Trackfiend
Civil/Environmental
- Jan 10, 2008
- 128
In sizing pumps, I understand that it is an iterative process between choosing an outflow rate and what the available storage is in the drainage system and sump. My question is, what is the proper method to determine the inflow rate and volume of runoff getting to that sump? I realize that the rational method is meant to produce a peak runoff rate and the NCRS (formerly SCS) method is meant to produce a volume of runoff, so I would assume that the NCRS method controls in this case. However, in digging through certain county and state stormwater guidelines (particularly Texas DOT), I see that the rational method seems to be approved to size pumps. Is this an acceptable method? I've read several of the past threads on avoiding the use of the rational method for volume calculations so I may be answering my own question.
Another question is what duration to use (if using the NCRS method), 3hr, 6hr, or 24hr? Obviously the 24hr will produce more volume than the shorter events. Would judgement as to the type of storms and their durations in that particular region (gulf coast) give any hint as to what duration to use?
What I've done to help expedite some of the work is compile hydrograph information into an excel spreadsheet and then copy/paste this information into SWMM 5.0, connect a sump (with a ponded area equal to the drainage basin), a pump with certain controls, and an outflow. Varying the pump on/off levels gives me a good feel for how much volume is being stored at any given time. My concern is in choosing the right hydrologic method to determine the proper runoff volume. Since garbage in = garbage out, I want to make sure that I am not improperly using a method that will give improbable results. Any comments are welcome.
Another question is what duration to use (if using the NCRS method), 3hr, 6hr, or 24hr? Obviously the 24hr will produce more volume than the shorter events. Would judgement as to the type of storms and their durations in that particular region (gulf coast) give any hint as to what duration to use?
What I've done to help expedite some of the work is compile hydrograph information into an excel spreadsheet and then copy/paste this information into SWMM 5.0, connect a sump (with a ponded area equal to the drainage basin), a pump with certain controls, and an outflow. Varying the pump on/off levels gives me a good feel for how much volume is being stored at any given time. My concern is in choosing the right hydrologic method to determine the proper runoff volume. Since garbage in = garbage out, I want to make sure that I am not improperly using a method that will give improbable results. Any comments are welcome.