Alarming fall in ground water level
Monday, 25 April 2011
Khadiza Begum
Ground water is a precious resource of nature. Water existing in soil pores under the land surface is known as ground water .Ground water meets multitudinous of the hydrologic needs of people everywhere. Ground water can be compared with the money which is deposited in the bank. If withdrawal of money is faster compared to the deposits then a liquidity crisis will be created in the bank. Likewise, ground water is now under threat due to it's over exploitation. With a present population of about 12.5 million, Dhaka city's population projected to be around 22 million by 2025. It is now the 7th most populated city in the world and it is anticipated that Dhaka will be the 2nd largest city in the world by 2020. Due to rapid population growth, an increasing portion of the city's water needs are being met from the ground water. About 90 per cent of the municipal water supply comes from ground water storage whereas surface water contributes only 10 per cent. To meet the increasing demand for water, additional wetlands or wells is needed, but the existing wetlands in and around Dhaka city is being filled up for industrial, commercial and residential purposes. Without adhering to the wetland act and other relevant regulations, many real estate companies are running their development projects by filling up the wetlands, canals and rivers in and around the city, which play an important role as a source of surface water and also accumulation of ground water. The municipal water demand was only 150 million litres per day (mld) in 1963, but over the last few decades it has increased to 1500 mld in 1998 and 2100 mld in 2005, according to the figures of Dhaka WASA. At present, Dhaka WASA can only meet about 70 per cent of the total water demand of the city. The present water supply capacity of Dhaka WASA is 1930 mld against the demand of 2470 mld. According to a projection of IWM and DWASA, water demand will be 4990 mld in 2030 and Dhaka WASA would be able to supply only 1971.5 mld, in which ground water will contribute 1679 mld (87 per cent) and surface water 292.5 mld (13 per cent). Thus, it is estimated that only 39 per cent of the city's water demand will be fulfilled in 2030. The ground water table has decreased by 35 metres in the last decade, according to a recent study conducted by Bangladesh Agricultural Development Corporation (BADC). In Dhaka city, ground water level has gone down to 61.18m below the surface. The average rate of decline of water level varied from 1 m to 2.50m, as per the report of the Water Development Board (WDB). The ground water depletion is more severe in the central part of the city compared to the areas close to the river banks. Withdrawal of ground water at a rapid rate will have some negative impact on the environment. Increased pumping cost, land subsidence, decrease of water quality, reduction of water in wetland, drying up of wells and impact on ecological balance are associated with the negative effect of environment. Khandakar Fazal Hasan, chief geologist of Bangladesh Agricultural Development Corporation (BADC), said "If the water table collapse continues to fall then a vacuum will be created in the aquifer which could cause a sudden collapse of the surface". Already, many in the city, especially the densely-populated areas, do not get sufficient quantity of drinking water, and if they are lucky to get a little, it is dirty and has a bad odour. Shrinkage of open spaces reduces the scope of ground water recharge. For natural recharge, these wetlands, canals and open spaces should be conserved. Infiltration wells can be dug at a very low cost and these could greatly speed up the water recharging system. It is highly recommended to carry out studies on the probable consequences (especially geochemical) before setting up artificial recharge wells. The government should immediately formulate a sustainable water management policy. Integrated use of surface and ground water, and harvesting of rainwater may be the alternate way to minimize the over use of ground water. The writer is environmental researcher and she can be reached at e-mail: khadiza.du88@gmail.com
Ground water is a precious resource of nature. Water existing in soil pores under the land surface is known as ground water .Ground water meets multitudinous of the hydrologic needs of people everywhere. Ground water can be compared with the money which is deposited in the bank. If withdrawal of money is faster compared to the deposits then a liquidity crisis will be created in the bank. Likewise, ground water is now under threat due to it's over exploitation. With a present population of about 12.5 million, Dhaka city's population projected to be around 22 million by 2025. It is now the 7th most populated city in the world and it is anticipated that Dhaka will be the 2nd largest city in the world by 2020. Due to rapid population growth, an increasing portion of the city's water needs are being met from the ground water. About 90 per cent of the municipal water supply comes from ground water storage whereas surface water contributes only 10 per cent. To meet the increasing demand for water, additional wetlands or wells is needed, but the existing wetlands in and around Dhaka city is being filled up for industrial, commercial and residential purposes. Without adhering to the wetland act and other relevant regulations, many real estate companies are running their development projects by filling up the wetlands, canals and rivers in and around the city, which play an important role as a source of surface water and also accumulation of ground water. The municipal water demand was only 150 million litres per day (mld) in 1963, but over the last few decades it has increased to 1500 mld in 1998 and 2100 mld in 2005, according to the figures of Dhaka WASA. At present, Dhaka WASA can only meet about 70 per cent of the total water demand of the city. The present water supply capacity of Dhaka WASA is 1930 mld against the demand of 2470 mld. According to a projection of IWM and DWASA, water demand will be 4990 mld in 2030 and Dhaka WASA would be able to supply only 1971.5 mld, in which ground water will contribute 1679 mld (87 per cent) and surface water 292.5 mld (13 per cent). Thus, it is estimated that only 39 per cent of the city's water demand will be fulfilled in 2030. The ground water table has decreased by 35 metres in the last decade, according to a recent study conducted by Bangladesh Agricultural Development Corporation (BADC). In Dhaka city, ground water level has gone down to 61.18m below the surface. The average rate of decline of water level varied from 1 m to 2.50m, as per the report of the Water Development Board (WDB). The ground water depletion is more severe in the central part of the city compared to the areas close to the river banks. Withdrawal of ground water at a rapid rate will have some negative impact on the environment. Increased pumping cost, land subsidence, decrease of water quality, reduction of water in wetland, drying up of wells and impact on ecological balance are associated with the negative effect of environment. Khandakar Fazal Hasan, chief geologist of Bangladesh Agricultural Development Corporation (BADC), said "If the water table collapse continues to fall then a vacuum will be created in the aquifer which could cause a sudden collapse of the surface". Already, many in the city, especially the densely-populated areas, do not get sufficient quantity of drinking water, and if they are lucky to get a little, it is dirty and has a bad odour. Shrinkage of open spaces reduces the scope of ground water recharge. For natural recharge, these wetlands, canals and open spaces should be conserved. Infiltration wells can be dug at a very low cost and these could greatly speed up the water recharging system. It is highly recommended to carry out studies on the probable consequences (especially geochemical) before setting up artificial recharge wells. The government should immediately formulate a sustainable water management policy. Integrated use of surface and ground water, and harvesting of rainwater may be the alternate way to minimize the over use of ground water. The writer is environmental researcher and she can be reached at e-mail: khadiza.du88@gmail.com