of possible explanations, we have concluded that failure of the water balance to close is due to seepage. DRAINMOD performs a daily water balance which accounts for rainfall,

Since some sites did not include all combinations of the various

4 8

OBSERVED AND PREDICTED CUMULATIVE OUTFLOW CAHOON SITE, 1 / 1 / 8 6 TO 9/27/87, N O CONTROL TILE DRAINAGE

u 44 40

T 36 132- v E 28 24 -- 20 --

T 16.-

I _..-... - * -s

............ - ... -- . . OBSERVED

- PREDICTED --

f --

r' "

Figure 55. Observed and predicted cumulative outflow, Cshoon s i t e , 1/1/86 Eo 9/27/87. No control t i l e drainage, t i l e spacing 24 m, (Includes both surface and subsurface f l o w . )

- -

OBSERVED AND PREDICTED CUMULATIVE OUTFLOW REID SITE, 1/1/86 TO 12/31/87, NO CONTROL DITCH DRAINAGE

- ._ . . . . . . . . . . . -

.*

OBSERVED

- PREDICTED

,._....... ............ /-

c 36

32

; 28 I 24 v E 20 0 16 -

U T l 2 F L 8 0 4 W

0 C M

Figure 56. Observed and predicted cumulative outflow, Reid s i t e , 1/1/86 to 12/31/87. No control d i tch drainage, d i t ch spacing 100 m. (Includes both surface and subsurface f low. )

4 9

OBSERVED AND PREDICTED CUMULATIVE OUTFLOW CAHOON SITE, 1 /1/86 TO 9/27/87, CONTROLLED TILE DRAINAGE

U

A T 24 I v 20 E

16 0 u 12 T F 8 - - L 0 4 - W

L Z8

O-.

C

I . OBSERVED

- PREDICTED

- -

..

-. . - --

. .-- --. .- . - -

* -

. .-- r - -- _ _ _ - . . - - <

_ _ . . - - - _ --.

-

U M 32 T

Figure 57. Observed and predicted cumulative outflow, Cahoon s i t e , 1/1/86 t o 9/27/87. Controlled t i l e nage, t i l e spacing 24 m . (Includes both surface and subsurfa

OBSERVED AND PREDICTED CUMULATIVE OUTFLOW REID SITE, 1 /1/86 TO 12/31 /87, CONTROLLED TILE DRAINAGE

C f;t 36

; 28

32 OBSERVED

- PREDICTED - . . . . . . . . . . I . . . . . . . I 24 v E 20

0 16 U T ' 2 F

W

L a 0 4

0 1 61 121 181 241 301 361 56 116 176 236 296 356

JULIAN DAY m

Figure 5 8 . Observed and predicted cumulative outflow, Reid s i t e , 1/1/86 t o 12/31/87. Controlled t i l e drainage, t i l e spacing 24 m . (Includes both surface and subsurface f low.)

.

5 0

U L 24 A

; 20 V E ' 6 - .

0 12- U T F L 0 4 - - W

0.

OBSERVED AND PREDICTED CUMULATIVE OUTFLOW REID SITE, 7 11/86 TO 12/31 /87, CONTROLLED DITCH DRAINAGE

- -

- .-... ... OBSERVED

- PREDICTED - -

2

.-- _ - _-.. ,- .-....-.. e

.. . i

c

Figure 60. Observed and predicted cumulative outflow, Reid site, 1/1/86 t o 12/31/87. Controlled ditch drainage, ditch spacing 100 m. (Includes both surface and subsurface flow.)

51

evapot ranspi ra t ion , sur face runoff , subsurface drainage and changes i n s o i l s to rage . Control led drainage w i l l l i k e l y increase both ET and seepage as a r e s u l t of a higher water t a b l e . Increased ET is accounted f o r i n DRAINMOD; b u t , any water loss due t o seepage is not considered. Thus, t h e p o t e n t i a l dec l ine i n the water t a b l e and increased p o t e n t i a l s o i l s to rage due t o seepage i s no t accounted for. subsurface drainage and surface runoff . We be l i eve t h a t t h i s is one explana t ion f o r p a r t of t he d i f fe rence between s imulated and measured outflows. would inc rease ET during dry per iods.

In DRAINMOD, the seepage component should be added t o

Another poss ib le explanation is ET. Use of a deeper r o o t depth

Simulated and measured outflows a r e summarized i n Table 4 . outflows were approximately 30 percent higher than what we measured i n the f i e l d . This d i f f e rence was assumed t o be unaccounted-for a s e i t h e r ET, seepage o r both. Whether t h i s unaccounted-for volume i n the f i e l d measurements i s due t o increased ET o r seepage i s not important from the s tandpoin t of drainage water q u a l i t y . As discussed e a r l i e r , any apparent increase i n seepage d i d n o t r e s u l t i n an increase i n n i t r a t e t r a n s p o r t t o groundwater. Therefore , t h e reduct ion i n outflow represents a b e n e f i t t o rece iv ing sur face waters i n terms of both reduced outflow and n u t r i e n t t r a n s p o r t . This may not be t h e case f o r o ther a g r i c u l t u r a l chemicals such a s p e s t i c i d e s i f these c o n s t i t u e n t s continue t o move with the seepage water . Future s t u d i e s t h a t address the f a t e o f p e s t i c i d e movement should at tempt t o quant i fy seepage l o s s e s .

The p red ic t ed

DRAINMOD w a s used t o simulate s i x water t ab le management s t r a t e g i e s f o r each s i t e t o eva lua te the inf luence of s o i l and s i t e p rope r t i e s on drainage water q u a l i t y . The predic ted outflows f o r the con t ro l drainage t reatments were ad jus ted by the d i f f e rence between measured and predic ted outflows from those s i t e s t h a t had f i e l d measurements (Table 4) . This provided an es t imate of t he

Table 4 . Comparison of observed and predic ted cumulative drainage outflow f o r t h e Cahoon and Reid s i t e s . (Total cumulative outflow through 12/31/87). .

---=_ssP=- i.EpEp=piii==

Drainage Outflow

S i t e Water Management Treatment Predicted Measured Unaccounted-for

c m c m c m % of pred ic ted

Cahoon Control led T i l e 29.18 19.22 9.66 34.1 Control led Ditch 27.81 21.57 6.24 22.4 No Control T i l e 46.97 43.85 3.12 6.6

Re i d Control led T i l e 33.39 25.42 7.97 23.9 Control led Ditch 26.96 16.76 10.20 37.8 No Control Ditch 30.57 34.18 -3.61 -11.8

Combined Control 117.34 82.97 34.37 29.3* No c o n t r o l 77.54 78.03 -0.49 -0.6

* Value used t o a d j u s t predicted con t ro l management s t r a t e g i e s f o r unmeasured treatments f o r comparison with f i e l d measured va lues . No c o n t r o l pred ic ted values were not ad jus ted .

52

seepage and increased ET components (unaccounted-for in the measured outflows). This then allowed evaluation of several water table management alternatives that were not measured in the field. considered valid only for the measured rainfall used in these simulations. During wetter years, simulated outflows without adjustment may be a better estimate of drainage outflow to receiving surface waters, The adjustment is used only to allow comparison of all treatments for the period studied where drainage outflow was not measured. During periods of normal to above normal rainfall, DRAINMOD predictions would compare more favorably to measured field values for both controlled and non-controlled water management treatments.

Predicted drainage outflows for the two year study period for each water management strategy for each site are shown in Table 5. After adjusting for the seepage component (unaccounted-for in Table 4 ) controlled drainage reduced estimated outflow by approximately 40 percent (range 17 to 56 percent) compared to the non-controlled treatments. This reduction is similar to the reduction in drainage outflow in response to controlled drainage reported by Gilliam et al. (1978) on soils at the Tidewater Research Station.

