Stream-restoration projects utilizing natural stream designs frequently are based on the bankfull-channel characteristics of stream reaches that can accommodate streamflow and sediment transport without excessive erosion or deposition and lie within a watershed that has similar runoff characteristics. The bankfull channel at an ungaged impaired site or reference reach is identified by use of field indicators and is confirmed with tools such as regional curves. Channel dimensions were surveyed at 14 streamflow-measurement stations operated by the U.S. Geological Survey (USGS) in the Gettysburg-Newark Lowland Section, Piedmont Lowland Section, and the Piedmont Upland Section of the Piedmont Physiographic Province in Pennsylvania and Maryland. From the surveyed channel dimensions, regional curves were developed from regression analyses of the relations between drainage area and the cross-sectional area, mean depth, width, and streamflow of the bankfull channel at these sites.
Bankfull cross-sectional area and bankfull discharge have the strongest relation to drainage area as evidenced by R2 values of 0.94 and 0.93, respectively. The relation between bankfull crosssectional area and drainage area has a p-value of less than 0.001; no p-value is presented for the relation between bankfull discharge and drainage area because of a non-normal residual distribution. The relation between bankfull width and drainage area has an R2 value of 0.80 and a p-value of less than 0.001 indicating a moderate linear relation between all stations. The relation between bankfull mean depth and drainage area, with an R2 value of 0.72 and a p-value of less than 0.001, also indicates a moderate linear relation between all stations.
The concept of regional curves can be a valuable tool to support efforts in stream restoration. Practitioners of stream restoration need to recognize it as such and realize the limitations. The small number of USGS streamflow-measurement stations available for analysis is a major limiting factor in the strength of the results of this investigation, as is the inherent problem of directly associating streamflow-measurement station data to geomorphic analysis of a stream reach. Subjective selection criteria may have unnecessarily eliminated streamflow-measurement stations that could have been included in the regional curves and (or) added those that may belong within a different region. A bankfull discharge with a recurrence interval within the 1- to 2-year range commonly is used as a criterion for the confirmation of the bankfull stage at each streamflow-measurement station. Many researchers accept this range for recurrence interval of the bankfull discharge; however, literature provides contradictory evidence.