|"Local River Widening (LRW)" is one of a potential option in small-middle rivers on valley plainsand fluvial fans for preventing hazardous sediment and woody debris and creating environment diversityin the same time. However, the effects and proper management have not been sufficiently studied. In thestudy, we discussed subjects for application of the LRW method by applying 2-dimensional morphodynamicsimulation model to a pilot site in the steep stream which damaged by flood disaster afterconstruction. The simulation showed water surface significantly destabilized with occurring hydraulicjump in case of under supercritical flow condition. As found in the field, bedload was deposited in thestream part, not in the local widening part. Smoothing of the outlet of is an effective countermeasure tostabilize the water surface and the river bed behavior. The environmental evaluation linked to themorpho-dynamic simulation provides useful results for decision making.