This adjustment is

The reduction in outflow does not appear to be related to soil properties that influence drainage nor the the type of drainage system, tile or ditch (predominately subsurface vs surface). Subirrigation negated any benefit of controlled drainage, at least in terms of drainage outflow at the management intensity allowable in DRAINMOD, (DRAINMOD considers minimum management only). However, as was demonstrated at the Cahoon site, subirrigation with intensive management and accomplished without any significant reduction in the benefit of controlled drainage.

good management decisions on "when to pump" can be

NUTRIENT TRANSPORT

Nutrient transport to receiving surface waters was estimated by multiplying the average concentrations from Table 3 by the outflow volumes in Table 5 . Estimated nutrient transport is shown in Table 6. the most dominant factor influencing total nutrient transport in drainage outflow. As discussed earlier, there was very little variation between concentrations for different water management treatments within each site, but there were variations between sites which appeared to be related to the intensity of surface v s subsurface drainage. all nutrients was nearly proportional t o the reduction in outflow volume. Soils with more intensive subsurface drainage showed the potential for nitrate concentration reduction. However, in terms of nutrient transport, concentration reduction was relatively insignificant compared to the influence on drainage volume. Thus, the most important management strategy, regardless of system type, is to retain as much rainfall on site to minimize drainage outflow. The use of water control structures in the drainage outlet is a very economical method to accomplish this objective. However, to attain the maximum potential water quality benefit to receiving surface waters, it is imperative that the system be managed throughout the entire year.

Estimated annual nitrogen and phosphorus transport are shown in Table 7. Drainage control reduced annual N transport by an average of 7.3 kg/ha on the tile treatments (subsurface drainage) and 6.7 kg/ha on the ditch treatments (surface drainage). Increasing the intensity of subsurface drainage slightly

Outflow volume was clearly

The reduction in transport of

53

Tab e 5. Simulated drainage outflows, estimated seepage volume and estimated drainage outflow contributing to surface water quality for all water table management strategies at all sites, January 1, 1986 to December 31, 1987

7- I__q_ _-- ---=E=-

Drainage Outflow', cm * Site Treatment Observed Simulated Unaccounted-for' AdjustedOutflow=

Cahoon 1 19.2 29.2 9.7 19.2 2 43.9 47.0 - 43.9 3 21.6 27.8 6.2 21.6 4 - 42.7 - 42.7 5 - 70.7 20.7 50.0 6 - 59.1 17.3 41.9

Ferebee 1 - 35.1 10.3 24.8 2 - 40.4 - 40.4 3 26.1 7.6 17.7 4 - 28.0 - 28.0 5 - 49.5 14.5 35.0 6 - 28.9 8.5 19.9

Reid 1 25.4 33.4 8.0 25.4 2 30.6 - 30.6 3 16.8 27.0 10.2 16.8 4 34.2 30.6 - 34.2 5 - 43.9 12.9 31.0 6 - 28.3 8.3 20.0

Stauldieun 1 - 37.2 10.9 2 - 49.5 - 3 - 27.1 7.9 4 - 27.4 - 5 - 57 .O 16 .O 6 - 27.2 8.0

Williford 1 - 47.8 14.0 2 - 51.3 - 3 - 41,9 12.0 4 - 43.8 - 5 - 63.7 18.7 6 - 43.1 12.6

26.3 49.5 19.2 27.4 41.0 19.2

33.8 51.3 29.6 43.8 45.0 31.2

* Treatment 1- controlled tile, 2 - no control tile, 3 = controlled ditch, 4 = no control ditch, 5 = subirrigation with winter controlled tile, 6 = subirrigation with winter controlled ditch.

Stauldieun simulated with Cahoon measured rainfall. was 265 feet at Cahoon site, 330 feet at all other sites. Tile spacing was 100 feet at all sites. 'Component of simulated drainage outflow on control treatments estimated as seepage or increased ET. Estimated drainage outflow influencing receiver surface water quality.

*Ferebee site simulated with Reid measured rainfall. Williford and Ditch spacing

=

5 4

Table 6. Predicted nutrient transport in drainage outflow for the period 1/1/87 to 12/31/87

~ _ _

Mass Transport, out -

Site Treatment flow NO3 M14 TKB OP TP *

- - - - - - - - - - - - - _ - - kgfia _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ cm

Cahoon 1 19.2' 21.3 .48 1.34 .06 .29 2 43.9" 48.4 .31 3.20 .09 .53 3 21.6" 15.7 .35 1.04 .06 .35

5s 50.0 55.5 1.25 3.50 * 15 .75 4 42.7 41.9 4.83 9.22 .38 .68

6$ 41.9 30.5 .67 2.01 .13 .67

Ferebee 1 24.8 2s 40.4

17.7 28.0 35.0 19.9

Reid 1 25.4' 2$ 30.6 3 16.8' 4 34.2'

6$ 28.3

Williford 1 33.8 2s 51.3 3 29.6 4$ 43.8 5$ 45.0 6$ 31.2

5s 43.9

9.5 15.4 6.0 9.5 13.4 6.8

10.7 12.9 6.9 13.2 18.4 11.6

12.2 18.5 9.2 13.6 16.2 9.7

26.3 23.7 49.5 44-6 19.2 13.4

4s 27.4 19.2 5$ 41.0 36.9 6$ 19.2 13.4

21$ Stauldieun

3$

.74 5.41 .10 .22 1.21 8.81 .16 .36 .35 5.13 .04 .14 .56 8.12 .06 .22

1.05 7.63 .14 .32 .40 5.77 .04 .16

.10 4.17 .05 * 20

.12 5.02 .06 .24 -05 2.42 .03 .10 .17 7.93 .21 .51 .18 7.20 .09 .35 .08 4.08 e 06 .17

-30 2.87 .03 .07 .46 4.36 .05 .10 .53 5.12 .06 .21 .79 7.58 * 09 .31 .41 3.83 .os .09 .56 5.40 .06 .22

.03 3.68 .03 .05 -05 6 . 9 3 0 05 * 18 .06 3.07 -04 .08 .08 4.38 .05 Ill .04 5.74 .04 ,08 .06 3.07 .04 -08

P P - - * Treatment 1 = controlled tile, 2 - no control tile, 3 = controlled ditch, 4 - no control ditch, 5 - subirrigation w/ tile, 6 - subirrigation w/ditch. All simulated controlled drainage and subirrigation treatments had year round control.

'Measured outflow. $Concentration values were estimated from measured values from most

All other volumes are simulated.

similar water table management treatment at the same site,

55

Table 7. Estimated annual nitrogen and phosphorus transport in drainage outflow. *

= - - - s c = - , - __I- =L-- &--=

Tiled (Subsurface drainage) Ditch (Surface drainage)

Site Soil Type No cont. Control Reduction No cont. Control Reduction

Cahoon Fe rebe e Reid Williford Stauldieun

Average

- - - - - - - - - - - - - - - - . . - Total Nitrogen, kg/ha------------------

Ballahack 25.8' 11.3* 14.5' 25.6 8.4' 17.2 Ponzer/Wasda 12.1 7.5 4.6 8.8 5.6 3.2 Wasda 9.0 7.4# 1.6 10.6' 4.7' 5.9* Hyde 11.4 7.5 3.9 10.6 7.2 3.4 Portsmouth 25.8 13.1 12.1 11.8 8.2 3.6

16.8 9.4 7.3 13.5 6.8 6.7

Cahoon Ballahack .53# .29# .24# .68 * 35# .33 Ferebee Ponzer/Uasda .36 ' 22 .14 .22 .14 * 08 Re id Wasda .24 .20# .04 .51# . lo# .41" Williford Hyde .10 .07 .03 .31 .21 .10 Stauldieun Portsmouth .10 .05 .05 .ll .08 .03

Average .27 .17 .10 .37 .18 .19

* A l l values based on simulated drainage outflow averaged for two year study period except as noted.

#Values based on field measured drainage outflow averaged for two year study period.

increased N transport on both the controlled and non-controlled treatments relative to surface drainage. The relative reduction in nutrient transport due to drainage control was about equal on both the tiled and ditch treatments.

Previous studies have suggested that the benefit of controlled drainage to reduce nitrate transport by reducing subsurface outflow might be counter productive for phosphorus sensitive surface waters. It has been suggested that a reduction in subsurface outflow would result in an increase in surface runoff which would also increase phosphorus transport. Table 7, both total nitrogen and total phosphorus transport was reduced by controlled drainage in this study. The reduction in phosphorus could result from both a reduction in surface outflow and settling of sediment containing attached phosphorus. drainage was not observed because rainfall was significantly below normal. During years of more noma1 rainfall, surface runoff may increase with controlled drainage as has been suggested. seepage will increase on controlled surface drainage systems and account for some reduction in potential surface runoff. phosphorus transport to groundwater. wells were nearly always less than 0.02 mg/L.

