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Research about Bridgewater, Vermont

Source-linked reports with geographic coverage including Bridgewater, Vermont.

At least 19 recordsLinked to original sources
USGS1997

Level II scour analysis for Bridge 32 (BRIDTH00050032) on Town Highway 005, crossing North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050032 on town highway 5 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge, available from VTAOT files, was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont. The 4.37-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the US left bank is lawn; DS left bank is pasture; US right bank is shrub and brushland and the DS right bank is forested. In the study area, the North Branch Ottauquechee River has an incised channel with a slope of approximately 0.0148 ft/ft, an average channel top width of 25 ft and an average channel depth of 9 ft. The predominant channel bed materials are gravel and cobbles (D 50 is 79.6 mm or 0.261 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 4, 1994, indicated that the reach was stable. The town highway 5 crossing of the North Branch Ottauquechee Riveris a 27-ft-long, onelane bridge consisting of one 25-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written commun., August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The DS left road approach is protected by type-1 stone fill (less than 12 inches). The DS right road approach is not protected and is eroded slightly by road wash. The US left bank is protected by type-2 stone fill (less than 36 inches). A stream confluence is located approximately 130 US of the bridge. The channel is skewed approximately 30 degrees to the opening. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗
USGS1996

Level II scour analysis for Bridge 43 (BRIDTH00040043) on Town Highway 004, crossing Dailey Hollow Branch, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00040043 on town highway 4 crossing Dailey Hollow Branch, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont. The 9.80-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the left and right banks are forested. Upstream of bridge 43, Town Highway 4 runs parallel to the left bank and DS of the bridge, parallel to the right bank. In the study area, Dailey Hollow Branch has an incised channel with a slope of approximately 0.02 ft/ft, an average channel top width of 63 ft and an average channel depth of 5 ft. The predominant channel bed materials are gravel and cobble (D 50 is 77.0 mm or 0.253 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 1, 1994, indicated that the reach was stable. The town highway 4 crossing of Dailey Hollow Branch is a 38-ft-long, one-lane bridge consisting of one 34-foot steel beam span with a timber deck (Vermont Agency of Transportation, written commun., August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 34 degrees to the opening while the opening-skew-to-roadway is 30 degrees. The footings of both abutments are exposed and the left abutment has experienced some undermining. Abutments are not protected by stone fill. However, upstream and downstream wingwalls are protected by type-2 stone fill (less than 36 inches). Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗
USGS1996

Level II scour analysis for Bridge 26 (BRIDTH00340026) on Town Highway 034, crossing Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00340026 on town highway 34 crossing the Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files were compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Bridgewater. The 38.0-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage except for the upstream right bank, which is grass covered. In the study area, the Ottauquechee River has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 62.5 ft and an average channel depth of 4.5 ft. The predominant channel bed material is cobble (D 50 is 97.3 mm or 0.319 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 8, 1994, indicated that the reach was stable. The town highway 34 crossing of the Ottauquechee Riveris a 69-ft-long, two-lane bridge consisting of one 63-foot clear-span steel-pony truss-type superstructure (Vermont Agency of Transportation, written commun., August 24, 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-to-roadway is 45 degrees. A scour hole 4.5 ft deeper than the mean thalweg depth was observed along the upstream left wingwall during the Level I assessment. The only scour protection measure at the site was type-1 stone fill (less than 12 inches diameter) at the upstream end of the upstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). These guidelines provide scour equations, which assume an infinite depth of erosive material and a homogeneous particle-size distribution. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗
USGS1996

