LAR 512 – Fall 2002
PROBLEM #12 – SIZING WET DETENTION &
EXTENDED DETENTION WETLAND BASINS
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- Determine the size of permanent water quality
stormwater wet detention basin for 85% pollutant removal for a suburban
small piedmont watershed. Use the method at Section 1.4, page 6 of
Stormwater Best Management Practices manual at <http://h2o.enr.state.nc.us/su/PDF_Files/SW_Documents/BMP_Manual.PDF>.
The watershed consists of 235-acres and after development should have
approximately 27.5-percent impervious surfaces. The detention pond should have a permanent pool depth of
9-feet. Determine the surface area
__________ acres, and volume of
the detention basin __________acre-feet.
- Determine
the size of the permanent water quality stormwater extended detention
wetlands basin for the same small piedmont watershed. Use the method at Section 2.6, page 17
of the manual. The wetlands basin
should have a maximum depth of 3-feet.
The basin marsh area (70%) should consist of 0 to 9-inch pool depth
(35%) and 9 to 18-inch pool depth (35%); the remaining 30% should have a
depth of 18 to 36-inches. Using
the volume calculated in question 1, calculate a new surface area making
sure to meet the 35, 35, and 30-percent for the respective pool
depths. The total pool area covers
__________ acres, the 0 to 9-inch depth area covers __________ acres, the
9 to 18-inch depth area covers __________ acres, and the 18 to 36-inch
depth area covers __________ acres.