One the lifeline of Bangalore, the water bodies are fast loosing water holding capacity, beauty and recharge capacity due to the indiscriminate use of these lakes as dumping grounds for garbage by the people living in the fringe areas. Arrival of bore wells which met the immediate water needs of the community further added to the problem. The water bodies were further ignored as the ownership became individual and private resource instead of the earlier status of community resource. All these resulted in,
With the emergence of these problems, the number and quality of water bodies have decreased corresponding to the fall in their value and environmental functions. Recycling nutrients, purification of water, recharging ground water, agumentation and maintenance of stream flow, providing habitat for wide variety of flora and fauna and also a get away place, recreation for people are also some of the emerging issues.
Effects of lakes on ground water
The decrease of water bodies had its serious effect on the level of Ground Water. With around more than a lakh bore wells in the city, there was overexploitation of existing ground water. In the absence of effective recharging of ground water by the lakes, it was a logical consequence that the city faced shortage of water.
A study from the Department of Mines & Geology, Government of Karnataka in 1985 highlighted the depth at which ground water was available had fallen to 250-300 feet from 35-40 feet in past 20 years.
Reduction in the number of the water bodies and higher rate of retrieval than discharge capacity have caused inefficiency in their function as the recharge zones of ground water in the city area. The resultant water shortage is the result of a depleted level of ground water and lack of recharging capacity. It has also reduced the moisture in air in turn resulting into change in the micro-climate of Bangalore. The seepage of toxic contents in the lake due to sewage, infestation of weeds etc., the sub soil water that could be retrieved in the bore wells for domestic use is now contaminated with harmful toxic substances.
Effects of lakes on urbanization
The rapid growth of population resulted in a high demand for housing and intensive land use. In the wake of high growth of the city many lakes and tanks were denuded and converted into buildings and housing layouts. Indiscriminate breaching of tanks for development initiatives with a single focused agenda has caused significant damage to the chain of lakes. The inter connectivity which is an important feature of the waterways have been threatened and even losing its characteristics.
The marginal lands adjoining natural valleys, which were open spaces decades ago where the trunk sewers were laid were encroached by buildings and sewage and salvage are let out into the storm water drains constructed in these valleys.
The encroachments in the catchment's area further added to inter connectivity problem. The loss of inter connectivity in the water bodies has resulted in the shrinkages of wetland area, reduction in water yield from the catchments and water holding capacity. In the absence of the channels that harvested flow of storm water along the natural slopes, water is now flowing away from Bangalore. This has affected the total rain water harvesting mechanism and capacity of Bangalore lakes.
Number of slums constructed on either side of valleys discharge wastewaters into the open drains. The damaged trunk sewers and direct discharge of sewage and salvage from the slums and buildings abutting the storm water drains in the three valleys namely Hebbal Valley, Vrishabhavathi Valley and Koramangala valley & Challaghatta valley had resulted in discharge of sewage into the lakes in the downstream side.
It is a great pity that many lakes and ponds of Bangalore had already been lost in the process of urban development and rest of the surviving lakes are polluted with sewage.
Effects of pollution on the lakes of Bangalore
Without proper cognition of the growth pattern that followed phenomenal increase in the city population, the water bodies succumbed to indiscriminate human interference. In the absence of prerequisite planning for management of liquid and solid waste the city produces, all wastes were routinely dumped into the lakes or the channels.
Sewage from layouts was released to storm water drains in the valleys that used to flow in the lakes. These drains carried the polluted water into the lakes on the downstream making the water turbid and stinking. The quality of water was further affected by washing of cattle and vehicle. Water mixed with detergents, chemicals from the dhobi ghats made the lake water acidic. Due to the presence of high percentage of pollutants, the lakes experienced an algal bloom. During day these algae released oxygen to the water but sucked it all up during night making it difficult to the organisms like fishes and aquatic plants to breathe and grow. This process is called Eutrophication or lake death.