Flood Types

Flooding typically occurs in our area when large amounts of rain falls over a short period of time from a single, heavy storm, tropical system, or hurricane. After these storms, we rely on a man-made flood control system to drain excess water from the low, flat lands. Existing surface waters levels (i.e. ocean or sound), impact the ability of the connecting drainage systems to receive or store new rainfall. If the surface water conditions are elevated, this impacts the drainage system's ability to transport additional water. If the underground water table is high, water cannot soak into the already saturated ground. We have observed these conditions occurring simultaneously, which has led to rainfall in streets, swales, yards and low-lying areas.

A majority of the existing development in Nags Head is concentrated in the lower-lying areas close to sea level. This is different from inland areas where watersheds have a natural fall line that directs run-off into creeks, streams, and rivers, which then carry excess water downstream. In our area, run-off will collect and stand wherever the ground is saturated, where run-off cannot access natural or man-made drainages, or along impervious surfaces such as roadways and parking lots where absorption is restricted.

Hurricane Matthew October 2016

Emergency Floodwater Dewatering Plan

Under emergency flood conditions, when public health and safety are endangered, approval may be issued by the North Carolina Department of Environmental Quality (NCDEQ) to allow the direct pumping of floodwaters to the Atlantic Ocean or Roanoke Sound. A comprehensive emergency floodwater dewatering plan has been developed by the Town and filed with NCDEQ Division of Water Resources (DWR) in order to expedite emergency approval. The emergency plan outlines the criteria by which the plan may implemented as authorized by NCDEQ-DWR.

  1. Coastal Flooding
  2. Surface Water Flooding
  3. Ground Water Flooding

Coastal flooding is caused by high tides coinciding with hurricanes, tropical storms, nor’easters or other low-pressure storm systems which raise sea and tidal water levels, overwhelming coastal defenses. This may be made worse by gale force winds blowing the raised body of water onto the coast. Flooding may be in the form of overwash, where floodwaters erode and overtop coastal dunes or estuarine shorelines. Coastal flooding may affect not only property along oceanfront and estuarine shorelines, but also property inland from the coastline, due to floodwater being forced up connecting ditches, canals and outfalls by raised sea levels. Land areas that are at high risk for coastal flooding are defined by Special Flood Hazard Areas or flood zones.