Preparation of Void-less Topographic Wetness Index for Hydrological Analysis using Digital Elevation Model

Abstract

Geographic information system (GIS) is an important tool to generate different types of information from digital elevation model (DEM) within a watershed region, where topographical and hydrological characteristics are very important. Topographic wetness index (TWI) is one of the essential parameters in topographical and hydrological modeling, which can be developed from DEM. Estimating the amount of soil moisture is directly correlated with TWI and amount of rainfall. There are several ways to calculate TWI, which uses DEM in different spatial resolution (cell size), different types of slopes, flow direction, flow accumulation, soil properties and rainfall distribution. In this research, TWI was calculated based on six topographic parameters generated from DEM of 30m spatial resolution. They are slope in degree, radian of slope, tan slope, flow direction, flow accumulation and scaled flow accumulation. The result shows that the slope factor has a greater correlation with an R-square value of 0.38. This type of void-less TWI data is most important for topographic and hydrologic modeling in a watershed region.