Stormwater Supplemental Resources

Hydrologic Models

• Small Watershed Hydrology (WinTR-55) - Software Download for TR55
• Rational Method - Stormwater Calcuations document

Nitrogen Loading: SNAP Tool

The Stormwater Nitrogen and Phosphorous (SNAP) tool was created by the North Carolina Department of Environmental Quality Division of Water Resources (DWR).

SNAP (Stormwater Nitrogen and Phosphorus) v4.2.0 is DWR’s updated spreadsheet tool used to estimate nitrogen and phosphorus in stormwater runoff from development sites and nutrient reductions provided by stormwater treatment.

In the future, Johnston County will require a completed SNAP tool to determine nitrogen loading for all new development applications. If you have questions about using SNAP you can send your questions directly to Trish D’Arconte trish.darconte@ncdenr.gov.

Culvert Design

NCDOT’s Guidance in the methods, procedures, policies, and criteria for Drainage Studies and Hydraulic Design is a good resource for culvert design.  Information can also be found from the US Army Corps of Engineers.

US Army Corps of Engineers (COE)

69 Darlington Ave
Wilmington, NC 28403
910-251-4626
sawweb-pao@usace.army.mil