Geology topics

Research about Barton, Vermont

Source-linked reports with geographic coverage including Barton, Vermont.

3 recordsLinked to original sources

USGS1996

Level II scour analysis for Bridge 8 (BARTTH00020008) on Town Highway 2, crossing Roaring Brook, Barton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BARTTH00020008 on town highway 2 crossing Roaring Brook, 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 VTAOT files, was compiled prior to conducting Level I and Level II analyses and can be 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 9.89-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have woody vegetation coverage except for the downstream left bank, which has a few trees and grass and brush coverage. In the study area, Roaring Brook has an incised, sinuous channel with a slope of approximately 0.019 ft/ft, an average channel top width of 35 ft and an average channel depth of 3 ft. The predominant channel bed material is gravel/cobble (D 50 is 49.1 mm or 0.161 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 18, 1994 indicated that the reach was laterally unstable. A cut-bank on the downstream right bank and overall channel configuration in the valley are indications of the lateral instability at this site. The town highway 2 crossing of Roaring Brook is a 30-ft-long, two-lane bridge consisting of one 26-foot span concrete T-beam type superstructure (Vermont Agency of Transportation, written communication, August 4, 1994). The bridge is supported by vertical, concrete abutments. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 2.5 ft deeper than the mean thalweg depth was observed near mid-channel downstream of the bridge during the Level I assessment. The only scour protection measure at the site was type-1 stone fill (less than 12 inches diameter) on the left upstream and downstream roadway embankments. 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 aggradation or degradation; 2) contraction scour (due to reduction in flow area caused by 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 scour depths for contraction and local scour and a summary of the results follows. Contraction scour for all modelled flows ranged from 1.4 to 2.8 feet and the worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 8.5 to 16.5 feet and the worst-case abutment scour 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↗

USGS1996

Level II scour analysis for Bridge 37 (BARTTH00080037) on Town Highway 8, crossing Willoughby River, Barton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BARTTH00080037 on town highway 8 crossing the Willoughby 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 60.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have sparse to moderate woody vegetation coverage. In the study area, the Willoughby River is probably incised, has a sinuous channel with a slope of approximately 0.009 ft/ft, an average channel top width of 108 ft and an average channel depth of 6 ft. The predominant channel bed material is cobble (D 50 is 95.1 mm or 0.312 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 20, 1994, indicated that the reach was stable. The town highway 8 crossing of the Willoughby River is a 96-ft-long, two-lane bridge consisting of one 94-foot steel-beam span (Vermont Agency of Transportation, written communication, August 4, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is 10 degrees. No scour was reported in the channel or along abutments or wingwalls during the Level I assessment. Type-2 stone fill (less than 24 inches diameter) was reported at each abutment and all four wingwalls. 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, 1993). Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. Data in appendix D (Vermont Agency of Transportation, written communication, August 4, 1994) indicate that the right abutment may be founded on or near marble bedrock which may limit scour depths. Bedrock was not detected by borings in the vicinity of the left abutment. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8. Contraction scour for all modelled flows was 0 ft. Abutment scour ranged from 7.3 to 10.7 ft and the worst-case abutment scour 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, 1993, 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↗

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↗