Report on the Hard Rock Ground Water Estimation

CHAPTER 2

REVIEW AND OBSERVATIONS OF THE COMMITTEE

2.1 REVIEW:

The Ground Water Estimation Committee 1997, shortly GEC-1997, revised the methodology GEC-1984. The important changes incorporated in the GEC-1997 are - (i) in hard rock areas the assessment is made with respect to watershed unit, (ii) the assessment is made separately for command and non-command areas, (iii) during the non-monsoon period recharge from rainfall and other sources is based on the Rainfall Infiltration Factor and other prescribed norms, (iv) the stage of development is determined considering the draft and availability for all uses instead of only irrigation, and (v) categorization of assessment unit is to be governed by long term water trends besides the stage of development.

The GEC-1997 methodology was re-looked in the light of presentations made on case studies in different types of hard rock terrain and feedback received from the State Ground Water Departments (SGDs) and Central Ground Water Board (CGWB).

2.2 OBSERVATIONS

Different aspects of the GEC-1997 were discussed at length and in all six modifications/recommendations emanated. Out of the six modifications only one namely " Categorization of Assessment Unit" could be resolved and has been duly recommended for implementation and adoption.

The remaining five modifications pertain to the accounting of the recycled ground water flow or the recharge component due to return seepage from ground water irrigation. In the GEC - 1997 the return ground water flow, termed as Rgw, has been added to the recharge from rainfall and other sources. There are serious reservations from different quarters against adding up of Rgw to the annual recharge. Because, with the increase of ground water draft and in turn the stage of development it is imperative that there will be a resultant increase in the total annual ground water recharge. On the other hand there is a school of thought in favor of retaining the Rgw, as done in the GEC-1997, for estimation of the total annual recharge to ground water. After several deliberations and discussions no consensus could be reached and the matter, hence, has been recommended for considerations by the "Standing Committee on Ground Water Resources Estimation", that is recommended to be constituted. The GEC-1997 also recommended a similar committee to pursue and take an overview of R & D activities.

Besides, it has been concern of one and all that there is a lack of adequate database to place the estimates on firm footing. In this direction detailed experimentations and studies are required to have a reliable assessment of important parameters used in the ground water resource estimation.

All the suggested modifications and aspects of the lack of data base are outlined below ;

(a) Issues recommended for implementation:

The committee has unequivocally accepted one modification related to the categorization of the assessment unit on the basis of ground water resource and trends of water level. The long term water level data should preferably be for the period of 10 years. The committee has also modified the term 'significant decline' to be of the order of 10 to 20cm per year. This modification has been recommended for implementation and adoption.

(b) Issues recommended for consideration of the "Standing Committee on Ground Water Resources Estimation":

Since no consensus has been arrived at other proposed modifications, the same are recommended for consideration of the proposed "Standing Committee on Ground Water Resources Estimation" under the GEC- 1997. These modifications and observations are related to:

1. Computation of recharge during the monsoon season in Command / Non-command areas - the issue is whether or not to exclude the recycled ground water (Rgw) term.

2. Estimation of Normal recharge during the Monsoon and Non- monsoon season: - whether or not to exclude the recycled ground water (Rgw) term as well as other issues related to normal recharge.

3. Natural loss during the Non- monsoon season: - this should be crosschecked using the equation of water level fluctuation.

4. The Stage of ground water development: - computation should be done based on the net draft instead of the gross draft.

5. It is common observation that there is a lack of database and the same should be adequately strengthened so as to arrive reliably at various parameters frequently used in ground water estimation.

2.3 CASE STUDIES IN DIFFERENT HYDROGEOLOGICAL TERRAINS

The Committee reviewed case studies on resource assessment using the GEC-1997 in different hydrogeological terrains. These were: in granitic terrain - a watershed in Karimnagar district, Andhra Pradesh, in basaltic terrain - a watershed in Latur district, Maharashtra and in limestone terrain - in few blocks in Durg and Bastar districts of Chattisgarh. The studies reflect that proper segregation of data is required on the basis of watershed and command and non-command areas. It is also observed that many parameters, like, water level fluctuations, seepage from water bodies, return flow from irrigation etc. are varying significantly from the empirical norms recommended in the GEC-1997 and these need micro-level field studies. Considering the anisotropy of the hard rock terrain, suggestions have been made to further segregate the watershed based on geomorphological and hydrogeological characteristics.

These case studies stress upon the work to be carried out to strengthen the database. A summary of these three case studies is given in Annexure III

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