Subcatchments are hydrologic units of land whose topography and drainage system elements direct surface runoff to a single discharge point. You are responsible for dividing a study area into an appropriate number of subcatchments, and for identifying the outlet point of each subcatchment. Discharge outlet points can be either nodes of the drainage system or other subcatchments.
Subcatchments can be divided into pervious and impervious sub-areas. Surface runoff can infiltrate into the upper soil zone of the pervious sub-area, but not through the impervious sub-area. Impervious areas are themselves divided into two sub-areas - one that contains depression storage and another that does not. Runoff flow from one sub-area in a subcatchment can be routed to the other sub-area, or both sub-areas can drain to the subcatchment outlet.
Infiltration of rainfall from the pervious area of a subcatchment into the unsaturated upper soil zone can be described using three different models:
Horton infiltration
Green-Ampt infiltration
SCS Curve Number infiltration
To model the accumulation, redistribution, and melting of precipitation that falls as snow on a subcatchment, it must be assigned a Snow Pack object. To model groundwater flow between an aquifer underneath the subcatchment and a node of the drainage system, the subcatchment must be assigned a set of Groundwater parameters. Pollutant buildup and washoff from subcatchments are associated with the Land Uses assigned to the subcatchment.
The other principal input parameters for subcatchments include:
Assigned rain gauge.
Outlet node or subcatchment.
Assigned land uses.
Tributary surface area.
Imperviousness.
Slope.
Characteristic width of overland flow.
Manning's n for overland flow on both pervious and impervious areas.
Depression storage in both pervious and impervious areas.
See Also Subcatchment Properties, Infiltration, Land Uses, Aquifers, Snow Packs