NATIONAL SEMINAR ON PUMP SET ENENGISATION AND GROUND WATER RESOURCE MANAGEMENT, CIRE, HYDERABAD, P.117-123, FEB 1999.
The enthusiasm shown towards exploitation of Groundwater through agricultural pump set energisation program lacking in simultaneous formulation of artificial groundwater recharge schemes and generation of additional power. This has led to steep decline of water table and power crisis in certain parts of the country. From groundwater point of view, water shed wise development projects in critical areas to reduce soil erosion, run-off and to increase groundwater recharge from annual rainfall are the suitable measures to tackle over-exploitation of groundwater.
The recurrence of droughts highlighted the importance of groundwater exploitation.
After 1970, large scale construction of irrigation wells started and with the introduction of SPA participative programs since 1978, the pace of ground water exploitation has increased manifold. Desired results of increased food production and establishment of ancillary units in rural areas were achieved in a satisfactory manner.
The pump set energisation programme is so fast particularly in few states covered by hard rock terrain like Maharashtra, Andhra Pradesh, TamilNadu, parts of Karnataka, Gujarat and Madhya Pradesh that the ground water draft exceeded the safe yield resulting in decline of water levels.
The initiation and enthusiasm shown for exploitation of ground water through energisation of agricultural pump sets were missing towards the artificial recharge of groundwater projects and additional generation projects to meet the growing demand. As a result, a number of white area blocks were transforming into grey blocks and grey into dark area from groundwater point of view and severe power crisis developed in many states. However, still there is a lot of demand for agricultural connections in these areas.
*Sr.Hydrogeologist, Rural Electrification Corporation Limited, Project Office, Chennai.
As the Groundwater related Departments were also established after 1970, taluk wise and district wise groundwater assessment studies were carried out taking some of the norms on Adhoc basis. After acquiring some field data and experience now modified norms are being adopted for assessment of groundwater particularly in areas where exploitation of groundwater exceeds safe Yields. The methods include 1) Watershed wise assessment of groundwater 2) Water level fluctuation and specific yield method.
WHAT IS WATERSHED.
Watershed is a drainage basin or catchment with natural stream outlet and is separated from another watershed by topographic ridge and slope. The catchment of bigger river like Ganga, Godavari, Krishna are called basin, the catchment of tributaries of bigger rivers are called sub Basin and the catchment of smaller stream is watershed. The groundwater assessment is done taking watershed as a unit which covers catchment of a small stream, covering about 12 to 15 villages. Even micro-watersheds comprising the area under the jurisdiction of one village is also suggested as this help in grouping the people in one co-operative society. These schemes depend mainly on the co-operation of people as multiple activities are involved.(Basin and Water Shed map enclosed)
The advantages of watershed approach are:
1). The entire rain fall experienced by a watershed could be accounted easily as the total Rainfall, evaporation, surface run-off and soil moisture are confined to the catchment of water shed only.
2). There is a specific entry point and outlet and a spread area in the form of catchment is available in watershed. Hence the budgeting of groundwater is possible with certain degree of accuracy than the assessment made on administrative boundaries like taluk/block.
IMPORTANCE OF WATERSHEDWISE DEVELOPMENT IN TACKLING OVER EXPLOITATION OF GROUNDWATER.
There are three important components in the assessment of groundwater.
1). Recharge of groundwater basin.
2). Surface run-off.
3). Evaporation and Transpiration.
It is estimated that in our country, 47% of rainfall goes as surface run-off, 30 to 35% as evaporation and 15 to 25% to groundwater recharge. The groundwater recharge depends on the nature of soil, rock formation and topography etc., if any watershed becomes dark or grey category due to overexploitation, the alternate methods to increase groundwater recharge are - to reduce surface run-off and evaporation.
The following watershed wise methods enable to increase the groundwater recharge from rainfall.
1. Gully plugging in minor streams.
2. Sub-surface dykes or percolation tanks along stream.
3. Contour bunding.
4. Trenching along hill slopes.
5. Farm ponds in the foot hill zone.
6. Check dam cum minor irrigation on the main stream.
7. Land leveling (terracing)
8. A forestation.
The above methods check the erosion of soil, reduce surface run-off and increase groundwater recharge.
