Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Engineering Structures”

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 379 records · Page 21Linked to original sources
USGS1997

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

This report provides the results of a detailed Level II analysis of scour potential at structure CHESVT01030016 on State Route 103 crossing the Williams River, Chester, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in southeastern Vermont. The 15.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture except for the downstream right overbank which is forested. In the study area, the Williams River has an incised, straight channel with a slope of approximately 0.008 ft/ft, an average channel top width of 56 ft and an average bank height of 6 ft. The channel bed material ranges from gravel to cobbles with a median grain size (D 50 ) of 67.5 mm (0.222 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 16, 1996, indicated that the reach was stable. The State Route 103 crossing of the Williams River is a 162-ft-long, two-lane bridge consisting of three steel-beam spans (Vermont Agency of Transportation, written communication, March 13, 1995). The opening length of the structure parallel to the bridge face is 157.7 ft.The bridge is supported by vertical, concrete abutments and piers with no wingwalls. The channel is skewed approximately 55 degrees to the opening while the opening-skew-to-roadway is also 55 degrees. The scour protection measures at the site included type-4 stone fill (less than 60 inches diameter) along the upstream left bank. There was type-3 stone fill (less than 48 inches diameter) along the upstream right bank and both spill-through embankments and both downstream banks. There was type-1 stone fill (less than 12 inches diameter) along the upstream right and downstream left road embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was 0.0. Abutment scour ranged from 6.4 to 9.0 ft. The worst-case abutment scour occurred at the 500-year discharge. Pier scour ranged from 7.9 to 10.1 ft. The worst-case pier scour occurred at the incipient-overtopping discharge for both piers. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 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 16 (GROTTH00170016) on Town Highway 17, crossing the Wells River, Groton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure GROTTH00170016 on Town Highway 17 crossing the Wells River, Groton, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in eastern Vermont. The 43.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly shrub and brushland, while the left bank downstream is forested. In the study area, the Wells River has an incised, straight channel with a slope of approximately 0.003 ft/ft, an average channel top width of 57 ft and an average bank height of 4 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 77.8 mm (0.255 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 29, 1995, indicated that the reach was stable. The Town Highway 17 crossing of the Wells River is a 43-ft-long, one-lane bridge consisting of one 41-foot steel-beam span with a concrete deck (Vermont Agency of Transportation, written communication, March 24, 1995). The opening length of the structure parallel to the bridge face is 39.4 ft. The bridge is supported by vertical, concrete abutments. The channel is skewed approximately 0 degrees and the opening-skew-toroadway is also zero degrees. A scour hole 1.7 ft deeper than the mean thalweg depth was observed from 30 ft upstream to 70 ft downstream in mid-channel during the Level I assessment. Scour protection measures at the site included: type-3 stone fill (less than 48 inches diameter) along the left and right bank upstream, and along the left and right bank downstream. The protection along the banks begins in the road embankment areas where the wingwalls would be located. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge is determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was 0 ft. Abutment scour ranged from 7.6 to 8.4 ft at the left abutment and from 9.9 to 14.8 ft at the right abutment. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A 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 27 (WSTOTH00070027) on Town Highway 7, crossing Jenny Coolidge Brook, Weston, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WSTOTH00070027 on Town Highway 7 crossing Jenny Coolidge Brook, Weston, 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 Green Mountain section of the New England physiographic province in southwestern Vermont. The 2.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture downstream of the bridge while upstream of the bridge is forested. In the study area, the Jenny Coolidge Brook has an incised, sinuous channel with a slope of approximately 0.04 ft/ft, an average channel top width of 51 ft and an average bank height of 6 ft. The channel bed material ranges from sand to boulders with a median grain size (D 50 ) of 122 mm (0.339 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 7 crossing of the Jenny Coolidge Brook is a 52-ft-long, two-lane bridge consisting of a 50-foot steel-beam span (Vermont Agency of Transportation, written communication, April 7, 1995). The opening length of the structure parallel to the bridge face is 49.2 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the computed opening-skew-to-roadway is 15 degrees. The legs of the skeleton-type right abutment were exposed approximately 2 feet (vertically) and approximately 2 feet (horizontally) during the Level I assessment. Scour protection measures at the site include type-1 stone fill (less than 12 inches diameter) along the downstream right wingwall, and type-2 stone fill (less than 36 inches diameter) along the upstream banks, upstream left wingwall, left abutment, downstream