Mountain Flood Control Reservoirs help protect mountain rivers from floods. The rapid changes in water levels can affect the stability of floodplains. By using computer simulations, researchers found that the slope angle of the floodplain determines its stability. For steep slopes over 26°, soil properties like cohesion and conductivity are crucial. For slopes under 26°, only cohesion matters. This means that different areas of the floodplain may need different types of soil surveys before building flood control reservoirs. Stabilization structures may be needed for slopes over 26° to prevent landslides during extreme floods.