Groundwater and Hydrogeology

Water is an essential natural resource for sustaining life and environment. The largest available source of fresh water lies underground. Inadequate, erratic rain fall, absence of perennial rivers in major parts of the country, non-availability of adequate surface water resources to meet the increased demands of domestic, industrial and irrigational requirements, failure of monsoons have resulted in over-exploitation of ground water leading to drastic fall of water levels, drying of wells/borewells, deterioration of ground water quality and ingress of sea water in coastal areas.

A case study around Hassan city shows the drastic fall in the water table and the drying of hundreds of borewells on account of destruction of traditional water conservation and recharge structures like village ponds, tanks, spreading basins etc. Conservation and recharge of ground water is immediately required by reviving and desilting ponds, lakes, tanks, by adopting low cost Rain Water Harvesting (RWH) techniques, by constructing check dams, nala bunds, underground dykes etc., by planting trees near ponds and village commons will help in recharging ground water. Annually replenishable resources of our country are assessed as 432 billion cubic metres (bcm). By adopting RWH, an additional 160 bcm water will be available for use. It is high time that government and people join hands to conserve and recharge ground water through different ways to avert water famine.

Water is an essential natural resource for sustaining life and environment. The available water resources are under pressure due to increased demands with an ever increasing population and the time is not far when water, which we have always thought to be available in abundance and as a free gift of nature, will become a scarce commodity. The fresh water is getting exhausted day by day and 26 countries around the globe are now considered to be water scarce. Conservation of water by reducing wastage, by recycling and reuse, by artificial recharge is urgently required to be done. Water management has always been practiced in our communities since ancient times, but today this has to be done on priority basis to ensure the availability of adequate water supplies in the future. More than 80% of rural and 50% of urban industrial and irrigation water requirements in our country are met from ground water. In Karnataka 97% of the water supply schemes are depending on ground water. The over exploitation of this natural resource is already creating problems all over the world. The cycle of the drought, poor irrigation facilities and bad management of water resources become a nightmare for the past few years in some of the states like Gujarat , Rajasthan, Andhra Pradesh and some parts of Karnataka. In cities fights over water have intensified and resulted in mass migration of man and cattle in several areas. In India hundreds of villages still do not have a single source of potable water. But the rich continue to over exploit ground water sinking tube wells deeper and deeper in to the earth to draw out this precious sustenance for cash crops like sugarcane. The number of wells and borewells for irrigation in the country has increased five fold to more than 175 lakhs during the past fifty years.

Ground water levels in some areas are falling at the rate of one metre per year and even more on account of following reasons.

• Over exploitation and excessive pumping either locally or over large areas to meet increasing water demands.

• Non availability of other sources of water. Therefore sole dependence is on ground water.

• Unreliability of municipal water supplies in terms of quantity and timings, driving people to find their own sources.

• Disuse of ancient means of water conservation like village ponds, percolation tanks and therefore, higher pressure on ground water development.

Though ground water is a replenishable resource, when the extraction exceeds the limit of dynamic recharge, it will cause irreversible damages. India comprises of 70% of hard rock regions and hence the natural rate of ground water recharge are low. Competitive exploitation of ground water resulted in drastic adverse effects like drastic fall of water levels in some areas, drying of wells / borewells, enhanced use of energy, deterioration in ground water quality and ingress of sea water in coastal areas.

Hassan city, located in semi malnad region is situated at 970 metres above MSL, lying on the National Highway 48 between Bangalore and Mangalore, is bestowed with pleasant climate, an average rain fall of 880mm. Hassan is surrounded by rich cultural and archaeological places like Belur, Halebeedu, Shravanabelagula, with beautiful scenery. Hence it is called the ‘poor man's Ooty'.

The study shows that there were no borewells in the early 1970s and the domestic water requirements of Hassan city were met from open wells for a population of around 25,000. The town was surrounded by a number of small, medium and large water tanks like Channapatna tank (southern side and is about 1km from the present KSRTC bus terminal); Beeranahally and Sathyamangala tanks (in the eastern side), Tejur tank (in the western side); Kattikere tank (middle of the town) and Ramanakatte (in the northern side).

In 1970s the water table in the town was hardly few meters below the ground and in some places it had intercepted the ground level and hence water was available at a very shallow depth (5 to 10 meters) in the open wells in accordance with the topography of the land. The borewells came in to existence only after 1970s to meet the demands of growing population.

In the early 1970s many tanks were breached / destructed. To name a few, Kattinakere tank (water spread area 4 ha) was destroyed to form the present KSRTC bus stand and the command area was converted into present commercial and residential places. The command area (20 ha.) of Ramanakatte was converted into residential extension by HUDCO and the water spread area (6 ha) was allotted to a private educational institute and Government organisations.

In the late 1970s Beeranahally tank (22 ha) was breached and the entire area was developed into housing board colony by HUDCO. The largest Channapatna tank (65 ha) was breached in 1996 for various purposes. Hunasekere tank command area (25ha is being converted into an Ayurvedic Medical College, commercial and residential areas.

In this way, over a period of 30 years majority of the tanks and ponds were destructed and converted into residential and commercial areas. The number of borewells increased with the growth of population.

A survey shows that the water table in and around Hassan city had drastically declined upto 200-300 feet and hundreds of borewells were dried (more in 2002) mainly due to the destruction of ponds, tanks and spreading basins which served as traditional water conservation and recharge structures for the past several centuries accompanied by unscientific drilling of thousands of borewells and more withdrawal of water exceeding the rate of recharge of aquifers (water bearing beds). Hassan city earlier had rich surface as well as sub surface water resources is now facing water crisis in the areas which solely depend on borewells to meet their domestic water requirements.

