49 Dudley Street_rev 9-14-20 RES20-0172 renarrative-calcs 2 of 5_1
2650 ROSSELLE STREET, Suite 2A Jacksonville FL 32204 Ph: 904-551-4945
Civil Design and Construction Management Professionals
September 8, 2020
Atlantic Beach Site Drainage Improvements
In-Fill Lots
Lot Address: 49 Dudley Street
Atlantic Beach, FL
NARRATIVE:
The attached calculations are provided to support the lot drainage design at 49 Dudley Street
in the City of Atlantic Beach, FL. The calculations were performed utilizing the equations in the
city ordinance sec 24-66(b).
The referenced project site was vacant and the calculations utilized this as the predevelopment
condition. The total lot area shown in the pre and post calculations was calculated from the
table in the survey.
The proposed project will construct a home, driveway, and stormwater storage facility.
The runoff coefficient was provided based on the impervious values and associated
coefficients of sec 24-66(b) of the code.
Comp. By:
Date:
Public Works Department
City of Atlantic Beach
Permit No:_____________________________
Address:49 Dudley Street
Required Storage Volume
Criteria:
Section 24-66 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
Where: 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 = 9,421 ft2
Impervious Area (A) = 1,889 ft2 =20.1%
V = 0.92 x 1,889.0 x 9.3 / 12
V = 1,347 ft3
Provided Storage:
Area 1 - Relative Elev.Area Storage Sideslope:4 :1
(ft)(ft2) (ft
3)
8.0 422 BOTTOM size:23.5 X 12
9.0 981 TOB size:31.5 X 20
Area 2 - Relative Elev.Area Storage
(ft)(ft2) (ft
3)
0.0 0 BOTTOM size:0 X 0
0.0 0 TOB size:0 X 0
Area 3 - Relative Elev.Area Storage
(ft)(ft2) (ft
3)
0.0 0 BOTTOM size:0 X 0
0.0 0 TOB size:0 X 0
Inground Storage: = A*d/pf
Total Storage Area at TOB (A) =981.0 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 =784.8 ft3
Required Treatment Volume =1,347 ft3
Supplied Treatment Volume =1,486 ft3
Reynold D. Peterson, P.E.
702
0
0
9/8/2020
Retention COAB_STORAGE CALCS_49 DUDLEY Street 9/8/2020