Level II scour analysis for Bridge 28 (BRIDTH00440028) on Town Highway 044 crossing Plymouth Brook, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00440028 on town highway 44 crossing Plymouth Brook, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont in the town of Bridgewater. The 11.3-mi 2 drainage area is a predominantly rural basin. In the vicinity of the study site, the left and right banks are pasture. In the study area, Plymouth Brook has an incised channel with a slope of approximately 0.0054 ft/ft, an average channel top width of 42 ft and an average channel depth of 3 ft. The predominant channel bed material is gravel (D 50 is 62.3 mm or 0.204 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 9, 1994, indicated that the reach was stable. The town highway 5 crossing of the Black River is a 70-ft-long, two-lane bridge consisting of one 65-foot clear span (Vermont Agency of Transportation, written commun., August 2, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. There is also a retaining wall along the upstream side of the road embankments. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 15 degrees. A scour hole 3.0 ft deeper than the mean thalweg depth was observed along the right abutment. The scour hole was 27 feet long, 15 feet wide, and was 2.5 feet below the abutment footing at the time of the Level I assessment. This right abutment had numerous cracks and had settled. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗
USGS1996

Level II scour analysis for Bridge 34 (BRIDTH00050034) on Town Highway 005, crossing North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050034 on town highway 5 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont in the town of Bridgewater. The 5.45-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, left and right banks are forested. Upstream of bridge 34, Town Highway 5 runs parallel to the right bank and DS of the bridge, parallel to the left bank. In the study area, the North Branch Ottauquechee River has an incised channel with a slope of approximately 0.015 ft/ft, an average channel top width of 32 ft and an average channel depth of 7 ft. The predominant channel bed material is sand and gravel (D 50 is 105 mm or 0.345 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 3, 1994, indicated that the reach was stable. The town highway 31 crossing of Lilliesville Brook is a 41-ft-long, one-lane bridge consisting of one 39-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written commun., August 24, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 35 degrees to the opening while the opening-skew-to-roadway is 0 degrees. Scour protection measures in place at the site were type-1 stone fill (less than 12 inches diameter) at the downstream left wingwall, left abutment, and upstream and downstream sides of the left road 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, 1993). Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗
USGS1996

Level II scour analysis for Bridge 27 (BRIDTH00490027) on Town Highway 049, crossing Broad Brook, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00490027 on town highway 49 crossing Broad Brook, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Bridgewater. The 13.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the left and right banks are pasture with moderate tree cover on the immediate banks. Upstream of bridge 27, a gravel road runs parallel to the left bank. In the study area, the Broad Brook has an incised channel with a slope of approximately 0.007 ft/ft, an average channel top width of 54 ft and an average channel depth of 4 ft. The predominant channel bed materials are gravel and cobble with a D 50 (median diameter) of 77.9 mm or 0.256 ft. The geomorphic assessment at the time of the Level I and Level II site visit on November 9, 1994, indicated that the reach was stable. The town highway 49 crossing of the Broad Brook is a 32-ft-long, one-lane bridge consisting of one 31-ft steel-beam span (Vermont Agency of Transportation, written commun., August 24, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The left abutment is noted as settled due to previous undermining. Type-2 (less than 3 ft diameter) stone fill protects the upstream left and right wingwalls, the downstream right wingwall, the right abutment, the upstream right road embankment, and the downstream left and right road embankments. Type-3 (less than 4 ft diameter) stone fill protects the downstream left wingwall, but it’s condition was reported as slumping. The channel is skewed approximately 10 degrees to the opening; the opening-skew-to-roadway is also 10 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. The scour analysis results are presented in tables 1 and 2 and a graph of the scour depths is presented in figure 8.

