Experts raise doubts on 250 check dams and 190 water-retention dams in the lakes catchment area
The Sukhna Lake was dedicated to the city by Le Corbusier in 1958. By 1988,its water-holding capacity went down by 66 per cent due to siltation.
Several intensive efforts were since then taken to save the lake. According to records,250 check-dams and 190 silt-retention dams have been constructed over the years on the catchment area. While crores have been spent on these,eyebrows and debates have always been raised about whether these dams have proved vital for the shrinking of the lake. Newsline visited the Kansal range of the catchment area to take stock of the situation.
A part of the catchment area of the Sukhna falls in the Shivalik Hills,which is prone to soil erosion during rains. The land that comprises the catchment area was acquired in 1962-63. Later,as part of efforts to check soil erosion,afforestation was suggested and seeds were showered on the hills for the purpose. While some managed to sprout,others did not.
In the 1980s,check dams were built along with efforts to stabilise soil on the hills. Grass and shrubs were grown at the bottom of the hills and gradually the construction of silt-retention dams was started. This also led to the development of the Sukhna Wildlife Sanctuary.
The catchment area has 250 check dams and 190 water-retention dams. Over two new silt-retention dams are being built every year for anything between Rs 10 and 20 lakh depending on the size of the dam.
Check dams are those where water from the slopes flows down a vertical wall to retain silt. Most of these dams are now full of a thick layer of silt.
Silt-retention dams in a particular area,meanwhile,can vary from one to five or more depending on the size of the area. The aim is to retain most silt when rainwater flows through these. As water keeps moving,the amount of silt reduces.
In such dams,water collects in holes that are 4-metres deep on an average. Silt settles down in these holes. Water overflows in these holes and later through suspension tunnels enters into a channel that gradually leads to the lake.
The dams tend to become defunct once with silt accumulation. Every year,8 to 10 dams are completely filled with silt after which de-silting is undertaken.
At many places in the Kansal range,suspension tunnels have developed cracks and are in dire need of repair. Experts say when these tunnels are built,there is less water available,which gradually affects their life. In some cases,water was brought to the site with the help of camels to build some of these tunnels.
Experts studying the lake believe that due to the construction of such a large number of dams,the amount of water entering the Sukhna has fallen drastically. Dams and watering holes prevent adequate amount of water from coming into the lake,drying it up severely.
S S Grewal,former director,Punjab Agricultural University Zonal Research Station for Chandigarh Area,said: The main aim of constructing check dams was to prevent soil from entering the lake as the area is prone to erosion. This has,however,led to retention of water in the catchment area. This aspect needs more thought.
Dr G S Dhillon,former chief engineer,Punjab Irrigation Department,said: The Environment department should conduct some survey to certify that adequate water is entering the lake and not just being retained in the catchment area.
Ishwar Singh,Director (Environment),claims the lake would have dried up years ago without the dams. The success of these dams is 100 per cent. The soil erosion that was 160 metric tonnes per hectare per year in 1988 has come down to 7 metric tonnes per hectare per day. Without these dams,silt would fill up the lake. The amount of water entering the lake is dependent on the rains as with heavy rainfall in 2008,the water level shot up, he said.
The watering holes are also important for the wildlife. The underground acquifiers are recharged because of the seepage of water. The dams are cleared of silt at regular intervals.