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At least 1,405 records · Page 78Linked to original sources
USGS1998

Level II scour analysis for Bridge 32 (TUNBTH00600032) on Town Highway 60, crossing First Branch White River, Tunbridge, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure TUNBTH00600032 on Town Highway 60 crossing the First Branch White River, Tunbridge, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in appendix D. The site is in the New England Upland section of the New England physiographic province in central Vermont. The 92.9-mi2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream and downstream of the bridge, while woody vegetation sparsely covers the immediate banks. In the study area, the First Branch White River has a sinuous channel with a slope of approximately 0.001 ft/ft, an average channel top width of 82 ft and an average bank height of 7 ft. The channel bed material ranges from sand to gravel with a median grain size (D50) of 24.4 mm (0.08 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 18, 1995, indicated that the reach was laterally unstable, as a result of block failure of moderately eroded banks. The Town Highway 60 crossing of the First Branch White River is a 74-ft-long, one-lane bridge consisting of a 71-foot timber thru-truss span (Vermont Agency of Transportation, written communication, August 24, 1994). The opening length of the structure parallel to the bridge face is 64 ft.The bridge is supported by vertical, laid-up stone abutments with upstream wingwalls. The channel is not skewed to the opening. The computed opening-skew-to-roadway is 5 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed in the upstream reach during the Level I assessment. Scour countermeasures at the site includes type-1 stone fill (less than 12 inches diameter) along the upstream right bank. Type-2 stone fill (less than 36 inches diameter) is present along the upstream right wingwall, the left abutment and 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 recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and Davis, 1995) for the 100- and 500-year discharges. In addition, the maximum free-surface discharge was determined and analyzed as another potential worst-case scour scenarios. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 2.2 to 6.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 20.6 to 30.4 ft. Right abutment scour ranged from 9.7 to 19.5 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and Davis, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 25 (ROCHTH00400025) on Town Highway 40, crossing Corporation Brook, Rochester, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure ROCHTH00400025 on Town Highway 40 crossing Corporation Brook, Rochester, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (FHWA, 1993). Results of a Level I scour investigation also are included in appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, from Vermont Agency of Transportation 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 4.97-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest on the upstream left and right overbanks, and the downstream left overbank. On the downstream right overbank, the surface cover is predominately brushland. In the study area, Corporation Brook has an incised, sinuous channel with a slope of approximately 0.04 ft/ft, an average channel top width of 37 ft and an average bank height of 6 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 101 mm (0.332 ft). The geomorphic assessment at the time of the Level I site visit on April 12, 1995 and Level I and II site visit on July 8, 1996, indicated that the reach was stable. The Town Highway 40 crossing of Corporation Brook is a 31-ft-long, one-lane bridge consisting of a 26-foot steel stringer span (Vermont Agency of Transportation, written communication, March 22, 1995). The opening length of the structure parallel to the bridge face is 24 ft. The bridge is supported by vertical, concrete abutments. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is 15 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed in the channel at the downstream bridge face during the Level I assessment. Additionally, it was observed that the left abutment footing was exposed 1.0 ft and the right abutment footing was exposed 2.0 ft. Scour countermeasures at the site included type-1 stone fill (less than 12 inches diameter) along the upstream left and right banks and the downstream left bank. Type-2 stone fill (less than 36 inches diameter) scour protection extended along the downstream right bank and the upstream and downstream ends of the abutments. Additional details describing conditions at the site are included in the Level II Summary and appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and Davis, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.1 to 1.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 6.5 to 7.0 ft. The worst-case left abutment scour occurred at the 500-year discharge. Right abutment scour ranged from 5.6 to 6.0 ft. The worst-case right abutment scour occurred 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 Davis, 1995, p. 46). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS2006

Digital data from the Questa-San Luis and Santa Fe East helicopter magnetic surveys in Santa Fe and Taos Counties, New Mexico, and Costilla County, Colorado

This report contains digital data, image files, and text files describing data formats and survey procedures for aeromagnetic data collected during high-resolution aeromagnetic surveys in southern Colorado and northern New Mexico in December, 2005. One survey covers the eastern edge of the San Luis basin, including the towns of Questa, New Mexico and San Luis, Colorado. A second survey covers the mountain front east of Santa Fe, New Mexico, including the town of Chimayo and portions of the Pueblos of Tesuque and Nambe. Several derivative products from these data are also presented as grids and images, including reduced-to-pole data and data continued to a reference surface. Images are presented in various formats and are intended to be used as input to geographic information systems, standard graphics software, or map plotting packages.

