Bankfull Hydraulic Geometry Relationships and Recurrence Intervals for North Carolinas Coastal Plain

Bankfull hydraulic geometry relationships relate stream channel geometry to watershed size for specific physiographic regions. This paper presents bankfull hydraulic geometry relationships and recurrence intervals for the Southeastern Plain ecoregion and the flatwoods subtype of the Middle Atlantic Coastal Plain ecoregion found within North Carolinaʹs Coastal Plain physiographic province. Cross-sectional and longitudinal survey data from gaged and ungaged streams were used to compute channel dimension and profile information. Power functions were developed, relating drainage area to bankfull discharge, cross-sectional area, width, and mean depth. Recurrence intervals of bankfull events were estimated from gaged streams using both a LogPearson Type III distribution of peak annual discharge and a partialduration series of average daily discharge. Results from both methods indicate that average bankfull recurrence intervals for the study area are below one year. Determinations of recurrence intervals by the Log-Pearson Type III distribution were for the most part inconclusive (less than one year), while a partial duration series estimated a 0.19 year average, ranging from 0.11 to 0.31 years.