Final Design Solutions

Multi-Inlet Riser

Rationale:

Installing a multi-inlet riser structure between Duck Pond and Silver Lake will help control flooding when the area is introduced to a 5-year storm. This structure will reduce the depth of the water in Duck Pond and Silver Lake. The riser structure will not have a significant impact on water quality, and subsequent additional solutions are necessary in order to reduce nutrient and sediment loading prior to discharge into the Elizabeth River.

Dimensions:

Bottom orifice – Circle 6 inches in diameter with an offset 2.5 feet above Duck Pond bottom.
V-Notch weir – 6 inches in width and 18 inches in height, with an offset 3.5 feet above Duck Pond bottom.
Riser crest – 18 inches in diameter, with an offset 5 feet above Duck Pond bottom.
Outlet pipe – 12 inches in diameter, with an offset 0 feet above Duck Pond bottom.

Top View

Discharge View

Side View

Vegetated Buffer Area

Rationale:

In order to mitigate TN, TP, and TSS within Silver Lake and Duck Pond, our design optimally entails an establishment of a 35 ft undisturbed, unmowed Bermuda and Zoysia turf grass buffer that would treat overland flow directly entering Silver Lake from residential areas. Implementation would reduce 8.2% of TN and TP entering the Elizabeth River and 10.9% of TSS.

Rain Barrel

Rain barrels' main goal is to reduce runoff, therefore limiting the transport of pollutants.

If 10% of homeowners installed a rain barrel, approximately 1000 gallons of water would be captured per rainstorm as runoff from 1/2 of each home's roof.

https://fcmponline.com/products/rc4000-rain-catcher-rain-barrel

Bioretention

Bioretention cells reduce runoff by collecting stormwater and removing nutrients using specific vegetation . If all homes installed bioretention cells, 4.32% of TN, 3.71% of TP, and 2.70% of TSS discharged into the Elizabeth River from Silver Lake would be removed.

https://www.3riverswetweather.org/green/green-solution-rain-garden

Floating Wetlands

Floating wetlands will reduce nutrients that are already in the pond and lake through uptake by the plants.

Removal rates are based on surface area coverage, and large-scale implementation of floating wetlands can become expensive.

13.6% coverage of Silver Lake and Duck Pond would remove 52.7% of TN and 54.5% of TP discharged to the Elizabeth River from Silver Lake.

http://www.floatingwetlandsolutions.com/

Optimally, a combination of practices entailing a vegetated buffer area, rain barrels, bioretention cells, and floating wetlands will yield the best results. However, the Poplar Hall homeowners' opinions in regards to the implementation of the solutions mentioned, in addition to the amount of available funding by private and city sources, will help dictate the scale of the installation of these solutions.

Cost Analysis:

Multi-inlet Riser Structure: $2,500
Trash Rack for Riser Structure: $500
Installation of Riser Structure: $1,500
35-ft Vegetated Buffer Strip and Installation: $312
Rain barrels: $125 per house (optional homeowner or other organization cost)
Bioretention: ~$800 per house (optional homeowner or other organization cost)
13.6% Coverage of Floating Wetlands: $60,060 (only feasible with additional funding)

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