THE EFFECTS OF BATANG KANDIS RIVER FLOOD CONTROL IN PADANG CITY-PALAPA METROPOLITAN URBAN AREA

Floods often occur in Lubuk Buaya residential housing in Padang city, which has a population of 6,500 citizens per km2. These natural phenomena happen due to sea level water rises and the change in the new river mouth of the Batang Kandis river. The construction of a 500 m floodway and a 700 m dike of Batang Kandis river were proposed to control flooding. The floodway was then damaged during the earthquake on September 30th, 2009, and wiped out by a flood on March 24th, 2016. Theoretically, to solve flood conditions downstream of Batang Kandis river with 70 km2 of watershed area, the floodway is expected to be able to discharge 307 m3/s. This study uses a numerical simulation using HEC-RAS software with three scenarios. The first scenario uses the existing condition of the river width of 50 m and a depth of 1 m, it experienced an inundated area of 0.60 km2 for 5 hours. The second scenario is done by increasing 2.50 m embankment height, which gave the result of 2x700 m2 flood inundation in several locations. The third scenario also carried out dredging of the river up to the elevation of 0.00 m above sea level, and there was no flood inundation. Thus, the third scenario is the best result that has been carried out to control the floods downstream of Batang Kandis river.