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USGS1996

Level II scour analysis for Bridge 94 (FERDVT01050094) on State Route 105, crossing the Nulhegan River, Ferdinand, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FERDVT01050094 on State Route 105 crossing the Nulhegan River, Ferdinand, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the White Mountain section of the New England physiographic province in northeastern Vermont. The 38.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is grass and brush with wetlands immediately adjacent to the stream channel. In the study area, the Nulhegan River has a meandering channel with a slope of approximately 0.002 ft/ft, an average channel top width of 60 ft and an average channel depth of 6 ft. The predominant channel bed material is sand with a median grain size (D 50 ) of 0.465 mm (0.00153 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 5, 1995, indicated that the reach was laterally unstable. The State Route 105 crossing of the Nulhegan Riveris a 44-ft-long, two-lane bridge consisting of one 42-foot steel-beam span (Vermont Agency of Transportation, written communication, March 6, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is zero degrees. Scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on the upstream right bank, the upstream right wingwall, the right abutment, the downstream end of the left abutment and the downstream wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.2 to 1.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.6 to 11.0 ft. The worst-case abutment scour also occurred at the 500-year discharge. Total scour depths computed for this site were not below the bottom of the footings, except for the 500- year discharge model at the left abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A crosssection of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 25 (CLARTH00100025) on Town Highway 10, crossing the Clarendon River, Clarendon, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CLARTH00100025 on town highway 10 crossing the Clarendon River, Clarendon, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Resultsof 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 Taconic Section of the New England physiographic province in westcentral Vermont. The 19.3-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 pasture and (or) fields. The right bank of Clarendon River is eroded due to stream-flow attack immediately upstream of the bridge. In the study area, the Clarendon River has a sinuous channel with a slope of approximately 0.007 ft/ft, an average channel top width of 44 ft and an average channel depth of 3 ft. There are large meanders approximately 100 feet upstream and downstream of the bridge. The predominant channel bed materials are 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 April 27, 1995, indicated that the reach was laterally unstable. The town highway 10 crossing of the Clarendon River was a 27-ft-long, two-lane bridge consisting of one 24-foot steel stringer with a timber deck (Vermont Agency of Transportation, written communication, March 13, 1995). The deck was removed at the time of the survey but the analysis was done as if the old deck was in place. The bridge is supported on the left by a vertical stone abutment and on the right by a vertical, concrete abutment with an upstream wingwall. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 0 degrees. A scour hole 3 ft deeper than the mean thalweg depth was observed along the right bank extending from 24 to 60 feet upstream of the bridge. No scour prevention measures were observed at this site at the time of the site visit. 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 0.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 5.7 to 10.6 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↗
USGS1996

