Government of India & Netherlands Groundwater Resource Assessment

Government of India & Government of The Netherlands
DHV CONSULTANTS &
DELFT HYDRAULICS with
HALCROW, TAHAL, CES,
ORG & JPS
VOLUME 8
DATA PROCESSING AND ANALYSIS
OPERATION MANUAL – PART IV
GROUNDWATER RESOURCE ASSESSMENT

Operation Manual – Data Processing and Analysis (GW) Volume 8 – Part IV
Data Processing and Analysis March 2003 Page i
Table of Contents
1 GROUNDWATER RESOURCE ASSESSMENTCONCEPT 1-1
1.1 RECHARGE COMPONENTS 1-1
1.2 DISCHARGE COMPONENTS 1-2
1.3 INDEPENDENT AND DEPENDENT COMPONENTS 1-3
1.4 STABILISING INFLUENCE OF THE DEPENDENT COMPONENTS 1-3
2 OBJECTIVES 2-1
2.1 ESTIMATION OF GROUNDWATER RESOURCE 2-1
2.2 VALIDATION 2-1
2.3 PRIORITISATION OF THE COMPONENTS 2-1
2.4 ESTIMATION OF AN UNKNOWN COMPONENT 2-2
3 CHOICE OF AREAL UNITS 3-1
3.1 MINIMISING THE DEPENDENT RECHARGE/ DISCHARGE COMPONENTS 3-1
3.2 IMMUNITY FROM EXTERNAL INFLUENCE 3-1
3.3 EVALUATION OF POSSIBLE AREAL UNITS 3-1
4 CHOICE OF WATER BALANCE PERIOD 4-1
5 COMPONENTS INCLUDED 5-1
6 ORGANIZATION OF THE DATABASE 6-1
6.1 DESCRIPTION OF THE AREA AND THE RETRIEVAL ZONES 6-1
6.2 DESCRIPTION OF THE AREAL BOUNDARY 6-1
6.3 DESCRIPTION OF THE PERIOD AND OBJECTIVE OF THE WATER BALANCE 6-1
6.4 RETRIEVAL OF DATA FROM THE BASIC MODULE 6-1
6.5 REVIEWING AND UPGRADING THE DATABASE 6-2
6.6 DIRECT ENTRY OF DATA 6-2
7 PROCESSING POINT DATA TO SPATIAL DISTRIBUTIONS 7-1
7.1 GENERATION OF CONTOURS/ SPATIAL DATA 7-1
7.2 WATER LEVEL DATA 7-1
7.3 AQUIFER PARAMETERS 7-1
7.4 RAINFALL 7-2
7.5 TOPOGRAPHICAL LEVEL 7-2
8 ESTIMATION OF WATER BALANCE COMPONENTS 8-1
8.1 STORAGE FLUCTUATION 8-1
8.2 RAINFALL RECHARGE 8-1
8.3 LATERAL FLOWS ACROSS BOUNDARY 8-2
8.4 STREAM AQUIFER INTER-FLOW 8-3
8.5 VERTICAL INTER-AQUIFER FLOW 8-3
8.6 EVAPOTRANSPIRATION FROM WATERTABLE 8-4
8.7 GW DRAFT 8-4
8.8 CANAL SEEPAGE 8-5
8.9 RECHARGE DUE TO RETURN FLOW FROM APPLIED IRRIGATION 8-5
8.10 RECHARGE FROM TANKS, PONDS, CHECK DAMS AND NALA BUNDS 8-5
9 TIME SERIES ANALYSIS 9-1
10 INTERFACING WITH THE GEC-97 NORMS 10-1
10.1 SALIENT FEATURES OF THE NORMS 10-1
10.2 IMPLEMENTATION OF THE NORMS 10-2
10.3 SUMMARY REPORT 10-4
11 REFERENCES 11-1

Data Processing and Analysis March 2003 Page 1-1
1 GROUNDWATER RESOURCE ASSESSMENT CONCEPT
A groundwater (GW) balance study involves an application of the continuity equation to an aquifer
(usually unconfined). The continuity equation in this context is a statement to the effect that the
difference between the net recharge volume (I) and net discharge volume (O) equals the change of
groundwater storage (∆S). I, O and ∆S must be in respect of the same aquifer area and the time
period.
I - O = ∆S (1.1)
The continuity equation may be applied to a large area treating the entire study area as a single entity.
The flow across the boundary is estimated by an application of Darcy’s law. Such a study is known as
lumped water balance (LWB). Alternatively, the continuity equation may be applied at a micro level.
Thus, the area of interest is divided into a finite number of cells and the continuity equation is applied
to each cell. The flow between the adjacent cells is estimated by Darcy’s law. This approach could be
termed as distributed water balance, and is conducted through the application of specialized software
for groundwater modelling (such as the widely used MODFLOW).
The dedicated software comprises a module on groundwater balance and GIS tools. The scope of the
dedicated software is restricted to only the lumped water balance. Therefore, only the lumped water
balance is addressed in the following text.
The main advantage of the lumped water balance approach is its simplicity. The data processing
comprises only simple arithmetic/graphical procedures devoid of any higher mathematics. In spite of
its simplicity, this approach leads to validation of various procedures/ parameters. It also yields
consistent estimates (that is, estimates satisfying the continuity equation) of various components of
the recharge and discharge. These estimates in turn permit an estimation of the permissible
groundwater development.
The LWB permits only an analysis of current and historical data and as such is not a good tool for
projection of the aquifer response. The area for a LWB study could be a basin (hydrologic and
hydrogeologic), inter-basin or an administrative/ political unit. The time period could be a year, a
season or a smaller unit like a fortnight or month and is only constrained by the frequency in which the
basic data are monitored.
The LWB study essentially comprises estimation of various components of the recharge/ discharge
and the change of storage in a given area of the given aquifer in a given time period followed by an
overall cross check for the consistency.
1.1 RECHARGE COMPONENTS
The various components of the recharge are as follows. The components are classified as per the
governing process. The governing processes are vertical flow through unsaturated and saturated
zones; lateral (that is, predominantly horizontal flow) through the saturated zone; and vertical inter-
aquifer flow (see Figure 1.1).
Recharge as a consequence of vertical unsaturated flow
• Rainfall recharge
• Recharge from applied irrigation- either surface water or groundwater or both

