Retention Basin
Retention Basin
(OP)
I need help to design a retention basing for an area 212,920 sq ft (4.89 acres)with a building of 24,000 sq ft located in the center of the lot. the coeeficient of runoff is 0.95 and i'm using a intensity of 2.85 I can use the Rational Method or other metohd for my volume calculations? Thanks in Avanced.





RE: Retention Basin
Where in the world is this site ?
Who will review your design ?
What are their design criteria ?
Is this to be retention or detention ?
Where did the C= 0.95 and intensity numbers come from ? Both seem very high.
Provide more information please and maybe someone can help you.
Good luck
RE: Retention Basin
The I of 2.85 sounds awful low. Here in Dallas, TX the intensity of 100 yr at 15 min. TOC = 7.56. Typically the C for paved/roof = 0.9
RE: Retention Basin
If this is a "detention" basin, you will need to generate an inflow hydrograph. This is not usually done with rational method.
If a "retention" basin, you need to calculate the total storm rainfall depth and store the entire thing (less losses).
PECPESC is correct, 2.85 inches sounds low. Here in the Sonorran Desert (Phoenix, Arizona) we would use 100-year, 2-hour rainfall of 2.8 inches and 100-year, 24-hour rainfall of 3.8 inches.
RE: Retention Basin
Use intensity if you are using the Rational Method and decrease amount for longer Tc. Here in southeastern PA, intensity ranges from 4.2 in/hr for 2yr to 8.2 in/hr for 100yr storms, at 5 minutes Tc.
If you go with SCS methods (TR20 of TR55), use 24hr rainfall amount, not intensity. Here, it ranges from 2.5 inches for 2yr to 7 inches for 100yr event. This amount will adjust itself by using the program algorithms; don't decrease them yourself.