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USGS1997

Level II scour analysis for Bridge 29 (LONDTH00410029) on Town Highway 41, crossing Cook Brook, Londonderry, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure LONDTH00410029 on Town Highway 41 crossing Cook Brook, Londonderry, 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 6.48-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is shrub on the left bank upstream and downstream of the bridge while the right bank is forest upstream and downstream of the bridge. In the study area, Cook Brook has a straight incised channel with a slope of approximately 0.02 ft/ft, an average channel top width of 80 ft and an average bank height of 8 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 70.9 mm (0.233 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 stable. The Town Highway 41 crossing of Cook Brook is a 25-ft-long, one-lane bridge consisting of one 22-foot steel-beam span (Vermont Agency of Transportation, written communication, April 6, 1995). The opening length of the structure parallel to the bridge face is 20.4 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the opening-skew-toroadway is 0 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the upstream left wingwall and left abutment during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches) along the downstream end of the left abutment and upstream end of the 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 0.0 to 1.5. Abutment scour ranged from 8.4 to 15.1 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 15 (TROYTH00290015) on Town Highway 29, crossing Beetle Brook, Troy, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure TROYTH00290015 on Town Highway 29 crossing Beetle Brook, Troy, 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 8.97-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest except for the downstream right bank which is grass. In the study area, Beetle Brook has an incised, sinuous channel with a slope of approximately 0.02 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 boulder with a median grain size (D 50 ) of 118 mm (0.387 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 29 crossing of Beetle Brook is a 30-ft-long, one-lane bridge consisting of one 25-foot steel-beam span (Vermont Agency of Transportation, written communication, March 7, 1994). The opening length of the structure parallel to the bridge face is 23.4 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the opening-skew-toroadway is 0 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. Scour counter measures at the site include type-3 stone fill (less than 48 inches diameter) at the downstream end of the downstream right wingwall, type-2 stone fill (less than 36 inches diameter) along the downstream left wingwall and the upstream left road embankment, and type-1 stone fill (less than 12 inches diameter) at the upstream right 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 0.0 to 0.6 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Left abutment scour ranged from 8.0 to 8.9 ft. The worst-case left abutment scour occurred at the 500-year discharge. Right abutment scour ranged from 15.4 to 16.5 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”. 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 16 (TROYTH00290016) on Town Highway 29, crossing Beetle Brook, Troy, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure TROYTH00290016 on Town Highway 29 crossing Beetle Brook, Troy, 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 8.70-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, Beetle Brook has an incised, sinuous channel with a slope of approximately 0.01 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 61.9 mm (0.203 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 8, 1995, indicated that the reach was stable. The Town Highway 29 crossing of Beetle Brook is a 26-ft-long, one-lane bridge consisting of one 23-foot log-beam span (Vermont Agency of Transportation, written communication, March 7, 1995). The opening length of the structure parallel to the bridge face is 20.0 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the measured opening-skew-toroadway is 10 degrees. A scour hole 1.2 ft deeper than the mean thalweg depth was observed along the failed downstream right wingwall during the Level I assessment. The scour counter-measures at the site included type-2 stone fill (less than 36 inches diameter) at the upstream end of the upstream right wingwall and at 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 1.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 9.2 to 13.4 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↗
USGS1997

Level II scour analysis for Bridge 39 (LOWETH00080039) on Town Highway 8, crossing Potter Brook, Lowell, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure LOWETH00080039 on Town Highway 8 crossing Potter Brook, Lowell, 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 4.69-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of shrub and brushland, except for the left overbank upstream which is forest. In the study area, Potter Brook has a sinuous channel with a slope of approximately 0.004 ft/ft, an average channel top width of 34 feet and an average bank height of 3 ft. The predominant channel bed materials are gravel and sand with a median grain size (D 50 ) of 18.7 mm (0.0613 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 15, 1995, indicated that the reach was laterally unstable. This assessment of the reach was primarily due to the meandering of the channel with cut-banks and narrow point bars and the fine bank and bed material near the site. The Town Highway 8 crossing of Potter Brook is a 23-ft-long, one-lane bridge consisting of one 21-foot steel-beam span (Vermont Agency of Transportation, written communication, March 7, 1995). 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 2.0 feet deeper than the mean thalweg depth was observed along the left 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 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 0.3 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 1.8 to 5.5 feet. The worst-case abutment scour 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 7 (WALDTH00020007) on Town Highway 2, crossing Coles Brook, Walden, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WALDTH00020007 on Town Highway 2 crossing Coles Brook, Walden, Vermont (figures 1–8). Coles Brook is also referred to as Joes Brook. 