This is the Author’s version of the paper published as

http://researchoutput.csu.edu.au This is the Author’s version of the paper published as:

Author: S. Khan, A. Abbas, J. Blackwell and A. A. Hamza F. Gabriel Author Address: [email protected], [email protected], [email protected] Title: Hydrogeological Assessment of Serial Biological Concentration of Salts to Manage Saline Drainage Year: 2007 Journal: Agricultural Water Management Volume: 92 Issue: 1-Feb Pages: 64-72 Date: August ISSN: 0378-3774 URL: http://dx.doi.org/10.1016/j.agwat.2007.05.011 Keywords: Serial Biological Concentration, irrigation, saline drainage, regional groundwater, groundwater model, waterlogging Abstract: Serial Biological Concentration (SBC) of salts is an innovative technology to manage salts in agricultural drainage. This approach utilises saline drainage water as a resource to produce marketable crops and, therefore provides a method to manage salts in a viable manner. However, there are associated risks of development of groundwater mound beneath the treatment facility and the consequent threats of groundwater contaminations. The water table in the shallow aquifers often rises to the ground surface following irrigations and rainfall events. In the SBC system, the intensive drainage system manages these events and enables the water table to be lowered rapidly. This paper describes the hydrogeological assessment of an SBC system to quantify the water table mound and the effect on the local groundwater. The deep leakage rates and lateral flows to adjoining lands are determined in order to asses the onsite and regional impacts under typical SBC operation. Modelling results show that the net watertable rise under a 50 ha site, in the first year of the system operation, is about 1.3 meters. However, there is no further water table rise during 25 years of simulated operation, mainly because of the high drainage efficiency of the tile drainage operation in the SBC system. The water table under the SBC site reaches quasi equilibrium with periodic rise and fall around the tile drain depth. The deep leakage beneath the SBC bays is approximately 1mm/day which is around 10% of the saturated groundwater flow above the tile drains. Simulation scenarios of various sizes of the SBC system in its present hydrogeological settings suggest that the lateral extent of groundwater mound does not extend beyond 50 m from the outer edge of its bays. In order to develop SBC systems at other locations, a GIS-based site suitability assessment model is recommended to evaluate the SBC effect under different soil and hydrogeological conditions.

Hydrogeological Assessment of Serial Biological Concentration of Salts to Manage Saline Drainage

S. Khan1,2,3,*, A. Abbas2, J. Blackwell1, H. F. Gabriel1,3,4 and A. Ahmad1

1 International Centre of Water for Food Security, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia

2UNESCO IHP-HELP, Australia

3 Commonwealth Scientific and Industrial Research Organization (CSIRO) Land and Water Division, Locked Bag 588, Wagga Wagga, NSW 2678, Australia.

4 NIT, National University of Sciences and Technology, Pakistan

*Corresponding author: [email protected], [email protected], Fax: +61 2 69332647, Phone: +61 2 69332927

ABSTRACT

Serial Biological Concentration (SBC) of salts is an innovative technology to manage salts in

agricultural drainage. This approach utilises saline drainage water as a resource to produce

marketable crops and, therefore provides a method to manage salts in a viable manner. However,

there are associated risks of development of groundwater mound beneath the treatment facility and

the consequent threats of groundwater contaminations. The water table in the shallow aquifers

often rises to the ground surface following irrigations and rainfall events. In the SBC system, the

intensive drainage system manages these events and enables the water table to be lowered rapidly.

This paper describes the hydrogeological assessment of an SBC system to quantify the water table

mound and the effect on the local groundwater. The deep leakage rates and lateral flows to

adjoining lands are determined in order to asses the onsite and regional impacts under typical SBC

operation. Modelling results show that the net watertable rise under a 50 ha site, in the first year of

the system operation, is about 1.3 meters. However, there is no further water table rise during 25

years of simulated operation, mainly because of the high drainage efficiency of the tile drainage

operation in the SBC system. The water table under the SBC site reaches quasi equilibrium with

periodic rise and fall around the tile drain depth. The deep leakage beneath the SBC bays is

approximately 1mm/day which is around 10% of the saturated groundwater flow above the tile

drains. Simulation scenarios of various sizes of the SBC system in its present hydrogeological settings

suggest that the lateral extent of groundwater mound does not extend beyond 50 m from the outer

edge of its bays. In order to develop SBC systems at other locations, a GIS‐based site suitability

assessment model is recommended to evaluate the SBC effect under different soil and

hydrogeological conditions.