Vermont↗
USGS1996

Level II scour analysis for Bridge 57 (BRIDTH00650057) on Town Highway 65, crossing Broad Brook, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00650057 on Town Highway 65 crossing Broad Brook, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge, available from VTAOT files, was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Bridgewater. The 26.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the US left bank is forested; DS left bank is shrub and brushland; US right bank is lawn and the DS right bank has very little vegetation and is largely coincident with the Ottauquechee River. In the study area, Broad Brook has an incised channel with a slope of approximately 0.0067 ft/ft, an average channel top width of 60 ft and an average channel depth of 3 ft. The predominant channel bed material is gravel (D 50 is 46.2 mm or 0.151 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 25, 1994, indicated that the reach was stable. The Town Highway 65 crossing of Broad Brook is a 47-ft-long, one-lane bridge consisting of one 44-ft steel-beam span with a timber deck, supported by vertical concrete abutments with wingwalls on the upstream and downstream sides (Vermont Agency of Transportation, written commun., August, 1994). The US right wingwall and road approach is protected by stone fill. The US and DS right wingwalls and the right abutment are reported as having 1.0 to 1.5 ft of scour at the time of the Level one assessment on 10/25/94. Erosion from road wash affects all road approach embankments. Broad Brook flows into the Ottauquechee River approximately 30 ft downstream of the bridge. The channel approach to the bridge is straight with the bridge skewed 20 degrees to flow and 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, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term aggradation or degradation; 2) contraction scour (due to reduction in flow area caused by a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute scour depths for contraction and local scour and a summary of the results follows. Contraction scour for all modelled flows ranged from 0.4 ft to 1.5 ft and the worst-case contraction scour occurred at the incipient overtopping discharge. Abutment scour ranged from 6.0 ft to 14.6 ft and the worst-case abutment scour occurred at the 100-year discharge. Scour depths and depths to armoring are summarized on p. 14 in the section titled “Scour Results”. Scour elevations, based on the calculated depths are presented in tables 1 and 2; a graph of the scour elevations is presented in figure 8 Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. For all scour presented in this report, “the scour depths adopted [by VTAOT] may differ from the equation values based on engineering judgement” (Richardson and others, 1993, p. 21, 27). It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results.

Vermont↗
USGS1996

Level II scour analysis for Bridge 3 (BRIDTH000100003) on Town Highway 1, crossing Dailey Hollow Branch, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00010003 on town highway 1 crossing Dailey Hollow Branch, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont in the town of Bridgewater. The 9.88-mi 2 drainage area is in a predominantly rural, forested basin. In the vicinity of the study site, the immediate channel banks have moderate tree cover and shrubs with residential properties on the overbank. In the study area, Dailey Hollow Branch has an incised, sinuous channel with a slope of approximately 0.009 ft/ft, an average channel top width of 46 ft and an average channel depth of 4 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 89.7 mm (0.294 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 27, 1994, indicated that the reach was vertically degrading. The town highway 1 crossing of Dailey Hollow Branch is a 45-ft-long, two-lane bridge consisting of one 42-foot steel-beam span (Vermont Agency of Transportation, written communication, August 24, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. Type-2 stone fill (less than 36 inches diameter) protects the downstream right and left wingwall. Type-3 stone fill (less than 48 inches diameter) exists on the downstream right bank. The left abutment is undermined by up to one foot. Horizontal probing under the abutment resulted in penetration up to 6 feet. The bridge is misaligned with the channel. Higher discharges may directly impact the left wingwall. The channel is skewed approximately 20 degrees to the bridge; the opening-skew-to-roadway is also 20 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term aggradation or degradation; 2) contraction scour (due to reduction in flow area caused by a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute scour depths for contraction and local scour and a summary of the results follows. Contraction scour for all modelled flows ranged from 0.6 ft to 1.3 ft and the worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.7 ft to 12.2 ft and the worst-case abutment scour occurred at the 500-year discharge. Scour depths and depths to armoring are summarized on p. 14 in the section titled “Scour Results”. Scour elevations, based on the calculated depths are presented in tables 1 and 2; a graph of the scour elevations is presented in figure 8 Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. For all scour presented in this report, “the scour depths adopted [by VTAOT] may differ from the equation values based on engineering judgement” (Richardson and others, 1993, p. 21, 27). It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results.

