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USGS1997

Level II scour analysis for Bridge 23 (WOLCTH00130023) on Town Highway 13, crossing the Wild Branch of the Lamoille River, Wolcott, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WOLCTH00130023 on Town Highway 13 crossing the Wild Branch Lamoille River, Wolcott, 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, collected 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 Green Mountain section of the New England physiographic province in northcentral Vermont. The 27.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture on the upstream right overbank. The upstream left overbank is brushland. Downstream of the bridge, the surface cover is forested on the right overbank. The downstream left overbank is pasture while the immediate bank has dense woody vegetation. In the study area, the Wild Branch Lamoille River has an incised, straight channel with a slope of approximately 0.009 ft/ft, an average channel top width of 65 ft and an average bank height of 7 ft. The channel bed material ranges from sand to boulders with a median grain size (D 50 ) of 85.3 mm (0.280 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 17, 1996 indicated that the reach was laterally unstable. The Town Highway 13 crossing of the Wild Branch Lamoille River is a 41-ft-long, one-lane bridge consisting of a 39-foot steel girder span (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the bridge face is 38 ft. The bridge is supported by vertical, concrete abutments. The right abutment has concrete wingwalls. The channel is skewed approximately 45 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 3.5 ft deeper than the mean thalweg depth was observed in the channel during the Level I assessment. Scour countermeasures at the site includes type-2 stone fill (less than 3 feet diameter) along the banks, the right wingwalls, the right abutment and the road embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 1.0 to 2.1 ft. The worst-case contraction scour occurred at the 100-year discharge. Left abutment scour ranged from 9.1 to 13.2 ft. Right abutment scour ranged from 15.7 to 22.3 ft. The worst-case abutment scour occurred at the 500- year discharge for both abutments. 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. During the August 1995 flood, the Wild Branch Lamoille River overtopped the bridge deck at structure WOLCTH00130023. Debris also was caught in the upstream I-beam of the structure. 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↗
USGS1997

Level II scour analysis for Bridge 26 (JAMATH00010026) on Town Highway 1, crossing Ball Mountain Brook, Jamaica, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure JAMATH00010026 on Town Highway 1 crossing Ball Mountain Brook, Jamaica, 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 Green Mountain section of the New England physiographic province in southern Vermont. The 29.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, Ball Mountain Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 74 ft and an average bank height of 6 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 82.6 mm (0.271 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 12, 1996, indicated that the reach was stable. The Town Highway 1 crossing of Ball Mountain Brook is a 80-ft-long, two-lane bridge consisting of one 78-foot steel-beam span (Vermont Agency of Transportation, written communication, March 29, 1995). The opening length of the structure parallel to the bridge face is 75.7 ft. The bridge is supported by vertical, concrete abutments with wingwalls. A scour hole 2 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. The scour protection measures at the site were type-4 stone fill (less than 60 inches diameter) along the left bank upstream and extending underneath the bridge and along the bank downstream and also along the right bank upstream tapering to type-3 stone fill (less than 48 inches diameter) at the upstream end of the upstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 the modelled flows ranged from 1.0 to 2.7 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 8.4 to 17.6 ft. The worst-case abutment scour for the right abutment occurred at the incipient-overtopping discharge. For the left abutment, 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↗
USGS1997

