TransCivil
Civil/Environmental
- Jun 8, 2006
- 3
I am new to drainage design and currently putting together a design for an urban road with curb & gutter, inlets, manholes, etc. and the storage is going to be infiltration trenches. I am able to get through the details of designing the storm drain pipe system, but I am having a hard time coming up with the volume for storage. The storm drain is designed for a 10-year frequency and the storage will be 100-year. When I read HEC-22 and other manuals, the storm drain system and the storage facilities are talked about completely separately (it never says "When you get a discharge calculated from your storm drain, do the following to determine the storage volume.") What is the proper connection between the two in hydrologic terms? Do I use the rational method to get all the inlets spaced, pipes sized, etc. and then develop a completely independent hydrograph for the same area just to calculate the total storage, ignoring the peak discharge from the storm drain system?
A friend that is a more experienced drainage engineer suggested that I take the peak discharge from the last pipe in the storm drain and the overall time of concentration produced by the software and apply those parameters to a triangular unit hydrograph. Time to peak = time of concentration, storm duration = 2.67*Tc, and calculate the area under the triangular hydrograph. Sounds pretty straightforward and makes sense, but how come none of the manuals outline a procedure like this?
A friend that is a more experienced drainage engineer suggested that I take the peak discharge from the last pipe in the storm drain and the overall time of concentration produced by the software and apply those parameters to a triangular unit hydrograph. Time to peak = time of concentration, storm duration = 2.67*Tc, and calculate the area under the triangular hydrograph. Sounds pretty straightforward and makes sense, but how come none of the manuals outline a procedure like this?