A jurisidiction requirement for water quality treatment is "0.5 in of post developed runoff from each storm". How would you go about determining flow rate from that to use to size a conveyance ditch? They also say to "provide a minimum water quality treatment rate of 0.05 inches per minute"...
For water quality treatment in roadside swales in highway design, the normal residence time in the swale is 9 minutes to get full treatment. You will have portions of the runoff from the highway that will hit the swale at the downstream reaches and will not meet the 9mins before discharging...