Key words: Serial Biological Concentration, irrigation, saline drainage, regional groundwater,

groundwater model, waterlogging

1. Introduction

Contaminated surface waters have been treated using a series of vegetated wetlands where intense

biological processing occurs (Kivaisi, 2001). Although effective, this approach is a non‐production

system. One option for managing inevitable drainage water from irrigation or other contaminated

surface waters is to sequentially use and re‐use it to grow increasingly salt‐tolerant crops while

concentrating the drainage to a manageable level (Oron, 1993; Tanji and Karajeh, 1993). This

treatment system is known as “serial biological concentration (SBC)”. SBC systems have emerged as

a viable option for using saline waters for irrigated cropping. The system makes productive use of

waters considered unfit for general irrigation and avoids the associated risks of saline water

irrigation which often proves non‐sustainable environmentally (Jayawardane et al., 1997;

Jayawardane, 2000; Blackwell, 2000). Specifically, the concept of SBC of salts aims to reduce

drainage effluent volumes from irrigated lands (Bethune et al., 2004). In 2003, SBC was being applied

on some 63,000 ha in the San Joaquin Valley, California, where it is the basis of an Integrated On‐

Farm Drainage Management System program (Pratt Water Solutions, 2003). Blackwell (2000) and

Jayawardane (2000) provided design guidelines and the field performance of a land‐based sewage

treatment system, Filtration, Land Treatment and Effluent Reuse (FILTER) in Australia. The SBC

system described and analysed herein was based on the function and operation of the FILTER

system. FILTER is an effective treatment system producing low nutrient drainage waters which meet

Environmental Protection Agency (EPA) criteria for discharge to surface water bodies (Jayawardane,

2000). A schematic view of the SBC system based on the FILTER approach is shown in Fig. 1. With

either FILTER or SBC there are associated risks caused by the required high hydraulic loading which

may have a deleterious effect on the surrounding groundwater quality. These risks could also bring

about a water table rise at local and sub‐catchment level causing waterlogging and salinization. This

would lead to production losses in surrounding irrigation lands and other potentially harmful off‐site

environmental impacts. (Su et al., 2005).

With the developing tension between future global fresh water needs and diminishing water

resources, agricultural water management should consider alternative sources of water (green, grey

and black) as a replacement for fresh water. Technologies such as SBC extract beneficial use from

water previously considered a waste and unfit for irrigation.

Irrigation globally uses 70 % of all freshwater withdrawals and comes under heavy scrutiny

in any discussion of freshwater governance (UNESCO, 2006). This scrutiny generally results in fresh

water leaving irrigation to satisfy increased demands for urban, industrial and environmental water.

The effect of this redistribution will be felt severely in regions already water stressed. About 40% of

the world’s population is already experiencing water stress, and about 30 countries are suffering

from water scarcity during a large part of the year (Kivaisi, 2001). Drainage must be an integral

aspect of irrigation schemes but discharge of this drainage and its management is one of the critical

issues facing agriculture today. Such situations are amenable to a system re‐use approach, which

may include the shandying of fresh water with drainage effluents to increase available water supply

for the sustainability of future agricultural systems. However, Rhoades et al. (1999) warn against this

approach because of the potential for harmful salt build‐up in the system. Drainage water should not

be returned to the land drained, rather, it should be used sequentially on other well managed

drained lands until it is too salty for productive use, the classic SBC approach.

The hydraulic loading of water applied in an SBC system to achieve a 33% leaching fraction

could affect the aquifer systems. Water table monitoring and groundwater modelling are required at

the local and sub‐regional level to provide in‐depth knowledge and concise understanding of the

hydrogeological behaviour. In particular, the operation of the SBC site demands an integrated

monitoring set‐up to help understand the development of the water table mound and associated

salinization hazards. Gallichard et al. (1997) described the importance of a monitoring system for

groundwater table control, soil salinity and collector discharge. Gupta et al. (1997) studied the

spatial variability and developed appropriate monitoring strategies for non‐uniform soils. Benyamini

et al. (2005) installed monitoring systems perpendicular to the parallel subsurface drains to study

the mechanisms of salinization and the dynamics of the water table regime.