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-eastern Vermont. The 12.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly shrub and brushland. In the study area, Coles Brook has a sinuous channel with a slope of approximately 0.005 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 cobble with a median grain size (D 50 ) of 32.9 mm (0.108 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 9, 1995, indicated that the reach was laterally unstable due to cut-banks, point bars, and loose unconsolidated bed material. The Town Highway 2 crossing of Coles Brook is a 74-ft-long, two-lane bridge consisting of one 71-foot steel-beam span (Vermont Agency of Transportation, written communication, April 5, 1995). The opening length of the structure parallel to the bridge face is 69.3 ft. The bridge is supported by spill-through abutments. The channel is skewed approximately 35 degrees to the opening while the measured opening-skew-to-roadway is 15 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed from 60 ft. to 100 ft. downstream during the Level I assessment. Scour protection measures at the site include: type-1 stone fill (less than 12 inches diameter) along the right bank upstream, at the downstream end of the downstream left wingwall and downstream right wingwall; and type-2 stone fill (less than 36 inches diameter) along the left bank upstream, at the upstream end of the upstream right wingwall, and along the entire base of the left and right abutments. 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 0.8 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge. Abutment scour ranged from 5.7 to 12.9 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 2 (RYEGTH00020002) on Town Highway 2, crossing the Wells River, Ryegate, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RYEGTH00020002 on Town Highway 2 crossing the Wells River, Ryegate, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in east-central Vermont. The 75.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of cut grass, trees, and brush on the flood plains while the immediate banks have dense woody vegetation. In the study area, the Wells River has an incised, sinuous channel with a slope of approximately 0.006 ft/ft, an average channel top width of 110 ft and an average bank height of 12 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 82.3 mm (0.270 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 24, 1995, indicated that the reach was laterally unstable with moderate fluvial erosion and meandering downstream of the bridge. The Town Highway 2 crossing of the Wells River is a 79-ft-long, two-lane bridge consisting of one 75-foot steel-beam span (Vermont Agency of Transportation, written communication, March 27, 1995). The opening length of the structure parallel to the bridge face is 75.1 ft. The bridge is supported by vertical, concrete abutments, the left has a spill-through embankment, with wingwalls. The channel is not skewed to the opening and the opening-skew-to-roadway is zero degrees. A scour hole 3 ft deeper than the mean thalweg depth was observed in the channel from upstream and through the bridge during the Level I assessment. The scour protection counter-measures at the site included type-4 stone fill (less than 60 inches diameter) along the base of the left abutment forming a spill-through embankment. There was also type-2 stone fill (less than 36 inches diameter) along the entire base length of the upstream right wingwall, the upstream right bank and downstream left bank. There was a stone wall along the upstream left bank extending 130 ft from the bridge. In addition there was type-1 stone fill (less than 12 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) for the 100- and 500-year discharges. 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 zero. Abutment scour ranged from 7.1 to 11.4 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↗
USGS1997

Level II scour analysis for Bridge 25 (REDSTH00360025) on Town Highway 36, crossing the West Branch Deerfield River, Readsboro, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure REDSTH00360025 on Town Highway 36 crossing the West Branch Deerfield River, Readsboro, 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 14.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture on the upstream right bank and forest on the upstream left bank. The surface cover on the downstream right and left banks is primarily grass, shrubs and brush. In the study area, the West Branch Deerfield River has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 65 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 117 mm (0.383 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 1, 1996, indicated that the reach was stable. The Town Highway 36 crossing of the West Branch Deerfield River is a 59-ft-long, two-lane bridge consisting of one 57-foot concrete T-beam span (Vermont Agency of Transportation, written communication, September 28, 1995). The opening length of the structure parallel to the bridge face is 54 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 30 degrees. During the Level I assessment, a scour hole approximately 2 ft deeper than the mean thalweg depth was observed along the upstream right wingwall and a scour hole approximately 1 ft deeper than the mean thalweg depth was observed along the downstream left wingwall. The scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) at the downstream end of the downstream left wingwall, at the upstream end of the upstream right wingwall, at the downstream end of the right abutment, along the entire base length of the downstream right wingwall, along the upstream right bank and along the downstream left bank. A stone wall was noted 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 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 0.6 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 15.1 to 16.3 ft along the left abutment and from 7.4 to 9.2 ft along the right abutment. The worst-case abutment scour occurred at the incipient-overtopping and 500-year discharges for the left abutment and at the 500-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 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 21 (MORETH00010021) on Town Highway 1, crossing Cox