Level II scour analysis for Bridge 30 (MNTGTH00410030) on Town Highway 41, crossing the Trout River, Montgomery, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MNTGTH00410030 on Town Highway 41 crossing the Trout River, Montgomery, 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 Green Mountain section of the New England physiographic province in northern Vermont. The 46.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the left bank is pasture upstream and downstream of the bridge with dense woody vegetation along the immediate banks. The upstream and downstream right bank surface cover is brush. In the study area, the Trout River has an incised, meandering channel with a slope of approximately 0.005 ft/ft, an average channel top width of 130 ft and an average bank height of 6 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 68.3 mm (0.224 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 27, 1995, indicated that the reach was laterally unstable. At this site there is visible lateral channel movement upstream and downstream of the bridge with meanders and cut banks. The Town Highway 41 crossing of the Trout River is a 90-ft-long, one-lane bridge consisting of one 87-foot steel-beam span (Vermont Agency of Transportation, written communication, August 3, 1994). The opening length of the structure parallel to the bridge face is 86.7 ft.The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-toroadway is 0 degrees. A scour hole 4.5 ft deeper than the mean thalweg depth, was observed 35 ft downstream of the bridge during the Level I assessment. The scour counter-measures at the site included type-1 stone fill (less than 12 inches diameter) at the upstream left wingwall, at the left abutment, along the upstream right bank, and at the upstream end of the downstream left wingwall. There was also type-2 stone fill (less than 36 inches diameter) along the downstream right bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 was 0.0 ft. Abutment scour ranged from 2.5 to 8.9 ft. The worst-case abutment scour occurred at the 500-year discharge. The computed scour depths are well above the pile depths set in bedrock. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scouredstreambed 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 particlesize 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↗
USGS1997

Level II scour analysis for Bridge 81 (NFIETH00PL0081) on Pleasant Street, crossing Union Brook, Northfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NFIETH00PL0081 on Pleasant Street crossing Union Brook, Northfield, 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 Green Mountain section of the New England physiographic province in central Vermont. The 6.1-mi 2 drainage area is in a predominantly rural and forested basin. The bridge site is located within a suburban setting in the Town of Northfield with homes, lawns, and pavement on the overbanks. There are trees and brush along the immediate banks. In the study area, Union Brook has an incised, straight channel with a slope of approximately 0.01 ft/ft, an average channel top width of 41 ft and an average bank height of 4 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 47.7 mm (0.157 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 24, 1996, indicated that the reach was stable. The Pleasant Street crossing of Union Brook is a 34-ft-long, two-lane bridge consisting of one 29-foot steel-beam span (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the bridge face is 26.6 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 30 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the upstream left wingwall and upstream end of the left abutment during the Level I assessment. The scour protection measures at the site were type-1 stone fill (less than 12 inches diameter) along the upstream left bank, the upstream left wingwall, and the downstream left bank, and type-2 stone fill (less than 36 inches diameter) along the downstream right bank. There is also a laid-up stone wall in front of the downstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 4.2 to 13.3 ft. 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↗
USGS1997

Level II scour analysis for Bridge 29 (PUTNTH00210029) on Town Highway 21, crossing East Putney Brook, Putney, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure PUTNTH00210029 on Town Highway 21 crossing East Putney Brook, Putney, 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 southeastern Vermont. The 10.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of pasture and forest. In the study area, East Putney Brook has an incised, sinuous channel with a slope of approximately 0.009 ft/ft, an average channel top width of 33 ft and an average bank height (channel depth) of 3 ft. The channel bed material is cobbles predominantly with a median grain size (D 50 ) of 80.7 mm (0.265 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 19, 1996, indicated that the reach was stable. The Town Highway 21 crossing of East Putney Brook is a 35-ft-long, one-lane bridge consisting of one 29-foot steel-beam span (Vermont Agency of Transportation, written communication, March 30, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 40 degrees to the opening. Historical records show an opening-skew-to-roadway of 10 degrees but 20 degrees was computed using field survey data and used in this study. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on each abutment wall, the upstream right wingwall and the upstream right bank, and type-3 stone fill (less than 48 inches diameter) on the left bank upstream, the upstream left wingwall, and the downstream right bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 feet. The worst-case contraction scour occurred at the incipient-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 6.1 to 18.4 feet. The worst-case abutment scour occurred at the 500-year discharge for the right abutment and the incipient overtopping discharge for the left abutment. 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 crosssection 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↗
USGS1997

