HydroCAD^{®} Stormwater Modeling  Since 1986

Inflow Area, Inflow Depth, & Runoff DepthStarting with HydroCAD 8.0, the inflow area and inflow depth are calculated for each node and shown at the top of the node summary. For a subcatchment, the runoff depth is displayed. HydroCAD 8.5 (and later) can also display the fraction of the inflow area that is impervious. What is the Inflow Area?The inflow area is the total runoff area contributing to a given point in the watershed. This is typically the sum of all subcatchment areas that lie upstream of a specific node.
What is the Inflow Depth?The inflow depth is determined by dividing the node's inflow volume by the inflow area. This yields an average runoff depth from the upstream watershed, adjusted by any routing operations. Inflow depths are subject to the same considerations that apply to hydrograph volumes: The volume is calculated based on the flow that occurs within the specified time span. A reduced time span will decrease the reported volume and inflow depth. To report the entire volume and depth, set the time span to cover the entire period of flow.
What is the Runoff Depth?The runoff depth is determined by dividing the subcatchment's runoff volume by the subcatchment area. In most cases, the runoff depth will be somewhat less than the rainfall depth, due to the effects of the applicable runoff calculation. Runoff depths are also subject to the time span issue discussed above. 