Figure 1.1: Recharge as a consequence of vertical saturated flow
• Recharge from canal seepage over the deep water table (depth below the canal bed more than
1.5 times the canal width at the free surface)
• Recharge from storage tanks, ponds, percolation tanks, check dams and nala bunds over deep
water table
Recharge as a consequence of lateral saturated flow
• Subsurface seepage from hydraulically connected drains
• Subsurface horizontal inflow across a non-hydraulic boundary
• Recharge from canal seepage to the shallow water table (depth below the canal bed less than 1.5
times the canal width at the free surface)
• Recharge from storage tanks, ponds, percolation tanks, check dams and nala bunds over shallow
water table
Recharge as a consequence of vertical inter-aquifer flow
• Recharge from an underlying leaky confined aquifer
1.2 DISCHARGE COMPONENTS
The various components of the discharge are as follows. The components have been classified in
accordance with the governing process. The governing processes are the vertical discharge through
an external sink, saturated vertical and lateral flow, and inter-aquifer flow.
Vertical discharge through an external sink
• Groundwater pumpage
• Evapotranspiration from shallow water table (within the capillary fringe/ root zone)
Discharge as a consequence of lateral saturated flow
• Subsurface outflow to hydraulically connected drains (rivers, sea)
• Subsurface horizontal outflow across a non-hydraulic boundary
Subsurface
outflow to
drains
Groundwater
draft
Recharge from
canal seepage
Recharge from
ponds or tanks
Recharge from
irrigation
Rainfall recharge
Evapotranspiration
Leakage to
underlying aquifer
Subsurface
groundwater
outflow
Subsurface
groundwater
inflow
Recharge from
underlying aquifer
Change in
groundwater
storage: ∆S

Discharge as a consequence of vertical inter-aquifer flow
• Leakage to an underlying leaky confined aquifer
1.3 INDEPENDENT AND DEPENDENT COMPONENTS
Recharge and discharge as a consequence of the lateral saturated flow and the inter-aquifer flow and
evapotranspiration are dependent upon the position of the water table. These are termed as the
dependent components. Other components of recharge and discharge are almost independent of the
position of the water table. These are termed as the independent components. This classification of
the components has an important bearing upon the choice of an areal unit for groundwater resource
assessment by LWB; and shall be referred back to subsequently.
1.4 STABILISING INFLUENCE OF THE DEPENDENT COMPONENTS
A close examination of variation of the dependent components as a consequence of any temporal
trend of water table, reveals that the variation tends to stabilise the causative trend. Thus, as the
water table declines, the recharge components increase and the discharge components (including
evapotranspiration) decrease. This tends to stabilise the falling trend. Similarly, as the water table
rises, the recharge components decrease and the discharge components increase. This tends to
stabilise the rising trend.

2 OBJECTIVES
Broadly speaking, a water balance study can serve one or more of the following objectives:
2.1 ESTIMATION OF GROUNDWATER RESOURCE
The LWB as enumerated above provides the validated historical estimates of different components of
recharge and discharge and as such may be used to estimate the status of the resource in a certain
time span. Such estimation is an essential management tool for arriving at permissible groundwater
draft and development stage.
2.2 VALIDATION
Unfortunately many components of recharge and discharge can not always be estimated rationally
either because of the complexity of the process or due to an inadequate database. These
components are estimated empirically using some locally accepted (or some times even imported)
norms/ practices.
Even if rational algorithms are available and adopted, there would still be some uncertainty in the
estimates on two counts. Firstly, even an apparently rational equation may have some hidden
assumptions. Secondly, it would invariably comprise some parameters, which may not always be well
known. Thus, there is some inherent uncertainty in the estimates of almost all the components of the
water balance equation. This calls for a validation criterion.
A water balance study can be taken up to validate various adopted algorithms (rational or empirical)/
norms/ practices/ parameter values. This can be accomplished by checking if the independently
estimated components of recharge and discharge; and the storage change satisfy the water balance
equation. For this purpose the water balance equation is rewritten as follows:
I - O - ∆S = ε.∆S (2.1)
Where: ε.∆S is the residue term in the water balance equation. This term can be viewed as the
volumetric imbalance between the net recharge (that is, recharge minus discharge) and the storage
fluctuation. The term ε is the normalized imbalance that is, the imbalance expressed as a fraction of
the storage fluctuation.
Ideally, the residue should be equal to zero. However, in practice it may at the best be a negligible
quantity. Thus, a small enough residue may provide the desired validation. However, there is always a
possibility that the errors in the estimates of the individual components may have compensated each
other. Thus, the validation can never be absolute. Nevertheless, if the residues turn out to be small
enough consistently over a number of time periods, one may be reasonably confident about the
validation. Thus, it is necessary to carry out a multiple period water balance study.
2.3 PRIORITISATION OF THE COMPONENTS
The above procedure apart from validating the various procedures/ parameters, also leads to an
understanding of the relative significance of the various component(s) of the water balance. Estimate
of each component is normalised by expressing it as a fraction of the storage fluctuation. These
fractions are thus indices of the relative significance of the respective components. The indices can
provide a basis for prioritisation of the components. Larger effort should be put in to estimate the high
priority components and vice versa. Larger effort implies refining the algorithm and carrying out direct
measurement of variables or conducting experimental field work to improve upon the estimates of the
concerned parameters.

2.4 ESTIMATION OF AN UNKNOWN COMPONENT
It follows from the preceding discussion that many components of recharge occur as a consequence
of flow through the unsaturated zone that extends from ground surface to the watertable. These
components thus, need to be estimated by simulating the flow through the unsaturated zone. This
simulation requires data on the soil and surface characteristics that are invariably not available on a
regional scale. Further, the computational efforts may be prohibitively large. Thus, these recharge
components are usually estimated empirically. This however, may introduce considerable uncertainty
in the results of a water balance study. The uncertainty can be quite severe if a dominant/ crucial
component is estimated empirically.
This problem can be overcome by first identifying the most crucial component (say X) which is not
amenable to a rational estimation. An example of X could be the rainfall recharge during a monsoon
season. Subsequently, this component can be estimated by substituting the estimates of all other
components and of the storage fluctuation into the water balance equation. The residual term (ε) is
assumed to be zero. Thus, the estimate of X shall be reliable provided the estimates of all other
components and of storage fluctuation are more or less error free. This calls for a precedent validation
of the procedures/ parameters adopted for estimating components other than X. This is possible only
if there exist seasons/ time periods during which these components are significant but the component
X is insignificant or absent. If the estimates of these components during such seasons satisfy the
water balance equation with consistently insignificant residue, the procedures/ parameters stand
validated. Subsequently, these validated procedures/ parameters can be used to estimate the
component X, as outlined above.
Typically, this approach may be adopted for estimating the recharge from monsoon rainfall. The
approach shall involve first dividing a hydrologic year into the monsoon and non-monsoon periods.
The procedures/ parameters adopted for estimating components other than the monsoon recharge
are first validated by carrying out multiple water balance of the non-monsoon seasons included in the
database. Subsequently, the rainfall recharge is estimated by carrying out the water balance study of
the monsoon seasons of the database. It is worthwhile to observe here that the average water
tablefluctuation method of estimating the groundwater resource (R = ∆h.A.Sy) is essentially a
simplified water balance of the monsoon period. In this method it is assumed that all discharge
components (e.g., pumpage, evapotranspiration, etc.) and the recharge components other than the
rainfall recharge (e.g., recharge from irrigation) are negligible as compared to the rainfall recharge.

