Planning for Retention Pools to Handle Floods in Kebondalem Hamlet, Kademangan Village, Mojoagung District - Jombang

Kademangan village is an area that often experiences flooding. Rainfall and the geographical location of the village which is flanked by three rivers also causes flooding. In planning flood control, careful calculations are needed taking into account daily rainfall for at least the last 10 years (Al Amin, 2016). A retention pond is a building/construction that functions to temporarily store rainwater by giving it the opportunity to seep into the ground, the operation of which can be combined with a sluice gate, then released back into the river. The concept of the retention pond itself is to hold the volume of water when the maximum discharge in the river arrives, then slowly drain it back into the river when the river discharge has returned to normal. The rainfall value obtained with a return period of 10 years using the Pearson III log method was 580 mm/day, while for the Gumbel method with a return period of 10 years it was 637 mm/day. It was found that the total planned capacity of the existing retention and discharge ponds was 48,009.84 m3 with an area of 4,008 m2 and 4,012 m2 which was considered sufficient, because the dimensions of the retention pond were greater than the capacity of the retention pond during a flood of 47,363.66 m3 with the water absorption time of the retention pond to in the soil for 34.96 hours.

Keywords: Rainfall, Maximum Discharge, Area Size, Retention Pool, Pearson III Log, Gumbel.