Level II scour analysis for Bridge 45 (NFIETH00250045) on Town Highway 25, crossing Union Brook, Northfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NFIETH00250045 on Town Highway 25 crossing Union Brook, Northfield, 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 Green Mountain section of the New England physiographic province in central Vermont. The 4.04-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, surface cover consists of shrubs and brush on all of the banks except the upstream right bank which is forested. In the study area, Union Brook has an incised, meandering channel with a slope of approximately 0.018 ft/ft, an average channel top width of 41 ft and an average bank height of 2 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 65.8 mm (0.216 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 24, 1996, indicated that the reach was unstable. The stream meanders and there is a cut bank on the upstream right bank and trees are falling into the channel. The Town Highway 25 crossing of Union Brook is a 28-ft-long, two-lane bridge consisting of one 26-foot concrete slab span (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the bridge face is 23.8 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 50 degrees to the opening while the opening-skew-to-roadway is 0 degrees. During the Level I assessment, a scour hole 3.0 ft deeper than the mean thalweg depth was observed at the upstream face of the bridge that extended from the center of the channel to the front of the upstream left wingwall. An additional scour hole 1.5 ft deeper than the mean thalweg depth was observed along the downstream right bank near the bridge. The scour counter measures at the site were a laid-up wall of concrete slabs along the upstream right bank beginning at the end of the upstream right wingwall and type-1 stone fill (less than 12 inches diameter) along the downstream right wingwall and bank, and type-2 stone fill (less than 36 inches diameter) along the downstream left wingwall and bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.4 to 0.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 4.5 to 9.1 ft. 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↗
USGS1997

Level II scour analysis for Bridge 25 (ROYATH00550025) on Town Highway 55, crossing Broad Brook, Royalton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ROYATH00550025 on Town Highway 55 crossing Broad Brook, Royalton, 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 central Vermont. The 11.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture on the upstream and downstream left overbanks and forest on the upstream and downstream right overbanks. In the study area, Broad Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 41 ft and an average bank height of 5 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 58.3 mm (0.191 ft). The geomorphic assessment at the time of the Level I site visit on April 13, 1995 indicated that the reach was laterally unstable. The stream impacts the upstream left bank where there is a cut bank. The Town Highway 55 crossing of the Broad Brook is a 35-ft-long, two-lane bridge consisting of one 31-foot steel-beam span (Vermont Agency of Transportation, written communication, March 22, 1995). The opening length of the structure parallel to the bridge face is 32 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening, while the opening-skew-toroadway is zero degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the left abutment and the downstream left wingwall during the Level I assessment. The scour countermeasure at the site was type-2 stone fill (less than 36 inches diameter) along the upstream and downstream left banks that extended to the ends of the wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.6 to 1.5 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge which was less than the 100-year discharge. Abutment scour ranged from 3.5 to 8.9 ft. The worst-case abutment scour occurred at the incipient road-overtopping discharge for the left abutment and at the 100-year discharge for the right abutment. 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 crosssection 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↗
USGS1997

Level II scour analysis for Bridge 63 (CHESTH00090063) on Town Highway 9, crossing the Williams River, Chester, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CHESTH00090063 on Town Highway 9 crossing the Williams River, Chester, 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 eastern Vermont. The 24.0-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is grass with trees and brush along the immediate banks. In the study area, the the Williams River has an incised, sinuous channel with a slope of approximately 0.005 ft/ft, an average channel top width of 64 ft and an average bank height of 6 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 57.7 mm (0.189 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 18, 1996, indicated that the reach was stable. The Town Highway 9 crossing of the Williams River is a 45-ft-long, two-lane bridge consisting of one 35-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, April 6, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 0 degrees. A scour hole 1.8 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. The scour hole undermines the left abutment and extends from 50 ft upstream of the upstream bridge face to 50 ft downstream of the downstream bridge face. The scour protection measures at the site included type-3 stone fill (less than 48 inches diameter) under the bridge along the entire base length of the right abutment and along the right bank from 50 to 88 ft upstream. Type-2 (less than 36 inches diameter) stone fill scour protection was observed along the downstream left bank from 18 ft to 115 ft, along the downstream right bank from 8 ft to 25 ft and along the upstream left bank from 50 to 75 ft. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 was computed to be 0.0 ft. Abutment scour ranged from 10.1 ft to 11.0 ft along the left abutment and from 14.1 ft to 15.1 ft along the right abutment. The worst-case abutment scour for the left abutment occurred at the 500-year discharge while the worst-case abutment scour for the right abutment occurred 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↗
USGS1997