This paper describes the hydrogeological assessment of an SBC trial in the Murrumbidgee

Irrigation Area (MIA) in southeast Australia. Owing to the hydrogeological system of the MIA, the

region has inherent drainage problems that have been aggravated by intensive irrigation

applications leading to problems of rising water tables and salinazation. By 2001, more than 80

percent of the MIA had water tables within 2 m from the land surface (Khan et al., 2001). The

average volume of irrigation water used per irrigation season (270 days) in the MIA is about 1000 GL

with an average electrical conductivity (EC) of 0.1 dS/m. Shallow groundwater salinity varies from

less than 2 dS/m to over 20 dS/m. In the MIA, the salt load diverted from the Murrumbidgee River

at Berembed Weir and delivered to farmers’ paddocks each year is about 115,000 tons. The

estimated average (1999‐2003) drainage volume of MIA is 212,340 ML per year (Pratt Water

Solutions, 2003) with an average winter salinity of 1.2 dS/m. These drainage volumes are well below

the long time average mainly because of drought conditions. This study focuses on understanding

the groundwater dynamics of the SBC system with the shallow aquifer and its interactions with the

deeper groundwater. The specific objectives are to determine groundwater movements (both lateral

and vertical) using a detailed monitoring network and to evaluate regional impacts of the SBC

system at different scales using a groundwater model.

2. Hydrogeology of the study area

The study area is situated in the Murrumbidgee Irrigation Area (MIA) on the northern side of a fluvial

plain formed by the Murrumbidgee River. The climate of the MIA is characterised as semi‐arid with

average annual rainfall ranging from 256 to 609 mm and annual evaporation is 2100 mm. Average

rainfall gets closer to average evapotranspiration during winter months of June and July. The total

irrigable area for the MIA is 156,605 ha and the main agricultural products are rice, grapes and

citrus. Rice is the most dominant water user with more than 32,000 ha (14 % of the total land use) in

2000. Rice growing started in the MIA in 1924, although rapid development of rice areas occurred in

the 1970s and 1980s. Rice is grown in bays using flood water irrigation, having the highest applied

water of any crop in the MIA of 15 ML/ha or 1500 mm. Previous studies have shown groundwater

accessions of 1.2 ML/ha under rice and 0.58 ML/ha under horticulture (Neeson et al., 1995)

The topography consists of flat plains with a mean elevation of less than 200m above sea

level although low hilly outcrops, extending to 240m above sea level exist on the north‐eastern

flank. The land surface has an average slope of 0.04% in an east‐west direction. The geology of the

MIA is described by three major aquifer systems i.e. Shepparton, Calivil and Renmark Formations

(Brown and Stephenson, 1991).

The Shepparton formations mainly consist of unconsolidated to poorly consolidated,

mottled, variegated clays, silty clays with lenses of polymictic, coarse to fine sand and gravel, partly

modified by pedogenesis.

The Calivil formations are mainly poorly consolidated, pale grey, poorly sorted, coarse to

granular quartz and conglomerate, with white kaolinitic matrix.

The Renmark formations overlay the basaltic bed rock and are distinguished from the Calivil

formations due to the presence of grey, carbonaceous sand, coal and lignite.

3. Methodologies

3.1. Experimental set-up

A detailed groundwater monitoring set‐up was used to understand the dynamics of the groundwater

mound. The experimental layout consisted of 11 experimental SBC bays (totalling 11 ha) and 1 full

sized bay of 4ha as shown in Fig. 2. The area of each of the SBC bays was 1 ha (250m x 40m) and 1

(bay 11) was 0.33 ha. Use of holding ponds was to store drainage water to adjust its salinity to

required application level. The instrument set‐up for this hydrological investigation comprised 2

replicates of 12 piezometers with a depth of 3 m perforated at the bottom over a length of 30 cm

and 6 test wells perforated over the whole length. One set in each replicate is located within the full‐

scale SBC bay and the remaining are located between the full‐scale SBC bay and the bay 9 of the

experimental bays (Fig. 2). The piezometers and test wells were fitted with data loggers to

continuously monitor the groundwater height at each location. This piezometric data was used to

develop, calibrate and validate a MODFLOW model to quantify the local impacts of the full scale bay.

Another array of 21 piezometers and test wells was installed in the experimental SBC bay 2 (Fig. 3).

These piezometers and test wells were used to determine the internal drainage characteristics of the

bays and the lateral and vertical leakage from them. All bays were artificially drained using

perforated polyethylene drainpipe. The drain depth was 1.0‐1.2 m below ground surface and drain

spacing of 5 m. Each bay was periodically flood irrigated and drained through the tile drainage

system, on a 14‐day cycle.

