369 12th St RESA23-0001 Drainage Calcs REV 3-3-23_1Comp. By: D. Martin
Date: 2/16/2023
Public Works Department
City of Atlantic Beach
Permit No: RESA23-0001
Address: 369 12th
Required Storage Volume
Criteria:
Section 24-68 of the City of Atlantic Beach's Zoning, Subdivsion, and Land Development Regulations requires
that stormwater runoff from impervious areas be stored onsite. Volume to be retained is as follows:
V = CAR/12 which is the Modified Rational Method for estimating stormwater runoff
W here:
V = Volume of Runoff to be stored (cubic feet)
C = Runoff Coefficient, 0.92, the difference between impervious area (C=1.0)
and undeveloped conditions (C=0.08).
A = Impervious Area (square feet)
R= 25 -yr / 24 -hr rainfall depth (9.3 inches for Atlantic Beach)
Onsite Storage Volume Required for Impervious Area:
Lot Area =
Impervious Area (A) =
V=
Provided Storage:
24,018
667
0.92
ft2
ft2 = 2.8%
x 667.0 x 9.3 / 12
V = 476 ft3
Area 1 - Relative Elev. Area Storage Sideslope: 2 :1
(ft) (ft2) (ft3)
1.0 162 236 BOTTOM size: 27 X 6
2.0 310 TOB size: 31 X 10
Area 2 - Relative Elev. Area Storage
(ft) (ft2) (ft3)
00 BOTTOM size: 0 X 0
0 TOB size: 0 X 0
0.0
0.0
Area 3 - Relative Elev. Area Storage
(ft) (ft2) (ft3)
0.0 00 BOTTOM size: 0 X 0
0.0 0 TOB size: 0 X 0
Inground Storage: = A*d/pf
Total Storage Area at TOB (A) = 310.0 ft2
Depth to ESHWT from BOTTOM (d) = 2.0 ft, default is 2.0 ft, verify onsite ESHWT
Pore Factor (pf) = 0.4 default is 0.4
Inground Storage Provided = 248.0 ft3
Required Treatment Volume =
Supplied Treatment Volume =
476 ft3
484 ft3
Retention W.R. for sending 369 12th RESA23-0001 (3) 2/16/2023