Search USGS⌕ Search

SEARCH · Search USGS

Results for “Engineering Analysis”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
USGS1996

Level II scour analysis for Bridge 14 (CLARTH00010014) on Town Highway 1, crossing Cold River, Clarendon, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CLARTH00010014 on town highway 1 crossing the Cold River, Clarendon, 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 Taconic Section of the New England physiographic province in westcentral Vermont in the town of Clarendon. The 36.2-mi 2 drainage area is in a predominantly rural basin. In the vicinity of the study site, the surface cover is primarily pasture, except for the right bank upstream which is forested. In the study area, the Cold River has a sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 104 ft and an average channel depth of 3 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 103 mm (0.339 ft). The geomorphic assessment at the time of the Level I and Level II site visit on April 27, 1995, indicated that the reach was laterally unstable. This assessment was due to the cut-banks and the local anabranching occurring upstream of the bridge. The town highway 1 crossing of the Cold River is a 80-ft-long, two-lane bridge consisting of one 77-foot span (Vermont Agency of Transportation, written communication, March 13, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The left abutment and upstream wingwalls are protected by type-2 stone fill (less than 36 inches diameter). The channel is skewed approximately 10 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, 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 modelled flows ranged from 0.0 to 0.6 ft. Abutment scour ranged from 17.4 to 23.3 ft. The worst-case contraction and 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↗
USGS1996