3 CHOICE OF AREAL UNITS
The choice of an areal unit for assessment of groundwater resource by the LWB is governed by the
following two considerations:
3.1 MINIMISING THE DEPENDENT RECHARGE/ DISCHARGE COMPONENTS
Evapotranspiration, recharge and discharge as a consequence of the lateral saturated flow and the
inter-aquifer flow are dependent upon the position of the water table. Thus, these components can not
be assigned historical estimates while planning for future groundwater development/ recharge. These
components (the dependent components) shall inevitably change as the planned groundwater
development/ recharge takes place and the water table declines/ rises accordingly. Other components
of recharge and discharge are almost independent of the position of the water table. Thus, the
historical estimates of these components (the independent components), after due normalisation may
hold for future planning.
3.2 IMMUNITY FROM EXTERNAL INFLUENCE
For the sake of uniqueness, the areal unit may preferably be so selected that the groundwater
resource is exclusively dependent upon the conditions there in and is independent of the
pumping/recharge activity occurring outside the aquifer volume contained in the unit.
3.3 EVALUATION OF POSSIBLE AREAL UNITS
A hydrogeological basin
This is essentially an area bounded by impervious hydrogeological boundaries. Thus, the water table
in the area is totally immune to the pumping/recharge activities occurring outside the area. It is also
immune to the pumping activities (inside or outside the area) and boundary conditions in respect of
the underlying confined aquifer. The resource of the unconfined aquifer in such a unit shall not
depend upon what is happening out side (laterally as well as vertically).
Thus, it shall not comprise any of the dependent components enumerated earlier (except for the
evapotranspiration, which may not be activated unless the area is water logged). As such, this is an
ideal unit for resource assessment by the LWB.
However, such a unit shall no longer remain an ideal unit if the unconfined aquifer in the unit is
underlain by a leaky confined aquifer. In such a case the unconfined aquifer is affected by the
piezometric elevation of the underlying leaky confined aquifer and its position relative to the water
tableelevation and hence by the pumping activities, and as such the resource can not be estimated
uniquely by the LWB. However, if the vertical inter-aquifer flow is relatively small in magnitude, these
effects may be negligible and as such, this may be a near ideal unit for resource assessment by the
LWB.
Hydrological (surface drainage) basin
This is essentially an area bounded by a topographical divide. It is usually believed that a
topographical divide is underlain be a water table divide but this may not always hold. Thus, the
external influence and the dependent components could be significant. A hydrological unit thus, need
not necessarily be an ideal unit for assessing the groundwater resource. As explained earlier in the
context of a hydrogeological unit, the uncertainty is further aggravated in case the unconfined aquifer
is hydraulically connected to an underlying leaky confined aquifer through an aquitard.

In hard rock areas the topographical and hydrogeological divides may generally overlap each other.
However, in alluvial areas and also in low relief hard rock terrain, an unconfined aquifer may cut
across a topographical water divide and the lateral flows in alluvial aquifers may be relatively far more
significant due to high transmissivities.
Doab (Inter-basin)
This is an area bounded by two major perennial streams fully penetrating the unconfined aquifer.
Such stream boundaries ensure that there are no flows across the boundary. Thus, the water tablein
the aquifer is immune to the pumping/ recharge activities out side the area. However, the component
of the stream-aquifer inter-flow is prevalent and is dependent upon the position of the water
tablerelative to the stream gauge. Further, even a doab would invariably have a non-hydraulic
boundary across which the external influence may occur. Thus, it is also not an entirely appropriate
unit for the estimation of resource by the LWB.
An administrative unit
In such a unit, all the dependent components of recharge and discharge are activated. The lateral
inflows/outflows across the boundary are dependent upon pumping/ recharge events outside the areal
unit. As such, an administrative unit is the least desirable but most commonly used areal unit. The
only advantage of such a unit (which should not be underestimated) is that it falls under a single
administration, which may enforce uniform data acquisition and management, practices.

4 CHOICE OF WATER BALANCE PERIOD
Theoretically speaking, a water balance study could be carried out for any period. However, in
practice there are certain constraints, which are essentially derived from the intended objectives of the
water balance study.
For an optimal validation of the norms/ parameters etc., the period must permit the maximum possible
activation of the concerned variables, and the components must be amenable to a reliable estimation.
For example, if the objective is to estimate the specific yield by analysing the depletion of the water
table/ storage during the dry season (as recommended in the GEC-97 norms), the period may
incorporate the maximum possible decline from the view point of activation of the specific yield. This
implies that the period may span between the discrete times of the highest and the lowest water table.
However, a split to monthly water balance may be considered to minimise the error in the draft
estimate (draft may be negligible in the first month after the monsoon season).
For estimation of a specific component of the water balance, it is necessary to select a period during
which the component is just fully generated. Any period less than that shall lead to an underestimation
of the component. A longer period shall attenuate the predominance of the component and hence
shall lead to a less reliable estimate of the component. For example, if the water balance is carried out
for estimating the rainfall recharge by analysing the build up of the water table/storage during the
monsoon season (as recommended in the GEC-97 norms), it shall be required to define a period
during which the entire rainfall recharge just occurs. This period shall be necessarily different from the
period of the monsoon rainfall because of the inevitable time lag. The period must span between the
discrete times of the lowest and the highest water table and not the start and end of the rainy season.
The frequency of manual monitoring of GW levels (usually two to four times a year under Indian
practice) is generally not sufficient to define the seasonal hydrograph and therefore may miss either
peak or low or both. The wide scale deployment of automatic water level recorders (DWLRs)
implemented through the Hydrology Project, shall provide comprehensive and almost continuous
water table hydrographs. These hydrographs shall permit a correct identification of the optimal period.

