STORMWATER MANAGEMENT POND DESIGN:

A. Drainage areas limitations must be considered.

* If DA is between 10-15 Ac, a water balance analysis per Appendix 5C-1 in the Virginia SWM Handbook must be performed to prove “permanent” pool is viable.

** If DA is below 10 Ac, a water balance analysis per Appendix 5C-1 in the Virginia SWM Handbook must be performed to verify that site hydrology supports the high and low marsh areas and to establish locations where drought-tolerant wetland species are necessary.

 B. Location of pond design information in plans.

 Text Box: Include all pond calculations, schematics, profiles, planting schedules, etc. in the same general area within a set of plans.  Spreading this information out arbitrarily in the plans leads to overlooked information, unnecessary review comments, and subsequently, longer review times.

C. Provide design calculations and back-up material.

Text Box: Stage-Storage and Stage-Discharge curves/values, inflow and outflow hydrographs (including Tc derivation), emergency spillway calculations, and all pertinent design information per Sections in Chapter 5 of the Virginia SWM Handbook must be provided for every pond design.

D. Profile View of Pond

Text Box: Provide a profile view of the facility depicting water surface elevations for the water quality volume and the 1-, 2-, 10-, and 100-year events.

E. Include a Sediment Forebay and Pertinent Information.

Text Box: •	Provide a profile or elevation view of the forebay with a non-erodible overflow section that safely passes the 10-year storm.      •	Include the required volume for the forebay in the calculation of a wet pond or an enhanced extended detention facility volume.      •	Do not include the required forebay volume in the calculation of a dry pond volume.

F. Design Low flow Orifices for Dry Ponds so that Realistic Drawdown (± 30 hr.) of WQV is Achieved & Basin Size Minimized:

* Notably, if there is no emergency spillway, provide 2’ of freeboard between the 100-year WSE and the top of the pond embankment.

 

G. Protect low flow and other orifice/weir outlet structures with one of the following devices:

H. Enhance stormwater ponds with additional safety features when appropriate.

Text Box: Regardless of the pollutant removal requirements, add an aquatic bench to a wet pond when its surface area exceeds 20,000 sf to reduce the chance someone will slip into the deeper areas of the pond.      Also, based upon accessibility issues surrounding the particular pond, always consider the need for fencing and/or signage – this is particularly important with dry pond, since the water surface elevation can change from basically zero to several feet within a short time during an intense storm event.

BACK