A GROUNDWATER BALANCE STUDY TO

DEVELOP A TECHNIQUE TO IMPROVE THE

GROUNDWATER SYSTEM IN A RESTRICTED

AREA

Research for the Degree of Doctor of Philosophy

of

Saravanamuttu Subramaniam SIVAKUMAR

Supervised by

Prof D.C.H.Senarath

Sequence of Presentation

Problem Statement of Water Resources

Thesis Statement

Object of the Research

Methodology of the Research

Summary of Operational Research

Summary of Economic Analysis of the Operational Research

Summary of the Research Finding

Conclusions

Generalization

Limitations

Recommendations for Future Study

Problem Statement of Water Resource

Economically feasible water storage sites

are limited

Unplanned utilization of various water

resources by various stake holders

Difficulty in analytical solution due to non

homogeneous and anisotropic nature of

groundwater resource

Thesis Statement

“It is observed that at present the water that isavailable is not utilized effectively to achievemaximum productivity in terms of foodproduction”

Objective of the Research

The objective of this research is a complete water balance study in a restricted catchmentarea incorporating few medium irrigation schemes, several minor Irrigation schemes andlarge number of dug wells to illustrate:

1. The possibility of developing and using a model to represent all the relevant variables connected with the movement and utilization of surface and groundwater

2. The possibility of using the above model to study the viability of conserving surface water by storage as groundwater by reducing the extent of cultivation using surface water and increasing the extent of cultivation using groundwater to achieve maximum crop yield

3. The economic viability of achieving maximum crop yield as in (2)

4. The possibility of creating an artificial aquifer boundary to optimize the effectiveness of groundwater use to achieve maximum crop yield

5. The economic viability of the creation of artificial boundary in terms of productivity

6. The possibility of combining both (2) and (4) for the increased crop production

7. The economic viability of achieving maximum crop yield as in (6)

Methodology of the Research

General relationship between crop yield and water applied to the cropshows a trend to increase linearly up to about 50% of the full irrigation andthen going in a convex curvature to the maximum yield and then reduce theyield with increase in applied water

Farmers whose sole objective is to get maximum net Income, tends toirrigate their crop by spending minimum cost for their irrigation water to getmaximum productivity for their crop

“Hence the main methodology adopted in this researchregarding the optimum crop yield to maximize productivity interms of food production is economizing the cost of theirrigation water and increasing the extent of cultivation per unitof irrigation water”

Concept

Methodology of the Research

A regional aquifer simulation model using integrated finite differencetechnique was formulated in spread sheet for a polygonal net work of arestricted catchments in Vavuniya with forty one observation wells

This aquifer was divided into forty one polygons by connecting theperpendicular bisectors of adjoining observation wells. Six yearseasonal water levels and one year monthly water levels, tankstorage, field issues and total withdrawal from agro and domestic wellsfor each polygon were taken for the water balance of each polygon

The model was calibrated by error optimization method using historicseasonal data. In each of the error optimization model four variables forpolygonal inputs, one variable for that particular polygonal specific yieldand five to seven variables for transmissibility for every polygonalconnection were formulated with constrains.

Model Formulation

A study was carried out to find out an operational policy for conserving surface water bystorage as groundwater by reducing the extent of cultivation using surface water andincreasing the extent of cultivation using groundwater to achieve maximum crop yield underminor and medium irrigation schemes together with creation of an artificial boundary to lift thewater table up

By changing every polygonal input (i.e. to change the operational policy of minor and medium irrigationschemes to reduce the extent of cultivation using surface water and increase the extent of cultivation usinggroundwater) the water levels in each polygon were analyzed

By changing the first interior boundary lateral flow to 50% in steps from its original value by assuming anartificial boundary, the variation of water levels in each polygon were analyzed

By adopting combination of the above two strategies in different possible combinations, the variation ofwater levels in each polygon were analyzed

The economic implication of the above three outcomes based on “Reducing the extent ofcultivation will appear to be a loss to the Gross Domestic Product and lead to reduction in theGross National Product too. But the gain in water table will reduce the cost of energy by wayof fuel and electricity for the pumping of water for the cultivation, domestic and industrialwater use. This will indirectly contribute to GDP and GNP positively”

Methodology of the Research

Operational Research

Summary of Operational Research

Changing the operational policy of minor and medium irrigation schemes by

forgoing cultivation by 25% to 35% to conserve surface water by storage as

groundwater is giving water table gain in almost all nodes except nodes 37and 38

by 1.75 ft to 3.0 ft during discharging season and by 2.5 ft to 3.75 ft during

recharging season. This is a reduction of almost 45% to 65% of water table loss

in between two consecutive seasons in 80% of the area of the catchments under

study

Creating artificial aquifer boundary to optimize the effectiveness of groundwater

in an elevated water table by peripheral boundary treatment to cause reduction of

permeability by 35% to 45% is giving water table raise of nodes closer to

treated boundary by 1.5 ft to 2.75 ft during recharging season.