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

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

Vermont↗
USGS1996

Level II scour analysis for Bridge 14 (FFIETH00010014) on Town Highway 1, crossing the Fairfield River, Fairfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FFIETH00010014 on Town Highway 1 crossing the Fairfield River, Fairfield, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in northwestern Vermont. The 7.84-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the upstream left and downstream right is row crops. The surface cover on the upstream right and downstream left is pasture. In the study area, the Fairfield River has a sinuous channel with a slope of approximately 0.006 ft/ft, an average channel top width of 33 ft and an average channel depth of 3 ft. The channel bed material ranges from silt to gravel with a median grain size (D 50 ) of 15.4 mm (0.0505 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 11, 1995, indicated that the reach was laterally unstable. The Town Highway 1 crossing of the Fairfield River is a 26-ft-long, two-lane bridge consisting of one 23-foot concrete 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 27 degrees to the opening while there is no opening-skew-to-roadway. The bridge is located on a sharp channel bend. Th e left abutment is impacted due to this bend. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I asse ssment. Scour protection measures at the site include type- 3 stone fill (less than 48 inches diameter ) along the immediate upstream banks and along the base of the upstream left wi ngwall. Type-2 stone fill (le ss than 36 inches diameter) was present along the downstream left wingwall. A dditional 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 5.4 to 8.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 3.0 to 8.3 ft. The worst-case abutment scour also occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are include d 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 38 (CONCTH00060038) on Town Highway 6, crossing the Moose River, Concord, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CONCTH00060038 on Town Highway 6 crossing the Moose River, Concord, 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. Approximately 85 percent of the drainage above the site is in the White Mountain section and 15 percent is in the New England Upland section of the New England physiographic province in northeastern Vermont. The 98.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover of the banks is primarily forest and brush. In the study area, the Moose River has an incised, sinuous channel with a slope of approximately 0.009 ft/ft, an average channel top width of 110 ft and an average channel depth of 6 ft. The channel bed material ranged from gravel to boulder and had a median grain size (D 50 ) of 74.4 mm (0.244 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 17, 1995, indicated that the reach was stable. The Town Highway 6 crossing of the Moose River is a 59-ft-long, two-lane bridge consisting of one 55-foot steel-beam span (Vermont Agency of Transportation, written communication, March 24, 1995). The bridge is supported by a vertical, laid-up stone abutment with wingwalls on the left and a vertical, concrete abutment with wingwalls on the right. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 0 degrees. The footing of the left abutment is exposed as much as 2.8 feet. The footing of the right abutment is undermined vertically by as much as 0.3 feet. Type-2 stone-fill (less than 36 inches diameter) protection can be found along the left abutment. Type-3 stone-fill (less than 48 inches diameter) protection can be found along 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 0.1 to 3.1 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour at the left abutment ranged from 10.4 to 12.5 ft with the worst-case occurring at the 500-year discharge. Abutment scour at the right abutment ranged from 25.3 to 27.3 ft with the worst-case occurring at the incipient-overtopping discharge. The worst-case total scour also occurred at the incipient-overtopping discharge. The incipient-overtopping discharge was in between the 100- and 500-year discharges. 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 12 (FFIETH00030012) on Town Highway 3, crossing the Fairfield River, Fairfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FFIETH00030012 on Town Highway 3 crossing the Fairfield River, Fairfield, 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-western Vermont. The 7.34-mi 2 drainage area is in a predominantly rural basin with forest on the valley walls and pasture/row crops on the valley bottom. In the vicinity of the study site, the surface cover is row crops with a few trees on the immediate banks. In the study area, the Fairfield River has a meandering channel with a slope of approximately 0.005 ft/ft, an average channel top width of 37 ft and an average channel depth of 6 ft. The predominant channel bed materials are sand and gravel with a median grain size (D 50 ) of 32.5 mm (0.107 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 16, 1995, indicated that the reach was stable. The Town Highway 3 crossing of the Fairfield River is a 24-ft-long, one-lane bridge consisting of one 20-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 40 degrees to the opening. Although bridge records show an opening-skew-to-roadway of 45 degrees, the skew measured from surveyed points was 30 degrees. At the time of the level I assessment, the left abutment had been undermined and settled into a scour hole at the upstream end. The right abutment footing was exposed but not undermined. The scour protection measures at the site were type-1 stone fill (less than 12 inches diameter) on the downstream right bank, and type-2 stone fill (less than 36 inches diameter) along the entire base of the upstream right wingwall, the upstream banks, and downstream left bank. The type-2 stone fill on the left bank downstream changes to type-1 about 55 feet downstream of the bridge. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 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 1.6 to 3.