PENELUSURAN BANJIR DAN KAPASITAS PELIMPAH SITU LEBAK WANGI, BOGOR JAWA BARAT

Sari

Situ Lebak Wangi condition is currently very deplorable due to sedimentation and landfilling by the community. This is being reinforced by the presence of land grabbing to convert into residential or agricultural area. Because of these conditions, Situ Lebak Wangi Design Review was carried out. Flood routing is necessary in order to plan  spillway and reservoir capacity. The purpose of the flood routing is to determine the magnitude of the inflow and outflow as well as being stored in the reservoir. The flood discharge values will become the input to the evaluation of spillway, channel, and volume that can be accommodated in the reservoir.

Calculation of floodroutingn using The Level Pool Routing Formula: I – Q = , where I is the average inflow (m³/sec) , Q is the average outflow (m3/sec), S is water storage (m³), and T is the time interval (hours). The calculation of hydrograph outflow determined by the equation: . While the spillway calculations using Strickler formula: Q = A.K_S.R I , where Q is the discharge (m³/sec), A is the  area (m²), K_S is the Strickler roughness coefficient, R is the hydraulic radius (m) , and I is the slope of the channel.

Based on the flood routing results and count spillway capacity at Lebak Wangi, it can be concluded that the discharge of floods the return period 5-years is 9.30 m³/sec. Once through the reservoir, it will be damped to 3.0 m³/sec. The return period 50-years discharge is 15.8 m³/sec. This discharge will be damped in the reservoir to 5.30 m³/sec. While the upstream spillway capacity is of 5.5 m³/sec, downstream capacity decreases to 3.60 m³/sec at 1.3 m water-level height.

Keywords: Flood routing, inflow, outflow, and spillway capacity