The document presents a groundwater balance study conducted to develop a technique to improve the groundwater system in a restricted area. The study aimed to: 1) develop an aquifer model to represent surface and groundwater variables, 2) study viability of conserving surface water as groundwater by reducing surface water cultivation, 3) assess economic viability of achieving maximum crop yield, 4) assess creating artificial aquifer boundaries, 5) assess economic viability of boundaries, and 6) assess combining strategies 2 and 4. The methodology included operational research and economic analysis which found changing irrigation operations and creating boundaries could recover 45-65% and 60-70% of water table losses, respectively.

1. 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

2. 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

3. 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

4. Thesis Statement
“It is observed that at present the water that is
available is not utilized effectively to achieve
maximum productivity in terms of food
production”

5. Objective of the Research
The objective of this research is a complete water balance study in a restricted catchment
area incorporating few medium irrigation schemes, several minor Irrigation schemes and
large 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)

6. Methodology of the Research
Concept
 General relationship between crop yield and water applied to the crop
shows a trend to increase linearly up to about 50% of the full irrigation and
then going in a convex curvature to the maximum yield and then reduce the
yield with increase in applied water
 Farmers whose sole objective is to get maximum net Income, tends to
irrigate their crop by spending minimum cost for their irrigation water to get
maximum productivity for their crop
“Hence the main methodology adopted in this research
regarding the optimum crop yield to maximize productivity in
terms of food production is economizing the cost of the
irrigation water and increasing the extent of cultivation per unit
of irrigation water”

7. Methodology of the Research
Model Formulation
 A regional aquifer simulation model using integrated finite difference
technique was formulated in spread sheet for a polygonal net work of a
restricted catchments in Vavuniya with forty one observation wells
 This aquifer was divided into forty one polygons by connecting the
perpendicular bisectors of adjoining observation wells. Six year
seasonal water levels and one year monthly water levels, tank
storage, field issues and total withdrawal from agro and domestic wells
for each polygon were taken for the water balance of each polygon
 The model was calibrated by error optimization method using historic
seasonal data. In each of the error optimization model four variables for
polygonal inputs, one variable for that particular polygonal specific yield
and five to seven variables for transmissibility for every polygonal
connection were formulated with constrains.

9. Methodology of the Research
Operational Research
A study was carried out to find out an operational policy for 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 under
minor and medium irrigation schemes together with creation of an artificial boundary to lift the
water table up
 By changing every polygonal input (i.e. to change the operational policy of minor and medium irrigation
schemes to reduce the extent of cultivation using surface water and increase the extent of cultivation using
groundwater) 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 an
artificial 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 of
water levels in each polygon were analyzed
The economic implication of the above three outcomes based on “Reducing the extent of
cultivation will appear to be a loss to the Gross Domestic Product and lead to reduction in the
Gross National Product too. But the gain in water table will reduce the cost of energy by way
of fuel and electricity for the pumping of water for the cultivation, domestic and industrial
water use. This will indirectly contribute to GDP and GNP positively”

10. 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.

11. 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 the
benefit cost ratio based on present worth greater than unity with considerable
rise in water table. The rise in water table occurred almost above 80% of the
observation wells. The rise in water table was around 45% to 65% of the loss
in water table between two consecutive seasons
 The boundary treatment showed positive results
 The combination of the above two alternatives yielded further improvement
that, at any time water table will recover 60% to 70% of loss in between two
consecutive seasons in 95% of the catchments under study. This implies that
the boundary treatment combined with changing the operational policy of
minor and medium irrigation schemes by forgoing a part of the cultivation is an
economically feasible policy alternative.

12. 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”

13. Conclusions
 Minor / medium irrigation schemes conserve surface run off and covey most part of it
to recharge groundwater and as such serves as a recharge shed for the wells situated
in the zone of influence. It is an insurance against water scarcity, as the yield increases
considerably for every unit of rainfall. The minor / medium irrigation schemes prevent
soil erosion and depletion of soil fertility. In the context of impending water deficiency
looming large, construction of minor / medium irrigation schemes will be a dependable
infrastructure in the development of water potential in any catchments.
 Acknowledgement of the remarkable role played by the minor / medium irrigation
schemes on replenishment of groundwater and its spread over a large area would be a
great asset in planning and execution of settlement and crop production projects
“Forgoing certain percentage of cultivation will be a loss to Gross Domestic
Product and lead to loss in Gross National Product also. The gain in water
table will reduce the cost of energy by way of fuel and electricity. This will
indirectly contribute to GDP and to GNP and also reduce the cost of
irrigation water and in turn increase the extent of cultivation per unit of
irrigation water. This will increase the crop yield per unit of irrigation water
and to increase economic productivity in terms of food production”

14. Generalization
The model formulated for this research was applied to a selected catchment in
Vavuniya (a shallow weathered and rarely fractured rock with thin soil mantle)
which covers 6 medium Irrigation schemes, 40 minor irrigation schemes and
around 2000 shallow wells within 71.5 sq.miles of area
“The rationale behind the selection of this study area is that the
aquifer of this region very well reflects the typical groundwater
problems of unconfined aquifers in shallow weathered and
rarely fractured rock with thin soil mantle. Study of this nature
of problems is the prime intention of this research. Hence the
findings pertaining to this restricted catchment can be
generalized to any type of restricted catchment with certain
limitations”

15. 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

16. 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”

17. Thank You