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 3.2 to 4.0 ft. at the left abutment and 9.7 to 11.7 feet at the right abutment. The worst-case left abutment scour occurred at the incipient over-topping discharge, which was less than the 100-year discharge. The worst-case right abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous 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 32 (NFIEVT012A0032) on State Route 12A, crossing the Dog River, Northfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NFIEVT012A0032 on State Route 12A crossing the Dog River, Northfield, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 13.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture (golf course). In the study area, the Dog River has a straight channel with a slope of approximately 0.01 ft/ ft, an average channel top width of 47 ft and an average bank height of 7 ft. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 39.0 mm (0.128 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 22, 1996, indicated that the reach was stable. The State Route 12A crossing of the Dog River is a 35-ft-long, two-lane bridge consisting of one 32-foot concrete span (Vermont Agency of Transportation, written communication, October 13, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening and the opening-skew-to- roadway also is 30 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the upstream end of the right abutment wall during the Level I assessment. The scour protection measures at the site were type-1 stone fill (less than 12 inches diameter) on the right bank downstream and type-2 stone fill (less than 36 inches diameter) on the upstream banks, the downstream left bank and the upstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.5 to 2.9 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 7.2 to 1 2.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross- section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 137 (FERRUS00070137) on U.S. Route 7, crossing Little Otter Creek, Ferrisburg, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FERRUS00070137 on U.S. Route 7 crossing Little Otter Creek, Ferrisburg, 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 Champlain section of the St. Lawrence Valley physiographic province in northwestern Vermont. The 56.7-mi 2 drainage area is in a predominantly rural and forested basin with some pasture on the valley bottom. In the vicinity of the study site, the surface cover consists of pasture upstream of the bridge. Downstream of the bridge the surface cover consists of trees, shrubs, and grass. In the study area, Little Otter Creek has a meandering channel with a slope of approximately 0.007 ft/ft, an average channel top width of 86 ft and an average channel depth of 3 ft. The predominant channel bed materials are cobbles and gravel with a median grain size (D 50 ) of 54.9 mm (0.180 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 1, 1996, indicated that the reach was laterally unstable. The U.S. Route 7 crossing of Little Otter Creek is a 157-ft-long, two-lane bridge consisting of three steel-beam spans (Vermont Agency of Transportation, written communication, December 12, 1995). The bridge is supported by vertical, concrete abutment walls with spill-through embankments in front of each abutment wall and two solid concrete piers. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is zero degrees. The scour protection measures at the site consist of type-3 stone fill (less than 48 inches diameter) on the banks upstream and downstream of the bridge and the lower half of the spill-through embankment slopes on each abutment. Type-1 stone fill (less than 12 inches diameter) protects the upper half of the spill-through embankments and each 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 1.8 to 2.3 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 10.4 to 14.9 ft. The worst-case abutment scour occurred at the 500-year discharge. There are two piers for which computed pier scour ranged from 7.5 to 13.4 ft. The left and right piers in this report are presented as pier 1 and pier 2 respectively. The worst-case pier scour occurred at pier 1 for the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 80 (JAMAVT01000080) on State Highway 100, crossing the West River, Jamaica, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure JAMAVT01000080 on State Route 100 crossing the West River, Jamaica, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in southern Vermont. The 227-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 left bank and downstream of the bridge while the immediate banks have dense woody vegetation. The upstream right bank of the bridge is forested. In the study area, the West River has an incised, straight channel with a slope of approximately 0.01 ft/ft, an average channel top width of 309 ft and an average bank height of 10 ft. The channel bed material is predominantly cobble with a median grain size (D 50 ) of 109 mm (0.359 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 13, 1996, indicated that the reach was stable. The State Route 100 crossing of the West River is a 246-ft-long, one-lane steel thru-truss bridge consisting of three spans, the longest is 161-feet (Vermont Agency of Transportation, written communication, March 30, 1995). The bridge is supported by vertical, concrete abutments and two piers. The channel is skewed approximately 5 degrees to the opening while there is no opening-skew-to-roadway. A scour hole 3 ft deeper than the mean thalweg depth was observed along the streamward (right) side of the left pier during the Level I assessment. A scour hole 5 ft deeper than the mean thalweg depth was observed along the streamward (left) side of the right pier 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 bank below the abutments forming a “spill-through” slope at each abutment. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and 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. Abutment scour ranged from 15.8 to 23.9 ft. The worst-case abutment scour occurred at the 500-year discharge. Pier scour ranged from 9.5 to 22.8 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 others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

