KAJIAN PROTEKSI GERUSAN DI HILIR KOLAM OLAKAN BENDUNG TIPE USBR-II

Abstract

In the downstream of a weir, especially in stilling basin, there is a phenomenon called hydraulic jump caused by flow change from supercritical flow to sub critical flow. The hydraulic jump in weir stilling basin causes bed scour, particularly in the downstream of weir that is not protected. Therefore, laboratory study of scour and its countermeasure in the downstream of weir is required. This study was conducted at Hydraulic Laboratory of Surakarta River Research Centre using recirculation flume. The recirculation flume dimensions were : length = 24 m; width = 49 cm; and height = 60 cm. The bed material of recirculation flume was fine sand (diameter of sieve = 2 mm) with 20 cm thickness layered along the flume. The slope of flume was 0.004, and it was assumed that there was no sediment load in the upstream of weir. This study used weir model USBR-II. The model was placed about ± 9 m from the upstream. The experiment was conducted using 4 discharge variation running and 3 protection variation running. The result shows that the maximum scour depends on flow velocity, shear velocity, and flow height in the downstream of stilling basin. In addition, it is also affected by Reynold number and gravitation (as Froude number). These parameters are interdependent significantly. Furthermore, there is significant scour reduction in the downstream of stilling basin which is protected using either ¼ Lmaks rip-rap, ½ Lmaks rip-rap, and Lmaks rip-rap. In addition, protection using Lmaks length rip-rap can protect scour with smallest scour depth. However, scour is still happened in the downstream of stilling basin although there is protection along Lmaks.