Combining peripheral reduction in permeability by 35% to 45% and forgoing

cultivation of minor and medium irrigation scheme by 45% to 55% result an

average gain of water table during discharging season (June – Sept) 3.0 to

4.75 ft excluding node 37 and 38. The same trend is observed in recharging

season to a lesser degree. This is a reduction of almost 60% to 70% of water

table loss in between two consecutive seasons in 95% of the area of the

catchments under study.

Summary of Economic Analysis of the

Operational Research The alternative policy on changing the operational policy of minor and

medium irrigation schemes by forgoing cultivation by 25% to 35% gave thebenefit cost ratio based on present worth greater than unity with considerablerise in water table. The rise in water table occurred almost above 80% of theobservation wells. The rise in water table was around 45% to 65% of the lossin water table between two consecutive seasons

The boundary treatment showed positive results

The combination of the above two alternatives yielded further improvementthat, at any time water table will recover 60% to 70% of loss in between twoconsecutive seasons in 95% of the catchments under study. This implies thatthe boundary treatment combined with changing the operational policy ofminor and medium irrigation schemes by forgoing a part of the cultivation is aneconomically feasible policy alternative.

Summary of the Research Finding

“A change in operational policy of minor / medium

irrigation schemes by forgoing one third of the

cultivation under minor / medium irrigation schemes

or keeping one fourth of the storage of minor / medium

irrigation schemes at any time will recover an average

of 45% to 65% of the loss of water table in any

consecutive seasons in almost 80% to 90% of the

catchments area under consideration”

Conclusions

Minor / medium irrigation schemes conserve surface run off and covey most part of itto recharge groundwater and as such serves as a recharge shed for the wells situatedin the zone of influence. It is an insurance against water scarcity, as the yield increasesconsiderably for every unit of rainfall. The minor / medium irrigation schemes preventsoil erosion and depletion of soil fertility. In the context of impending water deficiencylooming large, construction of minor / medium irrigation schemes will be a dependableinfrastructure in the development of water potential in any catchments.

Acknowledgement of the remarkable role played by the minor / medium irrigationschemes on replenishment of groundwater and its spread over a large area would be agreat asset in planning and execution of settlement and crop production projects

“Forgoing certain percentage of cultivation will be a loss to Gross DomesticProduct and lead to loss in Gross National Product also. The gain in watertable will reduce the cost of energy by way of fuel and electricity. This willindirectly contribute to GDP and to GNP and also reduce the cost ofirrigation water and in turn increase the extent of cultivation per unit ofirrigation water. This will increase the crop yield per unit of irrigation waterand to increase economic productivity in terms of food production”

Generalization

The model formulated for this research was applied to a selected catchment inVavuniya (a shallow weathered and rarely fractured rock with thin soil mantle)which covers 6 medium Irrigation schemes, 40 minor irrigation schemes andaround 2000 shallow wells within 71.5 sq.miles of area

“The rationale behind the selection of this study area is that theaquifer of this region very well reflects the typical groundwaterproblems of unconfined aquifers in shallow weathered andrarely fractured rock with thin soil mantle. Study of this natureof problems is the prime intention of this research. Hence thefindings pertaining to this restricted catchment can begeneralized to any type of restricted catchment with certainlimitations”

Limitations

An aquifer simulation model in Integrated Finite Difference Method used for this

research is applicable to any type of polygonal network with the following limitations

Aquifer is a two-dimensional flow system

Only one aquifer system is modeled

Aquifer is bounded at the bottom by an impermeable layer

There are no major irrigation schemes within the catchment

above the aquifer

Recommendation for Future Study

“Future study on policy alternatives towards

conjunctive use water management policy in any

nonrestricted multilayered aquifer system with

major irrigation schemes, will be very useful in

macro development of water resource in

developing country like Srilanka”

Thank You