HEC RAS W/ LATERAL FLOWS
HEC RAS W/ LATERAL FLOWS
(OP)
I've posted this on the Boss hec ras forum as well but have had no responses.
I'll try to keep this short. Initially we have modeled (steady state) what appears to be an inadequate culvert system on a blue line stream. It is at an older goverment facility. Culverts procede downstream with two 36", two 30", two 30", and two 36" RCPs among others above and below.
The initial model worked out okay and showed flooding on most storm events at most all culverts from top to bottom. It was a simple model assuming all flooding went over the road deck and back into the stream. The bad part is that over 30 years of observation shoots holes in our model.
An expert reviewed our model and input and saw no issues. Stream monitoring devices and rain gauges are set to be placed to aid in future model adjustment. However, the expert has suggested we look at lateral flows into a nearby parallel street to see if this would reduce flooding at the road decks. We have three such situations occuring with two 30", two 30", and two 36" RCPs. We have sectioned off approximate lateral weir dimensions and developed a rating curve for each. This was used as output from the system for these three occurences slightly upstream of the road decks. We also played with road deck min/max WSE settings to prevent runoff across them.
I finally have everything adjusted so that the program will run and pass all storm events lateral flow optimizations. The first culvert looks good upstream and has a WSE close to what was calculated in the original model. The area downstream of this culvert hits the channel and goes crazy. 1 and 2 year events look reasonable (previously the only flows not crossing the road deck). Then every higher storm event's flow and WSE gets progressively lower. My input in the flow table gets higher but the program begins to ignore the table and ramps down the flow of the 25, 50, 100, and 500 year events to values of less than 1 cfs. The remainder of the model is a mess after this.
Ever heard of the program ignoring the flow table? Any suggestions ou there?
I'll try to keep this short. Initially we have modeled (steady state) what appears to be an inadequate culvert system on a blue line stream. It is at an older goverment facility. Culverts procede downstream with two 36", two 30", two 30", and two 36" RCPs among others above and below.
The initial model worked out okay and showed flooding on most storm events at most all culverts from top to bottom. It was a simple model assuming all flooding went over the road deck and back into the stream. The bad part is that over 30 years of observation shoots holes in our model.
An expert reviewed our model and input and saw no issues. Stream monitoring devices and rain gauges are set to be placed to aid in future model adjustment. However, the expert has suggested we look at lateral flows into a nearby parallel street to see if this would reduce flooding at the road decks. We have three such situations occuring with two 30", two 30", and two 36" RCPs. We have sectioned off approximate lateral weir dimensions and developed a rating curve for each. This was used as output from the system for these three occurences slightly upstream of the road decks. We also played with road deck min/max WSE settings to prevent runoff across them.
I finally have everything adjusted so that the program will run and pass all storm events lateral flow optimizations. The first culvert looks good upstream and has a WSE close to what was calculated in the original model. The area downstream of this culvert hits the channel and goes crazy. 1 and 2 year events look reasonable (previously the only flows not crossing the road deck). Then every higher storm event's flow and WSE gets progressively lower. My input in the flow table gets higher but the program begins to ignore the table and ramps down the flow of the 25, 50, 100, and 500 year events to values of less than 1 cfs. The remainder of the model is a mess after this.
Ever heard of the program ignoring the flow table? Any suggestions ou there?





RE: HEC RAS W/ LATERAL FLOWS
Sounds like the model ran fine without lateral structures. I would begin with their input data. Try to balance your flows inorder to account for the discharge and where it leaves the main channel.
Also, try running a single larger storm event, say 100-year, to get the bugs worked out of the model.
Hope this helps!
RE: HEC RAS W/ LATERAL FLOWS
RE: HEC RAS W/ LATERAL FLOWS
Are you changing flow rates at any xsec? or is it uniform through the entire reach?
Also you can round your flow rates to the nearest cfs. It wont make any impact.
RE: HEC RAS W/ LATERAL FLOWS
My flow values change at numerous xsecs due to additional inflow as well as upstream flow changes due to lateral structures. But generally only one flow change input between culvets.
Another employ here suggested that maybe the s/w didn't agree to well with the majority of the channel flow being diverted through the lateral structure and the big loss of energy gradient in the main channel?
Anyway I've put that particular scenario aside for the moment and I am looking at modeling the same system with multiple reaches. Where previously I had a lateral structure I will continue a reach with a road deck and no culvert at the end to model the flow into the side street. Then I will add a lateral culvert from this reach to a downstream reach to simulate the culverts in the main channel. Hopefully this will work better.
Yeah, I've got a bad habit with decimals.
RE: HEC RAS W/ LATERAL FLOWS
RE: HEC RAS W/ LATERAL FLOWS