VARANASI: While the floods bring havoc to mankind with loss of lives and property, they also bring many benefits like reduction in pollution level, recharging ground water, making soil more fertile and providing nutrients. The water level of swelling Ganga recorded a rise of 2.38 metres in last 48 hours in Varanasi inundating all ghats and low lying areas.
"It is true that the flood causes disruptive effects on human settlements and economic activities, but it is essential for the river's own health as well as eco system," said Prof BD Tripathi, noted environmental scientist and expert member of National Ganga River Basin Authority (NGRBA). The floodwater not only diluted the concentration of pollutants but its strong current also acted as dredging for increasing river's depth, he said adding that the floodwater played a significant role in diluting or removing the...
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chemical pollutants.
It may be mentioned here that the national river Ganga is being polluted heavily in Varanasi. Over 250 MLD sewage is discharged in the city and major part of it is allowed to go untreated into Ganga. According to the records, the underground sewer system was introduced in the city during British period. The sewerage system was designed exclusively to carry domestic sewage only. But owing to the traditional pattern of open drains laid in the core city area, storm water also enters the trunk sewer directly or through manholes and branch sewers. This leads to tremendous pressure on the sewerage network, especially during monsoons. The sewage treatment plants (STPs) constructed under the first phase of Ganga Action Plan (GAP) become ineffective during rainy season leading to more pollution of Ganga and Varuna rivers.
There are three STPs in Varanasi at Dinapur, Bhagwanpur and Diesel Locomotive Works (DLW) with capacities of 80 MLD, 9.8 MLD and 12 MLD respectively. The Dinapur and Bhagwanpur STPs are under direct control of UP Jal Nigam for operation and maintenance purpose, whereas DLW is operated and maintained by railway authority.
"The flood helps greatly in reducing the pollution of the river," said Udai Kant Choudhary, river scientist and former professor and head of the department of civil engineering and coordinator of Ganga Research Centre, Institute of Technology, Banaras Hindu University (BHU). He said that the flood also enhanced the oxygen (O2) content in the river water and reduced the biochemical oxygen demand (BOD). He also advocated for the exploitation of river's own energy for pollution management. In his theory of three gradients for river pollution management, he said that in the body of the river all the processes of pollution management need to be done in the flood-plain area on the surface of the sand bed. It could be done by the utilization of river's energies available in the form of hydraulic gradient, velocity gradient and gradient in the soil property. According to him, integrated energy of soil, water and air at a river cross-section changes with the change in location of the section and time. The renewable energies, thus can be sustainably used for transporting, filtering and dispersing the pollutants at minimal cost.
According to him, floods play an important role in maintaining ecosystems in river corridors and are a key factor in maintaining floodplain biodiversity. Flooding adds a lot of nutrients to rivers for aquatic life. Besides, the spread of floodwater in the river basin also helps in recharging the groundwater.