Analisa Erosi Dasar Sungai Gajah Wong dengan HEC-RAS 5.0.7

Gajah Wong River is one of the rivers that crosses the city of Yogyakarta with the upper reaches of the river in a area of an active volcano. When this can greatly affect the rate of bottom erosion of the Gajah Wong River caused by the cold lava flood that accured. Where this has an impact on the erosion of the riverbeds, resulting in the collaps of existing cliffs or retaining walls. Therefore it is necessary to estimate riverbed erosion with the aim of knowing the location in the event of a collapse or landslide on the river bank. The analysis of the bottom erosion of the Gajah Wong River was carried out with the HEC-RAS 5.0.7 simulation. In this research, river flow modeling with unsteady and sediment simulation was carried out. The repeat flood data used in the simulation were obtained from the KPU-BBWS Serayu-Opak. Based on the data that has been obtained, modeling is carried out with a 2 year return period with a peak point of 28.5 m3/s. Based on these data, the result of riverbed erosion were obtained at cross 69 and after a field survey was carried out that point, cliff landslides were found that occurred due to bottom erosion.