Optimal Ecological Management Practices for Controlling Sediment and Water Yield from a Hilly Urban System within Sustainable Limit

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Urbanization is increasing at a rapid rate and in many places expanding into the hilly areas, thereby inducing significant alteration in the hydrological response of watershed. In the developing world, the process of urbanization is more often unplanned and disorganized, which results in higher yield of sediment and surface runoff, which manifest itself in the form of hazards like flash flood and landslide. Washing off of pollutants from the urbanized impermeable upper catchment is also causing downstream water quality declination. Therefore, urban developments in hilly watersheds require application of efficient management practices that can handle adverse consequences of urban developments in an ecologically sound and sustainable manner. Such ecofriendly sustainable management practices can be termed as Ecological Management Practices (EMPs). However, the cost, efficiencies and applicability of EMPs vary widely from place to place depending upon the site condition. Therefore, it is necessary to determine the optimal combination of EMPs that satisfies all requirements at minimum cost. In this study, allocation of EMPs for managing sediment and water yield from hilly urban watershed has been done through an optimization model. Due emphasis was given towards prioritization of EMP application projects based on severity of watershed degradation and their impacts on surroundings. A GIS based River Water Quality Information System (RWQIS) was developed with a primary objective of identifying most degraded watersheds by considering river water quality as an index of catchment degradation. To demonstrate applicability of the RWQIS, it was applied to Northeastern Region of India and two rivers of Guwahati City- Bharalu and Basistha were identified as most urban impacted rivers of the region. A systematic procedure for studying pattern of urban expansion by using geoinformatics was developed and applied to the Guwahati City along with a socioeconomic survey to help development planning associating hydrological aspects. Two adjacent watersheds were developed as disturbed and undisturbed watershed for studying hydrological response of residential development in terms of sediment and water yield and also for conducting experimentation on performance of some competitive EMPs. The study revealed that sediment yield and water yield per unit area increases by 2 - 21% and 3 - 54% respectively in the disturbed watershed as compared to the undisturbed watershed. Experimentation on erosion control efficiency of EMPs proved Grass (Paspalum conjugatum) and Golden glory (Tradescantia zebrina) to be highly efficient; Grass has efficiency of 75-100% and Golden glory has efficiency of 36-97% as compared to bare land. Analysis of chemical composition of rainwater and runoff samples showed significant ionic contribution from soil to the runoff water. Leaching study of soil revealed that leaching behavior of soil differs from site to site. Based on this study, a conceptual model was developed for determining limiting value of sediment yield from a watershed from the water quality perspective. Three optimization models, namely, OPTEMP-LS (OPTimal EMP model with Linear programming for Single ownership), OPTEMP-LM (OPTimal EMP model with Linear programming for Multiple ownership) and OPTEMP-LDM (OPTimal EMP model.
Supervisor: Arup Kr. Sarma AND Chandan Mahanta