Geology topics

Scott A. Olson

Publications and source records attributed to Scott A. Olson.

77 records · Page 5Linked to original sources

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 36 (RANDTH00480036) on Town Highway 48, crossing Snows Brook, Randolph, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RANDTH00480036 on town highway 48 crossing Snows Brook, 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). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province of central Vermont. The 3.72-mi2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, Snows Brook has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 27 ft and an average channel depth of 3 ft. The predominant channel bed material is cobble with a median grain size (D50) of 72.7 mm (0.238 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 9, 1994, indicated that the reach was laterally unstable. The town highway 48 crossing of Snows Brook is a 32-ft-long, two-lane bridge consisting of one 28-foot concrete span (Vermont Agency of Transportation, written communication, July 29, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 40 degrees to the opening while the opening-skew-toroadway 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, 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 6.1 to 11.6 ft. The worst-case abutment scour occurred at the incipient-overtopping discharge, which was 50 cfs lower than the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scouredstreambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particlesize distribution. It is generally accepted that the Froehlich 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↗

USGS1996

Level II scour analysis for Bridge 43 (HARDTH00CU0043) on Church Street, crossing the Lamoille River, Hardwick, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HARDTH00CU0043 on Church Street crossing the Lamoille River, Hardwick, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in north-central Vermont. The 87.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is best characterized as suburban except for the downstream right surface cover which is pasture. In the study area, the Lamoille River has an incised, straight channel with a slope of approximately 0.004 ft/ft, an average channel top width of 90 ft and an average channel depth of 8 ft. The predominant channel bed materials are cobble and gravel with a median grain size (DM 50 ) of 99.5 mm (0.327 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 Church Street crossing of the Lamoille River is a 100-ft-long, two-lane bridge consisting of one 97-foot steel-beam span (Vermont Agency of Transportation, written communication, March 17, 1995). The bridge is supported by a vertical, stone abutment with wingwalls on the left and a vertical concrete abutment with a stone spill-through slope on the right. 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 0.8 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 6.2 to 10.9 ft at the left abutment with worst-case occurring at the incipientovertopping discharge. Abutment scour ranged from 8.5 to 12.3 ft at the right abutment with worst-case occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A 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↗