Report on the Hard Rock Ground Water Estimation

CHAPTER 3

RECOMMENDATIONS

There are three distinct recommendations of the Committee as outlined below:

1) Issues Recommended for Implementation

The categorization of assessment unit (Block/watershed) has been rationalized and different possibilities have been considered.

2) Issues Recommended to Standing Committee

There are some issues that require revision and in-depth study for reliable estimates. It is an onerous task with differing views and has been appropriately referred to the Standing Committee to be formulated as per the outline recommended.

3) Formation of Standing Committee

To solve the outstanding issues as under recommendation (2) above and pursue R & D work, it is essential that a Standing Committee be formed with the Central Ground Water Board as nodal agency. It is reiterated that the GEC - 1997 Report, under recommendation No. 6.3.2 ( pp 78-81) emphasized to set up a similar committee.

3.1 ISSUES RECOMMENDED FOR IMPLEMENTATION

3.1.1 Categorization of Assessment Unit ;

This recommendation is to be implemented both in hard rocks and soft rocks.

(a) Long-term ground water level trend

The long term ground water level data should preferably be for the period of 10 years. The significant rate of water level decline may be taken between 10 and 20 cm per year depending upon the local hydrogeological conditions. Accordingly, in 'Detailed Guidelines for Implementing the Ground Water Estimation Methodology - 1997' page 153-154, the value of 'Z' would be read as 10 to 20 cm per year.

(b) Categorization of units

In order to remove ambiguities in the categorization by the existing methodology, the following procedure is suggested.

Note: 'To be re-assessed' means that data is to be checked for the purpose of categorization.2.2.6

The above modifications are to be adopted in all type of rock formations, that is, other than the hard rocks also.

3.2 ISSUES RECOMMENDED TO STANDING COMMITTEE

3.2.1 Ground Water Assessment In Non-Command Area

3.2.1.1 Computation of recharge in Monsoon Season

RG - DG -B+IS+I = S ( = h x SY x A ) (equ.2 of GEC-1997)

R- DG +Rgw-B+ IS +I = S ………….(modified)
where,
R = Recharge from rainfall and surface water sources during monsoon period
S = Ground water storage increase
RG = gross recharge due to rainfall and other sources including recycled water

RG is required to be changed to total recharge from rainfall and surface water sources only, that is excluding the recycled ground water (Rgw). Because increase in withdrawal of ground water will proportionately increase Rgw and would result in increase of the recharge.

R = S + DG (equ. 3 of GEC-1997)
(should be modified deducting the term Rgw)
R = S + DG - Rgw ……….(modified)

Rrf = R-Rgw-Rwc-Rt (eq 5 of GEC - 1997)

Rrf = R-Rwc-Rt ……….(modified)

Estimation of normal recharge during monsoon season (pp.44-45 of GEC-1997)

Criteria PD ..………(modified)
If PD is beyond the limit of 20%, the data representativeness of all the wells in the unit of assessment should be checked.

R(Normal) = Rrf (normal) + Rgw +Rwc + Rt (equ. 9 of GEC-1997)
R(Normal) = Rrf (normal) + Rwc + Rt ……….(modified)

Normal recharge should exclude the term Rgw

3.2.1.2 Computation of recharge in Non-Monsoon Season

Recharge from other sources …….…………………………(modified)

Recharge during the non-monsoon season from other sources, would include recharge from tanks (Rt), and from water conservation structures (Rwc) to be estimated from the norms given in GEC-1997. Recharge from return flow from ground water to be excluded.

Total recharge in non-monsoon season ……………….( modified)
Sum of recharge from rainfall in the non-monsoon season and recharge from other sources in the non-monsoon season excluding recharge from return flow of groundwater.

3.2.2 Ground Water Assessment In Command Area

3.2.2.1 Computation of recharge in Monsoon Season

R(normal) = Rrf (normal) + Rc + Rsw + Rt + Rgw + Rwc
(eq. 13 of GEC-1997, pp. 50)

The total recharge should be the sum of recharge from rainfall and surface water sources only, that is, recharge from ground water irrigation/ return flow from ground water (Rgw ) has to be excluded from the above. Thus,

R(normal) = Rrf (normal) + Rc + Rsw + Rt + Rwc ……( modified equation 13)

3.2.2.2 Computation of recharge in Non-Monsoon Season

Recharge from other sources ………………………………(modified)
Recharge during non-monsoon season from other sources would include canal seepage (Rc), surface water irrigation (Rsw), tanks (Rt) and water conservation structures (Rwc) are to be obtained using the norms presented in GEC-1997, and excluding recharge from return flow of groundwater (Rgw).

Total recharge in non-monsoon season ……………….(modified)
Sum of recharge from rainfall in the non-monsoon season and recharge from other sources in the non-monsoon season excluding recharge from return flow from groundwater.

Net Annual Ground Water Availability ……… (Section 5.10.1 of GEC-1997)

It is recommended that 5 to 10% of the total annual ground water recharge may be assigned to account for natural discharge in the non-monsoon season.

3.2.3 Natural Loss during the Non- monsoon season.

The figure of natural loss can also be crosschecked by using the equation of water level fluctuation for the non-monsoon period.

It is further recommended that in case the observed value of base flow in the rivers during non-monsoon season appears to vary widely from the calculated value arrived at using above mentioned norm, the Natural Loss during non-monsoon period may also be calculated as a second check using the following relationship.

