Flash Flood Analysis for Southwest-Hungary

The 15–18 May 2010 flood events on the watershed of the Bukkosd Stream, SW Hungary, are described, their general topographic and hydrologic characteristics are analyzed using the HEC-HMS numeric runoff model, and geomorphological impacts are surveyed. In addition to extreme rainfall volumes, the major reasons found to contribute to extreme impoundment were the fluctuating and locally reduced width of the valley, the confluence of tributaries, which create intermittent bottlenecks for drainage, and high soil moisture contents, which also caused slope instability in deeper soil mantle. Flash flood hazard is closely associated with landslide hazard in upland valleys.