NATIONAL
SEMINAR ON PUMP SET ENENGISATION AND GROUND WATER RESOURCE MANAGEMENT, CIRE,
HYDERABAD, P.117-123, FEB 1999.
C.SATYANARAYANA
ABSTRACT
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.
INTRODUCTION
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.
ONGOING STUDIES:
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.
CONCLUSIONS
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.
