Upstream Boundary Conditions for Dam Break Analysis in HEC-RAS

[smnnv]

I am performing a dam break analysis using HEC-RAS (my first time with unsteady modeling in RAS). The model is unstable from the get go so I guessing my boundary/initial conditions are causing it. My upstream boundary condition is the reservoir WSEL (no inflow hydrograph into reservior). I have the dam breach occur at the start of the simulation. The downstream condition is normal depth. Has anyone performed a successful unsteady model using similar boundary conditions?

 

[DMcGrath]

You might try adding some flow data prior to your breach event, say 50 to 200 cfs for a couple of minutes to give the model something to chew on while it starts. HEC-RAS does not like large, abrupt changes in flow, nor does it like to run dry (e.g. no inflow hydrograph. Considering the magnitude of a breach event, a small flow at the beginning will likely be inconsequential.