I have been told that the time of concentration can be lengthened by 5-15 min. when storm water is routed through a catch basin. I have not been able to find any technical data discussing this and was wondering if anyone has information on this subject.
Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Time of Concentration 1
- Thread starter mwrufener
- Start date
-
1
- #2
Sniff - Sniff...smells like fertilizer. The incoming water has to reach a point where the catch basin will discharge (if there is any storage). Depending on the rate of inlow, this could be a couple of seconds to a couple of minutes. Once the flow is going out, your Tc through the basin is essentially zero.
Crystalct1
Civil/Environmental
Do you mean catch basin or detention/retention basin? Detention basins can increase times of concentration for hours.
BelspringKen
Civil/Environmental
Crystal has a point - catch basin is usually an inlet.
The detention/retention basin or pond will hold water, and could make an impact.
Your pipe flow time may be used in the Tc, but it won't be very much time.
The detention/retention basin or pond will hold water, and could make an impact.
Your pipe flow time may be used in the Tc, but it won't be very much time.
- Thread starter
- #6
Thanks for the input. I was in a teleconference on detention basin design and the presentor specifically stated that 5-15 min. inlet concentration times could be added to the time of concentration. I had not ever heard that before and it seems like is it not a reasonable assumption.
The overland travel time (time to reach the inlet) for a one acre parking lot will be about 100 ft/2fps = 50 seconds. For this reason computer models that require a minimum Tc of 5 minutes are inherently invalid.
The Rational Method was never intended to be used with Tc --this misconception was invented in 1890.
The Rational Method uses the IDF correlations that estimate the ability of a raincloud to generate rainfall. This ability is determined by rain gage data.
The minimum duration for IDF correlations is 5-minutes. This duration can be used as long as the pipe network travel time is less than 5 minutes. For example, a 1000-ft long storm sewer flowing at 3.3 fps has a travel time of 5 minutes.
Rational Method Runoff coefficients can be reduced to allow for ponding and/or the longer travel time for heavily vegetated areas.
The Rational Method was never intended to be used with Tc --this misconception was invented in 1890.
The Rational Method uses the IDF correlations that estimate the ability of a raincloud to generate rainfall. This ability is determined by rain gage data.
The minimum duration for IDF correlations is 5-minutes. This duration can be used as long as the pipe network travel time is less than 5 minutes. For example, a 1000-ft long storm sewer flowing at 3.3 fps has a travel time of 5 minutes.
Rational Method Runoff coefficients can be reduced to allow for ponding and/or the longer travel time for heavily vegetated areas.
- Status
Similar threads
- Locked
- Question
- Locked
- Question
- Locked
- Question