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

This report provides the results of a detailed Level II analysis of scour potential at structure CRAFTH00390023 on town highway 39 crossing the Black River, Craftsbury, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I assessment is included in Appendix E of this report. A Level I assessment provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from VTAOT files, was compiled prior to conducting Level I and Level II analyses and is provided in Appendix D. The site is in the New England Upland physiographic province of North-central Vermont in the town of Craftsbury. The 30.9-mi 2 drainage area is in a predominantly rural and forested basin with some pasture grassland on the valley bottom. In the vicinity of the study site, the banks have very little woody vegetation coverage except for the downstream left bank, which has some trees and brush coverage. In the study area, the Black River has an meandering channel with a slope of approximately 0.0004 ft/ft, an average channel top width of 62 ft and an average channel depth of 3 ft. The predominant channel bed materials are sand and gravel with a median grain size (D 50 ) of 0.73 mm (0.0024 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 6, 1995, indicated that the reach was laterally unstable. The town highway 39 crossing of the Black River is a 65-ft-long, two-lane bridge consisting of three spans with a maximum span of 38-feet (Vermont Agency of Transportation, written communication, August 24, 1994). The bridge is supported by vertical, concrete abutments and two stone piers with concrete caps. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 10 degrees in the opposite direction. The scour protection measures at the site were type-1 stone fill (less than 12 inches diameter) on the upstream left and right roadway embankments and between the right pier and right abutment wall. Type-2 (less than 36 inches diameter) stone fill was evident on the upstream left bank, downstream right bank, between the left pier and left abutment wall, and streamward of the right pier. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term aggradation or degradation; 2) contraction scour (due to reduction in flow area caused by a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute scour depths for contraction and local scour and a summary of the results follows. Contraction scour for all modelled flows ranged from 20.1 to 25.2 and the worst-case contraction scour occurred at the 500-year discharge. Although this bridge has two piers, the flow through the spans between each abutment and pier is assumed to be negligible. Hence, abutment scour was computed assuming the forces contributing to scour actually occur on the main-span sides of each pier in this case. Abutment scour ranged from 8.8 to 10.6 and the worst-case abutment scour occurred at the 500-year discharge. Scour depths and depths to armoring are summarized on p. 14 in the section titled “Scour Results”. Scour elevations, based on the calculated depths are presented in tables 1 and 2. A graph of the scour elevations is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 7H (HUNTTH0001007H) on Town Highway 1, crossing Cobb Brook, Huntington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HUNTTH001007H on Town Highway 1 crossing the Cobb Brook, Huntington, Vermont (figures 1–10). 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. In August 1976, Hurricane Belle caused flooding at this site which resulted in road and bridge damage (figures 7-8). This was approximately a 25-year flood event (U.S. Department of Housing and Urban Development, 1978). The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 4.20-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest upstream of the bridge. Downstream of the bridge is brushland and pasture. In the study area, the Cobb Brook has an incised, straight channel with a slope of approximately 0.03 ft/ft, an average channel top width of 43 ft and an average bank height of 6 ft. The channel bed material ranges from sand to boulders with a median grain size (D 50 ) of 65.5 mm (0.215 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 24, 1996, indicated that the reach was stable. The Town Highway 1 crossing of the Cobb Brook is a 23-ft-long, two-lane bridge consisting of one 20-foot concrete slab span (Vermont Agency of Transportation, written communication, June 21, 1996). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 2.8 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. Protection measures at the site include type-1 stone fill (less than 12 inches diameter) at the downstream right wingwall, type-2 stone fill (less than 36 inches diameter) at the upstream right wingwall and the downstream end of the downstream left wingwall, and type-3 stone fill (less than 48 inches diameter) at 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). 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 1.3 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 4.0 to 8.7 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 10. 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 29 (HARDTH00310029) on Town Highway 31, crossing the Lamoille River, Hardwick, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HARDTH00310029 on town highway 31 crossing the Lamoille River, Hardwick, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province of north-central Vermont. The 64.4-mi 2 drainage area is in a predominantly rural basin. In the vicinity of the study site, the surface cover is pasture except for the immediate downstream channel banks and the downstream left overbank which are brush covered. In the study area, the Lamoille River has a sinuous channel with a slope of approximately 0.001 ft/ft, an average channel top width of 84 ft and an average channel depth of 4 ft. The predominant channel bed materials are cobble and gravel with a median grain size (D 50 ) of 36.1 mm (0.119 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 26, 1995, indicated that the reach was stable. The town highway 31 crossing of the Lamoille River is a 65-ft-long, one-lane bridge consisting of one 61-foot steel-beam span (Vermont Agency of Transportation, written communication, March 27, 1995). The bridge is supported by vertical, stone abutments with wingwalls. The right abutment has a concrete facing and a concrete subfooter. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 0 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 2.7 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 10.3 to 18.6 ft. The worst-case abutment scour occurred at the 100-year discharge 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↗
USGS1997