As shown in

An increased in surface runoff in response to controlled

However, it is also likely that

We observed no evidence of Phosphorus concentrations in groundwater

56

WATER CONSERVATION

While we did not attempt to quantify water conservation as a result of controlled drainage practices, some qualitative conclusions can be drawn from observations made during this study. Drainage outflow was obviously reduced on the controlled drainage treatments. Vhile vertical seepage may have accounted for up to 5 percent of the rainfall at the study sites, this alone would not account for the difference in outflow on the controlled vs non controlled drainage treatments. Some (and maybe most) of the rainfall that was retained on site by controlled drainage was likely used by the crop to satisfy evapotranspiration. deep well to supply irrigation when needed. 1986 which was the driest year during the study at this site, however, irrigation was not needed during 1987 even through rainfall was still below normal. that did occur more efficiently, Mr. Cahoon was able to achieve excellent yields

Several farmers in the Beaufort, Hyde, Tyrrell and Washington county areas relayed similar experiences during 1987. In Hyde county for example, the Williford site utilizes pumping stations to provide artificial drainage. pump is located less than one mile from the Pamlico Sound. Since the initiation of an RCA project and controlled drainage practices on his farm, Mr. Williford has reduced his pump discharges to the Pamlico Sound by modifying his pump management strategy. Williford's pumps were set to start pumping when the water level in the ditch reached 1.2 meters. His pump startup threshold has now been reduced to 1 meter during critical drainage periods and 0.6 meters at other times. In the Hales Lake watershed area, which represents nearly 4,000 hectares of agriculture, nearly every farmer has installed control structures on their main collector canals since the start of the RCA projects on the Ferebee and Reid farms. artificial drainage which increases the rate of freshwater discharge estuaries is detrimental as many perceive, then this must be considered a very positive step towards correcting one source of the problem.

For example, the Cahoon site is equipped with a Subirrigation was provided during

By simply controlling the drainage outflow and using the rainfall

in 1987 without utilizing groundwater,

His

Prior to the RCA project, Mr.

If to

57

REFERENCES CITED

their effects in predicting water stress in corn. PhD dissertation. North Carolina State University, Raleigh, NC.

Anderson. S. H. 1985. Spatial variability of soil hydraulic properties and

Bailey, A. D. and T. Bree. 1980. Effect of improved land drainage OR river flood flows. Institution of Civil Engineers, Flood Studies Report, London.

Burk, W., J. Mulgueen and P. Butler, 1974. Aspects of the hydrology of a gley soil on a Drumlin. Irish Journal of Agricultural Research.

Deal, S . C., J. W. Gilliam, R, W. Skaggs and K. D. Konyha. 1986. Prediction of nitrogen and phosphorus losses as related to agricultural drainage system design. Agriculture, Ecosystems and Environment, (18):37-51.

Eggelsmann, R. 1972. The water balance of low land areas in North East coastal region of the F64. Inst. Symp. Hydrology of Marsh Ridden Areas, Minsk, UNESCO.

Evans, R. O., P. W. Westerman and M. R. Overcash. 1984. Drainage water quality from land application of swine lagoon effluent. Transactions of ASAE. 27(2):473-480.

Fipps, G. and R. W. Skaggs. 1986. Effect of Canal Seepage on Drainage to Parallel Drains. TRANSACTIONS of ASAE. 29(5):1278-1283.

Gmbrell, R. P., J. W. Gilliam and S . B. Weed. 1975. Nitrogen losses from soils of the North Carolina Coastal Plain. Journal of Environmental Quality 4(3):317-323.

Gast, R. G., W. W. Nelson and G. W. Randall. 1978. Nitrate accumulation in soils and loss in tile drainage following nitrogen applications to continuous corn. Journal of Environmental Quality 7(2):258-261.

Gilliam, J. W., R. W. Skaggs and S . B. Weed. 1978. An evaluation of the potential for using drainage control to reduce nitrate loss from agricultural fields to surface waters. Tech. Report No. 128. Water Resources Research Institute of the University of North Carolina. Raleigh, NC.

Gilliam, J. W., R. W. Skaggs and S . B. Weed. 1979. Drainage control to reduce nitrate loss from agricultural fields. Quality 8( ):137-142.

Journal of Environmental

Gilliam, J. W. and R. W. Skaggs. 1985. Use of drainage control to minimize potential detrimental effects of improved drainage systems. Proceedings of the Specialty Conference "Development and Management Aspects of Irrigation and Drainage Systems".

In:

Ir Div., ASCE. pp 352-362.

Glass, R. 1988. PhD dissertation. Cornel1 University. In Progress.

Hillel, D. 1971. Soil and Water: Physical Principles and Processes. Academic Press, Inc., New York, NY. pp.76-77,

58

Jarrett, A. R. and Y. R. Hoover. 1979. Runoff and erosion reduction via drainage and increased infiltration. Tech. Report PB80-111 917, Office of Water Resources and Technology, Washington, DC. 81 pp.

Konyha, K. D., R. W. Skaggs and 9. W. Gilliam. 1988. Hydrologic impacts of agricultural water management. Ch. 17. In: The Ecology and Management of Wetlands. Vol. 2 . pp 148-159.

Magette, W. L. and R. A. Weismiller. 1984. Agriculture and the Bay. Maryland Agricultural Experiment Station and Cooperative Extension Service. Fact Sheet. 4p.

McLean, Y. P. 1981. Flood peak flow rates and subsurface drainage. M.S. Thesis, Agricultural Engineering Department, Ohio State University.

Schwab, G. 0. and J. L. Fouss. 1967. Tile flow and surface runoff from drainage systems with corn and grass cover. Trans. of the ASAE 10(4):492-493, 396.

Skaggs, R. W. 1980. A water management model for shallow water table soils. Report No. 134. Horth Carolina. Raleigh, NC.

Water Resources Research Institute of the University of

Skaggs, R. W., Y. W. Gilliam, T. 9. Sheets and J. S. Barnes. 1980. Effect of agricultural land development on drainage waters in the North Carolina Tidewater Region. Report No. 159. Water Resources Research Institute of the University of North Carolina. Raleigh, NC.

Skaggs, R. W. and Abdolhossim Nassehzadeh-Tabrizi. 1982. Effect of drainage system design on surface and subsurface runoff from artificially drained lands. Proceedings of the Inst. Symposium on Rainfall-Runoff Modeling. Mississippi State University, Mississippi State, M s .

Skaggs, R. W., A. Nassehzadeh-Tabrizi and G. R. Foster. 1982. Subsurface drainage effects on erosion. Journal of Soil and Water Conservation 37(3):167-172.

van Beers. W. F. J. 1970. The Auger Hole Method. International Institute for Land Reclamation and Improvement. H. Veenman and Zonen. Wageningen, The Netherlands.

59

APPENDIX A. S o i l Properties

SOIL PROFILE DESCRIPTION Reid S i t e , Camden county

(F ie ld Sample C 2 , 0-260 cm, #5, 260 - 570cm)

Descr ipt ion by

Tony Jacobs , Wendell G i l l i a m and Tomy Cone February 3 , 1986

S o i l Se r i e s : Wasda

0 -

30 -

78 - 88 -

105 -

115 -

125 - 150 - 178 - 181 - 210 - 260 - 300 -

depth ( c m l DescriDtion 30 Ap Sandy loam with much very fine sand, 7.5YR 1.7/1 to 2/1,

well incorporated crop stubble to 30 cm. Gradual.

Sandy loam, 5YR 1.7/1, slick, organic feel masks any feel o f fine sand if present, many roots fragments. Diffuse.