Level II scour analysis for Bridge 12 (NEWFVT00300012) on State Route 30, crossing Smith Brook, Newfane, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NEWFVT00300012 on State Route 30 crossing Smith Brook, Newfane, 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 and Green Mountain sections of the New England physiographic province in southeastern Vermont. The 9.55-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is primarily pasture with the exception of the downstream right bank which is forested. The immediate banks have dense woody vegetation except for the downstream right bank which has cut grass. In the study area, Smith Brook has a sinuous channel with a slope of approximately 0.01 ft/ ft, an average channel top width of 63 ft and an average bank height of 10 ft. The predominant channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 75.4 mm (0.247 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 21, 1996, indicated that the reach was stable. The State Route 30 crossing of Smith Brook is a 43-ft-long, two-lane bridge consisting of a 40-foot concrete T-beam span (Vermont Agency of Transportation, written communication, March 30, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 35 degrees to the opening while the measured opening-skew-to-roadway is 30 degrees. The scour protection measure at the site included type-2 stone fill (less than 36 inches diameter) from the upstream end of the left abutment to 35 ft. upstream, along the downstream end of the downstream left wingwall, along the right bank from 7 ft. to 90 ft. downstream, and along the left bank from 15 ft. to 40 ft. downstream. Also, there was type- 1 stone fill (less than 24 inches diameter) at the left abutment and downstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 modelled flows ranged from 1.2 to 1.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.6 to 14.1 ft. The worst-case abutment scour also 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↗
USGS1997

Level II scour analysis for Bridge 26 (ROYATH00540026) on Town Highway 54, crossing Broad Brook, Royalton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ROYATH00540026 on Town Highway 54 crossing Broad Brook, Royalton, 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 central Vermont. The 11.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the left bank upstream and downstream is pasture with trees and brush on the immediate banks. The right bank, upstream and downstream of the bridge, is forested. In the study area, Broad Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 37 ft and an average bank height of 4 ft. The channel bed material ranges from sand to boulders with a median grain size (D 50 ) of 66.3 mm (0.218 ft). The geomorphic assessment at the time of the Level I site visit on April 13, 1995 and the Level II site visit on July 11, 1996, indicated that the reach was stable. The Town Highway 54 crossing of Broad Brook is a 29-ft-long, one-lane bridge consisting of one 24-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, March 23, 1995). The opening length of the structure parallel to the bridge face is 23.3 ft. The bridge is supported by a vertical, concrete face laid-up stone abutment with concrete wingwalls on the left and a laid-up stone abutment on the right. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the downstream end of the right abutment during the Level I assessment. Also, at the upstream end of the left abutment, the footing is exposed 0.5 ft. The scour protection measures at the site included type-2 stone fill (less than 36 inches diameter) along the upstream left bank, at the upstream end of the upstream left wingwall, along the entire length of the downstream left wingwall, and at the upstream end of the right abutment. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 1.4 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 2.2 to 7.4 ft on the left and from 14.7 to 17.7 ft on the right. The worst-case abutment scour occurred at the incipient roadway-overtopping discharge for the left and at the 500-year discharge for the right. 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↗
USGS1997