left wingwall and downstream left bank. A stone wall levee extends 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 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 3.0 to 4.1 ft. The worst-case left abutment scour occurred at the 100-year discharge. The worst-case right abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particlesize 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 53 (CAMBTH00750053) on Town Highway 75, crossing the Brewster River, Cambridge, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CAMBTH00750053 on Town Highway 75 crossing the Brewster River, Cambridge, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in northwestern Vermont. The 4.30-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 overbank area which has a barn surrounded by grass and shrubs. In the study area, the Brewster River has an incised, straight channel with a slope of approximately 0.05 ft/ft, an average channel top width of 62 ft and an average bank height of 12 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 84.4 mm (0.277 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 11, 1995, indicated that the reach was stable. The Town Highway 75 crossing of the Brewster River is a 28-ft-long, two-lane bridge consisting of one 24-foot concrete tee-beam span (Vermont Agency of Transportation, written communication, March 8, 1995). The opening length of the structure parallel to the bridge face is 22.4 ft. 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 as surveyed is 10 degrees. A scour hole 1 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. The scour counter-measures at the site included type-3 stone fill (less than 48 inches diameter) along the entire base length of the upstream left wingwall. There was also type-4 stone fill (less than 60 inches diameter) along the downstream 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 1.1 to 1.4 ft. The worst-case contraction scour occurred at the 100-year discharge. Abutment scour ranged from 10.7 to 17.3 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 36 (STOWTH00430036) on Town Highway 43, crossing Miller Brook, Stowe, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure STOWTH00430036 on Town Highway 43 crossing the Miller 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 5.5-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, the Miller Brook has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 43 ft and an average bank height of 7 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 70.4 mm (0.231 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 15, 1996, indicated that the reach was stable. The Town Highway 43 crossing of the Miller Brook is a 24-ft-long, two-lane bridge consisting of one 21-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 21.5 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening and the computed opening-skew-to-roadway is also 10 degrees. The footing on the left abutment was exposed 2.5 ft and the footing on the right abutment was exposed 3.0 ft during the Level I assessment. Scour protection measures at the site were type-4 stone fill (less than 60 inches diameter) on the left and right bank upstream, type-3 stone fill (less than 48 inches diameter) along the entire base length of the upstream right wingwall, right abutment, and type-2 stone fill (less than 36 inches diameter) along the entire base length of the downstream right wingwall, and left and right banks 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 0.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 3.1 to 6.5 ft. 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 25 (DANVTH00610025) on Town Highway 61, crossing Water Andric Brook, Danville, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure DANVTH00610025 on Town Highway 61 crossing Water Andric Brook, Danville, 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 northeastern Vermont. The 9.69-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 downstream left bank while the upstream right bank is grass with trees along the immediate banks. The downstream right bank and upstream left bank are forested. In the study area, Water Andric Brook has a straight channel with a slope of approximately 0.007 ft/ft, an average channel top width of 45 ft and an average bank height of 4 ft. The predominant channel bed material is gravel with a median grain size (D 50 ) of 53.4 mm (0.175 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 61 crossing of Water Andric Brook is a 24-ft-long, two-lane bridge consisting of one 22-foot concrete slab span (Vermont Agency of Transportation, written communication, March 24, 1995). The opening length of the structure parallel to the bridge face is 22.9 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening and the computed opening-skewto-roadway is 5 degrees. The VTAOT computed opening-skew-to-roadway is zero degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the upstream half 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) at the upstream end of the upstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge is determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.7 to 1.3 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 9.1 to 12.5 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↗
USGS1997