Open-File Report↗
USGS2012

Updates to watershed modeling in the Potholes Reservoir basin, Washington-a supplement to Scientific Investigation Report 2009-5081

A previous collaborative effort between the U.S. Geological Survey and the Bureau of Reclamation resulted in a watershed model for four watersheds that discharge into Potholes Reservoir, Washington. Since the model was constructed, two new meteorological sites have been established that provide more reliable real-time information. The Bureau of Reclamation was interested in incorporating this new information into the existing watershed model developed in 2009, and adding measured snowpack information to update simulated results and to improve forecasts of runoff. This report includes descriptions of procedures to aid a user in making model runs, including a description of the Object User Interface for the watershed model with details on specific keystrokes to generate model runs for the contributing basins. A new real-time, data-gathering computer program automates the creation of the model input files and includes the new meteorological sites. The 2009 watershed model was updated with the new sites and validated by comparing simulated results to measured data. As in the previous study, the updated model (2012 model) does a poor job of simulating individual storms, but a reasonably good job of simulating seasonal runoff volumes. At three streamflow-gaging stations, the January 1 to June 30 retrospective forecasts of runoff volume for years 2010 and 2011 were within 40 percent of the measured runoff volume for five of the six comparisons, ranging from -39.4 to 60.3 percent difference. A procedure for collecting measured snowpack data and using the data in the watershed model for forecast model runs, based on the Ensemble Streamflow Prediction method, is described, with an example that uses 2004 snow-survey data.

Washington↗
USGS1951

Ground water for industrial use in the vicinity of Little Rock, Arkansas

Several inquiries about the availability of ground water and its quality for industrial use in the vicinity of Little Rock, Ark. have led to the assembling of the following information from the files of the United States Geological Survey in Little Rock and Fayetteville. There are large undeveloped reserves of ground water in the vicinity of Little Rock that can be made available through large-capacity wells. However, the water probably would require treatment for most industrial uses. Ground water is used in Little Rock and vicinity at an estimated rate of about 10 million gallons per day. The most productive water-bearing material consists of alluvial deposits along the Arkansas River and in a large area extending northeast, east, and southeast of the city. Records of 41 selected wells and chemical analyses of water from 28 wells tapping these deposits are given below. The areas in which the productive deposits occur and the location of the wells are shown on the map.

