Research about Barton River

USGS2014

Use of acoustic backscatter to estimate continuous suspended sediment and phosphorus concentrations in the Barton River, northern Vermont, 2010-2013

The U.S. Geological Survey, in cooperation with the Vermont Department of Environmental Conservation, investigated the use of acoustic backscatter to estimate concentrations of suspended sediment and total phosphorus at the Barton River near Coventry, Vermont. The hypothesis was that acoustic backscatter—the reflection of sound waves off objects back to the source from which they came—measured by an acoustic Doppler profiler (ADP) and recorded as ancillary data for the calculation of discharge, also could be used to generate a continuous concentration record of suspended sediment and phosphorus at the streamgage, thereby deriving added value from the instrument. Suspended-sediment and phosphorus concentrations are of particular interest in Vermont, where impairment of surface waters by suspended sediments and phosphorus is a major concern. Regression models for estimating suspended-sediment concentrations (SSCs) and total phosphorus concentrations evaluated several independent variables: measured backscatter (MB), water-corrected backscatter (WCB), sediment-corrected backscatter (SCB), discharge, fluid-absorption coefficient, sediment-driven acoustic attenuation coefficient, and discharge hysteresis. The best regression equations for estimating SSC used backscatter as the predictor, reflecting the direct relation between acoustic backscatter and SSC. Backscatter was a better predictor of SSC than discharge in part because hysteresis between SSC and backscatter was less than for SSC and discharge. All three backscatter variables—MB, WCB, and SCB—performed equally as predictors of SSC and phosphorus concentrations at the Barton River site. The similar abilities to predict SSC among backscatter terms may partially be attributed to the low values and narrow range of the sediment-driven acoustic attenuation in the Barton River. The regression based on SCB was selected for estimating SSC because it removes potential bias caused by attenuation and temperature fluctuations. The best regression model for estimating phosphorus concentrations included terms for discharge and discharge hysteresis. The finding that discharge hysteresis was a significant predictor of phosphorus concentrations might be related to preferential sorption of phosphorus to fine-grained sediments, which have been found to be particularly sensitive to hysteresis. Regression models designed to estimate phosphorus concentrations had less predictive power than the models for SSCs. Data from the Barton River did not fully support one of the study’s hypotheses—that backscatter is mostly caused by sands, and attenuation is mostly caused by fines. Sands, fines, and total SSCs in the Barton River all related better to backscatter than to sediment-driven acoustic attenuation. The weak relation between SSC and sediment-driven acoustic attenuation may be related to the low values and narrow range of SSCs and sediment attenuations observed at Barton River. A weak relation between SSC and sediment-driven acoustic attenuation also suggests that the diameters of the fine-sized suspended sediments in the Barton River may be predominantly greater than 20 micrometers (μm). Long-term changes in the particle-size distribution (PSD) were not observed in Barton River; however, some degree of within-storm changes in sediment source and possibly PSD were inferred from the hysteresis between SSC and SCB.

Vermont↗

USGS1996

Level II scour analysis for Bridge 37 (BARTUS00050166) on U.S. Route 5, crossing Barton River, Barton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BARTUS00050166 on U. S. Route 5 crossing the Barton River, Barton, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province of north-central Vermont in the town of Barton. The 65.2-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have a combination of dense woody vegetation coverage, brush, and field grasses. In the study area, the Barton River has an incised, sinuous-to-meandering channel with a slope of approximately 0.0065 ft/ft, an average channel top width of 58 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel (D 50 is 75.6 mm or 0.25 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 19, 1994, indicated that the reach was stable. The U. S. Route 5 crossing of the Barton River is a 126-ft-long, two-lane bridge consisting of one 60-foot steel beam span with two steel-beam approach spans (Vermont Agency of Transportation, written communication, August 4, 1994). The bridge is supported by two concrete piers. The left bank has a concrete retaining wall that is attached to the US face of the left pier; consequently this pier functions as an abutment for the analysis because no flow occurs to the left of the pier. For the purposes of computing scour, this pier was considered an abutment. The channel is skewed approximately 40 degrees to the opening while the opening-skew-to-roadway is 25 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the right pier during the Level I assessment. Scour protection measures at the site consist of type-1 stone fill (less than 12 inches diameter) along the entire base length of both piers. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.1 to 2.4 ft. Abutment-type scour was computed for the left pier; scour ranged from 9.1 to 11.3 ft. Abutment scour at the right abutment ranged from 6.1 to 11.3 ft. Pier scour, computed for the right pier, ranged from 31.3 to 33.3 ft. The severity of the pier scour was directly related to the attack angle of 25 degrees. The worst-case scour in all computations occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