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USGS1996

Level II scour analysis for Bridge 8 (HANCTH00020008) on Town Highway 2, crossing Hancock Branch White River, Hancock, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HANCTH00020008 on town highway 2 crossing the Hancock Branch White River, Hancock, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from VTAOT files, was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Hancock. The 8.4-mi 2 drainage area is predominantly rural and forested. In the vicinity of this site, the banks have dense woody vegetation coverage. In the study area, the Hancock Branch White River is an incised, sinuous channel with a slope of approximately 0.038 ft/ft, an average channel top width of 47.0 ft and an average channel depth of 3.0 ft. The predominant channel bed material is cobble (D 50 is 102 mm or 0.336 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 16, 1994, indicated that the reach was stable. The town highway 2 crossing of the Hancock Branch White Riveris a 33-ft-long, two-lane bridge consisting of one 30-foot steel-beam span with a concrete deck (Vermont Agency of Transportation, written commun., August 26, 1994). The bridge is supported by steep sloping, cement-grouted, cobble-stone abutments with wingwalls. The channel is skewed approximately ten degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the upstream left wingwall and left abutment during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches 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 rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term aggradation or degradation; 2) contraction scour (due to reduction in flow area caused by a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute scour depths for contraction and local scour and a summary of the results follows. Contraction scour for all modelled flows ranged from 0.6 ft to 1.3 ft and the worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 9.4 ft to 15.2 ft and the worst-case abutment scour occurred at the 500-year discharge. Scour depths and depths to armoring are summarized on p. 14 in the section titled “Scour Results”. Scour elevations, based on the calculated depths are presented in tables 1 and 2; a graph of the scour elevations is presented in figure 8 Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. For all scour presented in this report, “the scour depths adopted [by VTAOT] may differ from the equation values based on engineering judgement” (Richardson and others, 1993, p. 21, 27). It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results.

Vermont↗
USGS1996

Level II scour analysis for Bridge 46 (BRIDTH00050046) on Town Highway 05, crossing North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050046 on town highway 5 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Bridgewater. The 5.61-mi 2 drainage area is a predominantly rural and forested basin. In the vicinity of the study site, the banks are forested. Town highway 5 parallels the upstream left bank. In the study area, the North Branch Ottauquechee River has a sinuous channel with a slope of approximately 0.015 ft/ft, an average channel top width of 48 ft and an average channel depth of 6 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 66.2 mm (0.217 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 2 and 3, 1994, indicated that the reach was stable. The town highway 5 crossing of North Branch Ottauquechee Riveris a 40-ft-long, one-lane bridge consisting of a 34-ft steel-beam span, supported by vertical abutments with no wingwalls (Vermont Agency of Transportation, written communication, August 25, 1994). The left abutment is stone; the right abutment is log cribwork with type-2 stone fill (less than 36 inches diameter) along its base. Type-2 stone fill has also been placed on the upstream and downstream sides of the road embankments, except the upstream left which has type-3 (less than 48 inches diameter). The channel is skewed approximately 60 degrees; the opening-skew-to-roadway is 30 degrees. Additional details describing conditions at the site are included in the Level II Summary, Appendix D, and Appendix E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of these computed results follow. Contraction scour for all modelled flows was 0.0 ft. Abutment scour ranged from 5.7 ft to 7.7 ft. with the worst-case abutment scour occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated depths, are presented in tables 1 and 2. A cross-section of the computed scour at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 22). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Level II scour analysis for Bridge 46 (ENOSVT01080046) on State Route 108, crossing an Unnamed "The Branch" Tributary, Enosburg, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ENOSVT01080046 on State Route 108 crossing an unnamed "The Branch" tributary, Enosburg, 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 1.55-mi 2 drainage area is in a predominantly rural, pasture and forested basin. In the vicinity of the study site, the surface cover is pasture. In the study area, this unnamed "The Branch" tributary has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 45 ft and an average channel depth of 3 ft. The predominant channel bed material is gravel and cobbles with a median grain size (D 50 ) of 42.4 mm (0.139 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 29, 1995, indicated that the reach was laterally unstable. Block failure slumping of bank material was evident at an upstream cut-bank and another minor cut-bank was noted downstream. The State Route 108 crossing of this unnamed "The Branch" tributary is a 25-ft-long, twolane bridge consisting of one 22-foot concrete span (Vermont Agency of Transportation, written communication, March 8, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is zero degrees. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) at the downstream end of the downstream left wingwall. 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 0.3 to 0.