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USGS1996

Level II scour analysis for Bridge 28 (MNTGTH00190028) on Town Highway 19, crossing Wade Brook, Montgomery, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MNTGTH00190028 on town highway 19 crossing Wade Brook, 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). 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, gleaned from Vermont Agency of Transportation (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 north-central Vermont in the town of Montgomery. The 6.51-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage. In the study area, Wade Brook has an incised, sinuous channel with a slope of approximately 0.0253 ft/ft, an average channel top width of 58 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel and cobbles (D 50 is 81.8 mm or 0.269 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 9, 1994, indicated that the reach was stable. The town highway 19 crossing of Wade Brook is a 24-ft-wide corrugated steel, multi-plate pipe-arch (Vermont Agency of Transportation, written communication, August 3, 1994). The culvert is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is 26 degrees. There was no localized scour evident during the Level I assessment. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on all of the roadway embankments, the upstream left bank, and each wingwall. 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 0.5 to 1.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 8.6 to 16.1 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↗
USGS1996

Level II scour analysis for Bridge 99 (LUDLVT01000099) on State Highway 99, crossing Branch Brook, Ludlow, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure LUDLVT01000099 on State Highway 100 crossing Branch Brook, Ludlow, 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 15.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the channel banks are densely covered by trees and brush. The overbanks are primarily covered by field grasses. In the study area, Branch Brook has an incised, straight channel with a slope of approximately 0.003 ft/ft, an average channel top width of 73 ft and an average channel depth of 5 ft. The predominant channel bed materials are cobble and gravel with a median grain size (D 50 ) of 60.5 mm (0.198 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 13, 1995, indicated that the reach was stable. The State Highway 100 crossing of Branch Brook is a 84-ft-long, two-lane bridge consisting of one 82-foot steel-beam span (Vermont Agency of Transportation, written communication, March 13, 1995). The bridge is supported by vertical, concrete abutments. The abutments are set back from the channel edge and have a spill-through slope consisting of type-4 stone fill (median size less than 60 inches in diameter). The channel skew and the opening-skew-to-roadway is zero 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, 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 1.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 1.0 to 7.4 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↗
USGS1996

Level II scour analysis for Bridge 5 (CHELTH00030005) on Town Highway 3, crossing Jenkins Brook, Chelsea, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CHELTH00030005 on town highway 3 crossing Jenkins Brook, Chelsea, 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 study provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province of central Vermont in the town of Chelsea. The 6.97-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, Jenkins Brook has an incised, sinuous channel with a slope of approximately 0.04 ft/ft, an average channel top width of 48 ft and an average channel depth of 3 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 154 mm (0.506 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 17, 1994, indicated that the reach was stable. The town highway 3 crossing of Jenkins Brook is a 23-ft-long bridge consisting of one 20- foot concrete span (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The upstream wingwalls are protected by type-3 stone fill (less than 48 inches diameter) and the downstream wingwalls have type-2 stone fill (less than 36 inches diameter). The footings of both abutments are exposed. The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 15 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, 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 7.6 to 12.4 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↗
USGS1996