3.2. Groundwater Model

3.2.1 Quantification of local effects

A local scale 2‐D saturated groundwater model to explore lateral and vertical components of

groundwater flow was developed using MODFLOW (MacDonald and Harbaugh, 1988) under a

Processing MODFLOW for Windows (PMWIN) environment. PMWIN is a simulation system for

modelling groundwater flow and transport processes and is the most powerful graphical user

interface available for MODFLOW today (Chiang and Kinzelbach, 1998). The model domain consists

of a 30 m deep and 54.5 m long strip and is represented by a 20 intervals mesh (varying from 0.5 to 8

m size) in the x‐direction and a 13 intervals mesh (varying from 0.5 to 5 m size) in the z‐direction.

This mesh spacing ensures that the ratio of dimensions of two consecutive mesh intervals is less

than or equal to 2 to avoid errors in the Taylor’s approximation for spatial finite difference

approximation. The top model boundary is a transient water table boundary which means

groundwater pressure is zero and water table height equals elevation (h=z). The bottom model

boundary is a leakage boundary where the rate of leakage is specified by sinks at the centre of each

cell. The left and right hand side boundary conditions are no flow boundary (dh/dx=0) and a time

dependent head boundary respectively. The head variations are specified using data from the deep

piezometers.

3.2.2. Quantification of regional effects

To determine the regional impacts of the SBC system, a regional groundwater model was developed

by using spatial zooming techniques (Szekely, 1998; Leake and Claar, 1999) from an existing larger

groundwater model of the MIA region (Khan et al., 2002). The dimensions of the resulting regional

model of the SBC system are 8.25 km x 9 km. The modelled area was represented by 8448 cells (88

cells in x and 96 cells in y‐direction) with dimensions of 93.75 x 93.75m. In the vertical direction, the

model comprised four geologic layers: Upper Shepparton Formation, Lower Shepparton Formation,

Calivil Formation and Renmark Group Formation. The soil properties of each of the layers vary

considerably as shown in Table 1. The vertical thickness of the porous material beneath the model

domain varied between 17 and 166 m depending upon the depth to bedrock. The parameters used

in the regional model calibration are given in Table 1.

3.3. Model calibration and validation

3.31. Deep leakage and vertical flows at local scale

The model was calibrated by varying the initial values of model parameters (Table 2) within

reasonable limits to minimise the difference between the observed and calculated hydrographs. The

calibration was done for the data set from 20/12/1999 to 17/01/2000.

The initial piezometeric levels in the model domain were computed by fitting a second

degree polynomial to the water table levels. The first derivative of the polynomial equation

approximated to the lateral gradient. During the calibration process discrepancy was noted in the

observed and computed hydrographs using the estimates of the initial hydraulic properties (Table 2).

However, matching was significantly improved using the calibrated hydraulic properties and leakage

rates (Table 2). Fig. 4 shows a good match between computed and observed hydrographs for the

calibrated model parameters. Computed and observed hydrographs at the other piezometeric

locations were in similar agreement.

The sensitivity of model outputs to the parameters is determined by using root mean square

error (ERMS) and scale root mean square error (ESRMS) by the following equations:

ERMS = [ ] } )1()(11

2/12∑=

−⎩⎨⎧ n

i

HihiWin

ESRMS = )2()(

100

1∑ −−

n

i ii

RMS

Hh

E

where n is the number of observations, Wi the weighting factor, hi the computed head, Hi the

observed head, ∑ −−

n

i ii Hh1

)( is the accumulative difference between observed and computed

heads.

The ERMS and ESRMS obtained for different estimates of vertical leakage and hydraulic

conductivity parameters are given in Tables 3 and 4. The model sensitivity is tested for four scenarios

of both vertical conductivity and deep leakage rates. Table 3 shows that the model is not very

sensitive to the vertical hydraulic conductivity estimates in the range of 1 and 3 mm/day keeping

both horizontal consuctivity and deep leakage constant for all cases: Kx = 4 mm/day and q = ‐0.2

mm/day, respectively. The sensitivity to deep leakage is tested at Kx = Kz = 4 mm/day for all cases.

