Regional Relations in Bankfull Channel Characteristics determined from flow measurements at selected stream-gaging stations in West Virginia, 1911-2002

Abstract

Three bankfull channel characteristics—cross-sectional area, width, and depth—were significantly correlated with drainage area in regression equations developed for two regions in West Virginia. Channel characteristics were determined from analysis of flow measurements made at 74 U.S. Geological Survey stream-gaging stations at flows between 0.5 and 5.0 times bankfull flow between 1911 and 2002. Graphical and regression analysis were used to delineate an “Eastern Region” and a “Western Region,” which were separated by the boundary between the Appalachian Plateaus and Valley and Ridge Physiographic Provinces. Streams that drained parts of both provinces had channel characteristics typical of the Eastern Region, and were grouped with it. Standard error for the six regression equations, three for each region, ranged between 8.7 and 16 percent. Cross-sectional area and depth were greater relative to drainage area for the Western Region than they were for the Eastern Region. Regression equations were defined for streams draining between 46.5 and 1,619 square miles for the Eastern Region, and between 2.78 and 1,354 square miles for the Western Region. Stream-gaging stations with two or more cross sections where flow had been measured at flows between 0.5 and 5.0 times the 1.5-year flow showed poor replication of channel characteristics compared to the 95-percent confidence intervals of the regression, suggesting that within-reach variability for the stream-gaging stations may be substantial. A disproportionate number of the selected stream-gaging stations were on large (drainage area greater than 100 square miles) streams in the central highlands of West Virginia, and only one stream-gaging station that met data-quality criteria was available to represent the region within about 50 miles of the Ohio River north of Parkersburg, West Virginia. Many of the cross sections were at bridges, which can change channel shape. Although the data discussed in this report may not be representative of channel characteristics on many or most streams, the regional equations in this report provide useful information for field identification of bankfull indicators. Introduction Programs and policies developed following passage of the Federal Clean Water Act in 1972 have successfully reduced stream pollution from industrial and other point sources, yet some of the broad goals in the Clean Water Act have not been achieved (U.S. Environmental Protection Agency, 2000). For instance, the Clean Water Act specifies support of aquatic life and protection of biological integrity as primary uses of waters of the United States. In streams of the Mid-Atlantic Highlands (a region including West Virginia and parts of Pennsylvania, Maryland, and Virginia) during 1993 and 1994, over 31 percent of stream miles were in poor condition as measured with a fish Index of Biotic Integrity, and 27 percent of stream miles were in poor condition as measured with aquatic insect indicators. Physical habitat degradation is seen as one of the most common reasons that streams fail to adequately support aquatic life. In the Mid-Atlantic Highlands in 1993 and 1994, 24 percent of the total stream length had poor riparian habitat, and 25 percent of the regional stream length had excess sedimentation (U.S. Environmental Protection Agency, 2000). In addition to improving land-use and water-management practices in a watershed, stream-channel restoration is considered an important part of the strategy to restore many streams with degraded habitat to a condition that fully supports aquatic life. Stream-channel restoration is the practice of applying knowledge and principals of geomorphology in rebuilding damaged stream channels so that they transport sediment and remain stable. A crucial aspect of stream restoration is to design a stable size and shape for the stream, so that its channel will maintain its dimension, pattern, and profile over time without degrading or aggrading (Rosgen, 1996). The 1.5-year recurrence flow has been identified as bankfull flow in most streams (Leopold, 1994). Bankfull flow is of geomorphic significance because it moves the greatest amount of sediment in the stream channel over time; consequently, it is sometimes referred to as the “effective discharge” (Leopold and others, 1964). Estimates of bankfull flow have ranged from the 1.1-year flow to the 30-year flow, but geomorphic features that indicate the top of the stream channel most commonly corre2 Regional Relations in Bankfull Channel Characteristics Determined from Flow Measurements in West Virginia spond with flows between the 1and 2-year recurrence flow calculated from the annual peak series. The 1.5-year recurrence flow from the annual peak series corresponds to the 1-year recurrence flow from the partial duration series (Langbein, 1949). The 1.5-year recurrence flow was assumed to be bankfull flow for this study, and is the flow referred to as “bankfull” throughout the rest of this report; however, this usage is not meant to imply that field studies have verified the 1.5-year recurrence flow as bankfull flow in West Virginia. Flow measurements made at U.S. Geological Survey (USGS) stream-gaging stations provide a large body of data on stream-channel characteristics at specific cross sections (Leopold and Maddock, 1953; Leopold, 1994; Rosgen, 1996). The USGS, in cooperation with the West Virginia Department of Transportation and West Virginia Conservation Agency, with cooperation facilitated by the Canaan Valley Institute, has analyzed the relation between flow and stream channel crosssectional area, width, and average depth, and determined regional relations in these characteristics at the 1.5-year recurrence flow calculated from the annual peak series at streamgaging stations in West Virginia. This study was intended to help investigators locate bankfull indicators in stream channels near stream-gaging stations or at reference reaches, an important part of data collection done in the design phase of streamrestoration projects. The regional equations presented in this report are not intended to be used to design stream channels without first collecting additional data. The USGS is currently (2003) collecting information on stream-channel characteristics in West Virginia to be used to develop regional curves for designing channels; information on this study is available from the West Virginia District Office of the USGS.