CHARACTERISATION OF HYDROLOGIC RESPONSES OF MICRO WATERSHEDS USING GEOSPATIAL TECHNIQUES

Abstract

Water is one of the precious and vital resources essentially required for the sustenance of life and for the economic and social progress of any country. Scientific water management is a must to sustain the domestic, irrigation and other water needs. Quantifying the hydrologic responses at micro watershed scale plays an important role for water resources development of a locality. For understanding the watershed characteristics and behavior, models play an important role which are also useful for extrapolating the current conditions to potential future conditions. Hydrological modeling is considered as a powerful technique for water resources management. In this study, the hydrology of two small sub watersheds of Bharathapuzha river basin near Valanchery town, were modeled using GIS and SWAT watershed model. The study aims to quantify the morphometric characteristics using GIS, simulate the hydrologic elements and stream flow using SWAT model and to suggest water conservation measures for the study area. First, a comparison of different commonly available DEMs were made to assess their suitability to perform morphometric analysis and it was found that SRTM DEM gives best result. Further studies were carried out using SRTM DEM. The W1 sub watershed is devided into six micro watersheds and W2 sub watershed is devided into four micro watersheds and prioritized the micro watersheds using morphometric analysis. Further, datasets required for the SWAT model were collected through primary and secondary sources and calibrated the model by generated two years (2019 to 2020) of stream flow. An NSE = 0.87 and R 2 = 0.92 for W1 sub watershed and NSE=0.91 and R 2 = 0.91 for W2 sub watershed were obtained. With the calibrated model, simulations were made to predict the hydrologic elements of both the sub watersheds. The whole sub watersheds characteristics and behavior and that of micro watersheds were determined and predicted. It was found that ET values of sub watersheds were varying in the range of 16 to 28 % of the annual rainfall, surface flow and base flow were in the range of 36 to 44 % and 25 to 27 % for W1 and W2 sub watersheds respectively. Relationship between morphometric characteristics and water balance components were determined and it was found that drainage density has got direct relationship with surface runoff (SURQ) and total runoff (WYLD) is having inverse relationship with base flow. Similarly, the relationship with relief ratio, stream frequency and texture ratio were also found out. Further, regression analysis was done between the morphometric characteristics viz. drainage density, relief ratio, stream frequency and texture ratio with that of hydrologic responses viz. surface runoff (SURQ), lateral flow (LAT_Q), baseflow (GW_Q) and water yield (WYLD). It was found that drainage density, stream frequency and texture ratio was having good positive correlation with total runoff (WYLD) generated from the watershed. Drainage density was having negative correlation with baseflow (GW_Q). Using these vital information, soil and water conservation measures have been suggested scientifically and objectively at micro watershed scale.