Diversion of floodwaters to wetlands: Need for a calculative approach

Kangkana Goswami Bharadwaz

&

Nidarshan Nandan Koushik

Kangkana Goswami Bharadwaz is an Advocate at Gauhati High Court & Member of Assam Wetland Authority and Nidarshan Nandan Koushik is a Field Researcher at Piramal Swasthya Management and Research Institute.

In a recent move, the State government of Assam has announced its ambitious design to channelize flood waters of the Brahmaputra to nearby wetlands and oxbow-lakes as a part of its flood mitigation strategy. The government plans to initiate the entire process based on a well-planned scientifically backed mechanism through methodologies like flood hazard mapping, satellite imagery for identification of suitable and depleting wetlands, space technology intervention in flood management etc. For this, the government has roped in agencies like North East Space Application Centre (NESAC) and (Assam State Space Application Centre) which are engaged in providing satellite data.

This can prove to be a game-changer in terms of both flood mitigation and wetland restoration as wetlands are said to act as sponges that can easily absorb water. More specifically riparian wetlands can survive inundation by floodwaters and often actually benefit from mild flooding. Water diversion to wetlands may also hugely contribute to wetland restoration for filled up or dried up wetland, can add to its nutrition quotient, help in purification, support its flora and fauna and can also help wetlands execute its climate change mitigation services.

All said and done, this ambitious endeavour, however, needs to be a calculative one backed by adequate research as it has its fair share of pros and cons, advantages and limitations. While doing this, the range and array of ecosystem services that wetlands provide should be brought into screening to understand the impact of mild to severe flooding on each one of them.

Wetlands are known to provide a host of social-environmental services like (supporting services (primary production, soil formation), regulating services (water regulation, water quality, disease regulation, climate regulation), provisioning services (drinking water, food supply, livelihood), and cultural services (aesthetic value, recreation and tourism). Sudden changes in the configuration , proportion and orientation of the wetland due to unregulated and access flooding may lead to several disturbances as well. Alterations may include changes in nutrients and physical conditions of aquatic ecosystem, sediment transportation and resultant increased deposition, changes in concentration of nitrogen and phosphorus in water and resultant water quality due to increased nutrient transportation and release of disease-causing agents from sediments or overflowing sewer systems. Moreover, abrupt release of untreated flood waters into wetlands may also lead to changes in total coliform and metal concentrations due to bacteria and metals mobilized by floodwaters.

Flood water channelling can result in transportation of excessive nutrients and potentially stimulate excessive primary production (eutrophication) or even alter primary producer community composition, causing unfavourable species to dominate. For example 'Harmful algal blooms' (HABs) such as cyanobacteria resulting from excessive nutrient transportation from flood waters polluted Lake Winnipeg in Canada and Erie Lake in Colorado causing health hazards for people who were dependent on this water body for drinking water supplies. Other adverse impacts include change in aquatic environment for the indigenous flora and fauna, impact to wetland economic services and deterioration of its aesthetic value.

To add on, changes in 'climate change regulating quotients' of the wetland may also occur due to change in methane and carbon dioxide release as a result of aerobic /anaerobic microbial processes that influence organic matter decomposition. Other disruptions that may occur include fish distribution and abundance, unsafe water levels, increase in debris, plastics and other toxic contents in water and accelerated discharge of industrial and urban toxic materials and nutrients into waterways. In another incident reported in Bengaluru, chunks of dead fish were washed ashore in the banks of the Ulsoor Lake, depicting the toxic state of the water of the lake. Reportedly in Karnataka, the city lakes are drowned in the piles of waste and toxic liquid and experts have confirmed that oxygen levels in the lakes in Bengaluru have depleted because of leachate and sewage seeping into the lake water contaminating the water to a level which is absolutely poisonous to the aquatic ecology of the water bodies.

To conclusively summarize the purpose behind pointing out the concerns, it is crucial to consider that future research and a carefully curated preliminary environment impact assessment of the nuances of this ambitious initiative and bring in a more scientifically-proven process to rely on detailed research on the pros and cons of both the positive and negative ramifications on the wetland ecosystem services to improve our understanding of the proposed initiative. Additionally, studies linking ecosystem processes with ecosystem services should be undertaken to improve our understandingof the effects of disturbance on aquatic ecosystem services in general. The post-flood changes in the wetland ecosystem, the exacerbated changes introduced to the ecosystem configuration needs to be well addressed as recovery post flood is highly variable and can extend to a very lengthy period of time.

Legally speaking ,the entire gamut of activities ranging from considering the amount of water that can be safely diverted to the way in which the diversion to be executed should be regulated and monitored under scientifically curated legal guidelines.