Brook, Moretown, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MORETH00010021 on Town Highway 1 crossing Cox Brook, Moretown, 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 2.85-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly forested. In the study area, Cox Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 23 ft and an average bank height of 4 ft. The channel bed material ranges from gravel to cobble with a median grain size (D 50 ) of 47.5 mm (0.156 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 18, 1996, indicated that the reach was stable. The Town Highway 1 crossing of Cox Brook is a 29-ft-long, two-lane bridge consisting of one 27-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 24.8 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 60 degrees to the opening while the measured opening-skew-to-roadway is 40 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the left abutment downstream during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the left bank upstream. 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-year 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 ranged from 0.2 to 0.5 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 2.8 to 4.0 ft. The worst-case abutment scour occurred at the left abutment at the 100-year discharge and at the right abutment 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 31 (HUNTTH00220031) 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 HUNTTH00220031 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, obtained 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 west-central Vermont. The 5.01-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of trees and brush. In the study area, Brush Brook has an incised, straight channel with a slope of approximately 0.06 ft/ft, an average channel top width of 44 ft and an average bank height of 4 ft. The channel bed material ranges from boulder to gravel with a median grain size (D 50 ) of 107.0 mm (0.352 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 25, 1996, indicated that the reach was stable. The Town Highway 22 crossing of Brush Brook is a 34-ft-long, one-lane bridge consisting of one 30-foot steel I-beam span (Vermont Agency of Transportation, written communication, November 30, 1995). The opening length of the structure parallel to the bridge face is 31.2 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the computed opening-skew-to-roadway is 10 degrees. The VTAOT computed opening-skewto-roadway is 2 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed at the downstream end of the left abutment during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the upstream 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) 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 computed to be zero ft. Abutment scour ranged from 7.0 to 10.5 ft. The worst-case abutment scour occurred at the 500-year discharge for the left abutment and at the incipient-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 16 (RIPTTH00110016) on Town Highway 11, crossing the Middle Branch Middlebury River, Ripton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RIPTTH00110016 on Town Highway 11 crossing the Middle Branch Middlebury River, Ripton, 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 west-central Vermont. The 6.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of shrubs, brush and trees except for the upstream left bank which is completely forested. In the study area, the Middle Branch Middlebury River has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 68 ft and an average bank height of 5 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 97.6 mm (0.320 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 11, 1996, indicated that the reach was stable. The Town Highway 11 crossing of the Middle Branch Middlebury River is a 44-ft-long, two-lane bridge consisting of one 42-foot steel-beam span (Vermont Agency of Transportation, written communication, December 15, 1995). The opening length of the structure parallel to the bridge face is 40.2 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 40 degrees to the opening. The opening-skew-to-roadway value from the VTAOT database is 20 degrees while 30 degrees was computed from surveyed points. A scour hole, 3 ft deeper than the mean thalweg depth, was observed along the left abutment and upstream left wingwall during the Level I assessment. In addition, 1 ft of channel scour was observed just downstream of the downstream left wingwall along the left bank. Scour countermeasures at the site included type-2 stone fill (less than 36 inches diameter) along the upstream left and right banks and along the upstream end 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) for the 100- and 500-year discharges. 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 0.4 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.2 to 8.6 ft along the right abutment and from 11.7 to 13.7 ft along the left abutment. The worstcase 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 45 (BRNETH00070045) on Town Highway 7, crossing the Stevens River, Barnet, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRNETH00070045 on Town Highway 7 crossing the Stevens River, Barnet, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in east-central Vermont. The 41.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest upstream and pasture downstream of the bridge while the immediate banks have dense woody vegetation. In the study area, the Stevens River has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 100 ft and an average bank height of 17 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 105 mm (0.344 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 22, 1995, indicated that the reach was stable. The Town Highway 7 crossing of the Stevens River is a 37-ft-long, two-lane bridge consisting of one 34-foot concrete slab span (Vermont Agency of Transportation, written communication, March 16, 1995). The opening length of the structure parallel to the bridge face is 33 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 20 degrees. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the entire left and right abutments, upstream and downstream wingwalls, and upstream and 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 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 ranged from 0.8 to 5.4 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge, which was greater than the 100-year discharge. Left abutment scour ranged from 21.8 to 28.6 ft. The worst-case left abutment scour occurred at the 500-year discharge. Right abutment scour ranged from 14.6 to 17.4 ft. The worst-case right 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↗
