Potential impact of sub-urban development on the surface runoff estimations (a case study at Upper Ciliwung watershed)

Jakarta is a capitol of Indonesia which is located at downstream part of Ciliwung river. Statistic shows that in 2015, there are more than 750,000 people living in Ciliwung watershed which cost the changes in land use and uncontrolled use of river banks for settlement and population activities. Increases of impervious area will be correlated with the surface runoff. The aim of this paper is to analyse the potential impact of land use change on the surface runoff at upper Ciliwung watershed using hydrological model HEC-GeoHMS. Initial condition of this model adopt the SCS-CN model that represent the Upper Ciliwung Watershed characteristic. Rainfall event on 3 February 2007, the highest rainfall in last decade, were analysed at this simulation. This event applied for different land use from 1990 until 2017, with land use change increase by 12% each year, a flood hazard analysis has been carried out and it showed that the area in highly peak flood increased by 30%.