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Robert H. Flynn

Publications and source records attributed to Robert H. Flynn.

45 records · Page 3Linked to original sources
USGS1997

Level II scour analysis for Bridge 4 (DANVTH00010004) on Town Highway 1, crossing Joes Brook, Danville, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure DANVTH00010004 on Town Highway 1 crossing Joes 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 42.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture along the upstream and downstream left banks with trees and brush along the immediate banks. The upstream and downstream right banks are forested. In the study area, Joes Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 68 ft and an average bank height of 5 ft. The channel bed material ranges from gravel to bedrock with a median grain size (D 50 ) of 80.1 mm (0.263 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 1 crossing of Joes Brook is a 49-ft-long, two-lane bridge consisting of one 45-foot steel-beam span (Vermont Agency of Transportation, written communication, March 17, 1995). The opening length of the structure parallel to the bridge face is 45 ft.The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening and the computed opening-skew-to-roadway is 15 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. The scour hole also extends upstream and downstream of the bridge, along the right side of the channel. The scour protection measures at the site include type-2 stone fill (less than 36 inches diameter) at the upstream end of the upstream left wingwall and along the entire base length of the downstream right wingwall. Type-3 stone fill (less than 48 inches diameter) is along the entire base length of the upstream right wingwall and type-5 protection (stone block wall) is 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. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was computed to be zero ft. Abutment scour ranged from 11.7 to 13.0 ft along the right abutment and from 6.6 to 9.4 ft along 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 and Hire equations (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 6 (FAYSTH00010006) on Town Highway 1, crossing Shepard Brook, Fayston, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FAYSTH00010006 on Town Highway 1 crossing Shepard Brook, Fayston, 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 16.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, Shepard Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 56 ft and an average bank height of 3 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 72.6 mm (0.238 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 2, 1996, indicated that the reach was stable. The Town Highway 1 crossing of the Shepard Brook is a 42-ft-long, two-lane bridge consisting of one 40-foot concrete T-beam span (Vermont Agency of Transportation, written communication, October 13, 1995). The opening length of the structure parallel to the bridge face is 39.6 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the calculated opening-skew-to-roadway is 30 degrees. Scour, 2.0 ft deeper than the mean thalweg depth, was observed along the right abutment during the Level I assessment. The left abutment is undermined along the base of the footing. In addition, 1.5 ft of scour was observed along the left abutment during the Level I assessment. The only scour protection measure at the site was 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 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) 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 0.9 to 3.9 ft. The worst-case contraction scour occurred at the 500-year. Abutment scour ranged from 11.1 to 17.2 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 37 (CABOTH00410037) on Town Highway 41, crossing the Winooski River, Cabot, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CABOTH00410037 on Town Highway 41 crossing the Winooski River (also referred to as Coit’s Pond Brook), Cabot, 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 21.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is primarily shrub and brushland while the immediate banks have dense woody vegetation. In the study area, the Winooski River has an incised, straight channel with a slope of approximately 0.01 ft/ft, an average channel top width of 53 ft and an average bank height of 4 ft. The channel bed material is primarily cobbles and boulder with a median grain size (D 50 ) of 64.5 mm (0.212 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 16, 1996, indicated that the reach was stable. The Town Highway 41 crossing of the Winooski River is a 29-ft-long, one-lane bridge consisting of one 26-foot span (Vermont Agency of Transportation, written communication, October 13, 1995) with four steel I-beams and a wooden deck . The opening length of the structure parallel to the bridge face is 26 ft.The bridge is supported by “laid up” granite block abutments with concrete footings. The channel is skewed approximately 35 degrees to the opening while the computed opening-skew-to-roadway is 15 degrees. The VTAOT computed opening-skew-to-roadway is zero degrees. The only scour protection measure observed at the site during the Level I assessment was type-2 stone fill (less than 36 inches diameter) along the entire base length of the left abutment and upstream right wingwall, along the upstream left bank and along the downstream left and right 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 and maximum free-surface flow discharges were determined and analyzed as two other potential worst-case scour scenarios. 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 2.7 ft. The worst-case contraction scour occurred at the maximum free-surface flow (with road overflow) discharge, which was less than the 100-year discharge. Abutment scour ranged from 9.8 to 10.7 ft along the left abutment and from 16.2 to 19.9 ft along the right abutment. The worstcase abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scouredstreambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particlesize distribution. It is generally accepted that the Froehlich and Hire equations (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 (WEELTH00210023) on Town Highway 21, crossing Miller Run, Wheelock, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WEELTH00210023 on Town Highway 21 crossing Miller Run, Wheelock, 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 28.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest on the upstream and downstream right banks while the surface cover on the upstream and downstream left banks consists primarily of short grass and buildings with shrubs, brush and trees along the immediate banks. In the study area, Miller Run has an incised, straight channel with a slope of approximately 0.003 ft/ft, an average channel top width of 76 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 67.5 mm (0.221 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 2, 1995, indicated that the reach was stable. The Town Highway 21 crossing of Miller Run is a 46-ft-long, one-lane bridge consisting of one 43-foot steel-beam span with a wooden deck (Vermont Agency of Transportation, written communication, April 5, 1995). The opening length of the structure parallel to the bridge face is 42.1 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the computed opening-skew-to-roadway is 25 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed under the bridge, along the center of the channel, during the Level I assessment. The scour protection measures at the site included type-2 stone fill (less than 36 inches diameter) along the downstream left bank and along the entire base length of the upstream and downstream right wingwalls. Type-3 stone fill (less than 48 inches diameter) protection was observed along the upstream end of the upstream left wingwall and randomly scattered along the left abutment. Type-4 stone fill (less than 60 inches diameter) protection was observed along the entire base length 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 computed to be zero ft. Abutment scour ranged from 9.1 to 10.8 ft along the right abutment and from 9.8 to 12.3 ft along 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. 