Study of the Effect of River Basin Morphology Change on Threshold Parameters in Cimahi Flood Early Warning System

Abstract

Flood early warning systems are used for flood disaster preparedness to reduce disaster risks. The problem is damage of water level sensor due to aggradation which also results in river capacity reduced. The purpose of this research is to determine the effect of river basin morphology change on threshold parameters in flood early warning system. Measured hydraulic parameters are flow depth, flow velocity, and riverbed slope. Land cover was conducted using Cimahi river basin land use map to determine runoff coefficient. Rainfall-runoff model used is the Deconvolution Software program to determine unit hydrographs. Results of this study indicate that morphological changes of watershed significantly influence threshold parameters. A 0.5 m rise in river bed can reduce river capacity by 41.8% and narrowing of 16 m-wide river border dropped river capacity from 730 m3/s to 95.2 m3/s. An increase of 17 % runoff coefficient, increased direct runoff by 17%. Reducing this river capacity makes threshold parameters in flood early warning system invalid causing flood events cannot be detected earlier by the system.