Level II scour analysis for Bridge 36 (BRIDTH00050036) on Town Highway 5, crossing Bridgewater Hollow Brook, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050036 on town highway 5 crossing Bridgewater Hollow Brook, Bridgewater, 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 of central Vermont. The 3.60-mi 2 drainage area is in a predominantly forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage. In the study area, Bridgewater Hollow Brook has an incised, sinuous channel with a slope of approximately 0.028 ft/ft, an average channel top width of 24 ft and an average channel depth of 4 ft. The predominant channel bed material is cobble (D 50 is 196 mm or 0.644 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 2, 1994, indicated that the reach was stable. The town highway 5 crossing of Bridgewater Hollow Brook is a 30-ft-long, one-lane bridge consisting of one 27-foot steel-beam span (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening and the opening-skew-to-roadway is also 30 degrees. The scour protection measures at this site were sparse type-2 stone fill (less than 36 inches diameter) along both abutments, upstream wingwalls, and the downstream left wingwall and type-1 stone fill (less than 12 inches diameter) along 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 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. There was no contraction scour for all modelled flows. Abutment scour ranged from 4.9 to 7.0 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 94 (FERDVT01050094) on State Route 105, crossing the Nulhegan River, Ferdinand, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FERDVT01050094 on State Route 105 crossing the Nulhegan River, Ferdinand, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the White Mountain section of the New England physiographic province in northeastern Vermont. The 38.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is grass and brush with wetlands immediately adjacent to the stream channel. In the study area, the Nulhegan River has a meandering channel with a slope of approximately 0.002 ft/ft, an average channel top width of 60 ft and an average channel depth of 6 ft. The predominant channel bed material is sand with a median grain size (D 50 ) of 0.465 mm (0.00153 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 5, 1995, indicated that the reach was laterally unstable. The State Route 105 crossing of the Nulhegan Riveris a 44-ft-long, two-lane bridge consisting of one 42-foot steel-beam span (Vermont Agency of Transportation, written communication, March 6, 1995). 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 zero degrees. Scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on the upstream right bank, the upstream right wingwall, the right abutment, the downstream end of the left abutment and the downstream 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 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 1.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.6 to 11.0 ft. The worst-case abutment scour also occurred at the 500-year discharge. Total scour depths computed for this site were not below the bottom of the footings, except for the 500- year discharge model at the left abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A crosssection of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 42 (NEWFTH00350042) on Town Highway 35, crossing Stratton Hill Brook, Newfane, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NEWFTH00350042 on Town Highway 35 crossing Stratton Hill Brook, Newfane, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (FHWA, 1993). Results of a Level I scour investigation also are included in appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in appendix D. The site is in the New England Upland section of the New England physiographic province in southeastern Vermont. The 1.16-mi2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forested. In the study area, Stratton Hill Brook has an incised, striaght channel with a slope of approximately 0.1 ft/ft, an average channel top width of 36 ft and an average bank height of 8 ft. The channel bed material ranges from gravel to boulders with a median grain size (D50) of 121 mm (0.396 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 34 crossing of Stratton Hill Brook is a 34-ft-long, one-lane bridge consisting of a 32-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 30.8 ft. The bridge is supported by vertical, concrete abutments with upstream wingwalls. The channel is skewed approximately 20 degrees to the opening while the computed opening-skew-to-roadway is 15 degrees. During the Level I assessment, it was observed that the right abutment footing was exposed 1.5 feet. The only scour protection measure at the site was type-1 stone fill (less than 12 inches diameter) along the downstream 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 Davis, 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 ft. Abutment scour ranged from 2.3 to 3.3 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 Davis, 1995, p. 46). 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 15 (BRIDTH00220015) on Town Highway 22, crossing Dailey Hollow Branch, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00220015 on town highway 22 crossing Dailey Hollow Branch, Bridgewater, 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 of central Vermont in the town of Bridgewater. The 1.73-mi2 drainage area is a predominantly rural and forested basin. In the vicinity of the study site, the left and right banks have dense tree cover. The upstream right bank of Dailey Hollow Branch is adjacent to town highway 22. In the study area, Dailey Hollow Branch has a sinuous channel with a slope of approximately 0.035 ft/ft, an average channel top width of 30 ft and an average channel depth of 4 ft. The predominant channel bed material is cobble with a median grain size (D50) of 108 mm (0.354 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 1 and 2, 1994, indicates that the reach is stable. The town highway 22 crossing of Dailey Hollow Branch is a 22-ft-long, one-lane bridge consisting of one 22-ft. steel-beam span (Vermont Agency of Transportation, written communication, August 24, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. Type-1 stone fill (less than 12 inches diameter) protects the left abutment, but it’s condition was reported as eroded. Type-2 stone fill (less than 36 inches diameter) protects the upstream left wingwall; it’s condition was reported as slumping.The channel is skewed approximately 40 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, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.2 ft. with the worst-case contraction scour occurring at the 500-year discharge. Abutment scour ranged from 4.2 to 6.4 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. 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 24 (WODSTH00190024) on Town Highway 19, crossing North Bridgewater Brook, Woodstock, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WODSTH00190024 on Town Highway 19 crossing North Bridgewater Brook, Woodstock, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of east-central Vermont in the town of Woodstock. The 3.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the left and right banks are covered by moderate tree cover along the immediate banks with some pasture/ grassland beyond. In the study area, the North Bridgewater Brook has a sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 44 ft and an average channel depth of 4 ft. The channel bed materials ranges from sand to boulders with a D 50 (median diameter)of 70.1 mm or 0.229 ft. The geomorphic assessment at the time of the Level I and Level II site visits on August 17, 1994 and December 13, 1994, indicated that the reach was stable. Localized bank cutting existed at the immediate downstream left bank. The Town Highway 19 crossing of the North Bridgewater Brook is a 26-ft-long, one-lane bridge consisting of one 23-ft steel-beam span (Vermont Agency of Transportation, written commun., August 3, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. Type-2 (less than 3 ft diameter) stone fill protects the upstream left wingwall which is impacted by flow. The channel bed under the bridge is constructed of wood. This construction is preventing channel degradation along the impacted left abutment.The channel is skewed approximately 40 degrees to the opening; the opening-skew-to-roadway is 10 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.8 ft. Abutment scour ranged from 6.6 to 14.9 ft. with the worst-case scenario occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
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↗
USGS1996

