A Revision of OPTEMP-LS Model for Selecting Optimal EMP Combination for Minimizing Sediment and Water Yield from Hilly Urban Watersheds

摘要

Hilly watersheds are inherently susceptible to more sediment and water yield. Urban developments in hills cause conversion of the natural sloppy surface to bare steep cuts, which are imperceptible in orthorectified satellite images. Sediment yield from such hilly watersheds is underestimated when estimation is performed in GIS platform. In order to improve the sustainability of ecological management practices in urban hilly watersheds, this paper revises the well-established optimal ecological management practices (EMP) allocation model OPTimal EMP Model with Linear Programming for Single Ownership (OPTEMP-LS) by incorporating the effect of steep hill cut area associated with the urban settlements in hills. This incorporation has basically caused a significant modification in the sediment yield constraints of the model. The revised model has been applied to an urban hilly watershed of Guwahati city. It is found that due to the consideration of soil loss from steep hill cuts, the EMP cost per unit settlement area in the hilly portion becomes 4.77 times higher than the unit cost for the plain portion of the watershed. Again, the implementation of EMPs has reduced the sediment yield from the watershed more efficiently than the peak runoff. Although this revised version of OPTEMP-LS is computationally more intensive, it gives a more realistic scenario of the total cost and efficiency of a watershed management project through the choice of EMPs individually for the plain and hilly area of the watershed as well as for the steep hill cuts.