proletariat
Civil/Environmental
I have PreDev Drainage Area 1 (DA1) that goes to Study Point 1 (SP1). It has an onsite component and an offsite component. I have to reduce the peak 5yr post runoff rate to the pre 2yr rate, but only for runoff generated from the project property. (Basically I'm not responsible for reducing runoff from the neighbor's property. It is flow-through.)
How do I model this in HydroCAD? I want to stay true to the TR55/SCS method.
Here are the two options I have come up with:
1.
Make separate drainage areas (subcatchments) with the same Tc. The logic behind this is to essentially treat the offsite and onsite areas as one, except that I want to quantify the offsite contribution. Think of it as taking an extra step to do the CN weighting. The two subcatchments would go directly to Study Point 1, a Reach in hydrocad.
2.
Make separate drainage areas with unique Tc times. The offsite area Tc path would end at the upper property line and then I would Tt the offsite flow down to Study Point 1, maybe using a Reach. The ONLY problem I see with this is that Tt times are usually used when a subarea dumps into a linear drainage feature like a pipe or swale. In my case, the offsite area sheet flows onto my property, and then concentrates into concentrated flow all the way to the study point.
Opinions?
How do I model this in HydroCAD? I want to stay true to the TR55/SCS method.
Here are the two options I have come up with:
1.
Make separate drainage areas (subcatchments) with the same Tc. The logic behind this is to essentially treat the offsite and onsite areas as one, except that I want to quantify the offsite contribution. Think of it as taking an extra step to do the CN weighting. The two subcatchments would go directly to Study Point 1, a Reach in hydrocad.
2.
Make separate drainage areas with unique Tc times. The offsite area Tc path would end at the upper property line and then I would Tt the offsite flow down to Study Point 1, maybe using a Reach. The ONLY problem I see with this is that Tt times are usually used when a subarea dumps into a linear drainage feature like a pipe or swale. In my case, the offsite area sheet flows onto my property, and then concentrates into concentrated flow all the way to the study point.
Opinions?