Level II scour analysis for Bridge 36 (DUXBTH00040036) on Town Highway 4, crossing Crossett Brook, Duxbury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure DUXBTH00040036 on Town Highway 4 crossing the Crossett Brook, Duxbury, 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 4.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the upstream left overbank is pasture. The upstream and downstream right overbanks are forested. The downstream left overbank is brushland, while the immediate banks have dense woody vegetation. In the study area, the Crossett Brook has an incised, sinuous channel with a slope of approximately 0.006 ft/ft, an average channel top width of 55 ft and an average bank height of 9 ft. The channel bed material ranges from gravel to bedrock with a median grain size (D 50 ) of 51.6 mm (0.169 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 1, 1996, indicated that the reach was stable. The Town Highway 4 crossing of the Crossett Brook is a 29-ft-long, two-lane bridge consisting of a 26-foot concrete slab span (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the bridge face is 26 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 35 degrees to the opening while the computed opening-skew-to-roadway is 5 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the upstream left wingwall and the right abutment during the Level I assessment. Scour countermeasures at the site includes type-2 stone fill (less than 36 inches diameter) at the upstream end of the upstream left and right wingwalls and the upstream left and right banks and road embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 1.7 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 6.4 to 8.3 ft. Right abutment scour ranged from 6.0 to 7.0 ft. The worst-case left and right abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 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 8 (WELLTH00020008) on Town Highway 2, crossing Wells Brook, Wells, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WELLTH00020008 on Town Highway 2 crossing the Wells Brook, Wells, 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 Taconic section of the New England physiographic province in southwestern Vermont. The 14.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the right overbanks is predominantly suburban while the immediate banks are vegetated with trees and brush. The left bank upstream and downstream is predominantly pasture. In the study area, the Wells Brook has an incised, straight channel with a slope of approximately 0.005 ft/ft, an average channel top width of 51 ft and an average bank height of 7 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 48.6 mm (0.159 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 19, 1995, indicated that the reach was stable. The Town Highway 2 crossing of the Wells Brook is a 35-ft-long, two-lane bridge consisting of one 32-foot concrete span (Vermont Agency of Transportation, written communication, March 22, 1995). The opening length of the structure parallel to the bridge face is 31.7 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-toroadway is 5 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed 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) along the left bank upstream, and type-5 (placed stone wall) at the upstream end of the upstream left wingwall, at the downstream end of the downstream left wingwall, and 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 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 0.8 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 5.6 to 10.0 ft at the left abutment and from 3.1 to 4.2 ft at the right abutment. The worst-case abutment scour occurred at the incipient roadway-overtopping discharge 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 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↗
USGS1998

Level II scour analysis for Bridge 67 (MTHOTH00120067) on Town Highway 12, crossing Freeman Brook, Mount Holly, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MTHOTH00120067 on Town Highway 12 crossing Freeman Brook, Mount Holly, 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 Green Mountain section of the New England physiographic province in south-central Vermont. The 11.4-mi 2 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, Freeman Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 51 ft and an average bank height of 6 ft. The channel bed material ranges from sand to boulders with a median grain size (D 50 ) of 55.7 mm (0.183 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 5, 1995, indicated that the reach was stable. The Town Highway 12 crossing of Freeman Brook is a 34-ft-long, two-lane bridge consisting of a 30-foot prestressed concrete-slab span (Vermont Agency of Transportation, written communication, March 15, 1995). The opening length of the structure parallel to the bridge face is 29.5 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 15 degrees. Along the upstream right wingwall, the right abutment and the downstream right wingwall, a scour hole approximately 1.0 to 2.0 ft deeper than the mean thalweg depth was observed during the Level I assessment. Scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) along the downstream end of the downstream right wingwall; type-2 stone fill (less than 36 inches diameter) along the upstream left wingwall, the left abutment, the downstream left wingwall and the upstream left and right banks; type- 3 stone fill (less than 48 inches diameter) along the downstream left and right banks; and type-4 stone fill (less than 60 inches diameter) along 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 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 2.6 to 3.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 7.9 to 10.0 ft. Right abutment scour ranged from 12.7 to 15.2 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 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 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↗
USGS1996