The guidelines on groundwater modelling by the Murray Darling Basin Commission (Middlemis,

2001) show that the model calibration is good if ESRMS is less than 5 %. In the present study, assuming

isotropic soil hydraulic properties (Kx = Kz), the model results show minimum ESRMS values (ESRMS < 1.2)

for a vertical leakage rate of 0.2 mm/day. The initial hydraulic heads derived from the second order

regression of the water table level on the 8th of September 1999 were used to validate the model

results. Computed hydrographs for piezometers Pz‐6 and Pz‐8 (Fig. 2) for the validation period are in

close agreement with the observed hydrographs (Figs. 5 and 6). To determine the leakage rate

beneath the SBC system, two independent methods were used:

(1) computation of the leakage rate from the volumes of water contained between the

successive water table profiles after the water table falls below tile drains, and

(2) computation of the time dependent vertical gradient and leakage rate using Darcy’s flow

formula.

In the first method, the drainage rate (Q) from the underlying tile drains is computed using

the concept of declining of water table (∆d) over time (∆t) by the following equation:

)3(t

dPQ d

ΔΔ

=

Where Q is the drainage rate per unit area based on water table measurements (m/day), ∆d the

change in water table depth (m), Pd the drainable porosity (%), and ∆t is the time interval (day).

3.3.2. Deep leakage and vertical flows at regional scale

In the vertical direction, the model comprised of four layers varying considerably in thickness. Initial

pressures of the groundwater levels in different layers were based on the piezometer levels of

September 1995. Model parameters used in calibration are given in Table 1.

Monthly stress periods with six time steps were used to represent the time domain. Water

balance components such as fallow evaporation (ET – terminology used by MODFLOW package),

irrigation recharge and rainfall recharge based on monthly rainfall data were added to the model.

The ET was used simulate direct loss from the water table. The maximum from the bare soil surface

occurs when the water table is less than 0.7m below the soil surface and ET is assumed to decrease

linearly with the water table depth until reaching the limiting depth of 1.5m, where ET = 0. Regional

groundwater inflow and outflow from the model domain is represented by head boundaries. The

model was calibrated from observed data for piezometers in the model domain from 1995 to 1999

(stress period of 0 ‐ 1440 days). The data for this analysis was piezometric levels before and after the

winter rains. Fig. 7 shows that computed and observed piezometric levels compare well.

4. Results and discussion

4.1. Local impacts

Fig. 8 shows the flow vectors in the model domain at the end of calibration period. At the edge of

the re‐use bay the flow vectors are close to vertical and tending to be more inclined to the

horizontal axis away from the edge. This indicates that vertical leakage occurs beneath the bay and

lateral flow occurs away from the edge of the bay. The equipotential lines in the figure show

pressure heads which show a decreasing pattern both vertically and horizontally. Using the

groundwater levels in the model domain after 30 days of simulation, the differential of the second‐

degree polynomial at x = 54 m (distance from the bay) gives a horizontal gradient of 0.14. Therefore,

the lateral flow is the gradient multiplied by the hydraulic conductivity which is approximately

equivalent to 0.6 mm/day for K = 4 mm/day. The model sensitivity in Table 4 reveals that the vertical

leakage is 0.2 mm/day for minimum values of both ERMS and ESRMS. This situation illustrates that the

lateral flow is three times greater than the vertical flow from the full‐scale bay.

Fig. 9 shows the time variant response in 6 test wells (measuring shallow water tables) in bay

2 of the 11 experimental SBC bays. Test wells located close to both plugged (every other drain was

plugged to reduce the drainage rate) and unplugged drains (at 0.5 and 5.0 m from the unplugged tile

drain) show a rapid rise and decline in the water table level following an irrigation event. Test wells

located away from the tile drains show a steady rate of decline following the irrigation events. There

are three irrigation events shown in Fig. 9 coinciding with water table peaks closer to the plugged

drain. It is concluded that the plugged drain and the surrounding packing material provide

temporary storage and preferential flow and therefore act as sink lowering the water table above it.

The average change in water table level was used to determine the rate of drainage when

the watertable was above or below the tile drain. Using Eq. (3), the average rate of drainage (Q) was

11.67 mm/day when the water table was above the tile drains and 0.94 mm/day when it was below

the tile drains as shown in Tables 5 and 6. This indicates that average drainage rate to the tile

drainage system was 10.73 mm/day (92% of the total flux) and 8% of water was lost to the aquifer

through the deep leakage beyond the tile drains.