Arkansas↗
USGS1996

Level II scour analysis for Bridge 36 (RICHVT01050036) on State Route 105, crossing Stanhope Brook, Richford, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RICHVT01050036 on State Route 105 crossing Stanhope Brook, Richford, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in north-central Vermont. The 7.03-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is short grass except for the upstream left overbank area which is forested. In the study area, Stanhope Brook has a steep, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 47 ft and an average channel depth of 5 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 132 mm (0.432 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 28, 1995, indicated that the reach was laterally unstable. The State Route 105 crossing of Stanhope Brook is a 42-ft-long, two-lane bridge consisting of one 38-foot concrete T-beam 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 15 degrees to the opening while the opening-skew-to-roadway is 20 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the downstream end of the right abutment wall during the Level I assessment. The scour protection measures at this site were type-2 stone fill (less than 36 inches diameter) along the entire lengths of the upstream wingwalls, at the corner of the downstream left abutment and downstream left wingwall and the downstream end of 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. Contraction scour for all modelled flows ranged from 0.0 to 0.3 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.6 to 9.4 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 43 (SPRICYBRIG0043) on Bridge Street, crossing the Black River, Springfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure SPRICYBRIG0043 on Bridge Street crossing the Black River, Springfield, 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 191-mi 2 drainage area is a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consist of some grass, buildings, and pavement. The immediate banks are covered with trees, shrubs and brush. In the study area, the Black River has an incised channel with a slope of approximately 0.001 ft/ft, an average channel top width of 156 ft and an average bank height of 14 ft. The channel bed material is predominantly cobbles with a median grain size (D 50 ) of 90.7 mm (0.298 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 19, 1996, indicated that the reach was stable. The Bridge Street crossing of the Black River is a 123-foot-long, two-lane bridge consisting of one 119-foot steel-beam span (Vermont Agency of Transportation, written communication, March 30, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 degrees to the opening while the opening-skew-to-roadway is 20 degrees. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) along the downstream left bank and the downstream left wingwall. There was also type-1 stone fill (less than 12 inches diameter) along right abutment and the downstream right wingwall. There is a nine foot tall concrete wall along the downstream right bank to 89 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 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. Left abutment scour ranged from 9.9 to 11 ft. The worst-case left abutment scour occurred at the 100-year discharge. Right abutment scour ranged from 6.5 to 11.2 ft. 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 26 (WSTOTH00070026) on Town Highway 7, crossing Greendale Brook, Weston, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WSTOTH00070026 on Town Highway 7 crossing Greendale Brook, Weston, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in south central Vermont. The 3.13-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, the Greendale Brook has a sinuous, non-incised, non-alluvial channel with a slope of approximately 0.015 ft/ft, an average channel top width of 38 ft and an average bank height of 3 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 64.8 mm (0.213 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 19, 1996, indicated that the reach was laterally unstable. The channel has moved to the right, however, scour countermeasures are in place along the upstream right bank. The Town Highway 7 crossing of the Greendale Brook is a 52-ft-long, two-lane bridge consisting of one 50-foot steel-beam span with a concrete deck (Vermont Agency of Transportation, written communication, April 07, 1995). The opening length of the structure parallel to the bridge face is 48.6 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 50 degrees to the opening while the opening-skew-to-roadway is 30 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the upstream right wingwall and right abutment during the Level I assessment. Scour protection measures at the site include: type-2 stone fill (less than 36 inches diameter) at the upstream end of the upstream left wingwall, along the left bank upstream, at the downstream end of the downstream left wing wall, and along the entire length of the downstream right wing wall; type 4 (less than 60 inches) and type-3 stone fill (less than 48 inches) along the right bank upstream. 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 0.0 ft. Abutment scour ranged from 3.9 to 9.9 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 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). The Hire equation (abutment scour) is often used when the horizontal length blocked by flow divided by the depth of flow is greater than 25 (Richardson and others, 1995 p. 49). Although the Hire equation could be applied to the left abutment more conservative scour estimates were given by the Froehlich equation on the left abutment. 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 81 (MARSUS00020081) on U.S. Highway 2, crossing the Winooski River, Marshfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MARSUS00020081 on U.S. Highway 2 crossing the Winooski River, Marshfield, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in central Vermont. The 50.2-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream of the bridge while the immediate banks have dense woody vegetation. Downstream of the bridge is forested with buildings near the bridge on the right bank. In the study area, the Winooski River has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 83 ft and an average bank height of 10 ft. The channel bed material ranges from cobble to boulder with a median grain size (D 50 ) of 64.0 mm (0.210 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 23, 1996, indicated that the reach was stable. The U.S. Highway 2 crossing of the Winooski River is a 49-ft-long, two-lane bridge consisting of one 47-foot concrete T-beam span (Vermont Agency of Transportation, written communication, November 1, 1995). The opening length of the structure parallel to the bridge face is 44.9 ft. 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. A scour hole 1 ft deeper than the mean thalweg depth was observed near the upstream left wingwall during the Level I assessment. The scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) at the upstream end of the upstream left and right wingwall, the downstream end of the downstream left wingwall, and along the upstream left and right banks. There was also type-3 stone fill (less than 48 inches diameter) at the downstream left bank and type-2 stone fill (less than 36 inches diameter) along the downstream right bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge is determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 2.1 to 4.2 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 14.3 to 14.4 ft. The worst-case left abutment scour occurred at the incipient roadwayovertopping and 500-year discharge. Right abutment scour ranged from 15.3 to 18.5 ft. The worst-case right abutment scour occurred at the 100-year and the incipient roadwayovertopping 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) give “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 16, (NEWBTH00500016) on Town Highway 50, crossing Halls Brook, Newbury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NEWBTH00500016 on Town Highway 50 crossing Halls Brook, Newbury, 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 23.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is shrub and brushland. In the study area, Halls Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 53 ft and an average bank height of 7 ft. The channel bed material ranges from silt to gravel with a median grain size (D 50 ) of 40.4 mm (0.133 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 29, 1995, indicated that the reach was laterally unstable. The channel bed and banks are composed of fine material and show signs of erosion. There is also evidence of beaver activity in the area. The Town Highway 50 crossing of Halls Brook is a 44-ft-long, two-lane bridge consisting of one 38-foot prestressed concrete slab span (Vermont Agency of Transportation, written communication, March 27, 1995). The opening length of the structure parallel to the bridge face is 35.2 ft. The bridge is supported by vertical, stone masonry abutments. The channel is skewed approximately 40 degrees to the opening while the computed opening-skew-toroadway is 5 degrees. A channel scour hole 1.0 ft deeper than the mean thalweg depth was observed just upstream of the bridge behind the remains of a beaver dam during the Level I assessment. An additional channel scour hole 4.5 ft deeper than the mean thalweg depth was observed in the downstream reach. The scour countermeasures at the site included type-1 stone fill (less than 12 inches diameter) along the left abutment and type-2 stone fill (less than 36 inches diameter) along the right abutment and left bank upstream and downstream. Along the downstream right bank is type-3 stone fill (less than 48 inches diameter) and along the upstream right bank is type-4 stone fill (less than 60 inches diameter). Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was analyzed since it has the potential of being the worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 2.6 to 4.6 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge. The left abutment scour ranged from 11.6 to 12.1 ft. The worst-case left abutment scour occurred at the incipient road-overtopping discharge. The right abutment scour ranged from 13.6 to 17.9 ft. 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. 46). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS2000

