Why Does Flooding Occur?
Natural areas typically allow 90% or more of runoff to infiltrate into the ground. The roads, parking lots and roofs associated with development prevent infiltration. In a highly developed area, typically only about 50% of runoff infiltrates.
- Obstacles clogging the stormwater system or the downstream drainageways.
- High groundwater tables that cause ponding in low areas.
Who Should I Contact for Help with Flooding Issues?
- For flooding on your property, contact your local government. Questions your local government will likely ask you include:
- Does flooding occur during abnormally heavy rains or almost every time it rains?
- Has something upstream of your property changed the drainage or runoff pattern?
- Have you maintained the stormwater system on your property?
- For flooding on state-owned streets and rights-of-way, contact the N.C. Department of Transportation State Road Maintenance Division at (919) 733-2191. NCDOT's State Road Map Viewer indicates the locations of state-owned roads. If you are unsure whether a public street is state-owned, your local government can assist you.
- For flooding adjacent to streams and other waters, contact your Regional Floodplain Manager. You can find out if you live in a floodplain at the Federal Emergency Management Agency's web site Knowing Your Flood Risk. If your property is within a floodplain, this was disclosed when you purchased the property.
DEQ's Role in Stormwater Management
- DEQ has statutory authority to manage the state’s water resources to maintain, protect and enhance water quality [N.C.G.S. Article 21, Chapter 143].
- DEQ does not have statutory authority to regulate or remedy flooding issues.
Overview of DEQ's Post-Construction Program
- Low density projects must limit the amount and concentration of development to reduce pollution and to allow stormwater to naturally pond and infiltrate into the soil.
- High density projects must collect stormwater runoff and use engineered stormwater control measures (SCMs) such as infiltration systems, wet ponds, wetlands, bioretention cells, etc. to remove pollutants before the runoff leaves the site.
The requirements for low and high density projects are designed specifically for water quality. SCMs in high density development often capture and treat the “first flush” of runof from smaller storm events, often the 1" or 1.5" storm. These smaller storms carry most of the pollutants, thus the name "first flush." SCMs often bypass runoff from larger storms to maintain treatment capacity, although SCMs can be designed to achieve both state water quality and local government flooding requirements at the same time.
Post-construction stormwater permits are issued by either DEQ or a local government entity. If you have a water quality complaint involving a development project, you can determine the appropriate permitting authority to contact by using the Post-Construction Stormwater Map.
How to Minimize Flooding
- Avoid building alongside water bodies, in the flood plain, and in other flood-prone areas where structural damage is likely to occur.
- Maintain any privately owned stormwater collection system components on your property to keep them free-flowing.
- Immediately report publicly owned stormwater collection system issues to your local government.
- Collect litter, yard waste, debris, grass clippings and leaves so they do not enter and obstruct the stormwater collection system or local streams.
- Disconnect roof drains from paved areas.
- Install rain gardens to infiltrate runoff into the soil.
- Install water loving wetland plants in high water table areas.
- Install rain barrels to capture and use runoff.