Probable maximum flood of the Usk dam spillway in Wales

Hydrological studies are crucial and necessary for water and environmental resources planning and management. In this context, the role of hydrological model will become extremely useful, especially for a reservoir that lacks such studies and investigations. This project study focuses on examining and studying the probable maximum flood of the Usk Reservoir, situated in southern Wales, UK. Furthermore, the catchment area is delineated manually and automatically using DigiMaps by EDINA and HEC-GeoHMS, respectively. The catchment area of 16.66 km2 is subdivided into 17 sub-catchments. Moreover, geomorphologic maps, topographic data and meteorological data of the studied area are produced using several programs such as ArcGIS and HEC-GeoHMS. Estimation and analysis of discharges for the sub-catchments and are modeled as lumped and event-based. For the hydrological modelling, HEC-HMS 4.3 is used. The main input data that is required includes rainfall (Type IA synthetic distribution), DEM, soil map, land use and meteorological data. Representative maps and graphs are used for a clear illustration of results and data. Factors influencing the runoff such as loss of precipitation, CN values, initial abstraction and lag time are discussed. Three scenarios of the lag time are examined. These are 50%, 100% and 200% of the actual lag time. In conclusion, peak inflow, peak discharge, inflow volume and discharge are obtained and discussed thoroughly.