Rainfall runoff modelling using geographic information system

Abstract

In Peninsular Malaysia, states located at the east such as Kelantan, Terengganu, Pahang and southeast part of Johor face flood problem especially during Northeast monsoon. In the state of Johor, the town of Kota Tinggi has the most flood occurrence. This is due to high rainfall intensity, its location at low lying area and urbanisation activities, which increase impervious areas and created higher surface runoff. The purpose of this study was mainly to investigate and develop the relationship of rainfall and runoff using Geographic Information System (GIS). Sungai Johor river basin where Kota Tinggi is located was selected as the study area. The river basin was modelled by using Hydrology Engineering Centre - Hydrological Modelling System (HEC-HMS). The simulated hydrograph was calibrated against the observed hydrograph at Rantau Panjang station (19 January 2003 to 26 January 2003). Then, the model was validated against the data on 9 July 2006 to 13 July 2006. The result of calibration and validation showed that simulated hydrograph was in good agreement with the observed hydrograph. The calibration and validation were evaluated by using Nush and Sutcliffe (N-S) model efficiency index and the scores are 0.91 and 0.72, respectively. These scores considered as excellent and very good. A model simulation was also conducted for flood event in January 2007. However, the simulated hydrograph is higher than observed hydrograph. This can be due to the telemetric station located at Rantau Panjang station was inundated by the extreme streamflow. For future development scenario, 25% increment of impervious area at selected subbasin is modelled. The results showed an increment of the flow discharge at Kota Tinggi for about 4.2% (subbasin 7 and 8), 6.5% (subbasin 1 and 2) and 23% (whole area). Besides that, simulation by using IDF curve for 5 minutes storm duration of 100 years return period (ARI) using S.M. Bukit Besar station showed that the runoff is still lower than the runoff during flood event in January 2007. This result showed that the rainfall intensity in January 2007 is much higher. As a conclusion, the SCS-CN method in the HEC-HMS model with GIS application is suitable for Sungai Johor river basin