Level II scour analysis for Bridge 51 (BRIDTH00460051) on Town Highway 46, crossing Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00460051 on town highway 46 crossing the Ottauquechee River, Bridgewater, 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 division of central Vermont in the town of Bridgewater. The 103-mi 2 drainage area is a predominantly rural basin. In the vicinity of the study site, the immediate left and right banks are covered by trees and brush with residences beyond. In the study area, the Ottauquechee River has a straight channel with a slope of approximately 0.008 ft/ft, an average channel top width of 150 ft and an average channel depth of 6 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 81.8 mm (0.268 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 24, 1994, indicated that the reach was stable. The town highway 46 crossing of the Ottauquechee Riveris a 135-ft-long, two-lane bridge consisting of two 66-ft steel-beam spans, supported by vertical, concrete abutments with upstream wingwalls and one concrete pier (Vermont Agency of Transportation, written commun., August 24, 1994). Type-2 stone fill (less than 36 inches diameter) has been placed along the left abutment and both upstream wingwalls. The upstream side of both road embankments are also protected by type-2 stone fill. Abutments of a previous bridge still exist at the downstream side of the present structure’s abutments. The channel is skewed 10 degrees to the bridge face; the opening-skew-to-roadway is 0 degrees. There are remains of a breached dam 160 feet upstream of the bridge which deflect flow toward the left bank. Additional details describing conditions at the site are included in the Level II Summary, Appendix D, and Appendix 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 2.6 to 5.4 ft. The worst-case contraction scour occurred at the incipient overtopping discharge, which was between the 100- and 500-year discharges. Pier scour ranged from 9.9 to 10.9 ft with the worst-case scenario also occurring at the incipient roadway overtopping discharge. Abutment scour ranged from 25.3 to 33.6 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, 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↗
USGS1997

Level II scour analysis for Bridge 32 (NFIEVT012A0032) on State Route 12A, crossing the Dog River, Northfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NFIEVT012A0032 on State Route 12A crossing the Dog River, Northfield, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 13.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture (golf course). In the study area, the Dog River has a straight channel with a slope of approximately 0.01 ft/ ft, an average channel top width of 47 ft and an average bank height of 7 ft. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 39.0 mm (0.128 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 State Route 12A crossing of the Dog River is a 35-ft-long, two-lane bridge consisting of one 32-foot concrete span (Vermont Agency of Transportation, written communication, October 13, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening and the opening-skew-to- roadway also is 30 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the upstream end of the right abutment wall during the Level I assessment. The scour protection measures at the site were type-1 stone fill (less than 12 inches diameter) on the right bank downstream and type-2 stone fill (less than 36 inches diameter) on the upstream banks, the downstream left bank and 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, 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 1.5 to 2.9 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 7.2 to 1 2.7 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↗
USGS1998

Level II scour analysis for Bridge 33 (WWINTH00300033) on Town Highway 30, crossing Mill Brook, West Windsor, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WWINTH00300033 on Town Highway 30 crossing Mill Brook, West Windsor, 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 (FHWA, 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 24.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream of the bridge while the immediate banks have dense woody vegetation. Downstream of the bridge is forested. In the study area, Mill Brook has an incised, sinuous channel with a slope of approximately 0.004 ft/ft, an average channel top width of 58 ft and an average bank height of 5 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 65.7 mm (0.215 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 5, 1996, indicated that the reach was stable. The Town Highway 30 crossing of the Mill Brook is a 46-ft-long, one-lane covered bridge consisting of a 40-foot wood-beam span (Vermont Agency of Transportation, written communication, March 23, 1995). The opening length of the structure parallel to the bridge face is 36.3 ft. The bridge is supported by vertical, concrete capped laid-up stone abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is zero degrees. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the upstream right bank, the upstream right wingwall, the right 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 Davis, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was analyzed since it had 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 0.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.0 to 16.0 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. Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

