Irrigation in the Mississippi Delta: History and Future

Mississippi Delta (not the MS River Delta)

Lower Mississippi River Flood Plain Altered

Mississippi River Flood Plain prior to landscape modifications for agriculture

Land Characterization: Bottomland hardwood wetlands Annual flooding distributes

nutrient-rich matter Artesian conditions in underlying

alluvial aquifer

Logged, drained, channelizedLevees built

Land Characterization: > 80% Agriculture

Row crops Rice Aquaculture

Primary concerns for sustainability: Water Quality Water Availability

Arkansas

Louisiana Mississippi

Alluvial Aquifer

Agriculture / Irrigation 3rd most intensively

used aquifer in US in 2000

MS 2nd largest user behind AR

50-150 ft

Gravel/Sand

Alluvial extent

MS Alluvial aquifer Cone of Depression

0

1000

2000

3000

4000

5000

6000

7000

MRVA - TNMRVA - LA

MRVA - MOMRVA - MS

MRVA - AR

Estim

ate

d W

ithdra

wals in

MG

D

2000 Estimated Withdrawals

Irrigation a Necessity Irrigation is necessary in the Delta to

reach optimum productivity› 28% of annual precipitation› 4 billion gallons per day

Flow in Delta streams is at or near baseflow during the growing season (May-August)› Unknown amount comprised of irrigation

return flowThe Bogue Phalia (a northwest MS River) at lowest flow in July 2009

Mississippi River Alluvial Aquifer

What are the results of irrigation on water availability?

Declining Water Levels

1/1971

1/1977

1/1983

1/1989

1/1995

1/2001

1/2007

50

60

70

80

90

100

110

120

L0027 SUNFLOWER

Wat

er-l

evel

alt

itu

de

, in

fee

t ab

ove

sea

lev

el

~1 ft per year decline

Storage and base flow loss

-3,500,000

-3,000,000

-2,500,000

-2,000,000

-1,500,000

-1,000,000

-500,000

0

0

20

40

60

80

100

120

140

160

1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009

CU

MU

LA

TIV

STO

RA

GE

LO

SS W

ITH

IN C

ON

E O

F D

EP

RE

SSIO

N A

RE

A,

IN A

CR

E-F

EE

T

DIS

CH

AR

GE

, IN

CU

BIC

FE

ET

PE

R S

EC

ON

D

Cumulative Estimated Storage Loss within cone of depression area (acre-ft)

Annual Minimum Daily Discharge of the Big Sunflower River at Sunflower Gage

Annual Minimum Daily Discharge of the Bogue Phalia River near Leland Gage

Why is groundwater important for aquatic ecosystems?

Groundwater/Surface-Water Exchange Benefits:› Sustains baseflow in streams› Bank storage dampens overall flood impacts› Streambank stabilization – supplies moisture

to riparian vegetation› Temperature regulation for aquatic biota› Supplies nutrients and inorganic ions to

stream› Buffer the transport of contaminants through

the streambed interface

Stream/Aquifer in Connection Stream/Aquifer not in Connection

Losing Stream

Gaining Stream

-Increased flow in stream-Decreased deposition of fine sediments-NO3 concentrations in stream reduced-Stream recharges alluvial aquifer

-Decreased flow in stream-Increased deposition of fine sediments-NO3 concentrations in stream concentrated-What are the affects on recharge?

GW dilutes NO3 in stream

Anaerobic conditions in aquiferpromote denitrification

Disconnected Stream

Why is groundwater important for aquatic ecosystems?

What are the results of irrigation on flow paths through the aquifer?

A Complex System

Recharge 0.307

Mississippi River0.011

Bluff Hills0.052

Underlying Units-0.022

Discharge to wells-2.19

Stream Leakage0.120

Water-Table Conditions in 2007

How have water-level declines changed the condition of the alluvial aquifer?

Mississippi

River-0.002

Bluff Hills0.035

Underlying Units0.095

Recharge 0.066

Stream Leakage-0.192

Confined Conditions in 1870 (Predevelopment)

What are the Effects of Conservation (Management) on these Flow Paths in the Future?

Objectives

Employ existing regional flow model to assess future groundwater supply

Develop water use conservation scenarios that vary in amount and distribution

Assess the effects of amount and location of water use conservation

How will flow in the alluvial change in the future?

MS Delta Conservation Scenarios, 2010 - 2038

Water-Use

Reduction (%)

Delta Wide

Cone of depression areaConservation Location

0

10

20

30

40

50

60

5% Delta-wide

25% Delta-wide

5% Cone equiva-lent

25% Cone equiva-lent

Cone of Depression Area (approx. extent)

Change in Storage

5% Delta Wide5% Cone Equiva-

lent 25% Delta Wide25% Cone Equivalent

0%

5%

10%

15%

20%

25%

30%

35%

5%

6%

29

% 32

%

Pe

rce

nt

Inc

rea

se

in

Sto

rag

e R

ela

tiv

e

to B

as

e s

ce

na

rio

Base Flow

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160%

5%

10%

15%

20%

25%

25%Delta-wide 5% Delta-wide

25% Cone Equivalent 5% Cone Equivalent

Stress Period (2008-2038)

Per

cen

t in

crea

se i

n b

ase

flo

w r

elat

ive

to

bas

e sc

enar

io

How Can We Better Monitor Water Resources?

Real-time coupled groundwater streamgaging stations• Study Objective

• Assess the role of groundwater/surface-water exchange on the transport of nutrients in the northwestern MS

• Assess the feasibility of monitoring groundwater/surface-water exchange at existing streamgaging locations

• Near-stream piezometers installed July 2010 near existing stream gages• Big Sunflower at Clarksdale• Big Sunflower at Sunflower• Big Sunflower at Anguilla

Pressure Transducer: Head Conductance,

and Temperature

41.5’

EastWest

~100’

*not to scale

Deck for access during high

flow

Existing Gage House: Stage , Conductance, and Stream Temperature

DCP to relay transducer

data

Big Sunflower at Sunflower coupled groundwater/surface-water gage

Losing Conditions:Groundwater Level < Stream Stage

Pressure Transducer: Head Conductance,

and Temperature

41.5’

EastWest

~100’

*not to scale

Deck for access during high

flow

Existing Gage House: Stage , Conductance, and Stream Temperature

DCP to relay transducer data

85

90

95

100

105

110

115

Sta

ge

and

Gro

un

dw

ate

r L

ev

el,

in f

t ab

v m

sl

Big Sunflower at Sunflower, MSStage

Groundwater Level in near-streampiezometer

Streambed Surface

Affects of unsustainable groundwater withdrawals on the MS Delta

Loss of baseflow to streams› Groundwater is pumped into streams to

sustain flow - cost $$ and could exacerbate current water situation

› During the growing season, irrigation return flow can make up most of the water in streams

› Overuse of surface-water for irrigation has resulted in recent fish kills

Affects of unsustainable groundwater withdrawals on the MS Delta

Increased recharge from the surface› Increases the vulnerability of the aquifer to

surface contamination› Recharge is still not sufficient to replace

withdrawals

Affects of unsustainable groundwater withdrawals on the MS Delta

Future concerns over water supply for irrigation› State initiated Conjunctive Water Use task

force› Dissension over who actually is part of the

problem – within the cone of depression versus outside of the cone of depression

› Amount of irrigated acreage increasing each year along with new permits for groundwater and surface-water irrigation

Questions?