Level II scour analysis for Bridge 16 (CHESVT01030016) on State Route 103, crossing the Williams River, Chester, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CHESVT01030016 on State Route 103 crossing the Williams River, Chester, 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 southeastern Vermont. The 15.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture except for the downstream right overbank which is forested. In the study area, the Williams River has an incised, straight channel with a slope of approximately 0.008 ft/ft, an average channel top width of 56 ft and an average bank height of 6 ft. The channel bed material ranges from gravel to cobbles with a median grain size (D 50 ) of 67.5 mm (0.222 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 16, 1996, indicated that the reach was stable. The State Route 103 crossing of the Williams River is a 162-ft-long, two-lane bridge consisting of three steel-beam spans (Vermont Agency of Transportation, written communication, March 13, 1995). The opening length of the structure parallel to the bridge face is 157.7 ft.The bridge is supported by vertical, concrete abutments and piers with no wingwalls. The channel is skewed approximately 55 degrees to the opening while the opening-skew-to-roadway is also 55 degrees. The scour protection measures at the site included type-4 stone fill (less than 60 inches diameter) along the upstream left bank. There was type-3 stone fill (less than 48 inches diameter) along the upstream right bank and both spill-through embankments and both downstream banks. There was type-1 stone fill (less than 12 inches diameter) along the upstream right and downstream left road embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 was 0.0. Abutment scour ranged from 6.4 to 9.0 ft. The worst-case abutment scour occurred at the 500-year discharge. Pier scour ranged from 7.9 to 10.1 ft. The worst-case pier scour occurred at the incipient-overtopping discharge for both piers. 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↗
USGS1997

Level II scour analysis for Bridge 68 (NFIETH00960068) on Town Highway 96, crossing the Dog River, Northfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NFIETH00960068 on Town Highway 96 crossing the Dog River, Northfield, 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 Green Mountain section of the New England physiographic province in central Vermont. The 30.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the left bank upstream and downstream is pasture while the immediate banks have dense woody vegetation. The right bank upstream is forested and the downstream right bank is pasture. Vermont state route 12A runs parallel to the river on the right bank. In the study area, the Dog River has an incised, straight channel with a slope of approximately 0.004 ft/ft, an average channel top width of 70 ft and an average bank height of 7 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 47.9 mm (0.157 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 25, 1996, indicated that the reach was stable. The Town Highway 96 crossing of the Dog River is a 45-ft-long, one-lane bridge consisting of one 43-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the bridge face is 41.5 ft.The bridge is supported by vertical, concrete abutments with wingwalls. The channel is not skewed to the opening and the opening-skew-to-roadway is zero degrees. Channel scour 0.5 ft deeper than the mean thalweg depth, was observed under the bridge during the Level I assessment. The scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) along the left bank upstream and type-2 stone fill (less than 36 inches diameter) along the upstream and downstream right banks that extends partially in front of the right wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.8 to 1.2 ft. The worst-case contraction scour occurred at the 100-year and 500-year discharges. Abutment scour ranged from 8.5 to 12.2 ft. The worst-case abutment scour occurred at the incipient roadway-overtopping discharge for the right abutment. 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↗
USGS1997

Level II scour analysis for Bridge 22 (JAY-TH00400022) on Town Highway 40, crossing Jay Branch, Jay, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure JAY-TH00400022 on Town Highway 40 crossing Jay Tributary, Jay, 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 Green Mountain section of the New England physiographic province in northern Vermont. The 2.15-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is primarily pasture on the upstream and downstream left overbank while the immediate banks have dense woody vegetation. The downstream right overbank of the bridge is forested. In the study area, Jay Branch Tributary has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 26 ft and an average bank height of 3 ft. The channel bed material ranges from gravel to cobble with a median grain size (D 50 ) of 40.5 mm (0.133 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 7, 1995, indicated that the reach was stable. The Town Highway 40 crossing of Jay Branch Tributary is a 27-ft-long, two-lane bridge consisting of one 25-foot steel-beam span (Vermont Agency of Transportation, written communication, March 6, 1995). The opening length of the structure parallel to the bridge face is 23.5 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel skew and the opening-skew-to-roadway are zero degrees. The scour counter-measures at the site included type-2 stone fill (less than 36 inches diameter) at the upstream end of the left and right abutments, at the upstream right wingwall, and at the downstream left wingwall. There was also type-3 stone fill (less than 48 inches diameter) at the upstream left and downstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.7 to 1.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 4.6 to 4.9 ft. The worst-case left abutment scour occurred at the 100-year discharge. Right abutment scour ranged from 4.0 to 5.0 ft. The worst-case right 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↗
USGS1997

