Flood Routing Question
Flood Routing Question
(OP)
I'm modeling an 11 sq. mile watershed using WinTR-20 for the first time. The drainage area at an existing dam is 6 sq.mile. Approx. 1,500 feet downsream of the dam there is highway crossing A (D.A.=7 sq. miles). Approx. 6,000 feet from highway crossing A there is another crossing, let's call it B (D.A.= 8 sq. miles).
Increasing the storage area at the dam's reservoir, during a 100-year storm event a reduction of approx. 500 cfs of the peak discharge is achieved just downstream of the dam. The model's output shows that the 500 cfs reduction is carried over to crossing A but not to crossing B. At crossing B the peak discharge is approximately the same as in the existing condition (old, smaller reservoir). The schematic developed by the software looks just fine to me. I do not understand why the 500 cfs are not carried over further downstream on the watercourse.
Can anybody help? Where is the problem?
Increasing the storage area at the dam's reservoir, during a 100-year storm event a reduction of approx. 500 cfs of the peak discharge is achieved just downstream of the dam. The model's output shows that the 500 cfs reduction is carried over to crossing A but not to crossing B. At crossing B the peak discharge is approximately the same as in the existing condition (old, smaller reservoir). The schematic developed by the software looks just fine to me. I do not understand why the 500 cfs are not carried over further downstream on the watercourse.
Can anybody help? Where is the problem?





RE: Flood Routing Question
CODE
+ 1 sq mi hydrograph
= combined hydrograph --> routed through highway crossing --> routed through 6,000 ft channel
+ 1 sq mi hydrograph
= combined hydrograph 2 --> routed through highway crossing B
RE: Flood Routing Question
Yes, I'm modeling as you are suggesting and the schematic shows it. It's my understanding that "is quite typical for the peak flow reduction of a dam to be lost more and more as you look further downstream" of a watercourse but in my case there is only 1 sq. mile of additional drainage area...
RE: Flood Routing Question
You would have to look at your time of concentration of your 3 sq mi area and the time of concentration of the dam's 6 acres plus time taken to convey that peak to your area of interest. It could be that the peak of the dam flow arrives after your immediate watershed has peaked and reduced to such a level as the attenuated dam peak flow is lower.
I would expect this if your immediate 3 sq mi is an urban area and your dam catchment is rural. It would take longer for your 6 sq mi to peak, plus travel, than for your immediate 3 sq mi to peak and leave. In an urban environment, your 3 sq mi peak would be large with a shorter time of concentration due to the impervious, smooth surfaces of flow, whereas the dam catchment, being rural, would have significant losses (infiltration, depression storage, evaporation) and would travel more slowly over the vegetated terrain.
RE: Flood Routing Question
RE: Flood Routing Question