78

88 Sandy loam, 1OYR 4/2, traces o f bedding.

105 Sandy loam, 7.5YR 3/2, old wood fragments.

115 Sandy loam, 7.5YR 3/4, common 7.5YR 514 mottles and organic debris. Abrupt.

125 Sandy loam with very find sand, 7.5YR 3/4, with lOYR 6/4 sand lenses. Abrupt.

150 Sandy loam (very fine), 1OYR 7/2, few 5YR 5/8 mottles. Abrupt.

175 Sandy loam (very fine), 7.5Y 7/1. Abrupt.

181 Loamy sand, 2.5Y 6/4. Abrupt.

210 Loamy sand, bedded sandy clay, 1OY 6/1.

160 Loamy sand, 1 O Y 4/1, flowing, no return.

300 Loamy send, 7.51 5/1.

570 Loamy sand, 5GY 5/1.

Table A l . Example layout of ground water observat ion wel l s and f i e l d water t a b l e wel l a t one sampling s t a t i o n , Reid s i t e .

Well Layout X X 0 X X

1.85 m 3.0 m 2.25 m 1 . 0 m

Ground Water Observation wel l ## DeDth. m Perforated Zone. cm

155 - 185 315 3.0 270 - 300 316 2.25 195 - 225 317 1 . 0 70 - 100

314 1.85

X - Rela t ive p o s i t i o n of ground water observat ion wel l 0 - Location of f i e l d water t a b l e w e l l

60

=51=

v) 0

U 0 u) 0 2.

-CY r); 0 3

-. -

3

i +l 5 0 311

0 312

0 313

3 0 314

0 315 0

N a 0 316

0 317

0 318 0 % 0 319

c ” E l 0 320

0 321

0 322

0 323 0

* E l 0 324

0 325

i G s - 3 5

3 0 326 0 327

0 328

0 329

2 0 330 D m 0 331

0 332

0 333

2 0 334 n 3

0 335

0 326

GS-5

0

E4 0 337

0 ~15: 0 338

m E l 0 339

0 3.60

0 341 0 + 0 342 W

0 343

A P P E N D I X A. CONT.

depth (cm)

0 - 30 Ap

30 - 50

50 - 91

91 - 97

97 - 120

120 - 153

153 - 161

161 - 194

194 - 227

227 - 233

233 - 334

SOIL PROFILE DESCRIPTION

Ferebee S i t e , Camden county (F ie ld Sample C 1 2 B)

Description by

Lydia Nelson March 4 , 1986

S o i l Se r i e s : PonzerATasda

Descr ip t ion

Sandy loam, 7.51X 1 . 7 / 1 , common f i n e and medium r o o t s . Clear .

S i l t loam ( s l i g h t l y s t i c k y ) , 7.5YR 2/1 , common f i n e and medium r o o t s . Gradual.

Loam, mixed 101% 4/6 and lOYR 3/3, f e w coarse r o o t s . Clear .

Loam t o s i l t y c l a y loam, mixed lOYR 5/2, 1 O Y R 5/6, and 10’111 3/3. Gradual.

Loam ( s i l t y loam b o r d e r ) , 2.5Y 7/1. Abrupt.

Loam, 1OY 4/1. Gradual.

Very f i n e sandy loam, 7.5Y 4/1. Gradual.

Fine loamy sand, 2.5GY 4/1. Abrupt.

Very f i n e sandy loam (loamy sand bo rde r ) , 2.5GY 4/1, l i q u i d Abrupt.

Very f i n e sandy loam, 2.5GY 4/1, l i q u i d . Abrupt.

Fine loamy sand, 1 O Y 5/1, l i q u i d .

Table A2 . Example l ayou t o f ground water observa t ion we l l s and f i e l d water t a b l e w e l l a t one sampling s t a t i o n , Ferebee s i te .

Well Layout X X 0 X X

1.2” 3 . 3 m 2.2m 0.9m

Ground Water Observation w e l l # DeDth. m Per fora ted Zone. cm

420 1 . 2 90 - 120 421 3 .3 200 - 330 422 2.2 190 - 220 423 0.9 60 - 90

X - Rela t ive p o s i t i o n of ground water observa t ion we l l 0 = Location of f i e l d water t a b l e w e l l

62

APPENDIX A , cont.

c l t- erebee

c #11B 0 419 0 418 0 417 0 416

C # H A 0 415 0 414 0 413 0 412 0 411

Camden Count

C #12B 0 420 0 421 0 422 0 423

C #12A 0 424 0 425 0 426 0 427

Figure A2. Instrumentation at Ferebee site in Camden County.

63

APPENDIX A . CONT.

SOIL PROFILE DESCRIPTION

Cahoon Site, Pamlico county (Field Sample P7)

Description by

Wendell Gilliam, Tony Jacobs and Tomy Cone February 5, 1986

Soil Series: Ballahack

0 - 30 Ap Sandy loam, 7.5YR 3/2, few crop roots.

30 - 70 Sandy clay loam, 7.5YR 3/1.

70 - 85 Sandy loam, 7.5YR 3/2.

85 - 95 Sandy loam, lOYR 4/3.

95 - 135 135 - 200 200 - 230 Loamy sand, 2/5GY 4/1.

230 - 290

Sandy loam to loamy sand, 5Y 6/2.

Sandy loam to loamy sand, 2.5Y 6/3, many 1 O Y R 6/8 mottles.

Sandy loam, slightly sticky, 2.5GY 4/1.

290 - 320 Sandy to loamy sand, 5GY 4/1.

320 - 420 Loamy sand, 5GY 4/1, common shell fragments and identifiable shells.

Table A3. Example layout of ground water observation wells and field water table well at one sampling station, Cahoon site. -

Well Layout X X 0 X X X

0.8 m 2.0 m 4.2 m 3.2 m 1.3 m

Ground Water Perforated Zone. cm Observation well # Depth. m

22 0.8 50 - 80 23 2.0 170 - 200 24 4.2 390 - 420 25 3.2 290 - 320 26 1.3 100 - 130

X = Relative position of ground water observation well 0 = Location of field water table well

64

APPENDIX A. cont .

0 24 0 28 0 23 0 27 0 22

Cahoon Pamlico County

0 32 0 31

manning

Canal

0 14 0 13 0 17

0 12 0 16 8 11 0 15

/T-J#PI pJ D # P 3

Pump

I: 0

J c3' -cr

"Tiled Field .- > 2

0 26 0 30

0 21 0 20

0 19 0 18

D # P 6

I,x No Tile -5 e n >

0 34 i

Canal -+ F L

# Soil Description R 0 Water Quality Well 17 Water Level Recorder @ Grab Sample Recorder

\F, R Flashboard Riser

Canal +

esco - #2 ;o

3

N

Figure A3. Instrumentation at Cahoon s i t e in Pamlico County.

65

APPENDIX A . CONT.

SOIL PROFILE DESCRIPTION

Wil l i ford S i t e , Hyde county (F ie ld Sample W2 A)

Descript ion by

Lydia Nelson March 5 , 1986

S o i l Se r i e s : Hvde Loam

deDth ( c m l Descr ip t ion

0 - 24 Ap Loam, 7.5YR 2/1, common f i n e and medium r o o t s . Diffuse.

24 - 43 Sandy loam, 7.51’R 2/2, common f i n e and medium r o o t s . Gradual,

Clay loam, 1 O Y R 4/3, wood fragments ( o l d r o o t s ) . 43 - 66

66 - 96 Clay loam, 2.5Y 5/1, wood fragments.

96 - 100 Loam, 10Y.R 5/2, wood fragments.

100 - 150 Fine sandy loam, 7.5GY 4/1.

150 - 188 Fine t o medium sandy loam, 7.5GY 4/1.

188 - 360 Loam sand (sand bo rde r ) , 5GY 4/1, soupy.

Table A4. Example layout of ground water observa t ion we l l s and f i e l d

r <E;-==

water table we l l a t one sampling s t a t i o n , W i l l i f o r d s i t e .

Well Layout X X 0 X X 0.5 m 3.6 m 1.4 m 2.6 m

Ground Water Observation wel l # DeDth. m Pe r fo ra t ed Zone. c m

211 0.5 20 - 50 212 3.6 330 - 360 213 1.4 110 - 140 2 14 2.6 230 - 260

X - Relative p o s i t i o n o f ground water observa t ion we l l 0 - Location of f i e l d water t a b l e well

66

APPENDIX A , cont.

WiI I iford P Hyde Couniy

Road

< 3

D T

-. -I-

I'

0 218 0 217

0 216 0 215 #W2B

#W2A 0 214 0 213

0 212 0 211

0 219 0 220

0 221

# W l B

#Wl A 0 222 0 223

0 224

i F R

r Drainage 1 Pump

Canal -3

50 0 D L1

Road

# Soil Description

o Water Quality Well

@ Grab Sample Location

\F/ R Flashboard Riser

Figure A 4 . Instrumentation at Williford site in Hyde County.

67

APPENDIX A . CONT.

depth (cml

0 - 18 Ap

18 - 50

50 - 85

85 - 120

120 - 300

300 - 350 350 - ?

SOIL PROFILE DESCRIPTION

Stauldieun Site, Beaufort county (Field Sample H1 A)

Description by

Lydia Nelson March 4, 1986

Soil Series: Portsmouth

Description

Loamy sand, 7.512 1.7/1, common fine roots. Gradual.

Sandy loam, mixed 7.5YR 1.7/1 and lOYR 5/3, very few medium roots. Abrupt.

Medium sandy loam, roots. Diffuse.

Coarse loamy sand, Diffuse.

lOyR 5/3, few medium roots, some old tree

mixed lOYR 5/3 and lOYR 5/6.

Sandy loam (sticky, with find sand), 5GY 4/1, flowing sand. Abrupt.

Loamy sand (coarse), 5GY 4/1.

Sand, 5GY.

Notes: Dep.th are questionable after 120cm since samples were flowing sand.

Table A5. Example layout of ground water observation wells and field water table well at one sampling station, Stauldieun site. -

Well Layout X X 0 X X 2.5 m 1.2 m 5.0 m 0.5 m

Ground Water Observation well # Depth. m Perforated Zone. cm

111 0.5 20 - 50 112 5.0 470 - 500 114 2.5 230 - 250 113 1.2 90 - 120

X = Relative position of ground water observation well 0 = Location of field water table well

68

APPENDIX A. cont.

C. Van Stauldieun Beaufort County

\

I c:

c +- .-

I i

Ditch

#Hl A 0 111 0 112 0 113 0 114

#Hl B 0 115 0 116 0 117 0 118

+?-- Ditch

o Water Quality Well

@ Grab Sample Location

45 Flashboard Riser R

Figure A5. Instrumentation at Stauldieun site in Beaufort County.

69

APPENDIX A . CONT.

# Table A 6 . Satura ted Hydraulic Conductivity Measured a t Study S i t e s . ____ -

Number of Location Measurements Mean (m/day) Range (m/day ) S i t e

Cahoon Pamlico 13 18.7 2.10- 32.8

Fer ebe e * Camden 17 .58 .07 -2 .3

Re i d Camden 18

Stauldieun Beaufort 5

0.78 .05-1.9

3.8 1 .5 -8 .3

Hyde - 1 . 5 W i 11 i f o r d* -F-------- _I__-= --i==5===

- ' A l l measurements made by auger ho le procedure. * Values as repor ted by b a n e Hinson, D i s t r i c t Conserva t ion is t , SCS and

P ro jec t D i rec to r , 1983 t o 1986 f o r RCA water management demonstration s i t e s .

7 0

APPENDIX A, CONT,

* Table A7. Soil Water Characteristic cumes for study site.

OBS SITE HEAD

1 2 3 4 5 6 7 8 9

PO

11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

CAHSUB 0.00 7.62 9.82 17.82 37.22

CAHSUB 61.42 C B 108.62 CAHSUB 189.73 CAHSUB 439.78 CAHSUB 605.58

C 0.00 CAHSUR 7.62

9.82 17.82 37,22 61.42

108.62 CAHSUR 189.73

439.78 605.58

0.00 7.62 9.82 17.82 37.22 61.42

FERSUB 108.62 FE 189.73 FE 439.78 FERSUB 605 58

0.00 7.62 9.82 17.82 37.22 61.42

FERSUR 108.62 FERSUR 189.73 FERSUR 439.78 FERSUR 605.58

- TYPE- 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

- REQ- MTHETA YLBULKDEN

6 0.498500 1 * 15000 6 0.474500

6 0.344500 6 0.311667 6 0.298167

3 0.497667 1.15333 3 0.449000 3 0.411333 3 0.381667 3 0.328000 3 0.286000 3 0.25 3 0.229000 3 0.161333 3 0.114000

5 0.514400 1.09200

5 0.468200 5 0.454600 5 0.395750 5 0.374500

10 0.652500 0,59300 10 0.595000 10 0.583400

10 0.348250

APPENDIX A:Table A7. cont.

OBS SITE HEAD

41 42 43 44 45 46 47 48 49 50

51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

VANSUB VANSUB

VANSUB VANSUB

0.00 7.62 9.82 17.82 37.22 61.42 108.62 189.73 439.78 605.58

0.00 7.62 9.82 17.82 37.22 61.42 108.62 189.73

VANSUR 439.78 VANSUR 605.58

REIDSUB 0.00

REIDSUB 605.58

0.00 7.62 9.82 17. $2 37.22 61.42 108.62 189.73 439.78

REIDSUR 605.58

SAS 16:02 Thursday, January 21, 1988 12

- TYPE- -FREQ MTHETA MBULKDEN

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

2 0.522500

2 0.461500

2 0,446500 2 0.446500 2 0.338000 2

1.04000

3 0.651667 0.60000 3 0.593333 3 0.590333 3 0.59 3 0.50 3 0.455667 3 0.40 3 0.37 3 0.27 3 0.25

10 0.476400 1.27000 10 0.455300 10 0.451400 10 0.448300

10 0.430300 10 0.413778 10 0.399000 10 0.335500

6 0.588667 0,79333

6 0.513833

6 0.477833 6 0.389667 6 0.340600

7 2

APPENDIX A . Table A7, con t ,

OBS

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100

SITE

WI LLSUB WILLSUB WILLSUB WI LLSUB WILLSUB W I LLSUB WILLSUB WILLSUB WILLSUB WILLSUB

HEAD

0.00 7.62 9.82 17.82 37.22 61.42 108.62 189.73 439.78 605.58

WILLSUR 0.00 WILLSUR 7.62 WILLSUR 9.82 WILLSUR 17.82 WILLSUR 37.22 WILLSUR 61.42 WILLSUR 108.62 WILLSUR 189.73 WILLSUR 439 78 WILLSUR 605.58

SAS

P TYPE-

0 0 0 0 0 0 0 0 0 0

16:02 Thursday, January 21, 1988 12

-FREQ_ MTHETA MBULKDEN

3 0.467667 3 0.447000 3 0.440000 3 0.437333 3 0.425333 3 0.414667 3 0.403667 3 0.392667 3 0.356000 3 0.309500

0 3 0 3 0 3 0 3 0 3 0 3 0 3 0 3 0 3 0 3

0.580000 0.565000 0.563000 0.555333 0.535333 0.515333 0.496000 0.491667 0.482100

1.31333

0.82333

* Output d irec t ly from SAS. (10-20 cm). HEAD = suction (cm) MTHETA - water content (cm /cm ) MBULKDEN = bulk dens i ty . Freq = number of samples.

Sub- subsurface (45-60 cm). Sur 7 sugface

73

A P P E N D I X A: c o n t ,

D

N

P 16 0 R 12 0 S 8 I T 4 Y

0 C m

DRAINABLE POROSITY VS WATER TABLE DEPTH, CAHQON SITE

,’ // , ,’

/.- //

// //’.

/’ .H

- / - __ 0 20 40 60 80 100 120 140 160 80 200

M-ATER TABLE DEPTII, c m

Figure A 6 . Drainable po ros i ty ( p o t e n t i a l s o i l s torage) v s water t s b l e depth Cahoon s i t e .

DRAINABLE P O R O S I T Y VS WATER TABLE D E P T H , REID SITE

D

m ’WATER TAULE DEI’TII, CIU

Figure A 7 . Drainable po ros i ty ( p o t e n t i a l s o i l s torage) vs water t a b l e depth Reid s i te .

