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USGS2015

Updated tops file for Cretaceous and lower Tertiary units, Piceance Basin, northwest Colorado

Introduction Depths to selected Cretaceous and lower Tertiary stratigraphic units in the Piceance Basin, northwestern Colorado are presented here for 1,563 wells. This file is updated from the Piceance Basin Oil Shale Database with data for additional new drill holes. Also included in this report are elevations for the base of the Long Point Bed of the Eocene Green River Formation for 347 surface locations obtained by determining locations and elevations from published 7 ½-minute quadrangle maps for the Piceance Basin listed in the “Geologic Maps Used to Generate Long Point Control Points” section. Each entry for the base of the Long Point Bed was obtained at a location where the mapped Long Point Bed intersects a contour line on the published maps. Precision of each elevation is therefore dependent on the precision of the maps and the placement of the mapped contact by the authors.

Colorado↗
USGS2015

csa2sac—A program for computing discharge from continuous slope-area stage data

Introduction Continuous Slope-Area (CSA) gages were developed by the Arizona Water Science Center to enable the estimation of hydrographs when direct measurements of discharge cannot be made (Smith and others, 2010). CSA gages extend standard U.S. Geological Survey (USGS) methods for determining peak discharges to mid and high flows over a hydrograph computed at regular intervals with indirect measurement methods (Benson and Dalrymple, 1967; Dalrymple and Benson, 1967). CSA gages combine continuous stage records at two or more (typically three or four) cross sections with crosssection surveys and estimates of channel roughness to compute discharge over a range of flows. With standard indirect methods of determining peak discharge, water-surface elevation in the study reach at the peak flow is estimated from surveys of debris associated with the peak-flow water line. With CSA gages, stages are continuously measured at the cross sections, at regular and synchronized intervals (typically 5 minutes) over a flow event, and discharge can be calculated at each interval. Calculation of discharge using indirect methods has been automated with the slope-area computation (SAC) program (Fulford, 1994). SAC is a widely used program within the USGS; it is easily run and displays output in a clear and convenient format, which includes flags that alert the user to shortcomings in the calculation. Use of SAC has been facilitated by SACGUI (Bradley, 2012; SACGUI uses a version of SAC called SAC7), a user interface that directly reads and displays survey data, allows for specification of water-surface slope and channel roughness, writes the input file for SAC7, runs SAC7, and displays SAC7 output. csa2sac is a program (appendix 1) that repeatedly runs SAC7 using stage data and a SAC7 input template file to compute the discharge at CSA gages. It is written in the C programming language, and is compatible with 64-bit Windows operating systems. The program reads a SAC7 input file and a file containing stage-data time series. It writes a new version of the SAC7 input file with the stage data for one time step, runs SAC7, then extracts computed discharges from the SAC7 output file and collates the discharges and stages to a separate file. It repeats these steps for each time interval in the stage file to produce a discharge time series from the stage data. csa2sac has been tested with two, three, four, and six cross sections and found to operate successfully. By running SAC7, csa2sac maintains consistency and comparability of both discharges calculated from CSA gages and of standard USGS methods for computing discharges indirectly. Brown and Metcalfe (2014) have made available alternative software for producing CSA discharges. In addition to csa2sac, the SAC7 program is required. It is the same as the original SAC program, except that it is compiled for 64-bit Windows operating systems and has a slightly different command line input. It is available online (http://water.usgs.gov/software/SAC/) as part of the SACGUI installation program. The program name, “SAC7.exe,” is coded into csa2sac, and must not be changed.