5 COMPONENTS INCLUDED
The dedicated software package includes modules and tools that permits a comprehensive water
balance computation, which can be applied for estimation of groundwater resource in general, and in
accordance with the GEC-97 norms in particular. The components of the water balance included in
the module are (see also Figure 5.2):
∆S - the change of groundwater storage
Rrf - recharge from rainfall
Rc - seepage from canals
Ri - recharge from irrigation
Rt - recharge from storage tanks and ponds
Rwc - recharge from conservation structures
I - algebraic sum of lateral outflow (+) and inflow (-) across the boundary
Dg - gross draft
B- algebraic sum of subsurface outflow to (+) and inflow from (-) hydraulically connected streams
L - algebraic sum of vertical inter-aquifer outflow (+) and inflow (-)
E - outflow from the aquifer due to evapotranspiration from the aquifer
The volumetric estimates of these components are substituted in the following equation:
(Rrf + Rc + Ri + Rt + Rwc) - (I + Dg + B + L + E) - ∆S = ε.∆S (5.1)
and ε is estimated.
Figure 5.2: Components of the water balance
Ri
Rrf
Rc Rt
E
L
B
Dg
I
∆S
Rwc

6 ORGANIZATION OF THE DATABASE
The database necessary for estimating the components included in the above equation is organised
in the following steps.
6.1 DESCRIPTION OF THE AREA AND THE RETRIEVAL ZONES
The assessor is prompted to input the digitised boundary of the water balance area (termed
henceforth as the unit area) and four reference circumscribing rectangles for the search of the
observation wells, rain gauge stations, river gauging points and the pumping test points. The
reference rectangles, oriented along the N-S and E-W directions, are defined in terms of the
longitudes and latitudes of the sides.
It may be appreciated that the data not only from the unit area, but also from beyond the boundary of
the unit area could be relevant and useful for the study. The water level from an area extending up to
the hydraulic boundaries (that is, a dyke or a hydraulically connected river or a GW divide) should be
retrieved. The aquifer parameter data from area of similar hydrogeology should be retrieved. The
rainfall data from meteorologically similar area should be retrieved. The river stage data from the
upstream and down stream reaches having similar slope should be retrieved. This extension of the
search areas shall permit more reliable spatial distributions, such as contouring, zoning, Thiessen`s
polygons, interpolation, extrapolation; and identifying/ reconfirming hydrological/ hydrogeological
boundaries.
6.2 DESCRIPTION OF THE AREAL BOUNDARY
The assessor is then prompted to input the hydraulic description of the digitised boundary or its parts
which could be a hydraulically connected river boundary, an impervious boundary or a GW divide, or
a non-hydraulic (that is, administrative) boundary. Further, the assessor is prompted to extend the
river alignment up to the corresponding reference rectangle.
6.3 DESCRIPTION OF THE PERIOD AND OBJECTIVE OF THE WATER
BALANCE
The assessor is then prompted to input the period of the water balance and the objective of the study
(as already stated, the objective could be either validation or estimation). In case the objective is
estimation, the assessor is prompted to indicate the component to be estimated.
6.4 RETRIEVAL OF DATA FROM THE BASIC MODULE
Based upon the response of the assessor, the module retrieves the necessary basic data from the
Basic module. The data comprise the following:
• Coordinates and ground levels (above MSL) of the observation wells falling within and on the
relevant reference rectangle, and the corresponding available water levels at all the discrete
times falling in the period of the LWB. The water levels at the beginning and at the end of the
period are mandatory. The water levels shall comprise water table elevations; and also
piezometric elevations in case the vertical inter-aquifer flow is to be accounted for. Pre and post
monsoon water table elevations of the preceding ten years are also retrieved for the trend
analysis stipulated in the GEC-97 norms. However, if the database of the Basic module is not
exhaustive enough to permit such retrieval, these data may be entered externally.
• Coordinates of the rain gauge points falling within the relevant reference rectangle and the
corresponding recorded rainfall depths within the stipulated period. However, if the database of

the Basic module is not exhaustive enough to permit such retrieval, these data may be entered
externally.
• Processed thematic maps (topographical contours, forest cover, hydrogeological and
geomorphic units) in respect of the unit area. The forest cover may be defined in terms of
boundary of well-defined forest area. In case there are no well-defined forests in the unit area,
the average forest/ canopy cover expressed as a fraction of the geographical area may be
entered.
• In case a part (or whole) of the unit boundary comprises a river, the coordinates of the gauge
stations (if any) falling within or on the relevant reference rectangle and the associated stage
values at discrete times falling within the stipulated period. However, if the database of the Basic
module is not exhaustive enough to permit such a retrieval, interpolated/ extrapolated river stage
at a few points within the unit area along with the coordinates of the points may be entered
externally.
• Coordinates of the pumping test points falling within and on the relevant reference rectangle and
the corresponding estimates of the relevant parameters. The relevant parameters are
transmissivity and specific yield and also the hydraulic resistance of the aquitard in case the
vertical inter-aquifer flow is to be accounted for. However, if the database of the Basic module is
not exhaustive enough to permit such a retrieval, these data may be entered externally.
• Blocks falling within the unit area, total area and the effective area (that is, area falling in the unit
area) of each block, type wise number of groundwater production structures falling within the
effective area of each block. However, if the database of the Basic module is not exhaustive
enough to permit such a retrieval, these data may be entered externally
6.5 REVIEWING AND UPGRADING THE DATABASE
The retrieved/ entered database in respect of water table, piezometric head, rainfall, pumping tests
and river gauge are displayed. The database comprises the locations and the corresponding data
magnitudes. These data locations symbolised appropriately shall be displayed superposed over the
unit area and the reference rectangles. The data magnitudes shall be displayed at the respective
locations.
The assessor may view the database. There upon using his professional judgement he may exercise
one of the following options:
• Accept the database as such without any modification.
• Delete any number of the retrieved data points (apparently inconsistent data, water level data
from beyond a dyke or a hydraulically connected river, aquifer parameter data from a different
hydrogeological zone, etc.). The data corresponding to the deleted points shall not be used for
the subsequent calculations.
• Redefine the domain(s) of any one or more of the reference rectangles to enhance the database.
Thus, the assessor can iteratively modify his database till he is satisfied.
6.6 DIRECT ENTRY OF DATA
The assessor shall be prompted to enter the following data directly:
• Population density and fractional load on groundwater for domestic and industrial water supply,
in the unit area (refer page 57 of the GEC-97 norms).
• Wetted areas, bed reduced levels and running days in respect of the lined and unlined canals
falling in the unit area.
• The volumes of the canal water (released at the outlet) in the unit area during the stipulated time
period for paddy and non-paddy crops.

