Abstract
Bankfull hydraulic geometry relationships relate bankfull stream dimensions, such as cross-sectional area, width, mean depth, mean velocity, width to depth ratio, and slope to bankfull discharge. These relationships can assist in determining a design discharge for stream restoration and management projects. This study assessed 27 stable streams located in the Inner Bluegrass and Outer Bluegrass regions of Kentucky. Reaches were selected based on the presence of a U.S. Geological Survey gage, as well as other conditions such as presence of readily identifiable bankfull indicators, stability indices, and site accessibility. Bankfull channel dimensions and discharges were determined, and hydraulic geometry relationships were developed for both the Inner Bluegrass and Outer Bluegrass regions. These scaling relationships for karst-influenced streams were similar to others reported in the literature for non-karst areas. Significant differences between the regions were found only for bankfull width and width-to-depth ratio. Streams in the Inner Bluegrass tended to be more narrow and deep at bankfull discharges less than 10 m3s−1 and wider and shallower at bankfull discharges greater than 20 m3s−1 as compared to stream in the Outer Bluegrass. It is suspected that physiographic conditions related to local geology and/or riparian vegetation at three sites in the Outer Bluegrass accounted for these differences. Results of this study indicate that in instances of geologic variation within a physiographic region, hydraulic geometry relationships may require evaluation at the watershed scale.
Highlights
Hydraulic geometry provides a means for enhancing our ability to assess and design stream projects [1,2,3]
Stream morphology data were collected at 12 U.S Geological Survey (USGS) gaged sites in the Inner Bluegrass for drainage areas between 2.5 and 111 km2 and 15 USGS gaged sites in the Outer Bluegrass for drainage areas between 8.0 and 357 km2 (Table 1)
Inner Bluegrass region, gage sites with higher percentages of imperviousness were not concentrated in smaller watersheds, as might be expected
Summary
Hydraulic geometry provides a means for enhancing our ability to assess and design stream projects [1,2,3]. Hydraulic geometry equations describe the relationship between a stream’s form, such as cross-sectional area, width, mean depth, mean velocity, and slope, and a single representative discharge such as bankfull discharge [3,4,5,6]. Bankfull discharge is the discharge at which the stream flows at the top of its banks just before waters spill onto the floodplain [6,7,8,9]. As defined by Copeland et al [6], the channel-forming discharge is a single discharge that over a long period of time would theoretically “produce the same channel geometry as the natural long-term hydrograph.”. As defined by Copeland et al [6], the channel-forming discharge is a single discharge that over a long period of time would theoretically “produce the same channel geometry as the natural long-term hydrograph.” While
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