Level II scour analysis for Bridge 42 (RANDVT00120042) on State Highway 12, crossing Third Branch White River, Randolph, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RANDVT00120042 on State Highway 12 crossing the Third Branch White River, Randolph, 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 Randolph. The 61.9-mi 2 drainage area is in a predominantly rural drainage basin. In the vicinity of the study site, the left and right banks have moderate tree cover with residential and commercial buildings on the overbank areas. In the study area, the Third Branch White River has a sinuous channel with a slope of approximately 0.013 ft/ft, an average channel top width of 133 ft and an average channel depth of 5 ft. The predominant channel bed material is gravel with a median grain size ( D 50 ) of 49.6 mm (0.163 ft). Bank material is sand and gravel (D 50 is 3.08 mm or 0.010 ft). The geomorphic assessment at the time of the Level I site visits on July 8, 1994 and December 13, 1994, indicated that the reach has experienced vertical degradation. A drop structure has been constructed downstream of the bridge to prevent further degradation. In addition to the degradation of the stream bed, there is local pier scour at the bridge site as well. At the nose of the pier in the main channel, the bed is approximately three feet below the mean thalweg and two feet below the bottom of the pier footing. The State Highway 12 crossing of the Third Branch White Riveris a 220-ft-long, two-lane bridge consisting of four concrete spans. The maximum span length is 57 ft. (Vermont Agency of Transportation, written commun., July 29, 1994). The bridge is supported by vertical, concrete abutments and three concrete piers. The toe of the left abutment is at the channel edge. The toe of the right abutment is set back on the right over-bank. The roadway centerline on the structure has a slight horizontal curve; however, the main channel is skewed approximately 5 degrees to the bridge. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗
USGS1997

Level II scour analysis for Bridge 29 (DORSTH00100029) on Town Highway 10, crossing the Mettawee River, Dorset, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure DORSTH00100029 on Town Highway 10 crossing the Mettawee River, Dorset, 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 Taconic section of the New England physiographic province in southwestern Vermont. The 9.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest on the upstream left overbank and the upstream and downstream right overbanks. The downstream left overbank is pasture and brushland. In the study area, the Mettawee River has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 66 ft and an average bank height of 8 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 79.0 mm (0.259 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 5, 1996, indicated that the reach was stable. The Town Highway 10 crossing of the Mettawee River is a 26-ft-long, two-lane bridge consisting of a 24-ft steel-stringer span (Vermont Agency of Transportation, written communication, September 28, 1995). The opening length of the structure parallel to the bridge face is 24.1 ft. 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. At the upstream end of the right abutment, there is a scour hole 1.0 ft deeper than the mean thalweg depth. Scour counter-measures at the site include type-1 stone fill (less than 12 inches diameter) along the downstream right wingwall. Type-2 stone fill (less than 36 inches diameter) is present along the downstream left and right banks. Type-3 stone fill (less than 48 inches diameter) is present along the upstream left bank and sparsely in front of the right abutment. A concrete wall (old abutment) extends 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 ranged from 0.4 to 1.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 10.5 to 10.8 ft. The worst-case left abutment scour occurred at the 500-year discharge. Right abutment scour ranged from 11.4 to 11.9 ft. The worst-case right 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 68 (NFIETH00960068) on Town Highway 96, crossing the Dog River, Northfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NFIETH00960068 on Town Highway 96 crossing the Dog River, Northfield, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 30.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the left bank upstream and downstream is pasture while the immediate banks have dense woody vegetation. The right bank upstream is forested and the downstream right bank is pasture. Vermont state route 12A runs parallel to the river on the right bank. In the study area, the Dog River has an incised, straight channel with a slope of approximately 0.004 ft/ft, an average channel top width of 70 ft and an average bank height of 7 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 47.9 mm (0.157 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 25, 1996, indicated that the reach was stable. The Town Highway 96 crossing of the Dog River is a 45-ft-long, one-lane bridge consisting of one 43-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the bridge face is 41.5 ft.The bridge is supported by vertical, concrete abutments with wingwalls. The channel is not skewed to the opening and the opening-skew-to-roadway is zero degrees. Channel scour 0.5 ft deeper than the mean thalweg depth, was observed under the bridge during the Level I assessment. The scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) along the left bank upstream and type-2 stone fill (less than 36 inches diameter) along the upstream and downstream right banks that extends partially in front of the right wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.8 to 1.2 ft. The worst-case contraction scour occurred at the 100-year and 500-year discharges. Abutment scour ranged from 8.5 to 12.2 ft. The worst-case abutment scour occurred at the incipient roadway-overtopping discharge for the right abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 4 (RYEGTH00050004) on Town Highway 5, crossing the Wells River, Ryegate, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RYEGTH00050004 on Town Highway 5 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 eastern Vermont. The 84.