04-Variance Request
ENGINEERING | DESIGN | TECHNOLOGY
5410 Trinity Road
Suite 102
Raleigh, NC 27607
P 919.866.4951
F 919.859.5663
www.timmons.com
6/12/2024
Variance Request- Castle Hayne Fire Station
Per Section 7.12 of the New Hanover County Stormwater Ordinance, a design variance can be
requested. The Castle Hayne 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 (including a septic system, well, fire storage tank, existing outlet ditch on the
southern boundary of the property), the dry detention basin has been maximized as much as possible
providing 16,797 cubic feet of volume storage. The bottom elevation of the pond is 18.0 and the top
of dam is 22.0. 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 and the ditch on the southern
property boundary, the freeboard requirements are not able to be met. The top of dam is at 22.0 and
the emergency spillway is at 21.0. The 25-year elevation is 20.72 and the 100-year elevation is at
21.12. The culvert under the drive access at Parmale does not require a 15” pipe for capacity based
on the culvert calculations in the SIA. We are unable to provide proper cover at this culvert and are
proposing a 10” pipe. 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