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 4.0 to 8.0 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 59 (NWPCVT01050059) on State Route 105 crossing an unnamed Mud Creek Tributary, Newport, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NWPCVT01050059 on state route 105 crossing an unnamed Mud Creek tributary, Newport, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province of north-central Vermont in the town of Newport. The 9.18-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture while the immediate banks are brush covered with some trees. In the study area, this unnamed Mud Creek tributary has an incised, sinuous channel with a slope of approximately 0.005 ft/ft, an average channel top width of 42 ft and an average channel depth of 5 ft. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 54.1 mm (0.178 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 21, 1994, indicated that the reach was stable. The state route 105 crossing of an unnamed Mud Creek tributary is a 33-ft-long, two-lane bridge consisting of one 29-foot concrete-slab span (Vermont Agency of Transportation, written communication, August 5, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening and the opening-skew-to-roadway is 15 degrees. Scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on each bank upstream and both upstream wingwalls. The downstream wingwalls are protected by remnant abutment walls from a previous structure. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.2 to 0.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 5.2 to 16.6 ft. The worst-case abutment scour also occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 38 (ANDOVT00110038) on State Route 11, crossing the Middle Branch Williams River, Andover, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ANDOVT00110038 on State Route 11 crossing the Middle Branch Williams River, Andover, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in south central Vermont. The 5.65-mi 2 drainage area is in a predominantly rural and forested basin. Upstream and downstream of the study site banks and overbanks are forested. In the study area, the Middle Branch Williams River has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 44 ft and an average bank height of 4 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 54.0 mm (0.177 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 5, 1996, indicated that the reach was stable. The State Route 11 crossing of the Middle Branch Williams River is a 33-ft-long, two-lane bridge consisting of one 31-foot concrete T-beam span (Vermont Agency of Transportation, written communication, March 29, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 55 degrees to the opening while the measured opening-skew-to-roadway is 45 degrees. There were no scour problems observed during the Level I assessment. Type-4 stone fill (less than 60 inches diameter) and type-3 stone fill (less than 48 inches diameter) was present on the left bank upstream and right bank upstream respectively. Type-2 stone fill (less than 36 inches diameter) was present in the upstream left wing wall area. 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 1.8 to 3.4 ft. The worst-case contraction scour occurred at the 500-year flow. Abutment scour ranged from 12.0 to 14.0 ft. The worst-case abutment scour occurred at the 500-year flow at 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↗
USGS1996

Level II scour analysis for Bridge 34 (RANDTH00660034) on Town Highway 66, crossing Second Branch White River, Randolph, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RANDTH00660034 on town highway 66 crossing the Second 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 51.3-mi 2 drainage area is in a predominantly rural basin. In the vicinity of the study site, the left and right banks are covered by fields with some brush on the upstream left and downstream right banks and with row crops on the downstream left overbank. In the study area, the Second Branch White River has a sinuous channel with a slope of approximately 0.002 ft/ft, an average channel top width of 60 ft and an average channel depth of 7 ft. The predominant channel bed material is sand (D 50 is 1.34 mm or 0.0044 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 11, 1994, indicated that the reach was laterally unstable. Channel scour is evident along the left half of the channel from about 30 feet upstream to about 20 feet downstream of the bridge. There is a cut bank with block failures along the left bank upstream of the bridge further indicating instability of the stream reach. The town highway 66 crossing of the Second Branch White Riveris a 57-ft-long, one-lane covered bridge consisting of one 45-foot span (Vermont Agency of Transportation, written communication, July 29, 1994). The bridge is supported by vertical, concrete abutments with one wingwall on the upstream left side. The base of the left abutment was protected by type-1 stone fill (less than 12 inches diameter). The channel is skewed approximately 40 degrees to the opening while the opening-skew-to-roadway is 45 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term aggradation or degradation; 2) contraction scour (due to reduction in flow area caused by a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute scour depths for contraction and local scour and a summary of the results follows. Contraction scour for all modelled flows ranged from 6.3 ft to 7.8 ft and the worst-case contraction scour occurred at the 100-year discharge. Abutment scour ranged from 7.9 ft to 20.3 ft and the worst-case abutment scour occurred at the 500-year discharge. Scour depths and depths to armoring are summarized on p. 14 in the section titled “Scour Results”. Scour elevations, based on the calculated depths are presented in tables 1 and 2; a graph of the scour elevations is presented in figure 8 Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. For all scour presented in this report, “the scour depths adopted [by VTAOT] may differ from the equation values based on engineering judgement” (Richardson and others, 1993, p. 21, 27). It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results.