It is observed that the vertical gradient between the 4 and 7m deep piezometer at 2.5 m

distance from the tile drain varies with time where as the vertical gradient just below the tile drain

remains unaffected. This is due to the two dimensional nature of flow at 2.5 m distance from the tile

drain (Khan and Rushton, 1996a,b,c). The average vertical gradient just below the tile drain is

computed as 0.307 and it can be used to determine the deep leakage rate to the regional aquifers.

Using the calibrated hydraulic conductivity of 4 mm/day and vertical hydraulic gradient of 0.307, the

vertical leakage according to Darcy’s flow formula is 1.2 mm/day. The difference of the deep leakage

below the tile drains by two different methods of calculation (Eq. (3) and Darcy’s Law) is 22% (the

vertical leakage rate of 0.94 mm/day was obtained from the average rate of drainage in the

preceding section). It is concluded, therefore, that the deep leakage below the tile drains is

approximately 1 mm/day.

4.2 Regional impacts

The following scenarios were run to evaluate groundwater impact of the following sizes of SBC

operations:

• No SBC operation (Base scenario)

• 50 ha site (Scenario – 1)





For each of the modelled scenarios the model was run for 25 years. The difference in

hydraulic pressures in layer‐1 (Upper Shepparton Formation) at the end of simulation period (25th

year) was deducted from the base scenario (no SBC operation). This allowed calculating the rise of

piezometeric levels due to each of the operational scenarios.

The modelling results show that the overall watertable rise under the SBC site is around 1.3

meters for the 50 ha site. This water table rise occurs in the first year but it does not change during

the 25 years of operation, because of induced heavy drainage from the tile drains laid at 1.2 metre

depth. The lateral spread of the groundwater mound did not extend beyond 50 m from the outer

edge of the bays.

Fig. 10 shows the net water table change of the 100, 500, 1000 and 2000 ha sizes of

operation of the SBC. Similar to the 50 ha site, the overall depth of the water table under the SBC

bays remains at the depth of the tile drains which causes a rise of 1.0 ‐ 2.5 m (depending on initial

depth to the water table) under the site and to a distance of 50 m from the site. The water table

under SBC site reaches quasi equilibrium at the depth of the drain with periodic rise and fall around

the tile drain depth. The increasing size of SBC (for example 2000 ha) shows slightly increased

interactions with surrounding areas, this causes wider spreading of net water table change effects

exacerbated by spatially variable hydraulic conductivity and zones of groundwater pumping

influence from a nearby abstraction bore. The long‐term 25 year modelled operation of the SBC site

shows the tile drains maintaining the water table depth at drain depth.

5. Conclusions

The detailed monitoring of groundwater dynamics and the modelling of the SBC operations

demonstrate that the vertical and lateral leakage at the edge bays is around 0.2 and 0.6 mm/day,

respectively. The deep leakage beneath the SBC bays is approximately 1 mm/day. The shallow initial

water table and the very low hydraulic conductivity keep the lateral extension of the water table

mound within 50 m. During the irrigation/ponding operations 8% of the saturated groundwater flow

above the tile drains contributes to the deep leakage. The simulations show that the water table

reaches a quasi equilibrium at the depth of the drains with periodic rise and fall in tune with

irrigation application and drainage operation whenever an SBC system with intensive tile drainage is

set up on heavy clay soils with low saturated hydraulic conductivity.

Modelling scenarios of various sizes of SBC sites suggest that the overall water table levels

remain at the depth of the tile drains which brings about a groundwater mound of 1 ‐ 2.5 m on‐site

(depending on the initial water table depth) and to a distance of 50 m laterally over time. The local

and regional impacts of SBC systems in lighter soils and prior stream areas are likely to be quite

different than those presented in this study. In order to develop SBC operations at other locations, a

GIS‐based site suitability assessment model is recommended to assess the SBC effect under different

soil and hydrogeological conditions.

Acknowledgements

The authors wish to acknowledge the funding support of the National Heritage Trust and the

Cooperative Research Centre for Sustainable Rice Production (CRC‐Rice), which made this work

possible. Technical support provided by CSIRO scientists, L. Short, L. Best, J. Townsend, N.

Jayawardane, T. Biswas and J. Foley is greatly appreciated. Scientific comments from the anonymous

reviewers and Joint Editor‐in‐Chief Willy Dierickx have been very useful in improving the quality of

this paper.