USGS1997

Level II scour analysis for Bridge 21 (MIDBTH00230021) on Town Highway 23, crossing the Middlebury River, Middlebury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MIDBTH00230021 on Town Highway 23 crossing the Middlebury River, Middlebury, 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 west-central Vermont. The 44.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is suburban consisting of single houses, each with a lawn, trees, and shrubs on all of the overbank areas bordering the river. In the study area, the Middlebury River has a straight channel with a slope of approximately 0.02 ft/ft, an average channel top width of 87 ft and an average channel depth of 11 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 152 mm (0.498 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 18, 1996, indicated that the reach was stable. The Town Highway 23 crossing of the Middlebury River is a 52-ft-long, two-lane bridge consisting of one 49-foot steel-beam span (Vermont Agency of Transportation, written communication, December 14, 1995). The opening length of the structure parallel to the bridge face is 42.3 feet. The bridge is supported by vertical, concrete abutments with wingwalls at each end of the left abutment only. The channel is skewed approximately 10 degrees to the opening. The opening-skew-to-roadway from the VTAOT records is zero degrees while 5 degrees was computed from surveyed points. A scour hole 1.0 foot deeper than the mean thalweg depth was observed in the channel at the upstream bridge face during the Level I assessment. The scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) on the upstream and downstream banks and the upstream and downstream left 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) 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 ranged from 1.2 to 1.8 feet. The worst-case contraction scour occurred at the incipient overtopping discharge, which is less than the 500-year discharge. Abutment scour ranged from 17.7 to 23.7 feet. 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 20 (BRISTH00270020) on Town Highway 27, crossing Little Notch Brook, Bristol, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRISTH00270020 on Town Highway 27 crossing Little Notch Brook, Bristol, 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 west-central Vermont. The 8.43-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 with trees, shrubs, and brush along the road embankments and the stream banks, except for the downstream left overbank area. Surface cover on the downstream left overbank is forest with dense undergrowth consisting of vines, shrubs, and brush. In the study area, Little Notch Brook has a sinuous channel with a slope of approximately 0.006 ft/ft, an average channel top width of 47 feet and an average bank height of 3 feet. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 66.0 mm (0.216 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 19, 1995, indicated that the reach was stable. The Town Highway 27 crossing of Little Notch Brook is a 48-ft-long, one-lane bridge consisting of one 45-foot steel pony-truss span (Vermont Agency of Transportation, written communication, November 30, 1995). The opening length of the structure parallel to the bridge face is 42.8 feet. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 1.0 feet deeper than the mean thalweg depth was observed along the upstream left wingwall and the upstream end of the left abutment during the Level I assessment. The only scour protection measure at the site was a crude, block-cut stone wall, which extended from the upstream end of the upstream left wingwall to 45 feet upstream. 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 ranged from 0.0 to 0.2 feet. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 12.2 to 13.4 feet at the left abutment and from 3.6 to 5.0 feet 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 46 (BRNETH00610046) on Town Highway 61, crossing East Peacham Brook, Barnet, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRNETH00610046 on Town Highway 61 crossing East Peacham Brook, Barnet, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in east-central Vermont. The 15.8-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, East Peacham Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 59 ft and an average bank height of 5 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 121 mm (0.397 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 23, 1995, indicated that the reach was laterally unstable with cut banks both upstream and downstream of the bridge. The Town Highway 61 crossing of East Peacham Brook is a 28-ft-long, one-lane bridge consisting of one 26-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 24.5 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the opening-skew-toroadway is zero degrees. A scour hole 0.7 ft deeper than the mean thalweg depth was observed along the upstream left wingwall extending along the left abutment during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) at the upstream end of the upstream left wingwall extending along the upstream left bank and along the entire base 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) 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 ranged from 0 to 1.2 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 10.4 to 13.9 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 5 (MORRTH00060005) on Town Highway 6, crossing Bedell Brook, Morristown, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MORRTH00060005 on Town Highway 6 crossing Bedell 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 6.28-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, shrubs, and brushland. In the study area, Bedell Brook has a sinuous channel with a slope of approximately 0.01 ft/ ft, an average channel top width of 56 ft and an average bank height of 4 ft. The predominant channel bed material is gravel with a median grain size (D 50 ) of 35.8 mm (0.117 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 laterally unstable. There are wide point bars and cut-banks with slipping bank material noted upstream and downstream of this site. The Town Highway 6 crossing of Bedell Brook is a 44-ft-long, two-lane bridge consisting of one 42-foot concrete T-beam span (Vermont Agency of Transportation, written communication, October 26, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 45 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole up to 1.5 ft deeper than the mean thalweg depth was observed along the left abutment and upstream and downstream left wingwalls during the Level I assessment. The scour protection measure at this site was type-4 stone fill (less than 60 inches diameter) on the left bank and left wingwall upstream, the left abutment 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 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 1.1 to 2.0 feet. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 3.9 to 8.6 feet. The worst-case abutment scour occurred at the 500-year event. 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 39 (STOWTH00160039) on Town Highway 16, crossing Moss Glen Brook, Stowe, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure STOWTH00160039 on Town Highway 16 crossing Moss Glen Brook, Stowe, 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 4.75-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest upstream and on the right bank downstream. The downstream left bank is pasture while the immediate bank has dense woody vegetation. In the study area, Moss Glen Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 52 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 56.5 mm (0.185 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 10, 1996, indicated that the reach was stable. The Town Highway 16 crossing of Moss Glen Brook is a 22-ft-long galvanized plate arch culvert with an opening span width of 21 ft (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the culvert face is 20.6 ft. The culvert is supported by vertical, concrete abutments with no wingwalls. The channel is skewed approximately zero degrees to the opening. The opening skew-to-roadway value from the VTAOT database is 5 degrees while zero degrees was computed from surveyed points. The only scour counter measure at the site was type-3 stone fill (less than 48 inches diameter) at the upstream and downstream ends of the left and right abutments and extending along the banks upstream and downstream. 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. 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 1.2 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 12.6 to 16.2 ft. Right abutment scour ranged from 12.1 to 14.3 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 39 (TOPSTH00510039) on Town Highway 51, crossing Tabor Branch Waits River, Topsham, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure TOPSTH00510039 on Town Highway 51 crossing the Tabor Branch Waits River, Topsham, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in east-central Vermont. The 17.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly pasture. However, beyond one bridge length on the right bank upstream the surface cover abruptly changes to forest. In the study area, the Tabor Branch Waits River has a sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 53 ft and an average bank height of 6 ft. The predominant channel bed material is cobbles with a median grain size (D 50 ) of 86.4 mm (0.283 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 30, 1995, indicated that the reach was stable. The Town Highway 51 crossing of the Tabor Branch Waits River is a 34-ft-long, one-lane bridge consisting of one 32-foot concrete slab span (Vermont Agency of Transportation, written communication, March 28, 1995). The opening length of the structure parallel to the bridge face is 31.0 ft. 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 only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the left and right bank upstream, along the base of the upstream left wingwall, upstream right wingwall, left abutment, right abutment, downstream left wingwall, downstream right wingwall, and along the left and right bank downstream. 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 ranged from 0.0 to 0.4 ft. The worst-case contraction scour occurred at the maximum free surface flow discharge, which was less than the 100-year discharge. Abutment scour ranged from 4.8 to 8.0 ft. The worst-case abutment scour occurred at 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↗
USGS1997

Level II scour analysis for Bridge 50 (STARTH00250050) on Town Highway 25, crossing Lewis Creek, Starksboro, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure STARTH00250050 on Town Highway 25 crossing Lewis Creek, Starksboro, 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 west-central Vermont. The 10.9-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 left bank downstream and upstream of the bridge. On the right bank upstream and downstream of the bridge the surface cover is forest. In the study area, Lewis Creek has an incised, straight channel with a slope of approximately 0.007 ft/ft, an average channel top width of 64 ft and an average bank height of 7 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 35.4 mm (0.116 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 12, 1996, indicated that the reach was stable. The Town Highway 25 crossing of Lewis Creek is a 28-ft-long, one-lane bridge consisting of one 25-foot steel-beam span (Vermont Agency of Transportation, written communication, December 15, 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 on all corners except the downstream left. The channel is skewed approximately zero degrees to the opening and the opening-skew-to-roadway is also zero degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. Also, the footing is exposed along the left and right abutments and all three wingwalls. The scour countermeasures at the site included type-1 stone fill (less than 12 inches diameter) along the left abutment and type-2 stone fill (less than 36 inches diameter) along the right abutment and the upstream and downstream 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) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was 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 ranged from 5.2 to 9.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 13.1 to 18.2 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↗