Modeling Approach towards Eco-Restoration Strategies for the Polluted Tributaries of the Brahmaputra River System

Growing anthropogenic impacts have degraded several urban tributaries of the Brahmaputra River. The status of many wetlands adjoining large-scale oil drill sites and mining areas in the Brahmaputra valley is too alarming. While restoration of degraded streams and wetlands is mandatory, robust initiative for conservation and preservation of the pristine water systems will be equally important. In the current study carried out in one of the most degraded tributaries, spatial and temporal variations of water quality were evaluated for dissolved load and pollution level and fitted into a GIS model developed for the study area with four layers of information for assessing the influence of catchment characteristics. BOD, DO and total phosphorus were found to be the sensitive parameters that are adversely affecting the water quality. The impact of the urban drainage on a 12 mile stretch in the main Brahmaputra was also evaluated by developing water quality indices (WQI) and regression analysis models. For many determinants, both diffuse and point sources appeared to contribute to the dissolved load. Poor WQI of the main river stretch at the confluence demonstrated significant influence of tributary wastewater input. The current study in the Bharalu tributary showed that application of modeling tools such as ANN, taking BOD, total phosphorus, conductivity and alkalinity as inputs and DO as output can provide a suitable monitoring tool. Optimization studies carried out using contour plots involving contributions of each input parameter by improved stepwise method observed that conductivity is the most influencing parameter. It has been demonstrated that a developed ANN modeling approach can be extended to other polluted tributaries for control of priority pollutants. Integrating these tools to the overall water management strategy of the Brahmaputra River can fulfill the objectives of an ecological approach towards habitat restoration for the polluted stretches of the basin successfully.