Field estimates of gravity terrain corrections and Y2K-compatible method to convert from gravity readings with multiple base stations to tide- and long-term drift-corrected observations

Gravity observations are directly made or are obtained from other sources by the U.S. Geological Survey in order to prepare maps of the anomalous gravity field and consequently to interpret the subsurface distribution of rock densities and associated lithologic or geologic units. Observations are made in the field with gravity meters at new locations and at reoccupations of previously established gravity "stations." This report illustrates an interactively-prompted series of steps needed to convert gravity "readings" to values that are tied to established gravity datums and includes computer programs to implement those steps. Inasmuch as individual gravity readings have small variations, gravity-meter (instrument) drift may not be smoothly variable, and acommodations may be needed for ties to previously established stations, the reduction process is iterative. Decision-making by the program user is prompted by lists of best values and graphical displays. Notes about irregularities of topography, which affect the value of observed gravity but are not shown in sufficient detail on topographic maps, must be recorded in the field. This report illustrates ways to record field notes (distances, heights, and slope angles) and includes computer programs to convert field notes to gravity terrain corrections. This report includes approaches that may serve as models for other applications, for example: portrayal of system flow; style of quality control to document and validate computer applications; lack of dependence on proprietary software except source code compilation; method of file-searching with a dwindling list; interactive prompting; computer code to write directly in the PostScript (Adobe Systems Incorporated) printer language; and high-lighting the four-digit year on the first line of time-dependent data sets for assured Y2K compatibility. Computer source codes provided are written in the Fortran scientific language. In order for the programs to operate, they first must be converted (compiled) into an executable form on the user's computer. Although program testing was done in a UNIX (tradename of American Telephone and Telegraph Company) computer environment, it is anticipated that only a system-dependent date-and-time function may need to be changed for adaptation to other computer platforms that accept standard Fortran code.d del iliscipit volorer sequi ting etue feum zzriliquatum zzriustrud esenibh ex esto esequat.