• The assessor will be prompted to state whether the stream is fully penetrating. If the answer is
Yes, the attenuation factor shall be taken as 1.0. If the answer is No, the assessor is prompted to
either enter the values of Wp, d and e (necessary for estimating the attenuation factor) or to
directly enter the value (less than one) of the attenuation factor as per his hydrogeological
judgement.
• The assessor shall be prompted to enter the capillary height and evaporation rate for estimating
the direct evaporation loss from the shallow water table areas.
• The assessor shall be prompted to enter the root zone depth of the trees and the
evapotranspiration rate for estimating the evapotranspiration from the forested areas.

7 PROCESSING POINT DATA TO SPATIAL DISTRIBUTIONS
The database so created shall be processed on a GIS platform in the following steps:
7.1 GENERATION OF CONTOURS/ SPATIAL DATA
The module permits generation of contours and the corresponding spatial data in Raster/ Vector
modes. As discussed subsequently, the assessor may use this capability for processing discrete point
data of water level, aquifer parameters and rainfall. The processing involves the following steps:
• The available discrete point data are analyzed by an appropriate algorithm (such as Kriging,
Least squares polynomial, Spline function) and a Raster data set is generated. The pixel
spacings of the Raster data shall be chosen by the assessor.
• The assessor shall specify the desired contour interval. The Raster data are processed to
generate and store Vector data corresponding to the resultant contours.
• The assessor, using his professional judgement and guided by relevant maps etc. may edit some
or all the contours manually.
• Vector data and hence the Raster data corresponding to the edited contours are generated and
stored together with the data corresponding to the unedited contours (if any).
7.2 WATER LEVEL DATA
The retrieved water level and the river stage data are used for contouring. While drawing the water
table contours, the interpolated/ extrapolated stage values along the boundary, are treated as the
water table data. This ensures a compatibility along the boundary. The assessor is prompted to
exercise his choice of the contouring algorithm.
The module returns the contours of the water table and also of the piezometric head (if relevant) at all
the discrete times. It also returns the contours of water table fluctuation (that is, water table elevation
at the end of the period minus the water table elevation at the beginning of the season, or water table
depth at the beginning of the season minus the water table depth at the end of the season).
The assessor may edit the contours any number of times. Raster data corresponding to the finally
accepted contours are stored (refer Section 6.7.1).
7.3 AQUIFER PARAMETERS
The assessor has the following two options for obtaining the spatial distributions of transmissivity,
specific yield, and also the hydraulic resistance, if relevant.
• The assessor may decide to use the contouring capability of the dedicated software. There upon,
he is prompted to exercise his choice of the contouring algorithm. The module returns the
contours of the aquifer parameter. The assessor may edit the contours any number of times.
Raster data corresponding to the finally accepted contours are stored (refer Section 6.7.1).
• Usually the data are available at a very few points only and as such, automatic contouring (that
is, the first choice) may not be applicable. The assessor may ask for a display of the unit area
and thematic maps, with the concerned database superposed over it. He may define
homogenous zones and define a value for each zone. In the absence of any hydrogeological
support of such zones, the assessor may choose to define Thiessen’s polygons around the data
points (see the following Section on Rainfall). Corresponding Raster data are generated and
stored.

For obtaining the spatial distribution of the infiltration factor usually only the second option shall be
relevant.
7.4 RAINFALL
The assessor has the following two options for estimating spatial distribution of rainfall over the unit
area during the stipulated period. The estimation has to be essentially based upon the retrieved data
of point rainfall depths, corrected for orographic effects.
• The assessor may decide to use the contouring capability of the dedicated software. There upon,
he is prompted to exercise his choice of the contouring algorithm. The recommended algorithm is
Kriging. The module returns the contours (also known as isohyets) of the rainfall depth, with
topographical contours superposed over them. The assessor may edit the contours any number
of times. Raster data corresponding to the finally accepted contours are stored (refer Section
6.7.1).
• The assessor may opt to estimate the average rainfall by Thiessen’s polygon approach. A
Thiessen’s polygon is drawn for each rain gauge by joining the right bisectors of the straight lines
joining the neighboring rain gauge points. Thus, all the points falling within any polygon are closer
to the respective rain gauge station than to any other rain gauge point. Therefore, the rainfall
within a Thiessen`s polygon is assumed to be equal to the rainfall recorded at the respective rain
gauge. Corresponding spatial data are generated and stored.
7.5 TOPOGRAPHICAL LEVEL
In case a processed topographical map is not available in the database, the topographical contours
shall be obtained on the basis of the ground level data if available for the sites of the observation
wells/ piezometers. The assessor is prompted to exercise his choice of the contouring algorithm. The
module returns the contours of the topographical level. Corresponding Raster data are generated and
stored.

