Geology topics

Research about Woodstock, Vermont

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

3 recordsLinked to original sources

USGS1996

Level II scour analysis for Bridge 22 (WODSTH00180022) on Town Highway 18, crossing north Bridgewater Brook, Woodstock, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WODSTH00180022 on town highway 18 crossing North Bridgewater Brook, Woodstock, 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). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge, available 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 Green Mountain physiographic province of central Vermont. The 4.34-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the left bank is forested and the right bank is covered by shrub and brush and is adjacent to woods. The right bank of North Bridgewater Brook is parallel to town highway 18 upstream of the bridge. In the study area, North Bridgewater Brook has a sinuous channel with a slope of approximately 0.038 ft/ft, an average channel top width of 48 ft and an average channel depth of 7 ft. The predominant channel bed materials are gravel and cobbles (D 50 is 63.2 mm or 0.207 ft). Due to cut banks and other channel features the geomorphic assessment at the time of the Level I and Level II site visit on August 16, 1994, indicated that the reach was laterally unstable. In addition, the stream approach to the bridge has a high gradient. However, near the upstream face of the bridge the gradient shallows. Approximately 100 feet downstream of the bridge the gradient steepens again. The town highway 18 crossing of North Bridgewater Brook is a 40-ft-long, two-lane bridge consisting of one 35-foot concrete span (Vermont Agency of Transportation, written commun., August 2, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The left and right abutments are not protected by stone fill. 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. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗

USGS1996

Level II scour analysis for Bridge 24 (WODSTH00190024) on Town Highway 19, crossing North Bridgewater Brook, Woodstock, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WODSTH00190024 on Town Highway 19 crossing North Bridgewater Brook, Woodstock, 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). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available 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 Green Mountain physiographic province of east-central Vermont in the town of Woodstock. The 3.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the left and right banks are covered by moderate tree cover along the immediate banks with some pasture/ grassland beyond. In the study area, the North Bridgewater Brook has a sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 44 ft and an average channel depth of 4 ft. The channel bed materials ranges from sand to boulders with a D 50 (median diameter)of 70.1 mm or 0.229 ft. The geomorphic assessment at the time of the Level I and Level II site visits on August 17, 1994 and December 13, 1994, indicated that the reach was stable. Localized bank cutting existed at the immediate downstream left bank. The Town Highway 19 crossing of the North Bridgewater Brook is a 26-ft-long, one-lane bridge consisting of one 23-ft steel-beam span (Vermont Agency of Transportation, written commun., August 3, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. Type-2 (less than 3 ft diameter) stone fill protects the upstream left wingwall which is impacted by flow. The channel bed under the bridge is constructed of wood. This construction is preventing channel degradation along the impacted left abutment.The channel is skewed approximately 40 degrees to the opening; the opening-skew-to-roadway is 10 degrees. 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). 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 0.0 to 0.8 ft. Abutment scour ranged from 6.6 to 14.9 ft. with the worst-case scenario occurring 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. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗

USGS1996

Level II scour analysis for Bridge 49 (WODSTH00990049) on Town Highway 99, crossing Gulf Brook, Woodstock, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WODSTH00990049 on Town Highway 99 crossing the Gulf Brook, Woodstock, 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 in east-central Vermont. The 16.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the primary surface cover is pasture except for upstream right of the bridge which is cover by trees and brush. The immediate banks throughout the reach have scattered woody vegetation. In the study area, the Gulf Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 91 ft and an average channel depth of 6 ft. The channel bed materials range from sand to cobble with a median grain size (D 50 ) of 85.3 mm (0.280 ft). The geomorphic assessment at the time of the Level I site visits on September 15, 1994 and December 14, 1994, indicated that the reach was stable. The Town Highway 99 crossing of the Gulf Brook is a 56-ft-long, one-lane bridge consisting of one 55-foot steel-beam span (Vermont Agency of Transportation, written communication, April 4, 1995). The bridge is supported by vertical, concrete abutments with a spill-through slope constructed of large quarried stone. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 0 degrees. Erosion at the right abutment has undermined the toe of the spill-through slope by nearly a foot. Material has been removed from under the stone spill-through slope so that 0.5 feet of horizontal penetration was possible at the time of the visits. 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 0.0 to 0.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour at the left abutment ranged from 3.1 to 10.3 ft. with the worst-case occurring at the 500-year discharge. Abutment scour at the right abutment ranged from 6.4 to 10.4 ft. with the worst-case occurring at the 100-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↗