Level II scour analysis for Bridge 11R (ROCKTH0001011R) on Town Highway 1 (VT 121 & FAS 125), crossing the Saxtons River, Rockingham, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ROCKTH0001011R on Town Highway 1 crossing the Saxtons River, Rockingham, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in southeastern Vermont. The 68.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of houses, short grass, and scattered trees except along the immediate river banks, which are tree covered. In the study area, the Saxtons River has a sinuous channel with a slope of approximately 0.005 ft/ft, an average channel top width of 121 ft and an average bank height of 8 ft. The predominant channel bed materials are gravel and cobbles with a median grain size (D 50 ) of 109 mm (0.359 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 3, 1996, indicated that the reach was laterally unstable. Lateral instability was evident with respect to a cut-bank on the left bank upstream with slip failure of bank material. Furthermore, there is a wide point bar along the right bank upstream opposite the cut-bank. The Town Highway 1 crossing of the Saxtons River is a 184-ft-long, two-lane bridge consisting of three steel-beam spans (Vermont Agency of Transportation, written communication, March 30, 1995). The bridge is supported by vertical, concrete, skeletal-style abutment walls with spill-through embankments adjacent to each wall. The channel is skewed approximately 35 degrees to the opening while the opening-skew-to-roadway is 30 degrees. The only scour protection measure at the site was type-3 stone fill (less than 48 inches diameter) on the spill-through embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. There was no computed contraction scour for all modelled flows at this site. Abutment scour ranged from 9.0 to 13.4 feet. The worst-case abutment scour occurred at the 500-year discharge for the left abutment. There are two piers for which computed pier scour ranged from 9.0 to 18.4 feet. The left and right piers in this report are presented as pier 1 and pier 2, respectively. The worst-case pier scour occurred at pier 2 for the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 63 (CHESTH00090063) on Town Highway 9, crossing the Williams River, Chester, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CHESTH00090063 on Town Highway 9 crossing the Williams River, Chester, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in eastern Vermont. The 24.0-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is grass with trees and brush along the immediate banks. In the study area, the the Williams River has an incised, sinuous channel with a slope of approximately 0.005 ft/ft, an average channel top width of 64 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 57.7 mm (0.189 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 18, 1996, indicated that the reach was stable. The Town Highway 9 crossing of the Williams River is a 45-ft-long, two-lane bridge consisting of one 35-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, April 6, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 0 degrees. A scour hole 1.8 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. The scour hole undermines the left abutment and extends from 50 ft upstream of the upstream bridge face to 50 ft downstream of the downstream bridge face. The scour protection measures at the site included type-3 stone fill (less than 48 inches diameter) under the bridge along the entire base length of the right abutment and along the right bank from 50 to 88 ft upstream. Type-2 (less than 36 inches diameter) stone fill scour protection was observed along the downstream left bank from 18 ft to 115 ft, along the downstream right bank from 8 ft to 25 ft and along the upstream left bank from 50 to 75 ft. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was computed to be 0.0 ft. Abutment scour ranged from 10.1 ft to 11.0 ft along the left abutment and from 14.1 ft to 15.1 ft along the right abutment. The worst-case abutment scour for the left abutment occurred at the 500-year discharge while the worst-case abutment scour for the right abutment occurred at the 100- year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 8 (ATHETH00090008) on Town Highway 9, crossing Bull Creek, Athens, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ATHETH00090008 on Town Highway 9 crossing Bull Creek in Athens, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in southeastern Vermont. The 9.04-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the left overbank surface cover is shrub and brushland and the right overbank surface cover is pasture. In the study area, Bull Creek has an sinuous channel with a slope of approximately 0.01 ft/ ft, an average channel top width of 41 ft and an average bank height of 4 ft. The predominant channel bed materials are cobbles and gravel with a median grain size (D 50 ) of 72.1 mm (0.236 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 14, 1996, indicated that the reach was laterally unstable. There are several point bars and cut banks along the reach in the vicinity of this site. The Town Highway 9 crossing of Bull Creek is a 32-ft-long, one-lane bridge consisting of one 28-foot steel-beam span (Vermont Agency of Transportation, written communication, April 5, 1995). The bridge is supported by vertical, “laid-up” stone abutments with concrete caps and no wingwalls. The channel is skewed approximately 15 degrees to the opening. The VTAOT bridge records indicate the opening-skew-to-roadway is 9 degrees while that computed from surveyed points is 5 degrees. A scour hole 1.75 feet deeper than the mean thalweg depth was observed under the bridge during the Level I assessment. The scour hole has lowered the streambed along the entire length of the left abutment and the upstream end of the right abutment. The scour depth at each abutment wall is 0.75 feet deeper than the mean thalweg depth elsewhere in the reach. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) on the upstream banks and downstream left bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 1.4 feet. The worst-case contraction scour occurred at the incipient-overtopping discharge of 1730 cubic feet per second, which was less than the 100-year discharge. Abutment scour ranged from 7.6 to 11.4 feet. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS2007

Geologic Map and Map Database of Eastern Sonoma and Western Napa Counties, California