Natural loss = B + Et = R - S - DG +Rgw
where,
B = Baseflow in non-monsoon season
Et = Evapotranspiration in non-monsoon season
R = Recharge from rainfall and surface water sources in non-monsoon season
S = Change in Ground water storage in non-monsoon season
DG = Gross ground water draft from all sources in non-monsoon season
Rgw = Return flow from groundwater irrigation in the non-monsoon season

3.2.4 The Stage of Ground Water Development.

The stage of development of assessment unit in the GEC-1997 is determined with respect to the existing gross draft for all uses. Since, in the proposed computation of recharge, the net draft (DG - Rgw) instead of Gross Draft (DG) has been considered, the stage of development should be done based on the net draft.

Therefore, the Stage of ground water development (%) =

Existing Net Ground Water Draft for All Uses X 100 ………(modified)
Net Annual Ground Water Availability

where, the net ground water draft is equal to the gross draft (Dg) minus the return flow from ground water( Rgw).

3.2.5 Strengthening of Database Management System

Significant hydrogeological data have been generated for the last few decades by various Central and State Govt. agencies. However, the database management system in this field has remained weak that is required to be strengthened by documentation and exchange amongst the user agencies. Data on some of the other important parameters like baseflow and evapotranspiration are quite sparse and immediate action needs to be taken to generate data on these components, in the absence of which Alternate Methodologies For Ground Water Resources Estimation cannot be tried.

a. Refinement of Norms of recharge components - There are a large number of recharge components that are estimated by adhoc norms in the GEC 1997. There is a need to utilize all available data to improve these adhoc norms and identify possible data lacunae, which must be rectified by additional studies/observations.

b. Return flow from Irrigation - A study is necessary to estimate the dominant parameters affecting the magnitude actual percentage of return flow from irrigation for different combination of these parameters.

c. Ground Water Draft - The present exercise on estimation of ground water resources based on the GEC-1997 methodology heavily depends on Ground water draft. In the absence of realistic draft data, the water balance and stage of development figure go quit disarray. Attempts should be made to have a correct number of live structures and unit draft in varying agro-climatic conditions. State govt. should issue necessary directives / pass Government Resolutions to the concerned departments for registration of ground water abstraction structures for different uses.

Further, there is an urgent necessity for focused R&D efforts on the estimation of draft. The study should aim to determine: a) the expected levels of uncertainty in draft estimates by different methods, b) the seasonal variation of draft, c) the variation of draft with respect to normal, deficit and surplus rainfall, d) the effect of long term water level trend on draft, and e) the rate of development of draft over the years in different regions.

d. Baseflow - Another important parameter intimately involved in water balance exercises is baseflow, the data on which is quite lacking. The committee recommends a policy approach to be framed at the Central and State level which would insists on providing a stream gauging station at the outlet of all watersheds in hard rock areas.

e. Spring Discharge - In high elevation aquifers, spring discharge studies have to be taken up for rainfall recharge computation.

f. Specific Yield - In hard rock terrain, the specific yield of the aquifer is highly site specific and may vary within small distance. It is therefore suggested that specific yield may be estimated for different hydro-geomorphic units.

g. Ground Water Development Worthy Areas - Assessment of ground water should be carried out only in ground water development worthy areas. There is a need to demarcate such areas.

3.3 FORMULATION OF STANDING COMMITTEE

It is recognized that refinement of the methodology of the ground water resource estimate requires extensive Research and Developmental support. It is therefore recommended that a Standing Committee be constituted. The formulation of 'Standing Committee' has been recommended by the GEC-1997 also. The Standing Committee could be named as 'R & D Advisory Committee on Ground Water Estimation'.

To reproduce recommendations of the GEC-1997, the Standing Committee would look into the following broad issues -

(A) Applicability of the recommendations suggested in Chapter 3.3 (GEC-1997) regarding computation of ground water recharge and stage of ground water development.

(B) R&D studies with reference to ground water resources estimation.

The thrust areas of the R&D activities of the Standing Committee would include -

a) Periodic revision of norms to be adopted for ground water assessment.

b) Development of state of art Data monitoring, data storage and retrieval systems, management information systems, geographic information systems and decision support system.

c) Studies on Distributed parameter modeling using finite difference, finite element and boundary integral equation methods.

d) Development of Alternative methodologies for ground water resource estimation.

e) Strengthening of infrastructure facilities with national and state level ground water organisations and upgrading the technical skill of the human resources in these organisations.

The constitution of this Committee should be as follows:

1. Chairman, CGWB Chairman
2. Member (SAM), CGWB Member
3. General Manager, NABARD, Bombay Member
4. Representatives from State Ground Water Members (2) Departments in hard rock terrains

5. Senior Scientist, CGWB Member - Secretary

The terms of reference of the Committee will be as follows:

(i). To review the scientific studies done in the field of ground water resource assessment.
(ii). To review the validity of the recommendation of GEC-1997 and, if found necessary, suggest alternate methodology for assessment of ground water resource
(iii) To firm up the recommendations of the present committee namely, "Committee for Estimation of Ground Water Resources in Hard Rock Terrain".
(iv) Any matter referred to the Committee from time to time
(v). Any other aspect relevant to the terms referred above.

For efficient working of the 'R & D Advisory Committee on Ground Water Estimation', it is also recommended that from among the members of the above committee, different working groups may be formed to assist on different aspects under the preview of the committee.

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