Integration of HEC-RAS and geographical information system (GIS) in the hydrological study of peak flow response to deforestation on a small watershed in Malaysia

Abstract

Land use change is one of the most serious environmental and hydrological problems nowadays. It has become a global issue including Malaysia due to the greenhouse effect. Land use changes cause a significant adjustment of the hydrological balance of a watershed mainly by eliminating evapotranspiration, redistributing and modifying the amount of rainfall that reach the ground. A 20 years historical data were used to represent a geographical and hydrological data for a Kinta watershed, in the state of Perak. The geographical data were processed using geographical information system (GIS) to show the land use change in the study area. The hydrological data were analyzed through regression analysis, flow duration curve, and soil conservation service (SCS) method for analyzing runoff for land use change. The regression analyses have found significant increase of r2 value from 3.1% between year 1990 to 1996, 7.5% between year 1997 to 2000, and 13.2% between the years of 2001 to 2006. The flow duration curve has selected streamflow data event on December 28 to 29, 1996 on the Kinta River at outlet of Kinta watershed result which has shown volume of streamflow that was 2.209 × 106 m3. Meanwhile the direct runoff was 8.979 mm from volume divided by area of watershed 246 km2. The I• index calculated was 28.144 mm/h and I•Δt was 28.144 mm. Land use analysis shown result for runoff depth and S, potential max retention followed by CN for each year. The result showed increase of runoff depth and decrease of S, potential maximum retention. These findings have proved that the changes in land use in terms of the increasing deforestation activities or increasing new development will give a crucial impact to the hydrology response. Key words: Land use change, flow duration curve, soil conservation service (SCS) method, runoff depth, geographical information system (GIS).