You DO have the documentation, don't you ? Again, there is good guidance on the web and in the HEC-RAS documentation. During a flood, such as one caused by a sudden dam breach, most streams will overtop their banks and most of the flow will be out of the stream, in the overbank areas! For this reason, it is important to have wide cross sections and to make good estimates of Manning's "n" ( roughness). The 'plan view' is less important than the cross sectional views of the both the stream and overbank areas. The geometry of the stream is an essential input to HEC-RAS. "However there's a twist that I think will preclude use of a straightforward solution: the "channel" is of irregular geometry (roughly hourglass shaped in plan view, with the inlet and outlet about as wide as the dam is thick – say 10 m at water level - and a narrow "throat" about 2 m wide)." Bureau if Reclamation" and similar terms. There is some guidance on this based in actual dam failures. It is critical in a dam breach analysis to estimate as realistically as possible the TIME it takes for the breach to fully form. If you are only interested in flows, velocities and water surface elevations then it doesn't much matter whether the water is fresh, salty, or in between. "I'm an environmental scientist, interested in characterizing flow through a newly-developed breach in an earthen dam separating a (former) stream-fed lake from a tidal freshwater river."ĭon't know what a 'tidal freshwater river' is, but it may not matter unless you are trying to 'characterize' water quality, such as salinity. It can do dam break analyses but there are other programs ( DAMBRK and SWoper) are available that may be better in certain circumstances. Whether or not it can depends in part on how good your initial guesses are.Ĥ. This means that sometimes it can't converge on a solution. That is, it solves equations for the conservation of energy and momentum.Ģ. HEC-RAS is primarily an hydraulics program. Ok, although not an expert in HEC-RAS, I'll tell you what I think I know and understand about your questions.ġ. Thanks very much! RE: Modeling the "two-lake" problem with HEC-RAS? RWF7437 (Civil/Environmental) 3 Feb 09 19:05 I would be greatly appreciative if a more experienced hydraulic modeler could 1) advise me as to whether HEC-RAS is appropriate for a problem such as this, 2) if so, provide just a hint or two as to how to use the program in this manner, or 3) if not, recommend an alternate tool. Moreover, the program also seems geared towards problems with a definite channel-bed slope in the downstream direction (not the case here – the thalweg of the breach doesn't have an appreciable net slope towards either the lake or the river). I'm obviously more interested in computing discharge given water levels. it seems to require that discharge be specified, along with an upstream or downstream boundary condition, as input). However upon examining the HEC-RAS documentation, it seems as if the program is geared more towards computing water surface profiles given the discharge (i.e. However there's a twist that I think will preclude use of a straightforward solution: the "channel" is of irregular geometry (roughly hourglass shaped in plan view, with the inlet and outlet about as wide as the dam is thick – say 10 m at water level - and a narrow "throat" about 2 m wide).īeing essentially a lay person when it comes to hydraulic models, it occurred to me that I might construct a rating curve using a one-dimensional model like HEC-RAS: assuming for discussion that the breach geometry is stable, I could characterize it with a number of closely-spaced cross-sections, specify an arbitrary number of ordered pairs of fixed lake/river water levels as boundary conditions, and let the program compute steady flow for each instance. I understand this to be broadly similar to the "two-lake" problem described in texts on open-channel hydraulics. Specifically, I'd like to develop a rating curve relating flow into (or out of) the lake as a function of the difference in water levels between the lake and the river. I'm an environmental scientist, interested in characterizing flow through a newly-developed breach in an earthen dam separating a (former) stream-fed lake from a tidal freshwater river.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |