The Effect of Urban Drainage on the Determination the Time of Storage in the City Development Area

Increasing development activities in various fields in Surabaya will impact the occurrence of flooding, where the growth of residential buildings changes the function of the drainage area into runoff land. Therefore, there is a need for regional drainage recommendations. This study aims to provide a reference for a safe number that follows the storage needs and the duration of the peak partial drainage required by the region, following the study of water resources science. The data needed are rainfall data, average area, land function, and land slope maps. This study uses a 5-year return period probability. Moreover, the Nakayasu Hydrograph method is also used. It has a grace period starting from the rain surface to the top of the hydrograph, the area of the watershed, and the length of the main river channel. The comparison of the length of time of concentration (Tc) of the area with the length of waiting for time (Tp) of the urban drainage hydrograph shows that the area's Tc value is greater than the Tp value of the urban drainage.