Open-File Report↗
USGS2002

Isostatic gravity map of the Monterey 30' x 60' quadrangle and adjacent areas, California

The digital dataset consists of one file (monterey_100k.iso) containing 2,385 gravity stations. The file, monterey_100k.iso, contains the principal facts of the gravity stations, with one point coded per line. The format of the data is described below. Each gravity station has a station name, location (latitude and longitude, NAD27 projection), elevation, and an observed gravity reading. The data are on the IGSN71 datum and the reference ellipsoid is the Geodetic Reference System 1967 (GRS67). The free-air gravity anomalies were calculated using standard formulas (Telford and others, 1976). The Bouguer, curvature, and terrain corrections were applied to the free-air anomaly at each station to determine the complete Bouguer gravity anomalies at a reduction density of 2.67 g/cc. An isostatic correction was then applied to remove the long-wavelength effect of deep crustal and/or upper mantle masses that isostatically support regional topography.

California↗
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 32 (BRNATH00470032) on Town Highway 47, crossing Locust Creek, Barnard, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRNATH00470032 on town highway 47 crossing Locust Creek, Barnard, 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 Barnard. The 6.26-mi2 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 and brush covered. In the study area, Locust Creek has an incised, sinuous channel with a slope of approximately 0.029 ft/ft, an average channel top width of 44 ft., and an average channel depth of 5 ft. The predominant channel bed material is gravel and cobbles (D50 is 91.7 mm or 0.301 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 12, 1994, indicated that the reach was stable. The town highway 47 crossing of Locust Creek is a 28-ft-long, one-lane bridge consisting of one 25-foot span concrete slab superstructure (Vermont Agency of Transportation, written commun., August 23, 1994). The bridge is supported by vertical, concrete abutments with concrete wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 35 degrees. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on the banks upstream, the upstream wingwalls, the downstream right wingwall, and the downstream right bank. The downstream left wingwall and left bank are protected with 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 these computed results follow. Contraction scour for all modelled flows ranged from 1.4 to 2.2 feet. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 10.3 to 15.0 feet. 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 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. 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 15 (GRNVTH00230015) on Town Highway 23, crossing the Third Branch of the White River, Granville, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure GRNVTH00230015 on town highway 23 crossing the Third Branch of the White River, Granville, 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 Granville. The 23.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have woody vegetation coverage except for the downstream banks, which are residential. In the study area, the Third Branch of the White River has an incised, sinuous channel with a slope of approximately 0.0128 ft/ft, an average channel top width of 42 ft and an average channel depth of 4 ft. The predominant channel bed material is cobble (D 50 is 108 mm or 0.353 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 21, 1994, indicated that the reach was laterally unstable. The town highway 23 crossing of the Third Branch of the White River is a 35-ft-long, one-lane bridge consisting of one 31-foot steel beam span (Vermont Agency of Transportation, written communication, August 26, 1994). 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 10 degrees. The only scour protection measures in place at the site were type-1 stone fill (less than 12 inches diameter) along the upstream right bank, upstream right wingwall, and right abutment. Retaining walls are in place along the upstream left bank up to the upstream end of the upstream left wingwall and both downstream banks with the left bank wall extending from the downstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute scour 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 to 0.4 ft. The worst-case contraction scour occurred at the incipient overtopping discharge. Abutment scour ranged from 9.8 to 13.9 ft. The worst-case abutment scour occurred at the 100-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated 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 53 (CHESTH01180053) on Town Highway 118, crossing the Williams River, Chester, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CHESTH01180053 on Town Highway 118 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 southeastern Vermont. The 20.