8 ESTIMATION OF WATER BALANCE COMPONENTS
Subsequent to the contouring and spatial distribution, the components of the water balance
enumerated above are estimated as follows:
8.1 STORAGE FLUCTUATION
Using the Raster data of the water tablelevations at the period’s beginning (hb) and at the end (he)
and of the specific yield, the storage fluctuation shall be estimated by a GIS assisted integration of the
product of the spatially distributed water table fluctuation and the spatially distributed specific yield
over the unit area (A). The integration is as follows:
dASy)hbhe(S
A
∫ −=∆ (8.1)
The integration involves pixel by pixel calculation of the storage fluctuation (pixel area multiplied by
pixel water tableelevation multiplied pixel specific yield) and summation.
However if a uniform specific yield is assigned over the entire unit area or the area is divided into a
few homogenous parts, the storage fluctuation is estimated as follows:
∑ ∫ −=∆
i Ai
dAi)hbhe(SyiS (8.2)
Where, Ai is the ith homogenous part having an average specific yield Syi.
The assessor has an option of performing the calculations in a semi-automatic mode, if he so desires.
In case this option is exercised, the storage fluctuation shall be computed in the following steps:
• Draw contours of water table fluctuation (as described in 6.7.1).
• Draw zones of equal specific yield (as described in 6.7.3).
• Superpose the zones of the specific yield over the fluctuation contours.
• Delineate the areas lying in between each pair of successive contours and the areal boundary.
Divide each inter-contour area among the intersecting zones and measure the sub areas, so
obtained. All the sub-areas of an inter-contour area are assigned an average water
tablefluctuation equal to the arithmetic mean of the ratings of the enveloping contours. Estimate
the storage change in each sub-area by multiplying the sub-area by its respective specific yield
and the average water tablefluctuation. Estimate the total storage fluctuation by adding the
estimated storage fluctuations in the sub-areas.
8.2 RAINFALL RECHARGE
Using the Raster data of the rainfall (r) and the infiltration factor (α), the volume of rainfall recharge
(R) shall be estimated by GIS assisted computation of the following integration over the unit area (A):
∫ α=
A
dArR (8.1)
In case this option is exercised, the rainfall recharge shall be computed in the following steps:

• Draw contours/ Thiessen’s polygons of rainfall depth (as described in 6.7.4).
• Draw zones of assumed equal infiltration factor (as described in 6.7.3).
• Superpose the zones over the rainfall contours/ Thiessen’s polygons.
• In case rainfall contours have been drawn, delineate the areas lying in between each pair of
successive contours and the areal boundary. Divide each inter-contour area among the
intersecting zones and measure the sub areas, so obtained. All the subareas of an inter-contour
area are assigned an average rainfall equal to the arithmetic mean of the ratings of the
enveloping contours. Estimate the rainfall recharge in each subarea by multiplying the subarea
by it’s respective infiltration factor and the rainfall depth. Estimate the total rainfall recharge by
adding the estimated rainfall recharge in the subareas.
• In case Thiessen’s polygons have been drawn, estimate the average infiltration factor over each
polygon. Estimate the rainfall recharge by computing the recharge over each polygon by
multiplying the corresponding recorded rainfall depth and the polygon’s area with the averaged
infiltration factor.
8.3 LATERAL FLOWS ACROSS BOUNDARY
Using the following Raster data:
• Water tableelevations at the period’s beginning and end,
• Water tableelevations at other intermediate discrete times,
• Transmissivity,
and the Vector data of the non-hydraulic boundary, the volume (I) of subsurface lateral flows (inflows
and outflows) across the boundary shall be estimated in accordance with Darcy’s law, by integrating
the product of water table gradient normal to the boundary (i) and the transmissivity (T) over the
boundary (C) and the period (t) of the LWB. Since the water balance equation, as written in Section
6.5, treats the outflow as positive, an outward falling gradient is treated as positive and vice versa.
The integration has been programmed in the module.
∫ ∫=
t C
TidCdtI (8.4)
The estimation thus, shall essentially involve estimation of spatial gradients from the spatial water
table data and the boundary alignment, followed by numerical integration over the boundary and the
water balance period.
In case this option is exercised, the lateral flow shall be computed in the following steps:
• Obtain contours of water table(above MSL) at the beginning, end and at other intervening
discrete times, as per the data availability.
• Mark the boundary across which the flow is to be computed on each contour map.
• Divide the boundary length among segments of nearly uniform transmissivity.
• Estimate the average hydraulic gradient across each segment at each discrete time. Hence
estimate the corresponding flow rates by multiplying the segment length with the corresponding
transmissivity and the estimated average hydraulic gradient.
• Estimate the flow rate across the boundary at each discrete time by adding algebraically the
corresponding computed flow rates across the segments.
• Estimate the flow volume in each time period (falling in between two successive discrete times)
by multiplying the time duration with the average flow rate. The latter may be taken as the
arithmetic mean of the flow rates at the starting and the ending discrete time.
• Estimate the total flow volume by adding the individual period-wise flow volumes.

8.4 STREAM AQUIFER INTER-FLOW
This component can be computed in the same way as the subsurface lateral flow in case of fully
penetrating streams. However, in case of the partially penetrating streams, the integral shall have to
be multiplied by an attenuation factor (less than 1.0) to account for the attenuation of the stream-
aquifer inter-flows due to the partial penetration. The factor (f) can be computed as follows:
)ed)(e5.0Wp5(
)eWp5.0(Wp5
f ++
+
= (8.5)
Where Wp is the wetted parameter of the stream (defined as the length of contact between water and
the stream bed, normal to the flow direction), d is the water depth in the stream and e is the saturated
thickness of the aquifer below the stream.
8.5 VERTICAL INTER-AQUIFER FLOW
• Water table elevation at the period’s beginning and end
• Water table elevations at the intervening discrete times
• Piezometric elevation at the period’s beginning and end
• Piezometric elevation at the intervening discrete times
• Hydraulic resistance (C) of the intervening aquitard
the vertical inter-aquifer flow volume (L) across the unit area (A), in the water balance period (t) shall
be estimated by performing the following GIS assisted integration:
dtdAL
t A
C
hH
∫ ∫= −
(8.6)
where H and h are respectively the space-time variant water table elevation and the piezometric head.
In case this option is exercised, the vertical inter-aquifer flow shall be computed in the following steps:
• Estimate the spatially averaged water table(H) and piezometric elevation (h) at each discrete
time.
• Estimate the spatially averaged hydraulic resistance (C).
• Estimate the rate of vertical inter-aquifer flow rate (Lr) at each discrete time, using the following
equation:
C
hH
Lr
−
= (8.7)
• Estimate the flow volume in each time period (falling in between two successive discrete times)
by multiplying the time duration with the average flow rate. The latter may be taken as the
arithmetic mean of the flow rates at the starting and the ending discrete time.
• Estimate the total flow volume by adding the individual period-wise flow volume.

