Estimating Direct Runoff from Storm Rainfall Using NRCS Runoff Method and GIS Mapping in Vientiane City, Laos

Abstract

The amount of direct runoff present in a watershed indicates the hydrological condition of the area, reflecting the characteristics of land use, soil and rainfall distribution. This study aims to measure the hydrological condition of Vientiane city by examining the runoff potential. This study obtained direct runoff from storm rainfall for the city area which covered the Mark-Hiao River watershed. The rainfall-runoff calculation is useful for future design of drainage networks within a watershed to support flooding management. The Geographical Information System (GIS) software is the main technology used in this study for the purposes of assigning the estimating process, watershed delineation, extracting hydrologic parameters and mapping. There are two main parts discussed with useful results in this study, delineating the river watershed and estimating weighted direct runoff for a watershed area. The result of delineating river watershed process, showing the changing elevation data achieved by combining the two elevation data, Shuttle Radar Topography Mission 30m Digital Elevation Model (STRM 30m DEM), and digital contour data (Vientiane database), performed well in terms of representing surface flow networks and their topography. The calculated average of direct runoff in each small sub-watershed estimated by using Weigh-Q method of the National Resources Conservation Service (NRCS) very well showed the poor to good hydrologic condition in each specific area in 1-to5-day durations of storm events.