Level II scour analysis for Bridge 31 (BRNATH00470031) on Town Highway 47, crossing Locust Creek, Barnard, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRNATH00470031 on town highway 47 crossing Locust Creek, Barnard, 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, gleaned from VTAOT files, was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Barnard. The 4.47-mi 2 drainage area is a predominantly rural and forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage except for areas of grass and brush on the upstream banks. In the study area, Locust Creek has an incised, sinuous channel with a slope of approximately 0.006 ft/ft, an average channel top width of 34 ft and an average channel depth of 3 ft. The predominant channel bed materials are gravel and cobble (D 50 is 55.2 mm or 0.181 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 12, 1994, indicated that the reach was stable. The town highway 47 crossing of Locust Creek is a 28-ft-long, one-lane bridge consisting of one 25-foot span concrete slab superstructure (Vermont Agency of Transportation, written commun., August 23, 1994). The bridge is supported by vertical, concrete abutments with concrete wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 15 degrees. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on the right and left abutments and all wingwalls. The banks upstream and downstream are not protected. 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 1.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.6 to 9.2 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, 1993, p. 48). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 1 (BLOOTH00020001) on Town Highway 2, crossing Mill Brook, Bloomfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BLOOTH00020001 on town highway 2 crossing Mill Brook, Bloomfield, 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 Upland physiographic province of north-east Vermont in the town of Bloomfield. The 4.85-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage. In the study area, Mill Brook has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 28 ft and an average channel depth of 4 ft. The predominant channel bed materials are gravel and cobbles (D 50 is 57.3 mm or 0.188 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 6, 1995, indicated that the reach was stable. The town highway 2 crossing of Mill Brook is a 26-ft-long, one-lane bridge consisting of one 24-foot concrete span (Vermont Agency of Transportation, written commun., August 4, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is 10 degrees. No scour was observed along the channel or at the bridge during the Level I assessment. Type-2 stone fill (less than 24 inches diameter) was noted as present along all wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term aggradation or degradation; 2) contraction scour (due to reduction in flow area caused by a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute scour depths for contraction and local scour and a summary of the results follows. Contraction scour for all modelled flows ranged from 0 to 1.0 feet and the worst-case contraction scour occurred at the incipient overtopping discharge. Abutment scour ranged from 7.3 to 10.1 feet and the worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 43 (HARDTH00CU0043) on Church Street, crossing the Lamoille River, Hardwick, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HARDTH00CU0043 on Church Street crossing the Lamoille River, Hardwick, 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 north-central Vermont. The 87.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is best characterized as suburban except for the downstream right surface cover which is pasture. In the study area, the Lamoille River has an incised, straight channel with a slope of approximately 0.004 ft/ft, an average channel top width of 90 ft and an average channel depth of 8 ft. The predominant channel bed materials are cobble and gravel with a median grain size (DM 50 ) of 99.5 mm (0.327 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 26, 1995, indicated that the reach was stable. The Church Street crossing of the Lamoille River is a 100-ft-long, two-lane bridge consisting of one 97-foot steel-beam span (Vermont Agency of Transportation, written communication, March 17, 1995). The bridge is supported by a vertical, stone abutment with wingwalls on the left and a vertical concrete abutment with a stone spill-through slope on the right. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 0 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, 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 0.8 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 6.2 to 10.9 ft at the left abutment with worst-case occurring at the incipientovertopping discharge. Abutment scour ranged from 8.5 to 12.3 ft at the right abutment with worst-case 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 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↗
USGS1996

Level II scour analysis for Bridge 35 (BETHTH00190035) on Town Highway 19, crossing Gilead Brook, Bethel, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BETHTH00190035 on town highway 19 crossing Gilead Brook, Bethel, 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 in the town of Bethel. The 6.40-mi 2 drainage area is predominantly rural and forested. In the vicinity of the study site, the immediate banks have woody vegetation coverage with pasture beyond. In the study area, Gilead Brook is an incised, sinuous channel with a slope of approximately 0.015 ft/ft, an average channel top width of 31 ft and an average channel depth of 2.5 ft. The predominant channel bed material is gravel and cobble (D 50 is 62.5 mm or 0.205 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 20, 1994, indicated that the reach was stable. The town highway 19 crossing of Gilead Brook is a 30-ft-long, one-lane bridge consisting of one 24-foot steel-beam span with timber deck (Vermont Agency of Transportation, written commun., August 24, 1994). 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 10 degrees. The scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) at the downstream wingwalls, left abutment, and upstream right road embankment; type-2 stone fill (less than 36 inches diameter) is at 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 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 0.1 to 2.1 ft. with the worst-case scenario occurring at the 500-year discharge. Abutment scour ranged from 3.9 to 9.5 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, 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 (BETHTH00790049) on Town Highway 79, crossing Locust Creek, Bethel, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BETHTH00790049 on town highway 79 crossing Locust Creek, Bethel, 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 in the town of Bethel. The 24.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks are forested. In the study area, Locust Creek has an incised, sinuous channel with a slope of approximately 0.015 ft/ft, an average channel top width of 74 ft and an average channel depth of 6 ft. The predominant channel bed material is gravel and cobble (D 50 is 124 mm or 0.407 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 21 & 26, 1994, respectively, with a check on 12/15/94, indicated that the reach was stable. The town Highway 79 crossing of Locust Creek is a 55-ft-long, one-lane bridge consisting of one 50-foot concrete span (Vermont Agency of Transportation, written commun., August 24, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 50 degrees to the opening while the opening-skew-toroadway is 45 degrees. Scour protection measures in place at the site were type-1 stone fill (less than 12 inches diameter) at the upstream right and downstream left road embankment, type-2 stone fill (less than 36 inches diameter) at the upstream left bank, upstream wingwalls, 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 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 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 these computed results follow. Contraction scour for all modelled flows ranged from 0.0 ft to 1.0 ft. The worst-case contraction scour occurred at the 100-year discharge. Abutment scour ranged from 10.3 ft to 13.3 ft. with the worst-case abutment scour also 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 depths, are presented in tables 1 and 2. A cross-section of the computed scour 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. 22). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection, 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↗
USGS1997