Open-File Report↗
USGS1996

Level II scour analysis for Bridge 1 (BLOOTH00020001) on Town Highway 2, crossing Mill Brook, Bloomfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BLOOTH00020001 on town highway 2 crossing Mill Brook, Bloomfield, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the White Mountain section of the New England Upland physiographic province of north-east Vermont in the town of Bloomfield. The 4.85-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. In the study area, Mill Brook has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 28 ft and an average channel depth of 4 ft. The predominant channel bed materials are gravel and cobbles (D 50 is 57.3 mm or 0.188 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 6, 1995, indicated that the reach was stable. The town highway 2 crossing of Mill Brook is a 26-ft-long, one-lane bridge consisting of one 24-foot concrete span (Vermont Agency of Transportation, written commun., August 4, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is 10 degrees. No scour was observed along the channel or at the bridge during the Level I assessment. Type-2 stone fill (less than 24 inches diameter) was noted as present along all wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term 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 to 1.0 feet and the worst-case contraction scour occurred at the incipient overtopping discharge. Abutment scour ranged from 7.3 to 10.1 feet and 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 34 (CORITH0050034) on Town Highway 50, crossing the South Branch Waits River, Corinth, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CORITH00500034 on Town Highway 50 crossing the South Branch Waits River, Corinth, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province in central Vermont. The 35.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream and downstream of the bridge while the immediate banks have dense woody vegetation. In the study area, the South Branch Waits River has an incised, meandering channel with a slope of approximately 0.005 ft/ft, an average channel top width of 63 ft and an average bank height of 6 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 23.7 mm (0.078 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 5, 1995, indicated that the reach was stable. The Town Highway 50 crossing of the South Branch Waits River is a 56-ft-long, one-lane bridge consisting of one 54-foot steel thru-truss span (Vermont Agency of Transportation, written communication, March 24, 1995). The opening length of the structure parallel to the bridge face is 51.5 ft.The bridge is supported by vertical, concrete abutments with no wingwalls. Stone fill and bank material in front of the abutments create spill-through embankments. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is 15 degrees. A scour hole 2.5 ft deeper than the mean thalweg depth was observed along the left bank through the bridge during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the left and right banks extending from upstream to downstream through the bridge. The stone fill under the bridge creates spill-through embankments. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was determined and analyzed as other potential worst-case scour scenario. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 3.0 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 2.4 to 6.3 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich and HIRE equations (abutment scour) give “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 16 (RIPTTH00110016) on Town Highway 11, crossing the Middle Branch Middlebury River, Ripton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RIPTTH00110016 on Town Highway 11 crossing the Middle Branch Middlebury River, Ripton, 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 west-central Vermont. The 6.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of shrubs, brush and trees except for the upstream left bank which is completely forested. In the study area, the Middle Branch Middlebury River has an incised, sinuous channel with a slope of approximately 0.03 ft/ft, an average channel top width of 68 ft and an average bank height of 5 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 97.6 mm (0.320 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 11, 1996, indicated that the reach was stable. The Town Highway 11 crossing of the Middle Branch Middlebury River is a 44-ft-long, two-lane bridge consisting of one 42-foot steel-beam span (Vermont Agency of Transportation, written communication, December 15, 1995). The opening length of the structure parallel to the bridge face is 40.2 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 40 degrees to the opening. The opening-skew-to-roadway value from the VTAOT database is 20 degrees while 30 degrees was computed from surveyed points. A scour hole, 3 ft deeper than the mean thalweg depth, was observed along the left abutment and upstream left wingwall during the Level I assessment. In addition, 1 ft of channel scour was observed just downstream of the downstream left wingwall along the left bank. Scour countermeasures at the site included type-2 stone fill (less than 36 inches diameter) along the upstream left and right banks and along 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. 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 0.4 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.2 to 8.6 ft along the right abutment and from 11.7 to 13.7 ft along the left abutment. The worstcase 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 21 (WALDTH00450021) on Town Highway 45, crossing Joes Brook, Walden, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WALDTH00450021 on Town Highway 45 crossing Joes Brook, Walden, 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 VTAOT files state that the stream is Coles Brook, both the USGS and the VTAOT maps state that it is Joes Brook. The site is in the New England Upland section of the New England physiographic province in central Vermont. The 18.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream and downstream of the bridge while the immediate banks have dense woody vegetation. In the study area, Joes Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 76 ft and an average bank height of 5 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 75.4 mm (0.247 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 27, 1995, indicated that the reach was stable. The Town Highway 45 crossing of Joes Brook is a 35-ft-long, one-lane bridge consisting of one 29-foot steel-beam span with a wooden deck (Vermont Agency of Transportation, written communication, April 5, 1995). The opening length of the structure parallel to the bridge face is 26.2 ft. The bridge is supported by vertical, “laid-up” concrete block abutments with no wingwalls. The channel is skewed approximately zero degrees to the opening while the computed opening-skew-to-roadway is 5 degrees. The scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) along the upstream left bank and along the entire base length of the left abutment. There is also type-2 stone fill (less than 36 inches diameter) along the entire base length of 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 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 0.0 to 1.5 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 12.4 to 24.4 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”. Scouredstreambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particlesize distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 22 (BRADTH00270022) on Town Highway 27, crossing the Waits River, Bradford, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRADTH00270022 on Town Highway 27 crossing the Waits River, Bradford, 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, obtained 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 153-mi 2 drainage area is in a predominantly rural and forested basin. However, in the vicinity of the study site, the upstream and downstream left banks are suburban and the upstream and downstream right banks are shrub and brushland. In the study area, the Waits River has an incised, sinuous channel with a slope of approximately 0.0002 ft/ft, an average channel top width of 125 ft and an average bank height of 4 ft. The channel bed material ranges from silt and clay to bedrock with a median grain size (D 50 ) of 0.393 mm (0.00129 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 7, 1995, indicated that the reach was stable. The Town Highway 27 crossing of the Waits River is a 109-ft-long, one-lane bridge consisting of a 104-ft steel-truss span (Vermont Agency of Transportation, written communication, March 16, 1995). The opening length of the structure parallel to the bridge face is 99.2 ft. The bridge is supported by vertical, laid-up stone abutments. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is zero degrees. No evidence of scour was observed during the Level I assessment. Scour protection measures at the site included type-2 stone fill (less than 36 inches diameter) along the upstream right and downstream left banks and type-3 stone fill (less than 48 inches diameter) along the left and right 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. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.5 to 2.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 11.8 to 18.8 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 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↗
USGS1980