7 4

A P P E N D I X B. Daily R a i n f a l l a t Study S i t e s

TABLE B1. Rain fa l l a t Reid site (Camden County) 1986

DAY JAN FEB ABR

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

.08

.oo

.05

.13

.oo

. 00

. 00

. 00

. 00

. 00

. 00

. 00

. 00

.oo

. 00

. 00

. 00

.05 1.45

.oo

.oo

.oo 1.32 . 00

3.35 1.45 .08 .oo .oo .oo .oo

* 00 .oo . 00 . 00 * 00

1.22 f 00 . 00 . 00 * 00 .46 * 00 . 00 .oo .86 .03 . 00 .oo .lo .53 . 00 .oo .oo .03 . 00 '00 .58 .oo

.oo .oo

.OO .08

.03 .03

.05 .03

.oo .oo -00 -28 .oo .oo .OO .36 .OO .08 .oo .oo .oo .oo .oo .oo .03 -05

2.46 .05 .oo .oo .OO .13 .OO .03 .OO .05 .05 .05 .56 '05 .OO 1.14 .OO .03 .oo .oo .03 .OO .oo .oo .oo .oo .03 .oo .OO .03 .oo .oo .oo .oo . 00

---- TOTAL 7.96 3.81 3.24 2.47

MAY JUN JUL AUG SEP

. 00

. 00

. 00

. 00

.oo

. 00

.05

. 00

.oo

.oo

.oo * 00 .03 .13 . 00 * 00 . 00 . 00 . 00 . 00 .oo . 00 . 00 . 00 * 00 . 00 . 00 . 00 .oo . 00 . 00

.03

. 00

. 00 f 00 . 00 .36

1.50 . 00 .oo . 00 * 00 .oo . 00 .03 . 00 .03 * 00 . 00 . 00 . 00 . 00 -00 . 00 . 00 .oo .oo . 00

1.83 2.03 .97

.03 1.47 .03 . 00 . 00 . 00 . 00 . 00 . 00 . 00 . 00 . 00 . 00 . 00 * 00 .oo .oo . 00

1.17 . 00 .76 .10

1.88 . 00 .61 * 00 .oo .oo .94 .23 * 03

. 00

.25 6.73 , 00 .05 .05 .61

1.42 .30 .30

3.05 ,84 .66 .03 .03 .43

5.64 .05 .53

3.05 .23 * 25 * 00 * 00 .oo . 00

2.46 3.05 .03 . 00 . 00

.oo

.oo , 00 .03 .15 .99 .08 .05 . 00 .08 .15 .15 .03 . 00 .oo .oo .03 . 00 .oo .25 .41 . 00 . 00 . 00 .oo .oo . 00 . 00 . 00 . 00

- - -- - .21 6.78 7.25 30.04 2.40

OCT

. 00

.oo

.oo

. 00

.oo

. 00

.oo

.05

.15

.30

.03

.03

.03

.05

. 00

.oo

. 00

. 00

.oo * 00 .oo .03 .oo . 00 .oo . 00 * 00 . 00 .oo . 00 .oo

.67

NOV DEC YEAR

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.05 .03

.oo .oo

.oo .oo

.OO -03

.03 .13

.oo .18

.13 1.96 2.54 . 46 .18 .OO .15 .oo .86 .OO ,oo .oo .05 .oo .oo .38 .oo .oo .oo .oo .oo .oo .OO .03 .oo .13 .oo 4.88 .oo .oo .OO .03 .oo .oo .oo .oo .oo -00 .OO .28

.oo - 3.99 8.52 77.34

~

NORMAL 10.24 9.58 10.54 7.52 9.96 10.21 14.48 14.50 11.99 9.93 7.52 7.87 124.33

75

A P P E N D I X B . CONT,

TABLE B 2 . Rainfall at Reid site (Camden County) 3.987

DAY JAN FEB MAR ABW MAY JUN JUL BUG SEP OCT NOV DEC YEAR

1 2 3 4 5 6 7 8 9

10 11 1 2 13 14 15 1 6 1 7 18 1 9 20 21 2 2 23 24 25 26 27 28 29 30 31

8.56 .08 . 00 . 00 . 00 * 00 . 00 .20 .61

1.04 .03 . 00 . 00 . 00 .10 .43 .20

5.08 . 00 .05 * 00 .03 * 08 .08 .08 .18 * 00 .oo .03 . 00 . 00

.38

.05 * 00 . 00 .13 . 00 .13 * 80 . 00 .oo .03

1.92 . 00 . 00 . 2 1 .10

1.49 .03 03 -03 .03

2.36 .15 . 00 . 00 .oo .97 .25

2 . 2 1 .oo f 00 . 00 .05 .05 .05 .10 .36 .23 * 00 .66 .05 .08 .05 .15 .oo . 00 .33 . 00 . 00 * 00 .oo .03 . 00 .03

1 . 3 5 .36 -03 .36 .23

.08 * 08 .61 . 00 . 00 .03 . 00 .03 .03 .03 .03 .18 . 00 .03 .28

1.37 ‘05 .56 .15 .03 .05 .08 f 08

1 . 3 0 .10 .03 .oo . 00 . 00 . 00

.oo

. 00 * 00

1.60 - 0 3 .03 .03 .oo .oo . 00 . 00 .03 .03 .03 .33 . 00 . 00 . 00 .63 .05 .03 .46 . 6 1

1.85 . 00 .oo .03 . 00 .oo .20 .20

1.80 .05 .28 .53 .08 .03 . 00 .oo f 00 . 00 .03 . 00 .05 * 18 .13 * 20 .03 .03 . 00 . 00 . 00 .10 .20 -03 ,05 .76 * 20 ,20 .20 .20

* 20 .05 .15 .13 .05 .03 .10 . 00 . 00 . 00 -03 ,15 * 89 .79 . 00 . 00 . 00 . 00 -00 00 . 00 * 00 . 00 9 00 . 00 . 00 * 00 .oo . 00 .03 .05

.08

.05

.05

.30

.76 * 00 . 00 . 00 .oo . 00 * 00 . 00 . 00 .05 .61 .05 .03 .08

2.44 f00 .oo + 00 . 00 .oo .oo . 00 .oo * 00 . 00 , 00 . 00

.oo .oo

.oo .18

.OO .48

.OO .03

.oo .oo

.oo .28

.oo .10

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.03 .03

.oo .oo

.oo .oo

.oo .oo

. O O .03

.oo .oo

.oo .oo

.oo .oo

.OO .03

.oo .oo

.oo .oo

.OO .76

.oo 1 .75

.oo .oo

.oo .oo

.oo .oo . 00

. 00

.03

.03 s 00 . 00 . 00 . 00 . 00 . 00

1.24 1 .14

.46

. 00

.03

. 00

.05

.15

.33

. 00

.oo e 03 .03 . 00 . 00 .oo .05 .38

2.62 1 .07

.23

. 00

.03 e 03 .18 . 00 .03 . 00 00

. 00

. 00 2 . 2 9

.03

.oo ,08

1.75 . f 8 .20 .74 .08 . 7 1

2.24 .25 . 00 .oo . 00 . 00 .03 .53 .08 . 00 . 00

- - - - - - - - - - - _ _ s -

TOTAL 16.86 9.09 6.76 5 .21 6.17 5.36 2.65 4.50 .03 3.67 7.87 9.46 77.63 -

EORMAL 10.24 9.58 10-54 7.52 9.96 10.21 14.48 14.50 11.99 9.93 7.52 7.87 124.33

A P P E N D I X B . CONT.

