Effect Land Use Ratio Index to Reduce Flooding: A Case of Jirak Sub-watershed in the Arau Watershed, Padang

The flood may occur for both climatology and human action factors. The climatology factors can be in the form of land degradation, land-use changes, and population increase. The land-use changes can be identified when there is a conversion of the recharge area into a built area. When the population increases, space needed also enlarges. The Jirak located in the Arau watershed in Padang. In analyzing it, this study applied a descriptive quantitative method. The image used in the map is analyzed with Arcgis 10 to get a flood-prone map. The rainfall is calculated by using methods of Gumbel, and Log Pearson III, the debit is calculated by using rational. The difference discharge between these is 7.469 m3/second. It is necessary to regulate the type and use of land to reduce flooding by 7.469 m3/sec with a housing index ratio of 24.68% and plantations of 43.39%.