Study plan for the regional aquifer-system analysis of alluvial basins in south-central Arizona and adjacent states

The alluvial basins in the Southwestern United States constitute a major source of ground water and are relied upon extensively for agricultural, industrial, and public water supplies. Large-scale depletion of ground water is directly related to pumping that has occurred in the past few decades and is continuing today. The U.S. Geological Survey has started a 4-year study of the alluvial basins in south-central Arizona and parts of California, Nevada, and New Mexico. The study is designed to document and describe the hydrologic setting in the basins, the ground-water resources available, and the effects of historical development on the ground-water system. To aid in the study, mathematical models of selected basins will be developed for appraising the local and regional flow systems. Major tasks necessary to accomplish the study objectives include accumulating existing data on ground-water quantity and quality, entering the data into a computer file, identifying data deficiencies, and developing a program to remedy the deficiencies by collection of additional data. The approach to the study will be to develop and calibrate models of selected basins for which sufficient data exist and then to develop interpretation-transfer techniques whereby general predevelopment and postdevelopment conceptual models of the hydrologic system in other basins may be synthesized. The results will be applied to selected basins for testing, calibration, and modification. The end result of the project will be a better definition of the hydrologic parameters and a better understanding of the workings of the hydrologic system in the alluvial basins. The results will include models that can be used to study the effects of management alternatives and water-resources development on the hydrologic system.

Arizona↗
USGS1997

Level II scour analysis for Bridge 21 (MIDBTH00230021) on Town Highway 23, crossing the Middlebury River, Middlebury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MIDBTH00230021 on Town Highway 23 crossing the Middlebury River, Middlebury, 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 west-central Vermont. The 44.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is suburban consisting of single houses, each with a lawn, trees, and shrubs on all of the overbank areas bordering the river. In the study area, the Middlebury River has a straight channel with a slope of approximately 0.02 ft/ft, an average channel top width of 87 ft and an average channel depth of 11 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 152 mm (0.498 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 18, 1996, indicated that the reach was stable. The Town Highway 23 crossing of the Middlebury River is a 52-ft-long, two-lane bridge consisting of one 49-foot steel-beam span (Vermont Agency of Transportation, written communication, December 14, 1995). The opening length of the structure parallel to the bridge face is 42.3 feet. The bridge is supported by vertical, concrete abutments with wingwalls at each end of the left abutment only. The channel is skewed approximately 10 degrees to the opening. The opening-skew-to-roadway from the VTAOT records is zero degrees while 5 degrees was computed from surveyed points. A scour hole 1.0 foot deeper than the mean thalweg depth was observed in the channel at the upstream bridge face during the Level I assessment. The scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) on the upstream and downstream banks and the upstream and downstream left wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) 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 1.2 to 1.8 feet. The worst-case contraction scour occurred at the incipient overtopping discharge, which is less than the 500-year discharge. Abutment scour ranged from 17.7 to 23.7 feet. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 8 (WELLTH00020008) on Town Highway 2, crossing Wells Brook, Wells, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WELLTH00020008 on Town Highway 2 crossing the Wells Brook, Wells, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Taconic section of the New England physiographic province in southwestern Vermont. The 14.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the right overbanks is predominantly suburban while the immediate banks are vegetated with trees and brush. The left bank upstream and downstream is predominantly pasture. In the study area, the Wells Brook has an incised, straight channel with a slope of approximately 0.005 ft/ft, an average channel top width of 51 ft and an average bank height of 7 ft. The channel bed material ranges from gravel to boulder with a median grain size (D 50 ) of 48.6 mm (0.159 ft). The geomorphic assessment at the time of the Level I and Level II site visit on September 19, 1995, indicated that the reach was stable. The Town Highway 2 crossing of the Wells Brook is a 35-ft-long, two-lane bridge consisting of one 32-foot concrete span (Vermont Agency of Transportation, written communication, March 22, 1995). The opening length of the structure parallel to the bridge face is 31.7 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-toroadway is 5 degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the left bank upstream, and type-5 (placed stone wall) at the upstream end of the upstream left wingwall, at the downstream end of the downstream left wingwall, and along the downstream left bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and 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 0.0 to 0.8 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 5.6 to 10.0 ft at the left abutment and from 3.1 to 4.2 ft at the right abutment. The worst-case abutment scour occurred at the incipient roadway-overtopping discharge at the left abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A 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. 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 39 (TOPSTH00510039) on Town Highway 51, crossing Tabor Branch Waits River, Topsham, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure TOPSTH00510039 on Town Highway 51 crossing the Tabor Branch Waits River, Topsham, 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 17.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly pasture. However, beyond one bridge length on the right bank upstream the surface cover abruptly changes to forest. In the study area, the Tabor Branch Waits River has a sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 53 ft and an average bank height of 6 ft. The predominant channel bed material is cobbles with a median grain size (D 50 ) of 86.4 mm (0.283 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 30, 1995, indicated that the reach was stable. The Town Highway 51 crossing of the Tabor Branch Waits River is a 34-ft-long, one-lane bridge consisting of one 32-foot concrete slab span (Vermont Agency of Transportation, written communication, March 28, 1995). The opening length of the structure parallel to the bridge face is 31.0 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 10 degrees. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the left and right bank upstream, along the base of the upstream left wingwall, upstream right wingwall, left abutment, right abutment, downstream left wingwall, downstream right wingwall, and along the left and right bank downstream. 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 0.0 to 0.4 ft. The worst-case contraction scour occurred at the maximum free surface flow discharge, which was less than the 100-year discharge. Abutment scour ranged from 4.8 to 8.0 ft. The worst-case abutment scour occurred at 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↗
USGS1998

