HEC-RAS Dam breach

[WatrEngr]

Hi,

For a dam break flood analysis, I would like to know what extent of geometry of a creek should be set up in HEC-RAS on the upstream side of the dam.

Dam details:-

Earthen dam, 200m long and 44 feet hight
Reservoir, 8km lenth X 200 m width
Built on a creek which joins in a river at downstream of about 22 kms.

Thank you very much.

 

[rivermodeler]

Since HEC-RAS does a dynamic routing of flows through the impoundment (as opposed to a level-pool routing), the cross-sections that describe the impoundment should extend upstream to a point where there is very little backwater effects from the dam. The volume of the impoundment (which has a direct effect on the breach outflow) is a function of the cross-sectional area times the length between sections. The number of sections would be relative to the shape (from plan view) of the impoundment. If the impoundment has varying width, cross-sections should be located at each inflection point. If the impoundment is relatively consistent in cross-section, then the number of sections required is more a function of the numerical stability of the model (i.e., if it crashes, add more sections, either interpolated or actual measured). Hope this helps.