Why can I route a hydrograph through a subcatchment?
A subcatchment is used to generate a runoff hydrograph for a given area of land. But it does not include the information required to route an existing inflow hydrograph. In cases where a separate upstream flow must also be routed across the subcatchment, a separate reach routing is often used in conjunction with the subcatchment. Modeling Overland Flow If the “reach” flow is particularly shallow, such as general overland flow, this can be modeled with a corresponding reach geometry, such as a wide bottom and/or very low side slopes. In addition, a higher Manning’s value may be used to account for the low flow depth. This commonly occurs when a “level spreader” is used to re-create very shallow flow.