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

This report provides the results of a detailed Level II analysis of scour potential at structure JAMATH00010026 on Town Highway 1 crossing Ball Mountain Brook, Jamaica, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in southern Vermont. The 29.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, Ball Mountain Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 74 ft and an average bank height of 6 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 82.6 mm (0.271 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 12, 1996, indicated that the reach was stable. The Town Highway 1 crossing of Ball Mountain Brook is a 80-ft-long, two-lane bridge consisting of one 78-foot steel-beam span (Vermont Agency of Transportation, written communication, March 29, 1995). The opening length of the structure parallel to the bridge face is 75.7 ft. The bridge is supported by vertical, concrete abutments with wingwalls. A scour hole 2 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. The scour protection measures at the site were type-4 stone fill (less than 60 inches diameter) along the left bank upstream and extending underneath the bridge and along the bank downstream and also along the right bank upstream tapering to type-3 stone fill (less than 48 inches diameter) at the upstream end of the upstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for the modelled flows ranged from 1.0 to 2.7 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 8.4 to 17.6 ft. The worst-case abutment scour for the right abutment occurred at the incipient-overtopping discharge. For the left abutment, the worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 29 (CRAFTH00550029) on Town Highway 55, crossing the Black River, Craftsbury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CRAFTH00550029 on town highway 55 crossing the Black River, 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 section of the New England physiographic province of north-central Vermont in the town of Craftsbury. The 24.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have woody vegetation coverage except for the upstream left bank and the downstream right bank, which have more brush cover than trees. In the study area, the Black River has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 41 ft and an average channel depth of 5.5 ft. The predominant channel bed material is sand and gravel (D 50 is 44.7 mm or 0.147 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 55 crossing of the Black Riveris a 32-ft-long, one-lane bridge consisting of one 28-foot span steel stringer superstructure with a timber deck (Vermont Agency of Transportation, written communication, August 4, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 40 degrees to the opening while the opening-skew-to-roadway is 10 degrees. A scour hole 2 ft deeper than the mean thalweg depth was evident at mid-channel immediately downstream of the bridge during the Level I assessment. The only scour protection measure at the site was type-1 stone fill (less than 12 inches diameter) on the upstream right bank and road approach embankment. 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 0.9 to 1.4 ft. The worst-case contraction scour occurred at the 100-year discharge. Abutment scour ranged from 12.1 to 15.5 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, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 37 (BARTUS00050166) on U.S. Route 5, crossing Barton River, Barton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BARTUS00050166 on U. S. Route 5 crossing the Barton River, Barton, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province of north-central Vermont in the town of Barton. The 65.2-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have a combination of dense woody vegetation coverage, brush, and field grasses. In the study area, the Barton River has an incised, sinuous-to-meandering channel with a slope of approximately 0.0065 ft/ft, an average channel top width of 58 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel (D 50 is 75.6 mm or 0.25 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 19, 1994, indicated that the reach was stable. The U. S. Route 5 crossing of the Barton River is a 126-ft-long, two-lane bridge consisting of one 60-foot steel beam span with two steel-beam approach spans (Vermont Agency of Transportation, written communication, August 4, 1994). The bridge is supported by two concrete piers. The left bank has a concrete retaining wall that is attached to the US face of the left pier; consequently this pier functions as an abutment for the analysis because no flow occurs to the left of the pier. For the purposes of computing scour, this pier was considered an abutment. The channel is skewed approximately 40 degrees to the opening while the opening-skew-to-roadway is 25 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the right pier during the Level I assessment. Scour protection measures at the site consist of type-1 stone fill (less than 12 inches diameter) along the entire base length of both piers. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.1 to 2.4 ft. Abutment-type scour was computed for the left pier; scour ranged from 9.1 to 11.3 ft. Abutment scour at the right abutment ranged from 6.1 to 11.3 ft. Pier scour, computed for the right pier, ranged from 31.3 to 33.3 ft. The severity of the pier scour was directly related to the attack angle of 25 degrees. The worst-case scour in all computations occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