To mitigate this serious threat of fall in ground water levels, conservation and recharge of ground water is immediately required by reducing wastage, by recylcing and reuse of waste water, by reviving the dying traditional water harvesting structures and their rehabilitation as recharge structures and most importantly by adopting low cost Rain Water Harvesting (RWH) method to artificially recharge the aquifers. A variety of methods have been developed to artificially recharge ground water with the choice of a particular method being governed by local topographic, geologic and soil conditions, the quantity of water to be recharged. RWH is allowing rain water in to the ground rather than just letting if flow on the ground. Due to tarred roads and concrete structures, water instead of draining into the earth and recharging aquifers, flows into storm water drains and is wasted. If people begin conserving water, particularly rain water, the periodic water crisis can be averted. As per the statistics, we can capture and recharge 65,000 litres of rain water from 100sq.m size roof-top during one rainy season and meet drinking and domestic water requirements of a family of four for 160 days. According to Dr. D.K. Chadha, Chairman of the Central Ground Board (CGWB) some 210 billion cubic metres (bcm) of rain water that is lost as run-off can be stored underground and 160 bcm of this water utilised (Deccan herald, June 4, 2000). RWH is the solution for water problems where there is inadequate ground water supply or surface resources are absent or insignificant. Moreover rain water is soft water and free from bacteria and other organic matter. Rain water also helps dilute ground water that may be saline or high in nitrates and fluorides.

• Roof – top rain water harvesting and its recharge to underground through the use of abandoned dug wells (Fig. 1), abandoned or running hand pumps (Fig. 2), constructing new wells, borewells, shafts or spreading basins. Here, the water is collected from the roof and directed into the ground through a pipe where it is stored in a reservoir. Dugwells are recommended for buildings that have a roof area of 1000 sq.m . If a building has a roof area of just 100 sq.m , the recharge structure would be a pit. For a building with a roof area of 200 to 300 sq.m , the recharge structure is a trench 0.5 to a meter wide, 1 to 1.5 meter deep and 10 – 20 meter long (Fig. 3) depending on the availability of land. Harvested rain water can be used for non potable purposes like gardening, flushing, washing cloths etc.

• Capturing and recharging city storm water run-off through wells, shafts, spreading basins and storm water drains. Recharge wells are used to directly recharge the deep aquifers. Recharge wells could be dug through the material overlying the aquifer and these wells are suitable in the areas were fractured rocks exist between the surface of the soil and the aquifer to be replenished.

Recharge by spreading basins is most effective in the regions consisting of highly permeable soils. Shafts may be circular, rectangular or square in cross section and may be back filled by porous materials.

• Harnessing run-off in the catchments by constructing structures such as check dams, bhandaras , percolation trenches, surface dykes etc.

Check dams are small barriers built across the shallow rivers and streams in the direction of water flow to retain excess water flow during monsoon rains in a catchment area behind the structure, which automatically helps in rise of ground water levels in the surrounding areas.

Flat terrain with sandy or rocky soil provides an ideal site for the success of percolation trenches as recharge structures.

Sub surface dykes should be constructed in upper reaches where ground water flow velocity is high.

• Impounding surplus run-off in the village catchment and watersheds in village ponds and percolation tanks, which are the traditional structure in RWH.

• Farm ponds and nalas: These are small storage structures constructed in farm lands at a suitable location based on the factors like land topography, soil type, texture, permeability, water holding capacity of soils, etc.

• Recharging treated urban and industrial effluents underground by using it for direct irrigation or through recharge ponds, basins or wells etc.

RWH and its recharge helps rise in ground water levels in wells, increased availability of water from wells, prevent decline in water level, reduction in the use of energy for pumping water and consequently the costs, reduction in flood hazard and soil erosion, benefiting in the water quality, arresting sea water intrusion, mitigating the effects of droughts and achieving drought – proofing, reviving the dying traditional water harvesting structures, effective use of lakhs of defunct wells and tubewells as recharge structures etc.

Annually replenishable water resources of our country are assessed as 432 bcm. By adopting RWH, an additional 160 bcm shall be available for use.

• By adopting at least one roof –top rain water harvesting structure for every 200 sq.m plot in urban areas.

• Subject to technical feasibility, by providing atleast one check dam / sub surface dyke in each streamlet with a catchment of 1 to 3 sq.kms.

• By banning construction of irrigation wells / tube wells within a distance of 200metres or less (depending on scientific criteria) of the drinking water supply well.

• By organising mass awareness programmes involving district administration and NGOs to educate the different sections of users and to make the programme demand oriented.

• By making RWH and recharge mandatory in all urban dwellings as already made in some of the cities. This would help recharge ground water and also minimise utilisation of drinking water for secondary purposes such as gardening, washing etc.

The Central Ground Water Board, state Governments, NGOs already have implemented successfully RWH in many parts of India. It is high time that the Government and people join hands, for making this RWH programme much more successful to ease water crisis.

• Ground Water Resource Status of Karnataka 1994, Dept. of Mines and Geology, Bangalore.

• Water Resources Environmental Planning, Management and Development - By Asit Biswas, Tata McGraw Hill, Edition 1998.

Department of Civil Engineering,
Malnad College of Engineering,
Hassan – 573201, Karnataka, India
Phone: 0817 - 245538