Level II scour analysis for Bridge 17 (POMFTH00010017) on Town Highway 1 (FAS 166) crossing Mill Brook, Pomfret, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure POMFTH00010017 on Town Highway 1 crossing Mill Brook, Pomfret, 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 8.11-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture. In the study area, Mill Brook has a sinuous channel with a slope of approximately 0.009 ft/ ft, an average channel top width of 30 ft and an average channel depth of 3 ft. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 71.9 mm (0.236 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 1 crossing of Mill Brook is a 54-ft-long, two-lane bridge consisting of one 52-foot steel-beam span (Vermont Agency of Transportation, written communication, August 23, 1994). The bridge is supported by vertical, concrete abutments with spillthrough embankments. The channel is skewed approximately 15 degrees to the opening and the opening-skew-to-roadway is 15 degrees. The scour protection measures at the site were type-3 stone riprap (less than 48 inches diameter) on the spill-through embankments of each abutment and type-2 stone fill (less than 24 inches diameter) on the banks downstream. 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 ranged from 3.6 to 7.1 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 7 (MORRTH00020007) on Town Highway 2 (FAS 239), crossing Ryder Brook, Morristown, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MORRTH00020007 on Town Highway 2 crossing Ryder Brook, Morristown, 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 North-central Vermont. The 18.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture and forest. In the study area, Ryder Brook generally is straight and incised with a slope of approximately 0.002 ft/ft, an average channel top width of 48 ft and an average channel depth of 3 ft. The channel bed is bedrock with pockets of sand and gravel in several locations through the reach. The gravel has a median grain size (D 50 ) of 17.7 mm (0.0581 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 16, 1996 indicated that the reach was stable. The Town Highway 2 crossing of Ryder Brook is a 84-ft-long, two-lane bridge consisting of one 84-foot steel-beam span (Vermont Agency of Transportation, written communication, January 31, 1996). The bridge is supported by vertical, concrete abutment walls with spill-through embankments. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 15 degrees. The only scour protection measure at the site was type-3 stone fill (less than 48 inches diameter) on the spill-through embankments of each abutment. 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 predictions for all modelled flows at this site were zero. Abutment scour predictions ranged from 5.6 to 8.1 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. However, historical bridge records and field notes indicate the abutment footings may be set on bedrock. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 5 (IRASTH00010005) on Town Highway 1, crossing Lords Creek, Irasburg, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure IRASTH00010005 on town highway 1 crossing Lords Creek, Irasburg, Vermont (figures 1– 8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from VTAOT files, was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the New England Upland section of the New England physiographic province of north-central Vermont in the town of Irasburg. The 15.1-mi 2 drainage area is in a predominantly rural and forested basin with some pasture land mainly along the valley bottom. In the vicinity of the study site, the bank vegetation coverage is pasture grasses. In the study area, Lords Creek has a meandering channel with a slope of approximately 0.0026 ft/ft, an average channel top width of 32 ft and an average channel depth of 3 ft. The channel bed material ranged from gravel (D50 is 46.6 mm or 0.153 ft) to silt/clay material (D 50 of 1.006 mm or 0.0033 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 5 and 6, 1994, indicated that the reach was laterally unstable. The town highway 1 crossing of Lords Creek is a 65-ft-long, two-lane bridge consisting of one 61-foot, steel-beam span (Vermont Agency of Transportation, written communication, August 2, 1994). The bridge is supported by vertical, concrete abutments on wooden piles driven to bedrock with no wingwalls. Each abutment wall has a spill-through slope protected with type-2 stone fill (less than 36 inches diameter). The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 15 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, 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 2.4 to 4.6 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.2 to 9.8 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.