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

This report provides the results of a detailed Level II analysis of scour potential at structure WODSTH00990049 on Town Highway 99 crossing the Gulf Brook, Woodstock, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in east-central Vermont. The 16.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the primary surface cover is pasture except for upstream right of the bridge which is cover by trees and brush. The immediate banks throughout the reach have scattered woody vegetation. In the study area, the Gulf Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 91 ft and an average channel depth of 6 ft. The channel bed materials range from sand to cobble with a median grain size (D 50 ) of 85.3 mm (0.280 ft). The geomorphic assessment at the time of the Level I site visits on September 15, 1994 and December 14, 1994, indicated that the reach was stable. The Town Highway 99 crossing of the Gulf Brook is a 56-ft-long, one-lane bridge consisting of one 55-foot steel-beam span (Vermont Agency of Transportation, written communication, April 4, 1995). The bridge is supported by vertical, concrete abutments with a spill-through slope constructed of large quarried stone. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 0 degrees. Erosion at the right abutment has undermined the toe of the spill-through slope by nearly a foot. Material has been removed from under the stone spill-through slope so that 0.5 feet of horizontal penetration was possible at the time of the visits. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour at the left abutment ranged from 3.1 to 10.3 ft. with the worst-case occurring at the 500-year discharge. Abutment scour at the right abutment ranged from 6.4 to 10.4 ft. with the worst-case occurring at the 100-year discharge.Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 22 (BRADTH00270022) on Town Highway 27, crossing the Waits River, Bradford, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRADTH00270022 on Town Highway 27 crossing the Waits River, Bradford, 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 (FHWA, 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 New England Upland section of the New England physiographic province in east-central Vermont. The 153-mi 2 drainage area is in a predominantly rural and forested basin. However, in the vicinity of the study site, the upstream and downstream left banks are suburban and the upstream and downstream right banks are shrub and brushland. In the study area, the Waits River has an incised, sinuous channel with a slope of approximately 0.0002 ft/ft, an average channel top width of 125 ft and an average bank height of 4 ft. The channel bed material ranges from silt and clay to bedrock with a median grain size (D 50 ) of 0.393 mm (0.00129 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 7, 1995, indicated that the reach was stable. The Town Highway 27 crossing of the Waits River is a 109-ft-long, one-lane bridge consisting of a 104-ft steel-truss span (Vermont Agency of Transportation, written communication, March 16, 1995). The opening length of the structure parallel to the bridge face is 99.2 ft. The bridge is supported by vertical, laid-up stone abutments. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is zero degrees. No evidence of scour was observed during the Level I assessment. Scour protection measures at the site included type-2 stone fill (less than 36 inches diameter) along the upstream right and downstream left banks and type-3 stone fill (less than 48 inches diameter) along 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 Davis, 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 1.5 to 2.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 11.8 to 18.8 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results.” Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and Davis, 1995, p. 46). 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 11R (ROCKTH0001011R) on Town Highway 1 (VT 121 & FAS 125), crossing the Saxtons River, Rockingham, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ROCKTH0001011R on Town Highway 1 crossing the Saxtons River, Rockingham, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in southeastern Vermont. The 68.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of houses, short grass, and scattered trees except along the immediate river banks, which are tree covered. In the study area, the Saxtons River has a sinuous channel with a slope of approximately 0.005 ft/ft, an average channel top width of 121 ft and an average bank height of 8 ft. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 109 mm (0.359 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 3, 1996, indicated that the reach was laterally unstable. Lateral instability was evident with respect to a cut-bank on the left bank upstream with slip failure of bank material. Furthermore, there is a wide point bar along the right bank upstream opposite the cut-bank. The Town Highway 1 crossing of the Saxtons River is a 184-ft-long, two-lane bridge consisting of three steel-beam spans (Vermont Agency of Transportation, written communication, March 30, 1995). The bridge is supported by vertical, concrete, skeletal-style abutment walls with spill-through embankments adjacent to each wall. The channel is skewed approximately 35 degrees to the opening while the opening-skew-to-roadway is 30 degrees. The only scour protection measure at the site was type-3 stone fill (less than 48 inches diameter) on the spill-through embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term 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. There was no computed contraction scour for all modelled flows at this site. Abutment scour ranged from 9.0 to 13.4 feet. The worst-case abutment scour occurred at the 500-year discharge for the left abutment. There are two piers for which computed pier scour ranged from 9.0 to 18.4 feet. The left and right piers in this report are presented as pier 1 and pier 2, respectively. The worst-case pier scour occurred at pier 2 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.