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 7 (WARRTH00010007) onTown Highway 1, crossing Freemans Brook, Warren, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WARRTH00010007 on Town Highway 1 crossing Freeman Brook, Warren, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 6.45-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the predominant surface cover is grass and trees with the exception of the upstream left overbank which is forest. The banks of the channel are tree covered. In the study area, Freeman Brook has an incised, straight channel with a slope of approximately 0.03 ft/ft, an average channel top width of 51 ft and an average channel depth of 6 ft. The predominant channel bed material ranges from gravel to bedrock with a median grain size (D 50 ) of 86.8 mm (0.285 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 22, 1996 indicated that the reach was stable. The Town Highway 1 crossing of Freeman Brook is a 64-ft-long, two-lane bridge consisting of one 62-foot steel-beam span (Vermont Agency of Transportation, written communication, February 1, 1996). The bridge is supported by vertical, concrete abutments with spill-through slopes. The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 30 degrees. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the entire length of the left and right abutments and along the downstream channel banks. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. The computed contraction scour for all modelled flows was 0.0 feet. Abutment scour ranged from 5.3 to 8.2 ft. The worst-case abutment scour occurred at the right abutment for the incipient-overtopping discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 34 (SHERUS00040034) on U.S. Highway 4, crossing the Ottauquechee River, Sherburne, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure SHERUS00040034 on US Route 4 crossing the Ottauquechee River, Sherburne, 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 25.8-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, the banks are forested. In the study area, the Ottauquechee River has an incised, straight channel with a slope of approximately 0.028 ft/ft, an average channel top width of 66 ft and an average channel depth of 5 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 118.1 mm (0.387 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 25, 1995, indicated that the reach was stable. The US Route 4 crossing of the Ottauquechee River is a 187-ft-long, two-lane bridge consisting of three steel-beam spans (Vermont Agency of Transportation, written communication, March 14, 1995). The bridge is supported by vertical, concrete abutments above spill-through stone fill (< 36 inches diameter). The channel is skewed approximately 60 degrees to the opening while the opening-skew-to-roadway is 60 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was 0.0 ft. Abutment scour ranged from 4.7 to 7.4 ft. The worst-case abutment scour occurred at the left abutment for the 500-year discharge. Pier scour ranged from 7.5 to 11.4 ft. The worst-case pier scour occurred at the incipientovertopping 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 6 (RICHTH00030006) on Town Highway 3, crossing an unnamed tributary to the Missisquoi River, Richford, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RICHTH00030006 on Town Highway 3 crossing an unnamed tributary to the Missisquoi River, Richford, 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 northern Vermont. The 4.5-mi 2 drainage area is in a predominantly rural basin. In the vicinity of the study site, the surface cover is pasture upstream and downstream of the bridge. In the study area, the unnamed tributary to the Missisquoi River is a sinuous channel with a slope of approximately 0.008 ft/ft, an average channel top width of 39 ft and an average channel depth of 2 ft. The channel slope was obtained from a topographic map (USGS, 1986). The predominant channel bed material is gravel with a median grain size (D 50 ) of 26.2 mm (0.0861 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 28, 1995, indicated that the reach was stable. The Town Highway 3 crossing of an unnamed tributary to the Missisquoi River is a 26-ftlong, two-lane bridge consisting of one 24-foot concrete T-beam span (Vermont Agency of Transportation, written communication, March 9, 1995). 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 0.0 degrees. The only scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) along the upstream right wingwall and at the upstream end of the right abutment. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and 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 1.7 to 1.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Scour at the left abutment ranged from 7.6 to 12.6 ft with the worst case occurring at the 100-year event. Scour at the right abutment ranged from 1.6 to 5.6 ft with the worst case occurring at the 500-year event. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 9 (JAYVT02420009) on Vermont Highway 242, crossing the Jay Branch of the Missisquoi River, Jay, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure JAY-VT02420009 on Vermont highway 242 crossing the the Jay Branch of the Missisquoi River, Jay, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province of northern Vermont in the town of Jay. The 4.36-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is primarily forest and brush except for the downstream left overbank which is grass. In the study area, the the Jay Branch of the Missisquoi River has an incised, sinuous channel with a slope of approximately 0.021 ft/ft, an average channel top width of 38 ft and an average channel depth of 5 ft. A Level I visual inspection at the site indicates that the predominant channel bed material is cobble and boulder with gravel. Results of a pebble count indicate that the predominant channnel bed material is a very coarse gravel with a median grain size (D 50 ) of 41.7 mm (0.1369 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 stable. The Vermont highway 242 crossing of the the Jay Branch of the Missisquoi River is a 60- ft-long, two-lane bridge consisting of one 55-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 60 degrees to the opening while the opening-skew-to-roadway is 45 degrees. The scour protection measures at the site included type-2 stone fill (less than 36 inches diameter) at the upstream right wingwall, the downstream left and right wingwalls and the upstream end of the left abutment. Type-1 stone fill (less than 12 inches) was along the upstream end of the right abutment. Type-4 stone fill (less than 64 inches) was along 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 rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.6 ft. The worst-case contraction scour occurred at the 100-year discharge. Abutment scour ranged from 0.8 to 5.6 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.

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