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TABLES

Table 1: Hydraulic parameters for calibration of regional scale model

Layers Horizontal conductivity (m/day)

Drainable porosity (%) Layer thickness (m)

Min Max Min Max Min Max

Layer 1 0.0086 0.89 5.9 9.7 12 12

Layer 2 0.00055 0.99 6.1 10.2 5 9

Layer 3 0.12 11.87 NA NA 0.25 52

Layer 4 7.24 37.44 NA NA 0.25 100

Table 2: Hydraulic parameters for calibration of local scale model

Parameters Initial values

Optimized values

Horizontal Conductivity (m/day) 0.001 0.004

Vertical Conductivity (m/day) 0.001 0.004

Deep leakage (m/day) ‐0.001 ‐0.0002

Drainable porosity (%) 6 6

Table 3: Model sensitivity to vertical conductivity

Vertical conductivity (mm/day) Root Mean Square Error (ERMS) (m)

Scaled RMS Error (ESRMS) (%)

3.0 0.0465 1.112

2.5 0.0456 1.090

2.0 0.0451 1.079

1.5 0.0454 1.087

1.0 0.0472 1.130

Table 4: Model sensitivity to deep leakage rates

Deep Leakage (mm/day) Root Mean Square Error (ERMS) (m)

Scaled RMS Error (ESRMS) (%)

‐1 0.168 4.010

‐0.4 0.0585 1.400

‐0.2 0.0496 1.188

‐0.09 0.0671 1.606

Table 5: Rate of water table decline when above tile drain level

Date Time (h)

Area of the unsaturated zone as water table declines

(m2)

Average depth

to water table

(m)

Drainage rate

(mm/day)

09‐February 07:00 2.493 0.499

10‐February 07:00 3.506 0.701 12.2

04‐March 16:00 2.969 0.594

05‐March 16:00 3.927 0.785 11.5

18‐March 01:00 1.744 0.349

19‐March 01:00 2.682 0.535 11.3

Table 6: Rate of water table decline when below tile drain level

Date Time (h)

Area of the unsaturated zone as water table declines

(m2)

Average depth

to water table

(m)

Drainage rate

(mm/day)

14‐February 17:00 5.013 1.003

15‐February 17:00 5.070 1.014 0.7

16‐February 17:00 5.225 1.045 1.9

17‐February 17:00 5.363 1.073 1.7

18‐February 17:00 5.448 1.089 1.0

19‐February 17:00 5.484 1.097 0.4

20‐February 17:00 5.499 1.099 0.2

21‐February 17:00 5.561 1.112 0.7

FIGURES

Figure 1: Schematic view of possible layouts, flows and concentrations of the SBC system

Figure 2: Experimental set‐up to monitor groundwater dynamics

Figure 3: Vertical section of deep drainage experiment in SBC bay 2

116.8

117

117.2

117.4

117.6

117.8

118

118.2

0 5 10 15 20 25 30

Time (days)

Pz8 Calculated Pz8 Observed

Figure 4: Calibrated computed and observed Pz-8 hydrographs

116.6

116.8

117

117.2

117.4

117.6

117.8

118

0 5 10 15 20 25 30

Time (days)

Pz6 calculated Pz6 Observed

Figure 5: Validated computed and observed Pz-6 hydrographs

116.6

116.8

117

117.2

117.4

117.6

117.8

118

0 5 10 15 20 25 30

Time (days)

Pz8 calculated Pz8 Observed

Figure 6: Validated computed and observed Pz‐8 hydrographs

114

114.5

115

115.5

116

116.5

117

117.5

118

0 1 2 3 4Years

Computed Observed

Figure 7: Calibration results of the regional model for a given piezometer

5 10 15 20 25 30 35 40 45 50 55

95

100

105

110

115

Length of Section (m)

Piez

omet

ric L

evel

(m A

HD

)

Figure 8: Model simulations leakage showing flow vectors

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

25-Jan-00 04-Feb-00 14-Feb-00 24-Feb-00 05-Mar-00 15-Mar-00 25-Mar-00 04-Apr-00 14-Apr-00 24-Apr-00

Time

0.5 1 2.5 4 4.5 5

Distance from Open Drain (m)

Figure 9: Fluctuations of water table between the plugged and unplugged tile drains

Figure 10: Net rise of pressure levels in Upper Shepparton aquifer system after 25 years of operation of (a) 100 ha (b) 500 ha (c) 1000 ha and (d) 2000 ha sites

Documents

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