Introduction This report contains a new 1:100,000-scale geologic map, derived from a set of geologic map databases (Arc-Info coverages) containing information at 1:62,500-scale resolution, and a new description of the geologic map units and structural relations in the map area. Prepared as part of the San Francisco Bay Region Mapping Project, the study area includes the north-central part of the San Francisco Bay region, and forms the final piece of the effort to generate new, digital geologic maps and map databases for an area which includes Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, and Sonoma Counties. Geologic mapping in Lake County in the north-central part of the map extent was not within the scope of the Project. The map and map database integrates both previously published reports and new geologic mapping and field checking by the authors (see Sources of Data index map on the map sheet or the Arc-Info coverage eswn-so and the textfile eswn-so.txt). This report contains new ideas about the geologic structures in the map area, including the active San Andreas Fault system, as well as the geologic units and their relations. Together, the map (or map database) and the unit descriptions in this report describe the composition, distribution, and orientation of geologic materials and structures within the study area at regional scale. Regional geologic information is important for analysis of earthquake shaking, liquifaction susceptibility, landslide susceptibility, engineering materials properties, mineral resources and hazards, as well as groundwater resources and hazards. These data also assist in answering questions about the geologic history and development of the California Coast Ranges.

Scientific Investigations Map↗
USGS2014

Simulated and observed 2010 floodwater elevations in the Pawcatuck and Wood Rivers, Rhode Island

Heavy, persistent rains from late February through March 2010 caused severe flooding that set, or nearly set, peaks of record for streamflows and water levels at many long-term U.S. Geological Survey streamgages in Rhode Island. In response to this flood, hydraulic models of Pawcatuck River (26.9 miles) and Wood River (11.6 miles) were updated from the most recent approved U.S. Department of Homeland Security-Federal Emergency Management Agency flood insurance study (FIS) to simulate water-surface elevations (WSEs) for specified flows and boundary conditions. The hydraulic models were updated to Hydrologic Engineering Center-River Analysis System (HEC-RAS) using steady-state simulations and incorporate new field-survey data at structures, high resolution land-surface elevation data, and updated flood flows from a related study. The models were used to simulate the 0.2-percent annual exceedance probability (AEP) flood, which is the AEP determined for the 2010 flood in the Pawcatuck and Wood Rivers. The simulated WSEs were compared to high-water mark (HWM) elevation data obtained in a related study following the March–April 2010 flood, which included 39 HWMs along the Pawcatuck River and 11 HWMs along the Wood River. The 2010 peak flow generally was larger than the 0.2-percent AEP flow, which, in part, resulted in the FIS and updated model WSEs to be lower than the 2010 HWMs. The 2010 HWMs for the Pawcatuck River averaged about 1.6 feet (ft) higher than the 0.2-percent AEP WSEs simulated in the updated model and 2.5 ft higher than the WSEs in the FIS. The 2010 HWMs for the Wood River averaged about 1.3 ft higher than the WSEs simulated in the updated model and 2.5 ft higher than the WSEs in the FIS. The improved agreement of the updated simulated water elevations to observed 2010 HWMs provides a measure of the hydraulic model performance, which indicates the updated models better represent flooding at other AEPs than the existing FIS models.

Rhode Island↗
USGS2018

Fault displacement hazard for strike-slip faults

In this paper we summarize data, methods, and models developed for a probabilistic assessment of fault displacement hazards across the U.S. We compare earthquake displacement data and empirical fault displacement models that have been developed for normal faults, strike-slip faults, and reverse faults. In general, the data and models are similar near the center of the fault for the three faulting types, but differ near the ends with the strike-slip data being lower than the reverse and normal faulting data. We also compare these U.S. models with data and equations developed using Japanese fault displacement data. The Japan model is also similar to the U.S. models near the center of the fault but decays less rapidly near the ends of the fault. In addition, we discuss impacts of models developed to analyze off-fault strain on secondary faults, multi-strand displacement hazard, and various mapping quality factors. For our study, we show example fault displacements for a M 7 fault with recurrence of 800 and 1600 years. We conclude that a deterministic assessment of fault displacements is often higher than the probabilistic displacements for less active faults with earthquake rupture recurrence that is longer than the hazard return period of interest. Fault displacement hazard is applied in engineering applications for buildings, bridges, pipelines, and nuclear facilities. We present three applications for fault displacement hazard at nuclear facilities and important structures.

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