Changes in Flood Characteristics after a Major Event: Re-evaluating the Effect of Hurricane Floyd on Future Flood Response

Abstract

Hurricane Floyd had immediate impacts on the relatively slow-changing environment and undeveloped, unregulated watershed. The total flood water was 95% of the volume of Pamlico Sound, and many locations exceeded the record for rainfall in a 24-hour period. North Carolina flood mapping and hydrology projects were started after Floyd. The high water mark signs in the community reflect the social and policy legacy of the storm. When looking at long-term effects, the researchers did not see many changes in flow or channel characteristics based on stage–discharge relations and USGS rate curves. Data from three gauges were examined based on the NWS flood modeling program. At Rocky Mount, upstream of the Tar reservoir, flow is regulated. The inundation model is highly correlated with a well established relationship between stage and discharge. The timeline of Floyd follows the model very well; however, a moderate flood causes a different relationship between stage and discharge. The Tar River at Tarboro, using the same rating curve, showed change after Floyd. In Greenville, a partial duration series showed that, during extreme floods, the relationships are about the same, but there were changes at minor to moderate flood stage. Minor to moderate flood inundation maps might be different than the typical inundation maps currently used.