Hydrological Analysis of the Situ Gintung Dam Failure

Early on the morning ofMarch 27, 2009, the Situ Gintung dam, located near Jakarta, Indonesia, and with an catchment area of 3.1 km², failed and flooded the area below it. This disaster has awakened most of the Indonesian people, especially those who are concerned about hydraulic structures, natural disasters and sustainable water resources management. During the disaster, about 100 people died and a number of people went missing. There are hundreds of dams like the Situ Gintung dam and other big dams have been built in Indonesia. Most of these dams pose a high potential hazard to life and property if a failure or levee breach occurs. Dam failures may occur at different locations such as spillway, embankments and foundations. The failure may occur as a result of a number of problems such as overtopping, surface erosion, and piping. Dam failures due to spillway problems may occur, for instance, as a result of inadequate spillway capacity (overtopping) or spillway loss by erosion (surface erosion). In this study, the Situ Gintung dam failure has been analyzed based on hydrology analysis. Results show that heavy monsoon rainfall was not the main cause of the situ Gintung dam failure. The daily rainfall on March 26, 2009, was 113 mm that equal to a 10 year return period. Reservoir routing shows that there was no overtopping during March 27, 2009, flood, the maximum water depth on the spillway is 0.63 m. Assuming that maintenance was done well, the spillway was still safe under a 100 year return period with the maximum water level is +98.95 m. It means that the embankment was still safe with 1.05 m freeboard. Due to high water flow velocity, however, surface erosion may occur at the end of a chute spillway that consists of silt, clay and sand. Continuous scoring/erosion happened throughout the spill over the spillway, which started at around 06:00 pm and lasted until 03.00 am, resulting in a big pond at the chute spillways and surrounding areas. This phenomenon adversely affected the instability of the spillway structure. As a result, the spillway failure occurring resulted high flow discharge that reached more than 425 m³/s.