A catchment is an area on the earth’s surface where runoff from rainfall or snowmelt and groundwater discharge from springs and seeps is collected at the same discharge point. In a natural setting, the catchment area is equivalent to a drainage basin (Langbein and Iseri 1960). The water collected within a catchment may be discharged as stream flow into another stream or a body of water. A watershed is one or more catchments discharging to the same downgradient point. Determining the boundaries of a specific catchment uses topographic map or digital terrain model data to find where water would flow inward and downgradient to a particular catchment rather than into an adjacent one. The size of delineated natural catchments is controlled by the physical character of the landscape and the purpose for identifying the component catchments within a watershed. Within the built environment, a catchment would also include runoff from impermeable surface such as roofs and paved areas...