Vermont↗
USGS1997

Level II scour analysis for Bridge 29 (ROYATH00920029) on Town Highway 92, crossing the First Branch White River, Royalton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ROYATH00920029 on Town Highway 92 crossing the First Branch White River, Royalton, 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 central Vermont. The 101-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream and downstream of the bridge. In the study area, the First Branch White River has an incised, sinuous channel with a slope of approximately 0.001 ft/ft, an average channel top width of 81 ft and an average bank height of 9 ft. The channel bed material ranges from sand to bedrock with a median grain size (D 50 ) of 1.18 mm (0.00347 ft). The geomorphic assessment at the time of the Level I site visit on July 23, 1996 and Level II site visit on June 2, 1995, indicated that the reach was stable. The Town Highway 92 crossing of the First Branch White River is a 59-ft-long, one-lane bridge consisting of a 57-foot steel-stringer span (Vermont Agency of Transportation, written communication, March 23, 1995). The opening length of the structure parallel to the bridge face is 52.2 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 4.0 ft deeper than the mean thalweg depth was observed in the upstream channel during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the upstream left and right wingwalls, the left abutment and downstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 4.1 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge, which was less than the 100-year discharge. Left abutment scour ranged from 12.9 to 15.4 ft, where the worst-case abutment scour occurred at the 500-year discharge. Right abutment scour ranged from 14.5 to 15.0 ft, where 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↗
USGS1996

Level II scour analysis for Bridge 25 (CRAFTH00220025) on Town Highway 22, crossing the Wild Branch Lamoille River, Craftsbury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CRAFTH00220025 on town highway 22 crossing the Wild Branch Lamoille River, Craftsbury, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the New England Upland physiographic province of north-central Vermont in the town of Bridgewater. The 9.52-mi 2 drainage area is in a predominantly rural basin with some pasture on the valley bottom. In the vicinity of the study site, the banks have less than 25% woody vegetation coverage. In the study area, the Wild Branch Lamoille River has a meandering channel in a low relief valley setting with wide flood plains and a slope of approximately 0.0044 ft/ft, an average channel top width of 35 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel (D 50 is 38.6 mm or 0.127 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 9, 1994, indicated that the reach was laterally unstable. The town highway 22 crossing of the Wild Branch Lamoille Riveris a 31-ft-long, two-lane bridge consisting of one 29-foot span concrete slab superstructure (Vermont Agency of Transportation, written commun., August 4, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening and the opening-skew-to-roadway is 20 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the left bank side of the channel upstream during the Level I assessment. There are tall, steep stone fill embankments (artificial levees) that make up both banks between 50 feet upstream and the upstream face of the bridge, which straighten and constrict the channel. Type-2 stone fill (less than 36 inches diameter) is reported on the banks upstream, the upstream wingwalls, the abutments, the downstream left wingwall, and 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 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 2.5 ft. The worst-case contraction scour occurred at the incipient overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 4.7 to 8.6 ft. The worst-case abutment scour also occurred at 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). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1997

Level II scour analysis for Bridge 34 (CORITH0050034) on Town Highway 50, crossing the South Branch Waits River, Corinth, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CORITH00500034 on Town Highway 50 crossing the South Branch Waits River, Corinth, 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 central Vermont. The 35.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream and downstream of the bridge while the immediate banks have dense woody vegetation. In the study area, the South Branch Waits River has an incised, meandering channel with a slope of approximately 0.005 ft/ft, an average channel top width of 63 ft and an average bank height of 6 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 23.7 mm (0.078 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 5, 1995, indicated that the reach was stable. The Town Highway 50 crossing of the South Branch Waits River is a 56-ft-long, one-lane bridge consisting of one 54-foot steel thru-truss span (Vermont Agency of Transportation, written communication, March 24, 1995). The opening length of the structure parallel to the bridge face is 51.5 ft.The bridge is supported by vertical, concrete abutments with no wingwalls. Stone fill and bank material in front of the abutments create spill-through embankments. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is 15 degrees. A scour hole 2.5 ft deeper than the mean thalweg depth was observed along the left bank through the bridge 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 and right banks extending from upstream to downstream through the bridge. The stone fill under the bridge creates spill-through embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was determined and analyzed as other 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 3.0 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 2.4 to 6.3 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 and HIRE equations (abutment scour) give “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 33 (BRIDTH00050033) on Town Highway 5, crossing the North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050033 on town highway 5 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province of central Vermont in the town of Bridgewater. The 5.01-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the downstream banks are forested and the upstream banks have dense woody brush; the upstream right overbank is an open field. In the study area, the North Branch Ottauquechee River has an incised, sinuous channel with a slope of approximately 0.017 ft/ft, an average channel top width of 30 ft and an average channel depth of 3 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 83.2 mm (0.273 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 3, 1994, indicated that the reach was stable. Also at the time of the site visit, there was considerable backwater at the bridge site due to a three foot tall beaver dam 40 feet downstream. The beaver dam was assumed destroyed by flood flow and was ignored in the analyses. The town highway 5 crossing of the North Branch Ottauquechee Riveris a 25-ft-long, onelane bridge consisting of one 23-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 10 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the right abutment and upstream right wingwall during the Level I assessment. Scour protection measures at the site include type-2 stone fill (less than 36 inches diameter) at the ends of all the wingwalls except the upstream left which has type-3 stone fill (less than 48 inches diameter). Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.7 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 5.3 to 7.2 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 crosssection of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 27 (ANDOTH00290027) on Town Highway 29, crossing Middle Branch Williams River, Andover, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ANDOTH00290027 on Town Highway 29 crossing the Middle Branch Williams River, Andover, 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 12.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture on the left bank upstream of the bridge while the immediate bank has woody vegetation. The surface cover on the upstream right bank is forest. Downstream of the bridge the left bank is pasture and the right bank has woody vegetation. In the study area, the Middle Branch Williams River has an incised, straight channel with a slope of approximately 0.009 ft/ft, an average channel top width of 63 ft and an average bank height of 5 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 64.7 mm (0.212 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 10, 1996, indicated that the reach was stable. The Town Highway 29 crossing of the Middle Branch Williams River is a 34-ft-long, two- lane bridge consisting of one 32-foot steel-beam span (Vermont Agency of Transportation, written communication, April 5, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 0 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. Scour protection measures at the site include type- 2 stone fill (less than 36 inches diameter) along the upstream right bank and downstream left bank and around the upstream left and right wingwalls. Type- 3 stone fill (less than 48 inches diameter) is located along the base of the left abutment in the scour hole, at the end of the downstream left wingwall and along the upstream left bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.4 to 0.9 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge and the 100-year discharge. Abutment scour ranged from 10.7 to 13.6 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 41 (ANDOVT00110041) on State Route 11, crossing the Middle Branch Williams River, Andover, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ANDOVT00110041 on State Route 11 crossing the Middle Branch Williams River, Andover, 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 southeastern Vermont. The 12.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is grass on the upstream right overbank while the immediate banks have dense woody vegetation. The upstream left overbank and downstream right overbank are brushland. The downstream left overbank is forested. In the study area, the Middle Branch Williams River has an incised, sinuous channel with a slope of approximately 0.018 ft/ft, an average channel top width of 71 ft and an average bank height of 4 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 85.0 mm (0.279 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 10, 1996, indicated that the reach was laterally unstable due to a cut-bank present on the upstream right bank and a wide channel bar with vegetation in the upstream reach. The State Route 11 crossing of the Middle Branch Williams River is a 46-ft-long, two-lane bridge consisting of a concrete 44-foot tee-beam span (Vermont Agency of Transportation, written communication, March 29, 1995). The opening length of the structure parallel to the bridge face is 42 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 35 degrees to the opening while the opening-skew-toroadway is zero degrees. A scour hole 0.8 ft deeper than the mean thalweg depth was observed along the downstream end of the left abutment and downstream left wingwall during the Level I assessment. Type- 2 stone fill (less than 36 inches diameter) protects the upstream end of the upstream left wingwall, the downstream ends of the downstream left and right wingwalls and the downstream right road embankment. Type-3 stone fill protects the upstream end of the upstream right wingwall and 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). In addition, the incipient roadway-overtopping discharge was determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 2.