- Chandubi lake was formed in 1897 as the result of a major earthquake in the region during which a forest area went down and became a lake. Since then, the lake has evolved to become a critical habitat for flora and fauna.
- Of late though, the lake is receding and drying up fast and a part of it has transformed into a grazing field.
- Rampant sand mining, both legal and illegal, in Kulsi river, is one of the reasons that the river is increasingly getting deeper and water from the Chandubi lake is flowing into the river, resulting in Chandubi getting drained out.
“For the unsuspecting, this would appear to be any other normal grazing land. But the reality is that we are now walking on land that was actually part of the lake until just a few years ago,” says Sarzen, a local guide, referring to the Chandubi lake in the northeastern state of Assam. A herd of cattle and a group of local people doing their washing chores are in a nearby stream. The lake itself seems far away.
The shrinking of the famous Chandubi lake, located in the southern part of Kamrup district with Barduar Reserved Forest to its north and Mayang Hill Reserved forest to its south, has been rapid. According to a study conducted by the Assam Remote Sensing Application Centre (ARSAC), in 1954, Chandubi lake or wetland had a water-spread area of 481.19 hectares, but in 1967-68, it decreased to 392.61 hectares. In 1997, it further decreased to 203.20 hectares and in 2007, the area had become 186.52 hectares – almost 40 percent less than it was 50 years ago. The study used Survey of India toposheet and satellite imagery covering the period between 1911 and 2007. The study also noted that the depth of the lake reduced to 3 metres from 8 metres during the recent period. At present, the lake has visibly reduced further in size and depth.
Chandubi lake was formed as a result of an earthquake in 1897 when parts of land along the present Assam-Meghalaya border sank and led to the formation of the lake. Located at the foot of the Garo Hills, the lake is a biodiversity hotspot with a surrounding forest area and the Kulsi river flowing in close vicinity. It is home to dozens of fish species including some critically endangered species such as Nandhanl and ornamental fish such as phutiki-puthi.
The Kulsi connection
The Kulsi, a southern tributary of the Brahmaputra, surrounds Chandubi lake and even has a connecting water channel (locally known as lokeiyadar) with the lake, making it a perfect habitat for the world-famous Gangetic river dolphins. The 2.5 km long spiralling channel, apart from being a migratory channel for fishes, also helps in maintaining a balance in the water level of the lake. The dolphins often frequent the confluence of the lokeiyadar and the Kulsi river, known as the lokaiyamukh, to feed on the migratory fish. But recently, according to local residents, in the places in the river where earlier more than 20 dolphins were sighted, at present, only 2-3 dolphins are being seen.
Illegal sand mining
While Chandubi lake’s close proximity to Guwahati is a boon for tourism, it has its demerits too. Rapid urbanisation so close to an ecologically sensitive biodiversity hotspot impacts it negatively. The demand for sand from the Kulsi river has increased over the last few years. What started decades ago, as a small enterprise for the employment of local youth, has now taken a mammoth form with hundreds of illegal sand mining operations running in the Kulsi river.
“The peak mining season also coincides with the fish spawning season which is hampering the fishing grounds in Kulsi river. Due to decreasing fish production in the river, a major shift in the livelihood of the mainstream fishing communities towards sand mining has been observed in Kulsi, during my study period, which is further increasing the pressure on the river,” said Sunny Deori, Senior Biologist at Wildlife Institute of India, Dehradun, who has done her Ph.D. research on Ganges dolphin ecology in Kulsi river.
Rampant mining using motor pumps has led to excessive draining of the riverbed and as a result, the normal flow of water in the river has also been affected.
“This has led to the water level of the Kulsi river becoming significantly low and at a time when water from the river should have flowed into the Chandubi lake, the reverse is happening. Water from the already shrinking Chandubi lake is flowing out through the connecting channel into the Kulsi river,” says Sarzen R. Mego, a local environmental activist.
According to a study published in the WWF Review 2018, removing sediment stores and altering sediment transport, which can occur with sand mining, will promote physical changes in a river channel. In rivers with deeply incised channels, greater water volumes are required before rivers overtop their banks and hence floodplain inundation occurs less frequently. As a result, floodplains are no longer able to fulfil their important ecological and social roles.
The impacts of the incision may spread beyond a river’s banks. By deepening the base of the river the banks and surrounding permeable areas drain to this lowered level, hence the groundwater level can also decrease, affecting groundwater availability and recharge.
Demands for a dam
Some locals are now demanding that a dam should be built at the point where the connecting stream (lokeiyadar) merges with Kulsi so that water from the Chandubi lake does not flow out through the channel into the river.
“Unscientific sand mining in Kulsi is a major reason as the Kulsi river has become deeper and water from the lake is flowing out through the connecting channel. A dam needs to be built on the channel so that water outflow stops from Chandubi lake,” said Matiram Rabha, a local artisan and environmental activist from the Chandubi area.
But building a dam to prevent water from the lake flowing out into the river has its own demerits and might not be a sustainable alternative according to experts.
“Blocking the connectivity with the mainstream river channels by building dams will actually cause floods. With the disappearing connectivity of rivers with wetlands and lakes, the prey resources of Ganges dolphins will further reduce not only in rivers but also in the wetlands because the entire process of hydromorphology is connected to each other. The life history of many fishes is associated with such migrations from lakes to rivers and back or else the population will decline,” Deori said.
“The plankton abundance (lower trophic level of aquatic system or the food source of fishes) is decreasing and significantly less, compared to Brahmaputra or Subansiri which are other hubs of Ganges dolphin in Assam,” she further added.
Chandubi lake is getting shallower
“There are multiple reasons for Chandubi lake drying up. One reason being the growth of aquatic plants and weeds in the lake because of which the lake itself is getting shallower and water holding capacity of the lake has reduced. The lake needs to be cleaned but the government has not done anything in this regard so far,” said Rabha.
“Also there used to be multiple underground water streams acting as feeders for the lake which have lost connection after the deposition of sediment in the lake and it becoming shallower,” he further added.
The growth of wild vegetation in the lake and the surrounding catchment area according to the experts is a major issue and needs to be addressed.
“If the catchment area is not properly conserved then sediment deposition happens in the lake and thus the water holding capacity of the lake lessens. Wild vegetation has grown in the lake since it has got a platform of sediment to grow,” said Jayanta Kr Sharma, an independent researcher and freelance environment consultant based in Guwahati.
“Catchment area treatment in the short term can be done by installing sediment traps at the points from where water from the surrounding high areas inflows to the lake. This can be done with locally available materials with community participation. Most of the wetlands are managed by various government departments but a community-based approach in an institutional way is not seen and it has become the need of the hour,” he further added.
Banner image: Wild vegetation growing on the Chandubi lake. Photo by Anuraag Baruah.