Regional Hydraulic Geometry Characteristics of Stream Channels in the Ouachita Mountains of Arkansas

Many channel restoration projects are being undertaken throughout Arkansas on small streams with limited data on streamflow relations that would be useful for the design of these projects. Equations relating bankfull discharge and channel dimensions to the size of the drainage area at gaged stream reaches and their associated basin characteristics are needed to predict bankfull discharge and channel dimensions at ungaged stream sites, providing needed information for the design of channel restoration and other stream channel projects and studies. The U.S. Geological Survey and the Arkansas Natural Resources Commission in cooperation with the U.S. Army Corps of Engineers, Little Rock District, undertook a study to develop these equations for streams in Ouachita Mountains of Arkansas. Seventeen USGS stream gage locations, operated by the U.S. Geological Survey, distributed across the Ouachita Mountains of Arkansas were selected for analysis. Streambed-bed material sampling was conducted to obtain information on the particle-size distributions of the streambed materials and to determine the shapes of the individual particles comprising the streambeds. The stream reaches at each study site were classified to the Rosgen level II stream type based on the average of stream channel metrics collected from site cross-sections and profiles. Regional hydraulic geometry curves relating drainage area to bankfull dimensions: cross-sectional area, top width, mean depth, and discharge, were developed from the data collected at the 17 gaged stream site locations within the Ouachita Mountains of Arkansas. Regression equations derived from hydraulic geometry curves express the mathematical relation between the bankfull channel dimensions and the contributing drainage areas. Streambed-material collected were used to develop particle-size distribution plots and to calculate particle-size quantile values corresponding to 16, 50, and 84 percent finer, descriptive statistics of particle size distributions, and particle size distribution percentages of substrate type at each study site. Of the 17 selected stream reaches; 1 was classified as a B4 stream type, 4 as B4c/1 stream type, 1 as a C3 stream type, 4 as C4 stream type, and 3 as C4/1 stream type.