Emphasis has been laid since long on the need for integrated catchment management and impact of landuse on catchment hydrology; but the two disciplines have not been amalgamated for creating catchment sensitive ‘City Landuse plans’. This study aims at (a) utilizing hydrological modeling to understand the dynamics of an urban Himalayan catchment; and (b) identifying the impacts of Proposed Development Plan for Shimla on the city's water resources. This study successfully tested TOPMODEL in a humid, temperate urban Himalayan catchment to simulate catchment behaviour in an ungauged catchment. Unlike other TOPMODEL studies, TOPMODEL parameter m was found to vary with depth; with hydrological interactions governing runoff generation extending beyond the shallow soil matrix into the weathered bedrock/detritus profile. This assumption was found consistent with the large scale presence of rainfed seasonal/perennial springs flowing through the bedrock in the Himalayan region. Proposed Planning Area for Shimla City (200 sqkm) forms a part of four catchments: Ashmi, Nayaseri, Gambhar and Ghumma; all of which are ungauged catchments. TOPMODEL was used to simulate discharge and impacts of landuse change on low flows in two catchments (Ashmi and Nayaseri) where urbanization pressures are high. Knowledge of critical parameters dominating catchment hydrology (based on TOPMODEL simulations) was applied to identify the least hydrologically sensitive catchments so that urbanization can be diverted to the more resistant catchments.
Himalayas, TOPMODEL, dynamic m, landuse change, catchment sensitive planning
