Western Ghats News

Towards effective harnessing of groundwater

Hindu News Network Tuesday, May 14, 2002

Bangalore May 13. Karnataka can boast of substantial natural and geographical endowments of rivers, hills, valleys, and forests. Bordered by the Western Ghats with tall peaks and lush greenery in the west, the tableland is fertile because of its black soil and river and tank irrigation facilities. The coastal strip of the west of the ghats is renowned for its silvery beaches and rich green paddy fields. Based on the basis of climate and relief, the State has four physiographic regions viz: Coastal tract, Malnad, Northern Maidan, and Southern Maidan extending over 700 km. from the north to south, and 400 km. from the east to west.

Despite such attractive features, inadequate rainfall in one season can adversely impact the most basic need of life -- drinking water.

This has been a problem off and on, and this year several districts are facing serious shortage of drinking water. Of the 27,000 villages (inhabited), about 15,000 (56 per cent) are in drought-prone areas.

Although sustainable supply of safe drinking water is a primary responsibility of any Government, meeting this goal can be a difficult task due to vagaries of monsoon and given the difficulties in the conditions of the terrain.

Though the average rainfall in Karnataka is about 1,139 mm. per year, its spatial and temporal distribution are uneven, it and occurs over 40-55 rainy days.

The rainfall varies from as low as 569 mm. in the east to as high as 4,029 mm. in the west. About two-thirds of the geographical area of the State receives less than 750 mm. of annual rainfall. Even high rainfall districts such as Dakshina Kannada, Udupi, Uttara Kannada, and Kodagu experience drinking water scarcity during April and May.

This being the case, management and provision of potable water in the drought-prone areas require strategic planning and long-term effort, besides large capital investments.

The problem has been compounded by over-exploitation of ground water, particularly in the dry land tracts. Even deeper drilling may not help.

In the early 1970s, Karnataka's rural population, which constitutes about 42 million of the total population of 53 million, could meet its drinking water needs largely from open wells as ground water levels were at an average depth of three to five metres.

One estimates suggests that about three lakh wells dug in the 1970s have gone dry, and shallow open wells have been replaced by deeper borewells. There are now about two lakh drinking water borewells in the State and 12 lakh irrigation tubewells as against about two lakh irrigation wells in the 1970s. Added to this is the quality of potable water drawn from deeper depths.

Borewells that are drilled to greater depths are found to have higher dissolved chemicals, particularly fluoride, which is harmful in excess of 1.5 parts per million.

Experience has shown that borewells going down beyond 150 metres are found to be dry, particularly those located in the vicinity of habitations in the elevated regions.

Groundwater resource evaluation

Groundwater recharge in the State is mainly through precipitation and partly by seepage from tanks and return flow of water applied to irrigation. Groundwater resource in the hard rocks of the region is limited unlike an alluvial (sediment) terrain.

Though groundwater is a replenishable resource, if the extraction exceeds the limit of dynamic recharge, it will cause irreversible damage. Considering this, groundwater evaluation in the State was carried out in 1994. It was found that 21 taluks had exceeded 85 per cent of the groundwater available limit and another 22 taluks were in the range of 65 to 85 per cent in the northern regions of the State. In the southern region, 29 taluks exceeded utilisation of groundwater more than 50 per cent. This amply establishes that groundwater has been over exploited in some taluks, especially in drought-prone areas, causing its rapid depletion.

Subsequently, the Department of Mines and Geology made an assessment in 1999 based on watershed (natural entity of a region) instead of on taluk (politically boundary) as a unit for evaluating the stock of groundwater.

The salient feature of the evaluation is that the entire State has been divided into 380 watersheds ranging in extent from 300 to 1,400 sq.km. and have been assigned alphanumeric code for easy identification.

Watersheds have been categorised as "safe," "critical," "semi-critical," and "over exploited" based on the level of groundwater development. Watersheds, where the exploitation is more than 100 per cent, are considered as over exploited, 90 to 100 per cent as critical, 70 to 90 per cent as semi-critical, and less than 70 per cent as safe. It has been observed that of the 380 watersheds as many as 324 are found to be in the "safe" category. In the other 56 watersheds, seven are categorised as "semi-critical," 11 as "critical," and 38 watersheds as "overexploited."

Groundwater quality

In Karnataka, large tracts of lands in Dharwad, Bijapur, Bellary, Belgaum, and Gulbarga districts are covered with thick mantle of black cotton soil. Even though groundwater in these regions is available at a reasonable depth, it is difficult to make use of it because it is rich in salt and brackish. The total dissolved chemicals often exceed 5,000 mg/l rendering the water non-potable and also unsuitable for irrigation. Also worry is that in some of the dry districts such as Kolar, Chitradurga, Tumkur, Bellary, Raichur, Gulbarga, and Bijapur, groundwater at deeper levels is contaminated with fluoride varying six to 13 parts per million (tolerable range being 1 to 1.5 mg/1).

Groundwater Bill

Regulation of drilling activity and prioritisation of water use is, therefore, a matter of urgent need. One method is to provide a legislative basis for such regulation. Considering the grim situation of overexploitation and unscientific drilling of borewells, the Government proposed the Karnataka Groundwater Bill in 1996. The Bill suggested the following parameters for extraction and use of groundwater:

1. The distance between two successive borewells and the successful dug-cum-borewell shall be 250 metres, and between two-dug-wells it shall be 182 metres. In command areas, the distance between two-dug-wells shall be 130 metres.

2. No person shall sink a well, install devices to extract groundwater for any purpose either on personal or community basis unless he has obtained a permit from the authority in accordance with the provisions of this Act.

3. No such permit shall be necessary (i) to sink a well and extract groundwater for individual domestic purpose, (ii) to sink a well and to extract groundwater by Government organisations for the purpose of public water supply system, and (iii) to sink a well in water logging areas.

4. The Bill did not become an Act, although the obstacles are not quite clear. Such legislation is a necessity if not a sufficient condition.

Remote-sensing applications

The 22 per cent of fresh water appears to be hidden below the surface of the earth -- not visible to the naked eye. Therefore, an extraordinary eye, sensitive also to the other frequencies of electro-magnetic radiation (EMR) is needed. Such a vision has come to be known as "remote sensing."

A photographic base with a perspective view offered by satellite imagery serves as a better database for plotting the field observations, making extrapolations and preparation of accurate maps covering comparatively large areas in a shorter time.

Satellite data of different seasons provide fairly good understanding of different factors that govern the movement and occurrence of groundwater.

The use of satellite-based remote sensing data has proved to be an effective means of mapping of lithological (rock types), structural (fractures), and geomorphological (landforms) features controlling groundwater. Such derived information from remote sensing coupled with conventional data in Geographical Information System (GIS) helps in identifying groundwater potential zones.

Presently, an effort is going on under the Rajiv Gandhi National Drinking Water Mission, funded by the Ministry of Rural Areas and Employment, for preparation of groundwater prospects maps for the State.

This work is carried out by the Karnataka State Remote Sensing Applications Centre, which is part of the Department of Information Technology, Government of Karnataka, as well as by other agencies, including private entrepreneurs.

It is important that in this project, the thrust is not only to identify potential site suitable for groundwater exploration for drinking water, but also to identify suitable sites for groundwater recharge.

The use of these maps by the State will no doubt go a long way in effective, sustainable harnessing of groundwater as well as ensuring recharge of groundwater, which is absolutely essential for long-term sustenance.

(The writer is Minister of State for Information Technology).