Vermont↗
USGS1996

Level II scour analysis for Bridge 51 (BRIDTH00460051) on Town Highway 46, crossing Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00460051 on town highway 46 crossing the Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont in the town of Bridgewater. The 103-mi 2 drainage area is a predominantly rural basin. In the vicinity of the study site, the immediate left and right banks are covered by trees and brush with residences beyond. In the study area, the Ottauquechee River has a straight channel with a slope of approximately 0.008 ft/ft, an average channel top width of 150 ft and an average channel depth of 6 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 81.8 mm (0.268 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 24, 1994, indicated that the reach was stable. The town highway 46 crossing of the Ottauquechee Riveris a 135-ft-long, two-lane bridge consisting of two 66-ft steel-beam spans, supported by vertical, concrete abutments with upstream wingwalls and one concrete pier (Vermont Agency of Transportation, written commun., August 24, 1994). Type-2 stone fill (less than 36 inches diameter) has been placed along the left abutment and both upstream wingwalls. The upstream side of both road embankments are also protected by type-2 stone fill. Abutments of a previous bridge still exist at the downstream side of the present structure’s abutments. The channel is skewed 10 degrees to the bridge face; the opening-skew-to-roadway is 0 degrees. There are remains of a breached dam 160 feet upstream of the bridge which deflect flow toward the left bank. Additional details describing conditions at the site are included in the Level II Summary, Appendix D, and Appendix E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 2.6 to 5.4 ft. The worst-case contraction scour occurred at the incipient overtopping discharge, which was between the 100- and 500-year discharges. Pier scour ranged from 9.9 to 10.9 ft with the worst-case scenario also occurring at the incipient roadway overtopping discharge. Abutment scour ranged from 25.3 to 33.6 ft. with the 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 cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Level II scour analysis for Bridge 42 (BRIDTH00040042) on Town Highway 04, crossing Dailey Hollow Brook, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00040042 on town highway 4 crossing Dailey Hollow Brook, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont in the town of Bridgewater. The 2.20-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the overbanks are covered by shrubs and trees except for the upstream right overbank where there is a house. Dailey Hollow Brook enters Dailey Hollow Branch at the downstream face of the bridge. In the study area, Dailey Hollow Brook has an incised, sinuous channel with a slope of approximately 0.035 ft/ft. The channel top width and channel depth upstream of the bridge is 19 ft and 3 ft, respectively. Downstream of the bridge and the confluence the channel top width and channel depth is 39 ft and 2 ft respectively. The predominant channel bed material is cobble and gravel (D 50 is 64.7 mm or 0.212 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 1, 1994, indicated that the reach was stable. The town highway 4 crossing of Dailey Hollow Brook is a 25-ft-long, one-lane bridge consisting of one 23-foot concrete span (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. Type-2 stone fill (less than 36 inches) exists along all four wingwalls, the downstream right road approach, and the channel banks in the immediate vicinity of the bridge. The channel is skewed approximately 20 degrees to the opening; the opening-skewto-roadway is also 20 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term 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 modelled flows was 0.0 ft. Abutment scour ranged from 3.9 to 5.4 ft. with the worst-case abutment scour occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Level II scour analysis for Bridge 45a (BRIDUS00040045a) on U.S. Route 4, crossing Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDUS00040045a on U.S.. Route 4 crossing the Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Bridgewater. The 72.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the overbank areas are lawn or pasture with a few residences. The immediate channel banks have moderately dense woody vegetation. In the study area, the Ottauquechee River has a sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 81 ft and an average channel depth of 3 ft. The predominant channel bed materials are gravel and cobble (D 50 is 54.9 mm or 0.180 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 26, 1994, indicated that the reach was stable. The U.S. Route 4 crossing of the Ottauquechee Riveris a 172-ft-long, two-lane bridge consisting of three steel-beam spans supported by spill-through abutments and two concrete piers (Vermont Agency of Transportation, written commun., August 25, 1994). The abutment and road approaches are protected by type-2 stone fill (less than 36 inches diameter). The North Branch of the Ottauquechee River joins the Ottauquechee River approximately 200 feet upstream of the bridge on the main branch’s left bank. The channel approach to the bridge has a mild bend with the bridge skewed 15 degrees to flow; the opening-skew-to-roadway is 30 degrees. Additional details describing conditions at the site are included in the Level II Summary, Appendix D, and Appendix E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term 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 3.1 to 4.0 ft. with the worst-case contraction scour occurring at the 500-year and incipient road-overflow discharges. Abutment scour ranged from 9.3 to 15.2 ft. The worst-case abutment scour also occurred at the 500-year discharge. Pier scour ranged from 11.4 to 12.4 ft. with the worst-case scenario occurring at the incipient roadway overflow discharge. The incipient roadway overflow discharge was 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, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Level II scour analysis for Bridge 29 (BRIDTH00360029) on Town Highway 36, crossing North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00360029 