163 Belvedere St-RES21-0345 Drainage Calculations Report REVISION 4-4-23163 Belvedere Street
DRAINAGE CALCULATIONS
For:
City of Atlantic Beach
Prepared by:
Certificate of Authorization: EB9951
12574 Flagler Center Boulevard, Suite 202
Jacksonville, FL 32258
Project No. S141206.01
Submittal Date:
March 2023
Rebecca K. Hiers-Bray, PE
FL Reg. No. 69829
City of Atlantic Beach: 163 Belvedere St Calculations
INDEX
SECTION
1
Project Narrative
2 Delta Volume Calculations
APPENDIX
A Miscellaneous Reference
β’ Report of Preliminary Geotechnical Exploration by Meskel & Associates
Engineering, dated January 5, 2023
City of Atlantic Beach: 163 Belvedere St Calculations
PROJECT NARRATIVE
PROJECT LOCATION AND DESCRIPTION
The proposed project 163 Belvedere Street is located southeast of the intersection of David Street and Belvedere
Street. The proposed drainage plan includes a house and 2 retention ponds with a 1-foot depth.
POST-DEVELOPMENT STORMWATER CALCULATIONS
Based on the impervious area of the lot, a required 1,494 ππ‘3 is to be held by the ponds. To ensure that the
supplied treatment volume meets the required treatment volume, the inground storage and the total pond
storage were calculated. Refer to the Delta Volume Calculations.
The depth to ESHWT from the Bottom was calculated using the Piezometer and Groundwater level measurements
provided in the Geotechnical Report, which was determined to be 3.28 feet. Refer to the Geotechnical Report
attached.
1
Permit No:
Address: 163 Belvedere Street
Required Storage Volume
Criteria:
Section 24-66 of the City of Atlantic Beachβs Zoning, Subdivision, and Land Development
Regulations requires that stormwater runoff from impervious areas be stored onsite. Volume to
be retained is as follows:
π½=πͺπ¨πΉ/ππ which is the Modified Rational Method of 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-yr rainfall depth (9.3 inches for Atlantic Beach)
Onsite Storage Volume Required for Impervious Area:
Lot Area = 10,000 ππ‘2
Proposed Impervious Area = 2,096 ππ‘2 = 21.0%
V = 0.92 x 2,096 x 9.3 / 12
V = 1494 ππ‘3 Required
Provided Storage:
Area 1 β
Relative
Elev. (ππ‘)
Area
(ππ‘2)
Storage
(ππ‘3)
7.6 134
297
BOT
8.6 450 TOB
Sideslope: 4:1 Around
Area 2 β
Relative
Elev. (ππ‘)
Area
(ππ‘2)
Storage
(ππ‘3)
7.8 63
195
BOT
8.8 326 TOB
Sideslope: 4:1 Around
2
Inground Storage = A*d*pf
Total Storage Area at TOB (A) = 776.0 ππ‘2
Depth to ESHWT from BOTTOM (d) = 3.28 ππ‘, taken from ground water level of PIEZOMETER
Pore Factor (pf) = 0.4 default is 0.4
Inground Storage Provided = 1018.1 ππ‘3
Total Pond Storage = 492.0 ππ‘3
Required Treatment Volume = 1494 ππ‘3
Supplied Treatment Volume = 1510 ππ‘3
City of Atlantic Beach: 163 Belvedere St Calculations
APPENDIX A-1
REPORT OF PRELIMINARY GEOTECHNICAL EXPLORATION