Vermot↗
USGS1996

Level II scour analysis for Bridge 35 (BRNATH00680035) on Town Highway 68, crossing Locust Creek, Barnard, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRNATH00680035 on town highway 68 crossing Locust Creek, Barnard, 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 in the town of Barnard. The 24.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have woody vegetation coverage. In the study area, Locust Creek has an incised sinuous channel with a slope of approximately 0.0133 ft/ft, an average channel top width of 58 ft and an average channel depth of 5 ft. The predominant channel bed material is cobble (D 50 is 135 mm or 0.443 ft). The geomorphic assessment at the time of the Level I and Level II site visits on September 21 and 27, respectively, with a check on December 15, 1994, indicated that the reach was stable. The town highway 68 crossing of Locust Creek is a 30-ft-long, one-lane bridge consisting of one 28-foot concrete slab type superstructure (Vermont Agency of Transportation, written commun., August 23, 1994). 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. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the right abutment and downstream right wingwall during the Level I assessment. The only scour protection measure in place at the site was type-2 stone fill (less than 36 inches diameter) at the left abutment and wingwalls except the downstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D. 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 3.4 ft. The worst-case contraction scour occurred at the incipient overtopping discharge, which was between the 100- and 500-year discharges. Abutment scour ranged from 11.5 to 25.7 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. and E.

Vermont↗
USGS1996

Level II scour analysis for Bridge 4 (CRAFTH00040004) on Town Highway 4, crossing Whitney Brook, Craftsbury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CRAFTH00040004 on town highway 4 crossing Whitney Brook, Craftsbury, 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 secton of the New England physiographic province of north-central Vermont in the town of Craftsbury. The 13.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage. In the study area, Whitney Brook has an incised, sinuous channel with a slope of approximately 0.014 ft/ft, an average channel top width of 40 ft and an average channel depth of 3 ft. The observed predominant channel bed material is cobble and boulder while results from the pebble count provided a D 50 of 78.5 mm or 0.258 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 4 crossing of Whitney Brook is a 41-ft-long, one-lane bridge consisting of one 39-foot span steel-beam and concrete superstructure (Vermont Agency of Transportation, written commun., August 3, 1994). The bridge is supported by slightly sloping, mortared stone block abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 20 degrees. A scour hole 2 ft deeper than the mean thalweg depth was observed along the upstream right wingwall and right abutment during the Level I assessment. There were no scour protection measures evident at the site. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock riprap 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 degradation; 2) contraction scour (due to accelerated flow caused by 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 computed scour results follow. Contraction scour for all modelled flows ranged from 0.7 to 1.7 feet. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 10.7 to 15.3 feet. 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 33 (HUNTTH00220033) on Town Highway 22, crossing Brush Brook, Huntington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HUNTTH00220033 on Town Highway 22 crossing Brush Brook, Huntington, 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 8.65-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest except on the downstream right overbank which is pasture. In the study area, Brush Brook has an incised, straight channel with a slope of approximately 0.04 ft/ft, an average channel top width of 42 ft and an average bank height of 3 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 76.7 mm (0.252 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 26, 1996, indicated that the reach was stable. The Town Highway 22 crossing of Brush Brook is a 40-ft-long, two-lane bridge consisting of one 23.5-foot concrete slab span (Vermont Agency of Transportation, written communication, November 30, 1995). The opening length of the structure parallel to the bridge face is 36.9 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 35 degrees to the opening while the opening-skew-to-roadway is 30 degrees. The scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the left and right banks upstream that extended through the bridge and along the downstream banks. 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 analyzed since it has the potential of being the 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 ranged from 0.0 to 1.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.5 to 14.9 ft. The worst-case abutment scour occurred at the incipient roadway-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↗
USGS1996