TABLE B3. Rainfall at Cahoon site (Pamlico County) 1986

BAY

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

TOTAL

JAN

.08

.oo -05 .13 a 00 0 00 . 00 . 00 D 00 . 00 * 00 . 00 * 00 . 00 .oo . 00 . 00 .05

1.45 00 . 00 f00

1.32 . 00

3.35 1.45

.08

. 00

. 00

. 00

. 00

7.96

FEB MAR

.oo .oo

.oo .oo

.OO .36

.oo .oo

.oo .oo 1.22 .05

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.46 .OO

.oo .oo

.oo .oo

.08 6.81

.13 .OO

.OO .23

.oo .oo

.58 .OO

.08 2.06

.OO 1.07

.OO .05

.oo .oo

.13 .OO

.10 .oo

.oo .oo

.oo .oo

.97 .oo

.oo .oo . 00 . 00 . 00

3.75 10.63 --

APR

.oo

. 00

. 00

.05

.oo

. 00

.08 * 00 . 00 . 00 . 00 . 00 * 00 .oo * 00 .46 .25 . 00 .oo .oo .74 .oo . 00 . 00 -00 . 00 .oo . 00 . 00 100

1.58

HAY JUN

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.OO 5.13

.OO .30

.OO .36

.OO 1.24

.oo .oo

.oo .oo

.oo .oo

.oo .oo

.oo .oo 2.29 2.16 .OO .61 .OO 1.32 .OO .03 .oo .oo .oo -00 .23 -63

2.06 .OO .oo .oo .oo .oo .10 1.45 .03 .OO .03 -00 .oo .oo .36 2.72 -00 .10 -00 -23 . 00 -- 5.10 16.28

JUL AUG

.OO .03 2.57 2.95 .13 4.24 .OO 1.04 .oo .oo .oo .oo .oo .20 .oo .oo .oo .oo -84 .03 .oo .oo .OO 1.50 .OO 1.07 .oo .oo .oo .oo

1.96 .46 .OO 4.24 .oo .oo .23 11.99 .13 .23 .oo .oo .48 .03

1.85 .OO .33 .03 .oo .oo .OO .03 .oo .oo .oo .oo

1.45 .03 .OO .15 .oo .10

9.97 28.35 --

SEP

. 00

.oo

. 00

.oo

. 00

.03

. 00 I O 0 .oo .oo .oo . 00 * 00 . 00 . 00 .03 .03 * 03 .05 .10

1.40 .oo . 00 . 00 .05 . 00 .oo . 00 .05 . 00

- 1.77

OCT NOV BEC YEAR

.OO .25 .38

.oo .oo 4.22

.oo .oo .oo

.OO .OO .03

.OO .23 .OO

.oo .oo .oo

.03 .03 .03

.03 .03 .OO

.05 .03 .OO 1.12 .OO .03 .03 1.70 .20 .OO .03 1.27 .03 .03 2.21

3.10 .OO .05 .OO 1.68 .OO .oo .oo .oo .OO .08 .05 .OO .OO . 8 6 .OO .OO .OQ .OO .48 .OO .oo .oo .oo .OO .OO ,05 .OO .OO - 0 5 .05 .20 .89 .23 .03 .03 .OO .03 -03 .OO .03 .OO .oo .oo .oo .OO .03 .OO .03 .69 .OO . 00 . 00 - 4.70 --- 5.58 10.38 106.05

NORMAL 10.19 10.08 9.19 7.57 11.20 13.03 17.15 16.08 14.61 8.61 7.82 9.37 134.90

APPENDIX B. CONT.

TABLE B4. Rainfall at Cahoon site (Pamlico County) 1987

DAY JAN FEB MAR A P R MAY JUN JUL AUG

1 -00 .oo 4.45 .oo .oo .oo 2 .OO .OO .03 . O O .OO .OO 3 .OO .03 .OO . O O .OO 1.14 4 .OO .03 .OO .OO .OO .08 5 .OO .03 .OO .OO .OO .OO 6 .OO .05 .OO .OO -00 .OO 7 . O O 1 .14 .OO .OO -58 .OO 8 .OS .OO .OO .03 .OO .OO 9 .OS .03 .OO .03 .OO .OO

10 .48 .OO . O O .03 .OO .OO 11 . O O -00 .05 .05 .OO 5.11 1 2 . O O .03 1.02 .03 2.26 .OO 13 .OO .OO .OO .OO .25 .OO 14 . O O -03 .OO .OO .OO .OO 15 .OO .OO .OO 1 .93 .OO .OO 1 6 1 . 1 2 1 .47 -03 1.65 .OO -00 1 7 .66 -46 .OO .OO .OO .OO 18 1 .65 .03 .03 .OO .OO .OO 1 9 .OO .03 1.57 . O O .OO .OO 20 .oo .oo .oo .oo .oo -00 2 1 .oo .oo .oo .oo .oo .oo 22 .oo .oo .oo .oo .oo .oo 23 -00 -00 .OO .OO .OO . O O 24 .OO .03 .OO .OO .OO .OO 25 .OO .03 .08 .OO .OO .OO 26 .OO .03 .08 .OO .OO 1 .35 27 .OO 2.08 1.42 .OO .OO .OO 28 .OO . 7 6 . f 8 . O O .05 .OO 29 .OO .OO .OO .05 .OO 30 .OO .53 .oo .oo .oo 31 .OO .51 . 00

3.30 .23 .41 3.43

6.05 .OO ,03 .OO .oo .oo .OO .03 .OO 2.84 .oo .oo .oo .oo .OO .84 .OO .41 .oo .oo . O O 13.92

1.09 .oo .43 .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .oo .30 .OO .oo 3.10 .oo .oo .oo .oo .oo .oo

-------- TOTAL 4.01 6.29 9.98 3.75 3.19 7 . 6 8 11.61 24.80

S E P

. 00

. 00

.03

.15 2.08

.15 2.03

.41

.oo

. 00

. 00 * 00 . 00 . 00 . 00 .05 .05 . 3 6 . 00 . 00 * 00 .08 .03 . 00 . 00 . 00 . 00 . 00 .03 . 9 1

SEAR

-__.

6.36 77.67

NOFMAL 10.19 10.08 9.19 7.57 1 1 . 2 Q 13.03 17.15 16,08 14.61 109.09

7 8

APPENDIX C . Measured F i e l d Water Table Depths.

W A T - 2 0 - -

WATER TABLE DEPTH CAHOON SITE, 1 1 / 2 5 / 8 5 TO 3/27/87 DRAIN SPACING 40 FEET

- NO CONTROL

" W A

E R -40

T A -60 B

-80 E

D -100 E P H C M

- NO CONTROL

. . CONTROLLED

T -20

..- ...--- .. T -120

-160 85324 86009 86059 86109 86159 86209 86259 86309 86359 87044

JULIAN DATE

Figure C1. Vater table depths measured at Cahoon site, 11/25/85 to 3/27/87. Drain spacing 12 m.

.. CONTROLLED

c M

-160 85324

Figure C2.

86009 86059 86109 86159 86209 86259 86309 86359 87044 JULIAN DATE

Water table depths measured at Cahoon site, 11/25/85 to 3/27/87, Drain spacing 18 m.

7 9

APPENDIX C . cont.

-

WATER TABLE DEPTH CAHOON SITE, 17/25/85 TO 3/27/87 DRAIN SPACING 80 FEET

: *

- NO CONTROL

. . CONTROLLED

.-

..I ..I

I

.: I.

.. . .. : . . . * . . . :.

: ' : ? . -....: '

=-. .: . - \ - . - % .

. -8 '- - -L5.

. .. *. . .

':

.. %.

* -. .. ._ I

*.-

H

-160 65324 86009 86059 86109 86159 86209 86259 86309 86359 87044

JULIAN DATE

C M -'.O~

Figure C 3 . Vater table depths measured a t Cahoon s i t e , 11/25/85 t o 3/27/87. Drain spacing 24 m .

WATER TABLE DEPTH CAHOON SITE, 11/25/85 TO 3/27/87 DITCH SPACING 265 FEET

0 W ; -20

E R -40

T

B E

A -60

-80

D -100 E

-140 C M I -160

85324 86009 86059 86109 86159 86209 86259 86309 86359 87044 JULIAN DATE

Figure C4. Water table depths measured at Cahoon s i t e , 11/25/85 to 3/27/87. Ditch spacing 80 m .

8 0

APPENDIX C . cont.

WATER TABLE DEPTH REID SITE, 4986

JULIAN DATE %

Figure C 5 . Vater table depths Ioeasurcd at Reid site, 1986.

JULIAN DATE

Figure C6. Water table depths measured at Reid s i t e , 1987.

81

APPENDIX D. N i t r a t e and Ni t r a t e Chlor ide R a t i o s I n Shal low

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS CAHOON SITE, NO CONTROL TILE DRAINAGE

Groundwater W e l l s . (F igu res n o t shown i n main r e p o r t ) .