Level II scour analysis for Bridge 48 (FFIETH00300048) on Town Highway 30, crossing Wanzer Brook, Fairfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FFIETH00300048 on Town Highway 30 crossing Wanzer Brook, Fairfield, 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 Green Mountain section of the New England physiographic province in northwestern Vermont. The 6.78-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover upstream of the bridge and on the downstream right bank is primarily pasture. The downstream left bank is forested. In the study area, Wanzer Brook has an incised, straight channel with a slope of approximately 0.03 ft/ft, an average channel top width of 65 ft and an average bank height of 5 ft. The channel bed material is cobble with a median grain size (D 50 ) of 111 mm (0.364 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 11, 1995, indicated that the reach was stable. The Town Highway 30 crossing of Wanzer Brook is a 31-ft-long, two-lane bridge consisting of one 28-foot steel-beam span (Vermont Agency of Transportation, written communication, March 8, 1995). The opening length of the structure parallel to the bridge face is 26 ft.The bridge is supported by vertical stone wall abutments with concrete caps and “kneewall” footings. The channel is skewed approximately 25 degrees to the opening while the measured opening-skew-to-roadway is 20 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the downstream left retaining wall (extended concrete footing) during the Level I assessment. It was also observed that the right abutment is undermined with a scour depth of 0.5 ft. The scour protection at the site was limited to four large boulders (type-4, less than 60 inches diameter) along the downstream right retaining wall. The channel under the bridge is a “corduroy” log mat floor composed of 13 logs which are parallel to the bridge face and extend from 5 ft under the bridge to the downstream bridge face. The most downstream log is approximately 0.3 to 0.4 ft higher than the other logs and controls flow at lower flows. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.3 to 0.6 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 14.1 to 16.0 ft at the left abutment and from 6.8 to 7.6 ft at the right abutment. 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↗
USGS1997

Level II scour analysis for Bridge 13 (SHARTH00040013) on Town Highway 4, crossing Broad Brook, Sharon, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure SHARTH00040013 on Town Highway 4 crossing Broad Brook, Sharon, 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 central Vermont. The 16.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is brushland on the downstream left overbank and row crops on the right overbank, while the immediate banks have dense woody vegetation. Upstream of the bridge, the overbanks are forested. In the study area, Broad Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 69 ft and an average bank height of 5 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 112 mm (0.369 ft). The geomorphic assessment at the time of the Level I site visit on April 11, 1995 and Level II site visit on July 23, 1996, indicated that the reach was stable. The Town Highway 4 crossing of Broad Brook is a 34-ft-long, two-lane bridge consisting of one 31-foot concrete tee beam span (Vermont Agency of Transportation, written communication, March 23, 1995). The opening length of the structure parallel to the bridge face is 30.1 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 15 degrees. A scour hole 2.0 ft deeper than the mean thalweg depth was observed along the upstream end of the right abutment. At the downstream end of the left abutment, a 1.0 foot scour hole was observed . Scour countermeasures at the site include type-2 stone fill (less than 3 feet diameter) at each road embankment. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.7 to 1.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 5.6 to 9.4 ft. The worst case left abutment scour occurred at the 500-year discharge. Right abutment scour ranged from 19.0 to 19.8 ft. The worst-case right abutment scour occurred at the incipient-overtopping 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↗
USGS1997