Level II scour analysis for Bridge 12 (BRAITH00230012) on Town Highway 23, crossing Ayers Brook, Braintree, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRAITH00230012 on town highway 23 crossing Ayers Brook, Braintree, 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 in the town of Braintree. The 18.8-mi 2 drainage area is in a predominantly rural watershed. In the vicinity of the study site, the surface cover of the left and right banks is pasture. In the study area, Ayers Brook has a meandering channel with a slope of approximately 0.003 ft/ft, an average channel top width of 46 ft and an average channel depth of 5 ft. The predominant channel bed material is sand and gravel (D 50 is 6.15 mm or 0.0202 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 16, 1994, indicated that the reach was laterally unstable. Also at the time of the site visit, there was considerable backwater at the bridge site due to a beaver dam downstream. The beaver dam was ignored in the analyses. The town highway 23 crossing of Ayers Brook is a 28-ft-long, one-lane bridge consisting of one 23-foot span (Vermont Agency of Transportation, written communication, August 24, 1994). The bridge is supported by vertical timber cribwork abutments with wingwalls on the upstream and downstream sides of the right abutment. The lower half of the right abutment and wingwalls are constructed of laid-up stone. The right abutment and wingwalls are also protected by stone fill. The channel is skewed approximately 45 degrees to the opening while the opening-skew-to-roadway is only 5 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 4.2 to 9.4 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge which was less than the 100-year discharge. Abutment scour ranged from 4.3 to 17.5 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, 1993, p. 48). 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 (PUTNTH00010026) on Town Highway 1, crossing Sacketts Brook, Putney, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure PUTNTH00010026 on Town Highway 1 crossing Sacketts 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 southern Vermont. The 10.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream and downstream of the bridge while the immediate banks have dense woody vegetation. In the study area, Sacketts Brook has an incised, straight channel with a slope of approximately 0.01 ft/ft, an average channel top width of 35 ft and an average bank height of 5 ft. The channel bed material is predominantly 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 August 20, 1996, indicated that the reach was stable. The Town Highway 1 crossing of Sacketts Brook is a 49-ft-long, two-lane bridge consisting of one 46-foot concrete T-beam span (Vermont Agency of Transportation, written communication, March 30, 1995). The bridge is supported by vertical, concrete abutments. The channel is skewed approximately 35 degrees to the opening while the opening-skew-to- roadway is 45 degrees. The scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) at the upstream end of the left abutment and along the entire base length of the right abutment. There was also a vertical stone wall along the upstream left bank. 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 modelled flows ranged from 0.0 to 2.7 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 7.9 to 9.9 ft. with the worst-case occurring at the 100-year discharge. Right abutment scour ranged from 12.6 to 17.0 ft. with the worst-case 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, 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 7 (WARRTH00010007) onTown Highway 1, crossing Freemans Brook, Warren, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WARRTH00010007 on Town Highway 1 crossing Freeman Brook, Warren, 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 6.45-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the predominant surface cover is grass and trees with the exception of the upstream left overbank which is forest. The banks of the channel are tree covered. In the study area, Freeman Brook has an incised, straight channel with a slope of approximately 0.03 ft/ft, an average channel top width of 51 ft and an average channel depth of 6 ft. The predominant channel bed material ranges from gravel to bedrock with a median grain size (D 50 ) of 86.8 mm (0.285 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 22, 1996 indicated that the reach was stable. The Town Highway 1 crossing of Freeman Brook is a 64-ft-long, two-lane bridge consisting of one 62-foot steel-beam span (Vermont Agency of Transportation, written communication, February 1, 1996). The bridge is supported by vertical, concrete abutments with spill-through slopes. The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 30 degrees. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the entire length of the left and right abutments and along the downstream channel banks. 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. The computed contraction scour for all modelled flows was 0.0 feet. Abutment scour ranged from 5.3 to 8.2 ft. The worst-case abutment scour occurred at the right abutment for 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 53 (WILMVT01000053) on State Route 100, crossing Cold Brook, Wilmington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WILMVT01000053 on State Route 100 crossing Cold Brook, Wilmington, 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 south-central Vermont. The 8.38-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover predominantly is pasture except for the immediate channel banks, which are tree covered. In the study area, Cold Brook has a straight channel with a slope of approximately 0.04 ft/ft, an average channel top width of 63 feet and an average bank height of 9 feet. The channel is constructed with stone fill completely covering both banks for 300 feet upstream of the site. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 66.2 mm (0.217 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 7, 1996, indicated that the reach was constructed. The State Route 100 crossing of Cold Brook is a 23-ft-long, two-lane bridge divided by a median strip consisting of one 20-foot concrete span (Vermont Agency of Transportation, written communication, November 1, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is not skewed to the opening and the opening-skew- to-roadway also is zero degrees. The scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) on the upstream banks, the upstream wingwalls, and 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 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 2.7 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 4.8 to 10.9 ft. The worst-case abutment scour occurred at the left abutment for 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.

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