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 11.1 to 18.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 30 (NEWHTH00050030) on Town Highway 5, crossing the New Haven River, New Haven, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NEWHTH00050030 on Town Highway 5 crossing the New Haven River, New Haven, 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 (Federal Highway Administration, 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 Champlain section of the St. Lawrence Valley physiographic province in west-central Vermont. The 115-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 right bank upstream and downstream of the bridge while the immediate banks have dense woody vegetation. The upstream left bank is also pasture. The downstream left bank is forested. In the study area, the New Haven River has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 127 ft and an average bank height of 5 ft. The channel bed material ranges from silt to cobble with a median grain size (D 50 ) of 20.4 mm (0.067 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 19, 1996, indicated that the reach was laterally unstable. The stream bends through the bridge and impacts the left bank where there is a cut bank and scour hole. The Town Highway 5 crossing of the New Haven River is a 181-ft-long, two-lane bridge consisting of four 45-ft concrete tee-beam spans (Vermont Agency of Transportation, written communication, December 15, 1995). The opening length of the structure parallel to the bridge face is 175.9 ft. The bridge is supported by vertical, concrete abutments with stone fill spill-through embankments and three concrete piers. The channel is skewed approximately 15 degrees to the opening while the computed opening-skew-to-roadway is 10 degrees. A scour hole 4.5 ft deeper than the mean thalweg depth was observed along the downstream left bank during the Level I assessment. Also observed was a scour hole 1.5 ft deeper than the mean thalweg depth at the upstream end of the middle pier. The only scour protection measure at the site was type-3 stone fill (less than 48 inches diameter) in front of the left and right abutments creating spill through slopes. 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 0.7 to 2.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 6.8 to 8.4 ft. The worst-case left abutment scour occurred at the 500-year discharge. Right abutment scour ranged from 11.2 to 14.0 ft. The worst-case right abutment scour occurred at the 500-year discharge. Pier scour ranged from 12.9 to 19.3 ft. The worst-case pier 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 25 (REDSTH00360025) on Town Highway 36, crossing the West Branch Deerfield River, Readsboro, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure REDSTH00360025 on Town Highway 36 crossing the West Branch Deerfield River, Readsboro, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in south-central Vermont. The 14.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture on the upstream right bank and forest on the upstream left bank. The surface cover on the downstream right and left banks is primarily grass, shrubs and brush. In the study area, the West Branch Deerfield River has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 65 ft and an average bank height of 4 ft. The channel bed material ranges from gravel to boulders, with a median grain size (D 50 ) of 117 mm (0.383 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 1, 1996, indicated that the reach was stable. The Town Highway 36 crossing of the West Branch Deerfield River is a 59-ft-long, two-lane bridge consisting of one 57-foot concrete T-beam span (Vermont Agency of Transportation, written communication, September 28, 1995). The opening length of the structure parallel to the bridge face is 54 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 50 degrees to the opening while the opening-skew-to-roadway is 30 degrees. During the Level I assessment, a scour hole approximately 2 ft deeper than the mean thalweg depth was observed along the upstream right wingwall and a scour hole approximately 1 ft deeper than the mean thalweg depth was observed along the downstream left wingwall. The scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) at the downstream end of the downstream left wingwall, at the upstream end of the upstream right wingwall, at the downstream end of the right abutment, along the entire base length of the downstream right wingwall, along the upstream right bank and along the downstream left bank. A stone wall was noted along the upstream left bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.6 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 15.1 to 16.3 ft along the left abutment and from 7.4 to 9.2 ft along the right abutment. The worst-case abutment scour occurred at the incipient-overtopping and 500-year discharges for the left abutment and at the 500-year discharge for the right abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for bridge 35 (BURKTH00310035) on Town Highway 31, crossing the West Branch Passumpsic River, Burke, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BURKTH00310035 on Town Highway 31 crossing the West Branch Passumpsic River, Burke, 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.