on town highway 36 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont in the town of Bridgewater. The 27.1-mi 2 drainage area is a predominantly rural basin. In the vicinity of the study site, the left and right banks are covered by pasture and (or) fields with the immediate stream banks covered by woody vegetation. The left bank of North Branch Ottauquechee River is adjacent to Bridgewater town highway 001. In the study area, the North Branch Ottauquechee River has a sinuous channel with a slope of approximately 0.008 ft/ft, an average channel top width of 73 ft and an average bank height of 6 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 61.0 mm (0.200 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 26, 1994, indicated that the reach was stable. The town highway 36 crossing of the North Branch Ottauquechee Riveris a 46-ft-long, one-lane bridge consisting of one 43-foot steel-beam span (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. Type-2 (less than 36 inches) stone fill protects the upstream and downstream wingwalls. Sparse type-2 stone fill was also observed along the right abutment. The channel approach to the bridge is not skewed, however, the measured opening skew-to-roadway is five degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term 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 1.4 to 2.8 ft. The worst-case contraction scour occurred at the incipient overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 7.3 to 13.2 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Level II scour analysis for Bridge 30 (BRIDTH00330030) on Town Highway 33, crossing Dailey Hollow Branch, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00330030 on town highway 33 crossing Dailey Hollow Branch, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Bridgewater. The 7.51-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, Dailey Hollow Branch has an incised, sinuous channel with a slope of approximately 0.013 ft/ft, an average channel top width of 45 ft and an average channel depth of 5 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 60.7 mm (0.199 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 1, 1994, indicated that the reach was stable. The town highway 33 crossing of Dailey Hollow Branch is a 31-ft-long, one-lane bridge consisting of one 25-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 0 degrees. Type-2 stone-fill (less than 36 inches diameter) protection was found at all four 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, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.5 to 3.1 ft. The worst-case contraction scour occurred at the incipient-roadway-overtopping discharge, which is between the 100- and 500-year discharge. Abutment scour ranged from 6.9 to 14.6 ft. with the worst-case scenario also occurring at the incipient-roadway-overtopping discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Level II scour analysis for Bridge 35 (BRIDTH00050035) on Town Highway 05, crossing the North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050035 on town highway 5 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont. The 6.70-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, surface cover is predominately forest. Town Highway 5 runs parallel to the upstream left and downstream right banks. In the study area, the North Branch Ottauquechee River has an incised, sinuous channel with a slope of approximately 0.015 ft/ft, an average channel top width of 33 ft and an average channel depth of 3 ft. The predominant channel bed materials are gravel and cobble (D 50 is 74.8 mm or 0.245 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 2, 1994, indicated that the reach was stable. The town highway 5 crossing of the North Branch Ottauquechee River is a 30-ft-long, one-lane bridge consisting of one 24-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by a timber cribwork abutment on the right and stone wall abutment on the left. A scour hole 3 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is 25 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.7 to 0.8 ft. The worst-case contraction scour occurred at the incipient-roadway-overtopping discharge and at the 100- year discharge. Abutment scour ranged from 8.0 to 15.1 ft. with the worst-case abutment scour occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Level II scour analysis for Bridge 37 (BRIDTH00050037) on Town Highway 5, crossing North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050037 on town highway 5 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic province of central Vermont in the town of Bridgewater. The 10.5-mi 2 drainage area is a predominantly rural basin. In the vicinity of the study site, the left and right banks are forested. Town highway 5 runs parallel to the upstream left and downstream right banks. In the study area, the North Branch Ottauquechee River has a sinuous channel with a slope of approximately 0.013 ft/ft, an average channel top width of 50 ft and an average channel depth of 5 ft. The predominant channel bed materials are gravel and cobble (D 50 is 79.3 mm or 0.260 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 2, 1994, indicated that the reach was stable. The town highway 5 crossing of the North Branch Ottauquechee Riveris a 38-ft-long, onelane bridge consisting of one 35-foot steel beam span (Vermont Agency of Transportation, written commun., August 25, 1994). The bridge is supported by vertical, stone abutments with wingwalls. The right abutment has settled due to scour. Type-3 stone fill (less than 36 inches diameter) provides protection to the upstream end of the upstream left wingwall and the base of the downstream right wingwall. The channel is skewed approximately 35 degrees; the opening-skew-to-roadway is 20 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendix E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.4 to 1.5 ft. The worst-case contraction scour occurred at the incipient overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 11.0 to 14.9 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A 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, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

