How does HEC-RAS use unsteady flow hydrograph boundary conditions

[godzilla]

For upstream boundary conditions, I assume one gets the hydrograph flow for the area entering the beginning only. How does the program know what flow to add for the remainder of the reach? For example a 21,000′ long natural channel incorporating 1200 acres with only 120 acres above the beginning of the reach? For a 10 year storm, create the hydrograph flow for the 120 acres and make that the boundary conditions? The entire watershed creates 850 cfs at the end.

[Chris G.]

The upstream inflow hydrograph should represent the flow from the watershed that contributes to the location of the upstream boundary. For the watershed that contributes flow along the length of your reach, you can use lateral, or uniform lateral inflow hydrographs for boundaries. Just add the cross sections in the unsteady flow editor for where you want to include lateral inflow hydrographs.

[godzilla]

Thank you Chris G. I mistakingly thought the lateral inflows were for junctions. I’ll do it.

[Author]

Posts