Level II scour analysis for Bridge 6 (VICTTH000110006) on Town Highway 1, crossing the Moose River, Victory, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure VICTTH00010006 on Town Highway 1 crossing the Moose River, Victory, 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 White Mountain section of the New England physiographic province in northeastern Vermont. The 27.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, the Moose River has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 108 ft and an average channel depth of 14 ft. The channel bed ranges from gravel to boulder with a median grain size (D 50 ) of 126 mm (0.412 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 20, 1995, indicated that the reach was stable. The Town Highway 1 crossing of the Moose River is a 101-ft-long, two-lane bridge consisting of one 98-foot steel-beam span (Vermont Agency of Transportation, written communication, March 28, 1995). The bridge is supported by vertical, concrete abutments with a spill-through slope at the face of each abutment consisting of type-3 stone fill (less than 48 inches diameter). The channel is skewed approximately 40 degrees to the opening while the opening-skew-to-roadway is 45 degrees. A scour hole 3 ft deeper than the mean thalweg depth was observed under the bridge during the Level I assessment. 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 0.2 to 0.4 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.3 to 8.2 ft. The worst-case abutment scour also 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↗
USGS1997

Level II scour analysis for Bridge 18 (GROTTH00480018) on Town Highway 48, crossing the Wells River Groton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure GROTTH00480018 on Town Highway 48 crossing the Wells River, Groton, 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 eastern Vermont. The 53.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture on the right bank upstream and the left bank downstream while the surface cover is shrub and brushland along the left bank upstream and the right bank downstream. The immediate banks are vegetated with brush and scattered trees. In the study area, the Wells River has an incised, straight channel with a slope of approximately 0.003 ft/ft, an average channel top width of 69 ft and an average bank height of 7 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 66.7 mm (0.219 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 28, 1995, indicated that the reach was stable. The Town Highway 48 crossing of the Wells River is a 38-ft-long, one-lane bridge consisting of one 36-foot steel-beam span (Vermont Agency of Transportation, written communication, March 24, 1995). The opening length of the structure parallel to the bridge face is 33.7 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 0 degrees to the opening and the opening-skew-toroadway is also 0 degrees. Local scour 3.25 ft deeper than the mean thalweg depth was observed underneath the bridge along the left and right abutments during the Level I assessment. In addition, a scour hole extends from 90 ft US to 50 ft DS for a total length of 115 ft with an average scour depth of 2.0 ft. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the left bank upstream, along the entire base length of the downstream right wingwall, and along the left and right banks downstream; and type-1 stone fill (less than 12 inches diameter) along the entire base length of the upstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge is determined and analyzed as another potential worst-case scour scenario. 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 was 0.0 ft. Abutment scour ranged from 2.0 to 2.3 ft at the left abutment and 8.8 to 14.6 ft at the right abutment. The worst-case abutment scour occurred at the 500-year discharge at the right abutment. 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↗
USGS1997

Level II scour analysis for Bridge 5 (DUMMVT00300005) on State Route 30, crossing Stickney Brook, Dummerston, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure DUMMVT00300005 on State Route 30 crossing Stickney Brook, Dummerston, 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 southeastern Vermont. The 6.31-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest and brush. In the study area, Stickney Brook has an incised, straight channel with a slope of approximately 0.04 ft/ft, an average channel top width of 80 ft and an average bank height of 7 ft. The channel bed material is predominantly cobble with a median grain size (D 50 ) of 80.3 mm (0.264 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 12, 1996, indicated that the reach was aggrading. The State Route 30 crossing of Stickney Brook is a 84-ft-long, two-lane bridge consisting of one 82-foot steel-beam span (Vermont Agency of Transportation, written communication, March 30, 1995). The opening length of the structure parallel to the bridge face is 79.7 ft. The bridge is supported by vertical, concrete abutments with spill-through embankments. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 0 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the toe of the right spill-through slope during the Level I assessment. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) along the left and right bank under the bridge forming a spill-through slope and type-2 stone fill from approximately 20 ft to 64 ft upstream on the right bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended 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 0.2 ft. The worst-case contraction scour occurred at the 100-year discharge. Left abutment scour ranged from 5.5 to 6.3 ft. Right abutment scour ranged from 2.0 to 3.8 ft. 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↗