Effect of land use change on water discharge in Srepok watershed, Central Highland, Viet Nam

Srepok watershed plays an important role in Central Highland in Viet Nam. It impacts to developing social-economic conditions. Therefore, it is necessary to research elements which impact to natural resources in this watershed. The Soil and Water Assessment Tool (SWAT) model and Geography Information System (GIS) were used to simulate water discharge in the Srepok watershed. The objectives of the research were to apply GIS and SWAT model for simulation water discharge and then, we assessed land use change which impacted on water discharge in the watershed. The observed stream flow data from Ban Don Stream gauge station was used to calibrate for the period from 1981 to 2000 and then validate for the period from 2001 to 2009. After using SWAT-CUP software to calibration, NSI reached 0.63 and R square value achieved 0.64 from 2004 to 2008 in calibration and NSI gained good level at 0.74 and R square got 0.75 from 2009 to 2012 in validation step at Ban Don Station. After that, land cover in 2010 was processed like land cover in 2000 and set up SWAT model again. The simulated water discharge in scenario 1 (land use 2000) was compared with scenario 2 (land use 2010), the simulation result was not significant difference between two scenarios because the change of area of land use was not much enough to affect the fluctuation of water discharge. However, the effect of land cover on water resource could be seen clearly via total water yield. The percentage of surface flow in 2000 was twice times more than in 2010; retard and base flow in 2000 was slightly more than in 2010. Therefore, decreased surface flow, increased infiltration capacity of water and enriched base flow resulted in the growth of land cover.