Hello all. I am new to HEC-RAS and am having some issues modeling a dam breach on a proposed reservoir in California. So far, all features have been digitized in ArcMap 10 using HEC-geoRAS. The dam to be breached is at the upper end of the river reach that I am modeling.... however, a few miles downstream from the proposed dam is an existing large reservoir. I have created polygons (StorageAreas) for both the proposed and existing reservoirs. I can not figure out how to connect the two storage areas because it seems that I need to actually have my stream centerline, bank lines and flow paths all digitized between the two reservoirs. If anyone can point me in the right direction I would be extremely thankful. This is my senior research project at CSU Sacramento and I need to wrap it up by the end of the week. Thanks in advance.
you need to have discrete streams and their compliments of flow lines and bank lines upstream, between, and downstream of the reservoirs. To connect the stream centerlines to the storage areas, read up on this post in the HEC-RAS Bloggery:
Thanks for your rapid reply. I have discrete streams, bank lines, and flow lines between the reservoirs and downstream beyond the lower reservoir. The upper reservoir is the one that will be breached and has a volume of around 2.3 MAF. Is it still necessary to have rivers upstream of this reservoir?
Also, I had previously read the article that you linked to. Although dynamic routing may be better for this situation, I am going to go with the level pool routing method instead. I'm curious as to how HEC-RAS determines where the flow will go once the flood wave hits the lower storage area since there are no cross section lines running across and beyond the boundaries of the reservoir. Just curious.
Thank you so much for your help. I just need to get this simulation to run as simply as possible and then I intend to refine it from there.
You do not have to have a river upstream of the storage area. However, to prevent the reach below the storage area from going dry, you may need to put in a lateral inflow to the storage area or the cross section just downstream of the storage area.
When the flow reaches the next downstream storage area, the water level will go up based on the elevation volume curve you enter. Just make sure that elevation volume curve extends to a high enough elevation to contain all of the volume that enters that storage area.