Geomorphology Based Semi-distributed Approach for Modeling Rainfall-runoff Modeling Using GIS

Abstract

Simulation of rainfall-runoff process for ungauged catchments is one of the most important areas of research in surface water hydrology. The Unit Hydrograph (UH) technique is widely used for runoff estimation, especially for design flood estimation. Geomorphology of a catchment has a strong relationship with the transformation process of rainfall in to runoff. For ungauged catchments, unit hydrograph may be derived using either regional unit hydrograph approach or alternatively Geomorphological Instantaneous Unit Hydrograph (GIUH) approach. The concept of the GIUH is a catchment transfer function in relating the shape, stream network topology and channel characteristics.In this study, Katteri watershed located in Tamilnadu, India is selected for applying the GIUH approach. Two different approaches are studied (1) Conventional Nash Unit hydrograph model, (2) Geomorphological based linear cascade model (GLCM). The geomorphological information of each sub-watershed i.e. cell to cell flow path, stream network are extracted from the ASTER Digital Elevation Model (DEM) of 30 m resolution. In the IUH based on geomorphologic association of linear reservoirs, it is assumed that the water courses are classified from the outlet to upstream. Effective rainfall is determined using the Soil Conservation Service Curve Number (SCS-CN) method. The developed model was applied to five storm events and the results are compared with observed hydrographs. According to these results, the derived flood hydrograph by using GLCM and Nash's IUH model were closely matching with the flow records of the watershed. This indicates the suitability of present modeling approach for predicting the flood hydrograph for an ungauged watershed.