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

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

Vermont↗
USGS1996

Level II scour analysis for Bridge 33 (BRIDTH00050033) on Town Highway 5, crossing the North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050033 on town highway 5 crossing the North Branch Ottauquechee River, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province of central Vermont in the town of Bridgewater. The 5.01-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the downstream banks are forested and the upstream banks have dense woody brush; the upstream right overbank is an open field. In the study area, the North Branch Ottauquechee River has an incised, sinuous channel with a slope of approximately 0.017 ft/ft, an average channel top width of 30 ft and an average channel depth of 3 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D 50 ) of 83.2 mm (0.273 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 3, 1994, indicated that the reach was stable. Also at the time of the site visit, there was considerable backwater at the bridge site due to a three foot tall beaver dam 40 feet downstream. The beaver dam was assumed destroyed by flood flow and was ignored in the analyses. The town highway 5 crossing of the North Branch Ottauquechee Riveris a 25-ft-long, onelane bridge consisting of one 23-foot steel-beam span with a timber deck (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 10 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the right abutment and upstream right wingwall during the Level I assessment. Scour protection measures at the site include type-2 stone fill (less than 36 inches diameter) at the ends of all the wingwalls except the upstream left which has type-3 stone fill (less than 48 inches diameter). Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.7 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 5.3 to 7.2 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A crosssection of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 36 (BRIDTH00050036) on Town Highway 5, crossing Bridgewater Hollow Brook, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050036 on town highway 5 crossing Bridgewater Hollow Brook, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province of central Vermont. The 3.60-mi 2 drainage area is in a predominantly forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage. In the study area, Bridgewater Hollow Brook has an incised, sinuous channel with a slope of approximately 0.028 ft/ft, an average channel top width of 24 ft and an average channel depth of 4 ft. The predominant channel bed material is cobble (D 50 is 196 mm or 0.644 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 2, 1994, indicated that the reach was stable. The town highway 5 crossing of Bridgewater Hollow Brook is a 30-ft-long, one-lane bridge consisting of one 27-foot steel-beam span (Vermont Agency of Transportation, written communication, August 25, 1994). 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 is also 30 degrees. The scour protection measures at this site were sparse type-2 stone fill (less than 36 inches diameter) along both abutments, upstream wingwalls, and the downstream left wingwall and type-1 stone fill (less than 12 inches diameter) along the downstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and 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 contraction scour for all modelled flows. Abutment scour ranged from 4.9 to 7.0 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