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ENGINEERING | DESIGN | TECHNOLOGY
5410 Trinity Road
Suite 102
Raleigh, NC 27607
P 919.866.4951
F 919.859.5663
www.timmons.com
7/24/2024
Variance Request- Gordon Road Fire Station
Per Section 7.12 of the New Hanover County Stormwater Ordinance, a design variance can be
requested. The Gordon Road Fire Station site is a compact site, with multiple challenges to overcome
that prevent the design to fully meet the Stormwater Design Manual requirements. With the site and
design constraints the bioretention pond has been maximized as much as possible providing 38,274
cubic feet of volume storage. The bottom elevation of the pond is 43.0 and the top of dam is 46.5.
Per Section 5.3.2 of the stormwater manual, the post development 100-year 24-hr storm event needs
to have at least 1-foot of freeboard below the top of dam. Also, the 25-year 24-hr storm must not
rise higher than 0.5 feet below the emergency spillway crest. For the 25-year storm the post
development flow shall be less than the post development flows. All pipes and culverts shall be a
minimum of 15”.
As mentioned above, due to the site constraints of available space, the freeboard requirements are
not able to be met. The top of dam is at 46.5’ and the emergency spillway is at 45.5’. The 25-year
elevation is 45.27 and the 100-year elevation is at 46. Due to minimizing the flow rates leaving the
site, the outlet pipe is required to be less than the 15” requirement. Refer to the Stormwater
Compliance plan and the SIA narrative and calculations book for all data referring to stormwater
management. We ask for a variance to these requirements mentioned above of the Stormwater
Design Manual.
Will Altman, PE
Senior Project Manager