Mt. Merapi is one of the most actives volcanoes in Indonesia. its eruptions have caused disasters in downstream areas. some of rivers that the origin located at Mt. Merapi have a large amount of sediment released during eruption is estimated at 150 million m3. Sediment was deposited at the upstream area of the rivers. When the rainfall which has a high intensity occurs, the deposited sediment will flows to the downstream area as bed-load transport. Furthermore, the phenomenon of flow with high concentration occurs in the rivers. Using numerical simulation, the impact of high concentration of bed-load transport is applied in Progo River, Yogyakarta, Indonesia. The results show that the high bed-load transport rate increase the bar grow rate. Its increase the bed degradation near the bank toe and then the bank collapse possibility its increase also. Furthermore, the bank erosion problem after 2010 Mt. Merapi eruption should be considered intensively.