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly suburban while the right bank upstream is pasture. There is a house on the right bank downstream and VT 103 runs parallel to the river along the left bank. In the study area, the Williams River has an incised, straight channel with a slope of approximately 0.005 ft/ft, an average channel top width of 64 ft and an average bank height of 7 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 58.0 mm (0.190 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 17, 1996, indicated that the reach was stable. The Town Highway 118 crossing of the Williams River is a 43-ft-long, one-lane bridge consisting of one 40-foot steel-beam span (Vermont Agency of Transportation, written communication, April 6, 1995). The opening length of the structure parallel to the bridge face is 37.6 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the computed opening-skew-to-roadway is 10 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed at both abutments during the Level I assessment. Scour protection measures at the site include: type-3 stone fill (less than 48 inches diameter) along the left bank upstream and downstream and type-2 stone fill (less than 36 inches diameter) along the entire base length of the upstream left wingwall, at the upstream end of the left abutment, and at the upstream end of the downstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge is determined and analyzed as another potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was 0.0 ft. Abutment scour ranged from 5.8 to 6.8 ft at the left abutment and 9.4 to 14.4 ft at the right abutment. The worst-case abutment scour occurred 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, 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 2 (RYEGTH00020002) on Town Highway 2, crossing the Wells River, Ryegate, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RYEGTH00020002 on Town Highway 2 crossing the Wells River, Ryegate, 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 75.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of cut grass, trees, and brush on the flood plains while the immediate banks have dense woody vegetation. In the study area, the Wells River has an incised, sinuous channel with a slope of approximately 0.006 ft/ft, an average channel top width of 110 ft and an average bank height of 12 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 82.3 mm (0.270 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 24, 1995, indicated that the reach was laterally unstable with moderate fluvial erosion and meandering downstream of the bridge. The Town Highway 2 crossing of the Wells River is a 79-ft-long, two-lane bridge consisting of one 75-foot steel-beam span (Vermont Agency of Transportation, written communication, March 27, 1995). The opening length of the structure parallel to the bridge face is 75.1 ft. The bridge is supported by vertical, concrete abutments, the left has a spill-through embankment, with wingwalls. The channel is not skewed to the opening and the opening-skew-to-roadway is zero degrees. A scour hole 3 ft deeper than the mean thalweg depth was observed in the channel from upstream and through the bridge during the Level I assessment. The scour protection counter-measures at the site included type-4 stone fill (less than 60 inches diameter) along the base of the left abutment forming a spill-through embankment. There was also type-2 stone fill (less than 36 inches diameter) along the entire base length of the upstream right wingwall, the upstream right bank and downstream left bank. There was a stone wall along the upstream left bank extending 130 ft from the bridge. In addition there was type-1 stone fill (less than 12 inches diameter) along the downstream right bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was zero. Abutment scour ranged from 7.1 to 11.4 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 31 (JERITH00350031) on Town Highway 35, crossing Mill Brook, Jericho, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure JERITH00350031 on Town Highway 35 crossing Mill Brook, Jericho, 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, gathered 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 and the Champlain section of the St. Lawrence physiographic province in northwestern Vermont. The 15.7-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. The downstream left overbank is pasture. The downstream right overbank is brushland. In the study area, the Mill Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 117 ft and an average bank height of 11 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 81.1 mm (0.266 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 3, 1996, indicated that the reach was laterally unstable. The Town Highway 35 crossing of the Mill Brook is a 53-ft-long, one-lane bridge consisting of a 50-foot steel-beam span with a wooden deck (Vermont Agency of Transportation, written communication, November 30, 1995). The opening length of the structure parallel to the bridge face is 48 ft. The bridge is supported by a vertical, concrete abutment with wingwalls on the left. On the right, the abutment and wingwalls are laid-up stone with a concrete cap. The channel is not skewed to the opening. The roadway is skewed 10 degrees to the opening. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. Scour countermeasures at the site were type-2 stone fill (less than 36 inches diameter) at the upstream and downstream left wingwalls, the upstream and downsteam left channel banks, and the downstream 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 recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). In addition, the incipient roadway-overtopping discharge is analyzed since it has the potential of being the worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.4 to 1.3 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 9.9 to 12.4 ft. Right abutment scour ranged from 13.8 to 17.8 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↗