8.6 EVAPOTRANSPIRATION FROM WATERTABLE
This component (ETV) has two parts, that is, direct evaporation and evapotranspiration. Loss of water
due to direct evaporation occurs from such unforested area where the depth to the water table is less
than the capillary height. This loss can be estimated by integrating the time varying loss rate (volume
per unit time) over the period of the water balance. The loss rate at different discrete times is the
product of the corresponding evaporating areas and the evaporation rates. Both, the evaporating area
as well as the evaporation rate varies with time. The dedicated software permits an estimation of the
evaporating area (A1) at various discrete times for a given capillary height. The capillary height may
vary from few tens of centimeters (for sands) to about three meters (for clays). The evaporation rates
(E) may be close enough to the potential evaporation rate which could be estimated from pan
evaporation rate.
Loss of water due to evapotranspiration occurs from such forested area where the depth to the water
tableis less than the root zone depth. This loss can also be estimated by integrating the time varying
loss rate (volume per unit time) over the period of the water balance. The loss rate at different discrete
times is the product of the corresponding evapotranspiring areas and the evapotranspiration rates.
Both, the evapotranspiring area as well as the evapotranspiration rate varies with time. The dedicated
software permits an estimation of the evapotranspiring area (A2) at various discrete times for a given
root zone depth. The root zone depth may be of the order of a few meters. Both the
evapotranspiration rates (ET) and the root zone depth could be ascertained from the local forest
authorities.
• Water table depth at the period’s beginning and end,
• Water table depth at the intervening discrete times,
• Forested area,
the areas A1 and A2 at different discrete times can be estimated through GIS. The volume of
evapotranspiration (ETV) can be computed by the following numerical integration over the period (t) of
the water balance. The integration has been programmed in the module.
∫ +=
t
dt)ET.2AE.1A(ETV (8.8)
In case there are no well defined forests in the unit area, the evapotranspiration may be estimated
from the average forest/ canopy fraction, β (that is, average forest/canopy area per unit geographical
area) and the area (A3) with water tabledepth ranging from the capillary height to the root zone depth.
The area A3 at different discrete times can be estimated from the Raster data of the water tabledepth.
The volume of evapotranspiration can be calculating by the following numerical integration
programmed in the module:
∫ +β+β−=
t
dt]ET)3A1A(E.1A)1[(ETV (8.9)
8.7 GW DRAFT
Since direct draft figures are almost non-existent, this component is estimated from the retrieved data
of the block areas, and the block-wise number of groundwater production structures of different types
(dug wells, various tube wells).

The number of structures (of different types) in the unit area shall be tentatively estimated assuming a
uniform distribution within each block. These numbers (block-wise and type wise) along with the basic
data shall be displayed on the console and the assessor shall be prompted to modify the numbers if
he so desires. The modification could be on the basis of the assessor’s knowledge of the spatial
distribution of the structures with in each block.
Upon a reconciliation of the numbers the assessor is prompted to enter the fractions of the total
annual pumpage occurring in the stipulated time period. The groundwater draft shall be computed
from these data and the average annual gross drafts incorporated in the GEC-97 norms (refer pages
61 and 62 of the norms). The computed figure shall be displayed on the console. The assessor shall
be prompted to modify the figure, if he so desires (refer paragraph 3 on page 60 of the GEC-97
norms).
8.8 CANAL SEEPAGE
This component is estimated using the retrieved canal data. The calculations shall be performed in
accordance with the criteria stipulated in the GEC-97 norms (refer Section 5.9.3, page 54 of the
norms).
However, the assessor may like to cross check and validate the estimated value by studying the data
(if available) of recorded discharge at the upstream and downstream of the study area. The difference
between the two discharge values is obviously the upper limit of the seepage. The true seepage has
to be less than that due evaporation and diversion of water. The assessor shall be prompted to enter
a new value, if he so desires.
8.9 RECHARGE DUE TO RETURN FLOW FROM APPLIED IRRIGATION
This component is estimated using the retrieved data of the canal irrigation and the Raster data of the
topographical levels and of the water tableelevations at the beginning and at the end of the stipulated
period. These data shall be used to estimate the spatially and temporally averaged depth to
watertable. The calculations shall be performed in accordance with criteria stipulated in the GEC-97
norms (refer Section 5.9.4, pages 54-55 of the norms).
8.10 RECHARGE FROM TANKS, PONDS, CHECK DAMS AND NALA BUNDS
These components shall be estimated using the data of average area spread (for storage tanks and
ponds) and of the gross storage (for percolation tanks, check dams and nala bunds). The assessor
shall be prompted to enter these data. The calculations shall be performed in accordance with the
criteria stipulated in the GEC-97 norms (refer Sections 5.9.5 and 5.9.6 on page 55 of the norms).
However, the assessor may like to cross check and validate the estimated value by carrying out a
water balance of the reservoir, considering among others, the storage fluctuation and evaporation.
The latter could be estimated from the pan evaporation data
.

9 TIME SERIES ANALYSIS
The water balance study provides estimates of the recharge and the discharge components of the
continuity equation. An excess of the net recharge over the net discharge should be reflected as a
rising trend in the time series of the water table; and vice versa. Thus, there must be a consistency
among the water balance estimates and the trend in the time series. This requirement can be used for
an indirect validation of the water balance estimates. As such, it is desirable to follow up the water
balance study by a time series analysis of spatially averaged as well as point water table data from a
few representative wells.
The analysis shall require GIS assisted spatial averaging followed by a check for first and second
order stationarity. In case stationarity is not inferred, a regression analysis shall be carried out to
determine the nature of the trend, that is, rising or falling and it’s rate over the years.