Vermont↗
USGS1996

Level II scour analysis for Bridge 24 (HARDTH00490024) on Town Highway 49, crossing Nichols Brook at Mackville Pond Outlet, Hardwick, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HARDTH00490024 on Town Highway 49 crossing Nichols Brook at Mackville Pond Outlet, Hardwick, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in north-central Vermont. The 10.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is best described as suburban with residences, lawns, trees and roadways. There is a dam 54 feet downstream of the bridge which controls Mackville Pond upstream of the bridge. The vertical drop over the dam is 15 feet. Immediately upstream of the bridge the width of the waterway is 146 feet. The predominant channel bed material is sand with a median grain size (D 50 ) of 0.576 mm (0.00189 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 25, 1995, indicated that the reach was stable. The Town Highway 49 crossing of Nichols Brook at Mackville Pond Outlet is a 42-ft-long, two-lane bridge consisting of one 38-foot steel-beam span (Vermont Agency of Transportation, written communication, April 3, 1995). The bridge is supported by vertical, concrete abutments with wingwalls on the downstream end of the left abutment and upstream and downstream ends of the right abutment. The channel is not skewed to the opening, but the opening-skew-to-roadway is 5 degrees. Scour protection measures at the site include type-3 stone fill (less than 48 inches diameter) on the upstream side of the left roadway embankment and at the upstream end of the left abutment. Type-2 stone fill (less than 36 inches diameter) was on the upstream right roadway embankment. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 4.7 to 21.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour at the left abutment ranged from 13.3 to 15.8 ft. with the worst-case occurring at the 500-year discharge. Abutment scour at the right abutment ranged from 8.1 to 9.8 ft. with the worst-case occurring at the incipient roadway-overtopping discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scouredstreambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particlesize distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 13 (IRAVT013300133) on State Route 133, crossing an Ira Brook Tributary, Ira, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure IRA-VT01330013 on State Route 133 crossing an Ira Brook Tributary, Ira, 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 westcentral Vermont. The 2.88-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture while the immediate banks have dense tree cover. In the study area, this Ira Brook Tributary has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 40 ft and an average channel depth of 7 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 71.9 mm (0.236 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 14, 1995, indicated that the reach was stable. The State Route 133 crossing of this Ira Brook Tributary is a 28-ft-long, two-lane bridge consisting of one 26-foot concrete span (Vermont Agency of Transportation, written communication, March 13, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 5 degrees. A scour hole, approximately 0.5 ft deeper than the mean thalweg depth, was observed at the downstream end of the left abutment wall during the Level I assessment. The scour protection measures at the site were type-1 stone fill (less than 12 inches diameter) on the upstream left bank and upstream left wingwall and type-2 stone fill (less than 36 inches diameter) on the upstream right bank, upstream right wingwall, the downstream wingwalls and downstream banks. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. There was no computed contraction scour for any of the modelled flows. Abutment scour ranged from 3.6 to 4.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 45b (BRIDTH00040045b) on Town Highway 4, crossing an unnamed Dailey Hollow Branch Tributary, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH0004045B on town highway 4 crossing an unnamed Dailey Hollow Branch Tributary, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 2.47-mi 2 drainage area is in a predominantly rural and forested basin. Surface cover in the vicinity of the study site is variable. A gravel road is adjacent to the left bank with the immediate upstream left bank covered by grass and the immediate downstream left bank covered by shrubs and brush. The upstream right bank is densely forested; the downstream right overbank is covered by grass with trees and brush on the immediate channel bank. In the study area, this unnamed Dailey Hollow Branch Tributary has an incised channel with a slope of approximately 0.04 ft/ft, an average channel top width of 29 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel with a median grain size (D 50 ) of 47.0 mm (0.154 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 15, 1994, indicated that the reach was stable. The town highway 4 crossing of the unnamed Dailey Hollow Branch Tributary is a 62-ft-long, corrugated steel multi-plate arch structure. It is supported by concrete footings leaving natural stream bed exposed (Vermont Agency of Transportation, written communication, January, 1996). The road embankments are protected by stone fill, however, the size is unknown due to sand and grass covering the fill except for the upstream left embankment which has type-2 stone fill (less than 36 inches diameter). The downstream left bank is protected by type-3 stone fill (less than 48 inches diameter) extending 25 feet downstream of the culvert. The channel approach to the culvert has a mild s-curve bend with the opening skewed ten degrees to flow. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.1 to 1.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.7 to 11.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