PRESENT STATUS OF WATERSHED PROJECTS:
The methods like bunding, land leveling, afforestation and other soil conservation measures were already taken up in most of the states. Construction of percolation tanks and assessment of groundwater by watershed method was taken up by Maharashtra government from 1973 onwards. About 7000 percolation tanks were constructed in Maharashtra state. Evaluation studies on selected percolation tanks in DPAP areas indicated that groundwater recharge has increased up to 50% of its gross storage. Under normal conditions the groundwater recharge from rainfall is 10 to 15% in hard rocks. With other artificial recharge projects like trenching at nala bed, contour trenching, flooding nala has increased the recharge to Groundwater from 30 to 40% of gross storage of projects.
1) Though large numbers of watershed development projects are now being taken up in several parts of the country, the results of these projects are not available to other agencies who are engaged in the same field.
2). The details of water level data, discharge of wells, run-off data, evapotranspiration data, soil/fertility cropping pattern before taking up watershed programme and collection of similar data after completion of project is necessary so that benefit due to watershed development programme could be quantified.
The publications of such results are very useful as it could act as a guide to other areas where similar programs are likely to be taken up.
OTHER METHODS TO TACKLE OVER-EXPLOITED AREAS
As the watershed projects involves long gestation period and involve lot of financial commitment, it is very difficult to cover even small number of watersheds in the coming 5 to 10 year period. Hence the alternative methods are to be searched to tackle the over draft conditions. Some of the alternatives are given below;-
a) Even in the dark category watersheds also, the groundwater conditions near the tanks, ponds, valley-fill areas, flood plains, natural levees, meandering courses of rivers, streams etc. palaeo channels, and foot -hill zones are some of the groundwater potential zones to be taken up for groundwater extraction. These areas can be delineated utilizing aerial photos and satellite imageries. Already several groundwater departments brought out district wise groundwater reports where the maps depicting the above aspects are demarcated.
b) In hard rock terrain where deep water level conditions are existing and deep bore wells are the only groundwater abstraction structures, the ‘deep fractured aquifers should be utilized for meeting the drinking water needs only. Drilling of bore wells for irrigation purpose in such areas should be discouraged as the groundwater potential in deep fractured terrain is limited.
c) Desilting of tanks and ponds should be carried out to increase the recharge of groundwater. During the dry seasons, farmers may be allowed to collect the silt/clay material accumulated at the bottom of the tanks. This will enable the farmers to put the silt in their agricultural fields to enhance the fertility of the soil. This program can enhance the recharge to groundwater from tanks and ponds. Desilting not only increase the discharge of wells but also reduce the total head of agricultural pump sets to Pump out water. This in turn will cause lot of savings in consumption of power in agricultural pumping systems. As the ultimate beneficiary for watershed development is power sector, SEB’s can associate with schemes formulated for watershed development in association with financial institutions, NABARD and minor irrigation departments.
d) At present both state and Central Groundwater Departments are carrying out monitoring of National Network observation wells periodically. Under the programme, monitoring of water level fluctuation and changes in quality of groundwater were carried out. But it is also advisable to establish some piezometers in representative areas in grey and white blocks particularly in hard rock terrain and carry out step drawdown test to monitor:
· Changes in efficiency of wells.
· Changes in Discharge, water levels and Drawdown of wells etc.
The collection of above data enables us to watch the groundwater system and can take preventive measures in case the aquifers are leading for overdraft conditions.
e). Artificial recharge of groundwater by channel spreading, induced recharge and injection some of the important methods to tackle over draft conditions. Few artificial recharge projects were taken already by CGWB and state GWD’s. But the studies are in preliminary stage only and projects are to be taken up to cover major portion of over exploited area.
Large scale groundwater exploitation through pump set energisation has taken up mostly in the States covered by hard rock terrain, like Maharashtra, Andhra Pradesh, Tamil Nadu, part of Gujarat, Madhya Pradesh and Karnataka etc., In some districts of these states, large scale exploitation of groundwater caused decline of water levels which involves lot of money in deepening of existing wells, construction of bore wells and requirement of additional power to meet the enhanced connected load which was caused due to increase in total head. The decline of water levels increased the total head and high density of irrigation wells reduces the discharge rate. These factors added to the high consumption of power. This has lot of impact on the existing power systems in the way of erecting additional distribution transformers, substations and generation of additional power.
For the above problems, watershed development projects to enhance the groundwater recharge are one of the important solutions besides artificial recharge of groundwater by several methods which are in vogue.