10 INTERFACING WITH THE GEC-97 NORMS
Groundwater estimation committee (97) has stipulated detailed norms for estimating the groundwater
resource of unconfined aquifers. The norms essentially lie within the broad frame work of the lumped
water balance approach described in the preceding paragraphs. Thus, the resource evaluation
module of the dedicated software can be used to implement the procedures incorporated in the
norms.
10.1 SALIENT FEATURES OF THE NORMS
The salient features are as follows:
Areal and time units
The recommended areal unit for the hard rock areas is a hydrological basin. It is suggested that in
hard rock areas the hydrological and hydrogeological boundaries may overlap and as such the
groundwater flow across the boundaries of a hydrological basin may be negligible. Recognizing that in
alluvial areas an aquifer may cut across a topographical divide, the recommended unit for alluvial
areas is an administrative block.
The recommended periods for the water balance are the monsoon and dry seasons. The dry season
water balance (recommended only for non-command areas) is aimed at estimating the specific yield.
The monsoon season water balance is aimed at estimating the rainfall recharge.
Normalization of the monsoon rainfall recharge
The recharge occurring in a normal monsoon year is estimated by analysing the results of the
monsoon season water balance for the current and the preceding years. The data of the monsoon
rainfall and the corresponding computed rainfall recharge are subject to a regression analysis,
assuming a linear relationship (with or without a constant) between the monsoon rainfall and the
corresponding recharge. The computed coefficient and the constant permit estimation of the rainfall
recharge corresponding to a pre computed value of the normal monsoon rainfall.
Categorization of areas for GW development
The GEC-97 norms suggest a categorization of the areas for groundwater development (that is, safe,
semi critical, critical and over exploited) on the basis of the stage of the groundwater development.
The stage is defined as the ratio of the existing groundwater draft to the net annual groundwater
availability. The net annual groundwater availability has been defined as the estimated resource
minus a certain allowance for the natural groundwater discharge. The latter has been defined as the
existing natural groundwater discharge during monsoon season plus a permitted natural groundwater
discharge during dry season. The suggested figure for the permitted discharge is five to ten percent of
the estimated resource.
However, keeping in view the inherent uncertainties in the estimates of the existing groundwater draft
and the resource, the norms further suggest a confirmation of the categorization by looking at the
long-term trend of the water level in the unit. It is stipulated that a composite plot of the pre and post
monsoon water levels of at least ten preceding years should be presented along with the stage
calculations.

Components not included
The component of subsurface lateral inflow/ outflow has not been included in the suggested
approach. However, it has been pointed out that this component may not always be negligible
especially in the case of alluvial areas where the transmissivities are relatively large and choice of the
assessment unit is based upon administrative consideration. Further, it is suggested that the assessor
may like to estimate this component and include in the water balance equation appropriately.
Stream-aquifer inter-flow has been ignored in the LWB for the monsoon season. This component
could be quite significant in high transmissivity areas. Evapotranspiration over water logged and
forested areas have been ignored for both the seasons. This component could be quite significant
during monsoon period when the water table may be quite shallow. The inter-aquifer flow has also not
been included.
10.2 IMPLEMENTATION OF THE NORMS
The water balance of the dry and monsoon seasons and the post water balance calculations,
envisaged in the norms can be implemented through integrated use of the resource assessment
module and the GIS tools of the dedicated software.
As discussed in the preceding Section, the norms suggest exclusion of a few components of the water
balance equation. These components have apparently been excluded to avoid the subjectivity
inherent in their manual/ graphical estimation. On the other hand the dedicated software, on account
of a computerised/GIS approach, permits an easy and objective estimation of these components.
Therefore, it is suggested that these components be included while implementing the norms through
the dedicated software.
Steps of the implementation shall be as follows:
Dry season water balance
The estimates of the all the recharge and discharge components and of the storage fluctuation are
substituted in the continuity equation. The imbalance, expressed as a fraction of the storage
fluctuation (magnitude) is computed and conveyed to the assessor. In case the imbalance is small
enough, the assigned specific yield distribution stands corroborated. In addition, the estimates of the
recharge components also stand corroborated. However, since the draft estimate is prone to possibly
large errors, the validation may not be beyond doubt.
Monsoon season water balance
The principal end product is the rainfall recharge. This is estimated by substituting the estimates of the
recharge components (other than the rainfall recharge), all the discharge components and the storage
change into the continuity equation.
Normalization of the rainfall recharge
The normalization of the recharge is aimed at estimating the monsoon rainfall recharge corresponding
to the normal monsoon rainfall. Such a study can be taken up provided the estimates of monsoon
rainfall recharge have been arrived at for the preceding years. The normalization is accomplished by
carrying out a regression analysis on the historical data of monsoon rainfall and the corresponding
estimated monsoon rainfall recharge. The analysis provides a functional relation between the
monsoon rainfall and the corresponding recharge.

The dedicated software permits a rigorous regression between the monsoon rainfall (r) and the
computed monsoon recharge (R). The analysis apart from estimating the coefficients, is aimed at
arriving at the optimal form of the functional relation between the monsoon rainfall and the monsoon
rainfall recharge. For example, it can be checked whether the suggested constant in the functional
relation is statistically significant or whether the assumed linearity holds (refer equations 8a and 8d on
pages 42-43 of the norms). The performance of more elaborate nonlinear functional relations could be
evaluated for possible adoption.
Functional relations included in the dedicated software are as follows. The assessor may design his
own functional relations as well.
R = Ar - B (R=0 if r < B/A) (10.1)
n
)Br(AR −= (R=0 if r< B) (10.2)
The goodness of the finally adopted functional relation is quantified by computing the statistics of the
regression including model efficiency (or the correlation coefficient).
The assessor is prompted to enter the normal monsoon rainfall. The normal monsoon rainfall is
usually taken as the arithmetic mean of last fifty years’ data. There upon, the normal monsoon rainfall
recharge is estimated in accordance with the regressed functional relation.
Estimation of the total annual recharge/net annual GW availability
The total annual resource is estimated by adding the normalized monsoon recharge and the dry
season recharge. The dedicated software permits estimation of the net annual groundwater
availability as per the GEC-97 norms (refer Section 6.10.1.3); and also permits the assessor to
suggest his own figures for the permitted natural discharge during the monsoon and the non-monsoon
periods. The prevalent natural discharge during the two seasons, as estimated by the LWB, are
displayed on the console to assist the assessor in taking a decision in this regard.
Estimation of the stage of GW development
The stage of the groundwater development is estimated in accordance with the GEC-97 norms (refer
equation 15 on page 57 of the norms).
Time series analysis
The time series analysis aims at identifying the trends (that is, rising or falling) in pre and post
monsoon water table elevations. The Raster data of the pre and post monsoon water table(elevation
above MSL or depth below the ground) of the preceding ten years are generated. These data are
integrated over the unit area to estimate the spatial averages.
The magnitude as well as the sign of the trend (if any) are identified by subjecting the time series of
these average levels/ depths to a trend analysis. The inferred trends in the pre and post monsoon
water levels are accompanied by computerised plots of the averaged water levels. The levels/depths
from all or a few representative wells are also plotted.

10.3 SUMMARY REPORT
GEC-97 norms require a presentation of a summary of the entire resource evaluation exercise in a
standard form given on pages 68 to 70 of the norms. The module permits a computerised
presentation of such a summary.

11 REFERENCES
Ministry of Water Resources, Govt. of India, Ground Water Resource Estimation Committee-1997.
New Delhi, 1997.

Government of India & Netherlands Groundwater Resource Assessment

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