Simulation of the effect of floodway on Batang Kandis River flood control

Abstract

Floods often occur in Padang City, mainly in the areas of Pasia Nan Tigo Village and Lubuk Buaya Village, caused by the overflow of Batang Kandis when heavy rains occur (intensity of rainfall >15mm/hours). To decrease the river overflow an artificial canal with 300 m long and 50 m wide (floodway) was constructed to bypassing the river flow from the Batang Kandis River to the ocean. In order to find out the effects of the floodway, four scenarios are performed the scenario 1 and 2 were the simulation condition of Batang Kandis River before and after the construction of floodway. While to increase the effectiveness of floodway, simulations 3 and 4 were carried out. Scenario 3 was the combination of floodway with normalization and embankment. To prevent the entry of seawater into the Batang Kandis River, because the floodway is affected by the tide of the sea, then 3-door motion weir was simulated namely scenario 4. Scenario 4 was the combination of floodway normalization, embankment, and a 3 door motion weir. From the simulations, we found that the floodway was effective to decrease the water surface level up to 15 m and 20 m during 10 years and 25 year return period of discharge respectively. From the scenario 3, we found that the embankment with 1.5 m and 2 m was effective to prevent overflow by 10-year and 25-year return period of discharge respectively. While for scenario 4 the water level rises 0.5 m due to motion weir So, that it is needed to extend the embankment with 0,5m high.