T

D t I: - I 1-87 2-87 3-87 4-81 1-81 8-81 3-81

0 L 3-81 4-81 1-01

JUUAN

Isi DEPTH

5 DEPTH

0 DEPTH

DEPTH

& 8-81

SAMPUNG DATE

(.5-.Pm)

(1.0-1.5m)

(1.7-2.1~1)

(3.0-4.0m)

I

1-87 t m .

2-87 3-87

Figure D1. Nitrate and nitrate chloride ratios in shallow groundwater wells. Cahoon site-no control tile drainage. Absent data implies w e l l was dry.

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS CAHOON SITE, CONTROLLED TILE DRAINAGE

11

14 N 0 12 ; 10

8 m

3 : L I

0

0.7 c1 DEPTH 1 (.S-.@m)

B DEPTH 2 (1 .O- 1 .Sm) N 0.1 0

0.5 0 DEPTH I (1.7-2.lm)

- D DEPTH 4 (1.0-4.Om) c 0.4 L

R

I Q 0.1

0 1

0 S-DI 4-81 1-14 1-80 1-87 1-17 3-D7

JUUAN SAMPUNG DATE

Figure D2. Nitrate and nitrate chloride ratios in shallow groundwater wells. Cahoon site-controlled tile drainage. Absent data implies well was dry.

82

A P P E N D I X D. cont.

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS CAHOON SITE, NO CONTROL DITCH DRAINAGE

116074 116161 17015 17041 117074 0.4

B DEPTH 1 (.5-.Dm) N 0

8 DEPTH 2 (1.D-1.5m) 3 0.1 N - 0 DEPTH 3 (1.7-2.lm) C L 0.2 m DEPTH 4 (3.0-4.Dm)

R A T 0.1 I 0

0

86074 111105 16111 11e227 67015 a7041 a7074 JUUAN SAMPUNG DATE

Figure D3. Nitrate and nitrate chloride ratios in shallow groundwater wells. Cahoon site-no control ditch drainage. was dry.

Absent data implies well

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS CAHOON SITE, CONTROLLED DITCH DRAINAGE

25 -r

11111 11117 17011 17044 17074 66D74 CRlQ.3 0.7 T

D DEPTH 1 (.S-.@m)

R DEPTH 2 (1 .D- 1.5m)

0 DEPTH 3 (1.7-2.lrn)

m DEPTH 4 (3.Q-4.Dm)

11116 B1127 17015 87041 17074 81074 81105 JUUAN SAUPUNG DATE

Figure 04. Nitrate and nitrate chloride ratios in shallow groundwater wells. Cahoon site-controlled ditch drainage. Absent data implies well was dry.

8 3

APPENDIX D. cont.

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS REID SITE, CONTROLLED TILE DRAINAGE

8b074 8S105 87015 87041 87074 871W 87135 871BI 87191 87117 67158 87266 87311 67UI 88015 88041 b8074

N - 0.5 C L 0.4

A T 0.2 1 I

O O” 0 L

0 DEPTH 1 (.5-.Bm)

f DEPTH 2 ( 1 .O- 1 .Om)

0 DEPTH 3 (1.P-2.7m)

E DEPTH 4 (3.D-4.Dm)

86074 B61W 87015 87046 87074 87105 871>5 87166 #7(16 87227 872% 8 7 3 M 87311 8 7 ~ 4 ) 8&015 8 6 ~ 7 4 JUUAN SAUPUNG DATE

Figure D5. Kitrate and nitrate chloride ratios in shallow groundwater wells. Reid site-controlled tile drainage. Absent data implies well vas d r y .

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS REID SITE, CONTROLLED DITCH DRAINAGE

’* T

0 DEPTH 1 (.5-.Bm)

t3 DEPTH 2 (1.0-1.8m)

N 0.7 0 3 0.8 N - 0.5 c L 0.4

R 0 3 A T Of I

.l

0

JUUAN SAUPUNG DATE

Figure 06. Nitrate and nitrate chloride ratios in shallow groundwater wells. Reid site-controlled ditch drainage. Absent data implies well was dry.

8 4

APPENDIX D. cont.

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOLY WELLS REID SITE, NO CONTROL DITCH DRAINAGE

E DEPTH 1 (.5-.Pm)

B DEPTH 2 (1.D-1Am)

I DLPTH 4 (3.D-4 Dm)

JUUAH SAUPUNG DATE

Figure 07. Nitrate and nitrate chloride ratios in shallow groundwster wells. Reid site-no control ditch drainage. Absent data implies well was d r y .

NITRATE AND NITRATE CHLORIDE RATIOS IN SHALLOW WELLS VANSTAU LDl E U N TE, CONTROLLEB TILE DRAINAGE

n

D DEPTH 1 (.Sm) f2 DEPTH 2 (1.0-1.2m)

D DEPTH 3 (2.0-2.5m)

DEPTH 4 (3.0-3.Sm)

Figure 08. Nitrate and nitrate chloride ratios in shallow groundwater wells. Stauldieun site-controlled tile drainage. was dry.

Absent data implies well

8 5

APPENDIX D. c o n t .

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTH 3 AND 4 REID SITE, CONTROL TILE DRAINAGE

0 DEPTH 3 (1.9-2.7m)

L DEFTH 4 (3.0-4.Dm)

105 17135 87118 871V1 87227 87258 8 7 1 M 8731) 8734D 88315 IDMI 88074 JUUAN SAUPUNG DATE

Figure D9. Kitrate and nitrate chloride ratios in shallow groundwater wel l s at depths 3 and 4 . Reid site-controlled tile drainage. inplies vel1 was dry.

Absent data

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTHS 3 AND 4

' T 2.3

N

m n .

REID SITE, CONTROLLED DITCH DRAINAGE

n n I 1 I I I

Be074 88105 17015 17044 87074 17105 171J5 17111 871D1 87227 872Ed 17288 87JlD 8 7 Y D 88015 18011 18074 0.1

N 0 0.08 3 N - 0.01 C L

A

0

0 DEPTH 3 (1.9-2.7m)

R DEPTH 4 (3.0-&Om) R 0.04

; 0.01

0 81074 88%01 17013 87041 17074 87105 1 7 1 s 871W 8 7 0 1 872.27 17258 87281) 17311 87341 8

JUUAN SAMPLING DATE

Figure D10. rate snd nitrate chloride ratios in shallow groundwater rc.ells at ths 3 and 4. Reid site-controlled ditch drainage. Absent data

implies well was dry.

86

A P P E N D I X D. cont.

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTH 2 AND 4 REJD SITE, NO CONTROL DITCH DRAINAGE

3

2.5

0 3 1 N

m 1.5

J 1 ' 0.5 0

16074 18105 17015 87041 87074 17105 17131 17181 17108 87117 872s 87268 17311 17U8 16015 1104.I 18074 0.1

N 0 0.DI 3 N - 0.01 6 DEPTH 2 (1.0-1.h) C L R DEPTH 4 (S.D-4.Om)

A R 0.04

0.D1 0

0 be074 1€1W 17015 87041 a7074 17105 171% 17181 1701 17117 17251 871M 17111 17JU 81015 b 1 M l be074

JUUAH SAMPUHC DATE

Figure Dll. Nitrate and nitrate chloride ratios in shallow groundwater wells at depths 2 and 4 . Reid site-no control ditch drainage. implies well was dry.

Absent data

NITRATE AND NITRATE CHLORIDE RATIOS AT DEPTH 3 AND 4 VANSTAULDIEUN SITE, CONTROLLED TILE DRAINAGE

2.5 0 3 2 N

m 1.5

9 ' LO,

0 11074 Ill05 11111 1 8 2 5 1 17015 17041 17074 17105 171s 17111 17111 17127 172% 171M 16074 1 6 1 0 5

0.1

N 0 0.m 3 N c 0.01 0 DEPTH 3 (2.0-2.5m)

L E DEPTH 4 (3.0-3.5~1) R 0.04

A

0 10.02

0 16074 18105 I808 161% 17015 17011 17074 17105 171S5 17III 17118 17117 17251 172M 11074 11105

JUUAN SAMPUNC DATE

Figure D12. Nitrate and nitrate chloride ratios in shallow groundwater wells at depths 3 and 4. Stauldieun site-controlled tile drainage. Absent data implies well was dry.

87