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover includes shrubs and brush on the upstream left bank and downstream right bank of the bridge. The upstream right bank and downstream left bank of the bridge is forested. In the study area, the Wells River has an incised, sinuous channel with a slope of approximately 0.008 ft/ft, an average channel top width of 107 ft and an average bank height of 11 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 67.4 mm (0.221 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 21, 1995, indicated that the reach was laterally unstable with mass wasting along the upstream right bank. The Town Highway 5 crossing of the Wells River is a 108-ft-long, two-lane bridge consisting of a 100-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 93.4 ft. The bridge is supported by vertical, stone block abutments with wingwalls. The channel is skewed approximately 50 degrees to the opening while the opening-skew-toroadway is 45 degrees. The scour protection counter-measures at the site included type-1 stone fill (less than 12 inches diameter) along the downstream left road embankment. Also, type-2 stone fill (less than 36 inches diameter) along the upstream right wingwall, extending 30 feet upstream along the right bank, along the downstream end of the downstream right wingwall, along the downstream right road embankment, and along the downstream left bank below the old railroad bed. 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 1.8 to 2.6 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 10.2 to 22.6 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 53 (CHESTH01180053) on Town Highway 118, crossing the Williams River, Chester, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CHESTH01180053 on Town Highway 118 crossing the Williams River, Chester, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in southeastern Vermont. The 20.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly suburban while the right bank upstream is pasture. There is a house on the right bank downstream and VT 103 runs parallel to the river along the left bank. In the study area, the Williams River has an incised, straight channel with a slope of approximately 0.005 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 58.0 mm (0.190 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 17, 1996, indicated that the reach was stable. The Town Highway 118 crossing of the Williams River is a 43-ft-long, one-lane bridge consisting of one 40-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 37.6 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the computed opening-skew-to-roadway is 10 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed at both abutments during the Level I assessment. Scour protection measures at the site include: type-3 stone fill (less than 48 inches diameter) along the left bank upstream and downstream and type-2 stone fill (less than 36 inches diameter) along the entire base length of the upstream left wingwall, at the upstream end of the left abutment, and at 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. In addition, the incipient roadway-overtopping discharge is determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was 0.0 ft. Abutment scour ranged from 5.8 to 6.8 ft at the left abutment and 9.4 to 14.4 ft at the right abutment. The worst-case abutment scour occurred at the incipient roadway-overtopping discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 40 (ROCKTH00140040) on Town Highway 14, crossing the Williams River, Rockingham, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ROCKTH00140040 on Town Highway 14 crossing the Williams 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 (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 99.2-mi2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture downstream of the bridge. Upstream of the bridge, the left bank is forested and the right bank is suburban. In the study area, the Williams River has an incised, sinuous channel with a slope of approximately 0.005 ft/ft, an average channel top width of 154 ft and an average bank height of 11 ft. The channel bed material ranges from silt and clay to cobble with a median grain size (D50) of 45.4 mm (0.149 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 4, 1996, indicated that the reach was stable. The Town Highway 14 crossing of the Williams River is a 106-ft-long, one-lane covered bridge consisting of two steel-beam spans with a maximum span length of 73 ft (Vermont Agency of Transportation, written communication, April 6, 1995). The opening length of the structure parallel to the bridge face is 94.5 ft. The bridge is supported by a vertical, concrete abutment with wingwalls on the left, a vertical, laid-up stone abutment on the right and a concrete pier. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 2.1 ft deeper than the mean thalweg depth was observed towards the left side of the channel under and just downstream of the bridge during the Level I assessment. Scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) at the upstream end of the upstream left wingwall and type-2 stone fill (less than 36 inches diameter) along the upstream left bank and the left abutment. Additional details describing conditions at the site are included in the Level II Summary and appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and Davis, 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 was zero ft. Left abutment scour ranged from 13.9 to 19.2 ft. Right abutment scour ranged from 7.0 to 11.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Pier scour ranged from 18.7 to 24.7 ft and the worst case 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 particlesize 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↗