Mt. Merapi is the active volcano in Indonesia. On 2010 erupted, the mountain produced sediment around 150 million m3. The sediment supplies to the downstream area through the tributaries. The hydraulics condition in tributaries of Progo River may change for long time period due to the sediment supply. Sabo dam is constructed in tributaries for controlling the sediment. The morphology around sabo may change due to the sediment supply. So, the erosion process near the sabo dam should be predicted to estimate the stability of the structure after the eruption. This research is to investigate the erosion around the sabo dam. Numerical simulation is performed using the horizontal two-dimensional flow model.