Vermont↗
USGS1996

Level II scour analysis for Bridge 28 (HARDTH00300028) on Town Highway 30, crossing the Lamoille River, Hardwick, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HARDTH00300028 on town highway 30 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 63.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover upstream and on the downstream right is primarily pasture with some row crops. Trees line the immediate channel banks. The left bank downstream surface cover is primarily brush. In the study area, the Lamoille River has an incised, sinuous channel with a slope of approximately 0.002 ft/ft, an average channel top width of 76 ft and an average bank height of 6 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 46.6 mm (0.153 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 25, 1995, indicated that the reach was laterally unstable. The site was revisited on August 21, 1995, after the August 5-6, 1995 flood on the Lamoille River. Findings from this follow-up visit are presented in Appendix G. The town highway 30 crossing of the Lamoille River is a 54-ft-long, one-lane bridge consisting of one 52-foot steel-beam span (Vermont Agency of Transportation, written communication, April 3, 1995). The bridge is supported by vertical, stone abutments with wingwalls. Scour, about one foot below the mean thalweg, exists along the right abutment and right upstream wingwall. Sheet piling has been driven around the right abutment and wingwalls and filled with concrete. 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 1.9 to 2.5 ft. The worst-case contraction scour occurred at the 100-year discharge. Abutment scour ranged from 11.2 to 17.8 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 23 (CRAFTH00390023) on Town Highway 39, crossing the Black River, Craftsbury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CRAFTH00390023 on town highway 39 crossing the Black River, 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). A Level I assessment is included in Appendix E of this report. A Level I assessment 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 is provided in Appendix D. The site is in the New England Upland physiographic province of North-central Vermont in the town of Craftsbury. The 30.9-mi 2 drainage area is in a predominantly rural and forested basin with some pasture grassland on the valley bottom. In the vicinity of the study site, the banks have very little woody vegetation coverage except for the downstream left bank, which has some trees and brush coverage. In the study area, the Black River has an meandering channel with a slope of approximately 0.0004 ft/ft, an average channel top width of 62 ft and an average channel depth of 3 ft. The predominant channel bed materials are sand and gravel with a median grain size (D 50 ) of 0.73 mm (0.0024 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 6, 1995, indicated that the reach was laterally unstable. The town highway 39 crossing of the Black River is a 65-ft-long, two-lane bridge consisting of three spans with a maximum span of 38-feet (Vermont Agency of Transportation, written communication, August 24, 1994). The bridge is supported by vertical, concrete abutments and two stone piers with concrete caps. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 10 degrees in the opposite direction. The scour protection measures at the site were type-1 stone fill (less than 12 inches diameter) on the upstream left and right roadway embankments and between the right pier and right abutment wall. Type-2 (less than 36 inches diameter) stone fill was evident on the upstream left bank, downstream right bank, between the left pier and left abutment wall, and streamward of the right pier. 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 20.1 to 25.2 and the worst-case contraction scour occurred at the 500-year discharge. Although this bridge has two piers, the flow through the spans between each abutment and pier is assumed to be negligible. Hence, abutment scour was computed assuming the forces contributing to scour actually occur on the main-span sides of each pier in this case. Abutment scour ranged from 8.8 to 10.6 and the worst-case abutment scour occurred at the 500-year discharge. Scour depths and depths to armoring are summarized on p. 14 in the section titled “Scour Results”. Scour elevations, based on the calculated depths are presented in tables 1 and 2. A graph of the scour elevations 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↗