Level II scour analysis for Bridge 33 (WWINTH00300033) on Town Highway 30, crossing Mill Brook, West Windsor, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WWINTH00300033 on Town Highway 30 crossing Mill Brook, West Windsor, Vermont (Figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (FHWA, 1993). Results of a Level I scour investigation also are included in appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in appendix D. The site is in the New England Upland section of the New England physiographic province in east-central Vermont. The 24.9-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream of the bridge while the immediate banks have dense woody vegetation. Downstream of the bridge is forested. In the study area, Mill Brook has an incised, sinuous channel with a slope of approximately 0.004 ft/ft, an average channel top width of 58 ft and an average bank height of 5 ft. The channel bed material ranges from sand to boulder with a median grain size (D 50 ) of 65.7 mm (0.215 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 5, 1996, indicated that the reach was stable. The Town Highway 30 crossing of the Mill Brook is a 46-ft-long, one-lane covered bridge consisting of a 40-foot wood-beam span (Vermont Agency of Transportation, written communication, March 23, 1995). The opening length of the structure parallel to the bridge face is 36.3 ft. The bridge is supported by vertical, concrete capped laid-up stone abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is zero degrees. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along the upstream right bank, the upstream right wingwall, the right abutment and 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 Davis, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was analyzed since it had 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 0.0 to 0.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.0 to 16.0 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. 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 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 49 (BRIDTH00530049) on Town Highway 53, crossing North Branch Ottauquechee River, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00530049 on town highway 53 crossing the North Branch of 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). 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 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 26.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the immediate banks have woody vegetation coverage with grass on the overbanks. In the study area, the North Branch Ottauquechee River has a sinuous channel with a slope of approximately 0.0075 ft/ft, an average channel top width of 66 ft and an average channel depth of 6 ft. The predominant channel bed material is cobble and gravel (D 50 is 68.4 mm or 0.224 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 stable. The town highway 53 crossing of the North Branch of the Ottauquechee Riveris a 51-ftlong, one-lane bridge consisting of one 49-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 not skewed to the opening and the opening-skew-to-roadway is zero degrees. The scour protection measures in place at the site are type-1 stone fill (less than 12 inches diameter) along the upstream left wingwall and type-2 stone fill (less than 36 inches diameter) along the upstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 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 was 0 feet. Abutment scour ranged from 2.3 to 12.0 feet and the worst-case abutment scour also occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 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↗
USGS1997

Level II scour analysis for Bridge 29 (LONDTH00410029) on Town Highway 41, crossing Cook Brook, Londonderry, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure LONDTH00410029 on Town Highway 41 crossing Cook Brook, Londonderry, 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 6.48-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is shrub on the left bank upstream and downstream of the bridge while the right bank is forest upstream and downstream of the bridge. In the study area, Cook Brook has a straight incised channel with a slope of approximately 0.02 ft/ft, an average channel top width of 80 ft and an average bank height of 8 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 70.9 mm (0.233 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 7, 1996, indicated that the reach was stable. The Town Highway 41 crossing of Cook Brook is a 25-ft-long, one-lane bridge consisting of one 22-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 20.4 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening while the opening-skew-toroadway is 0 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the upstream left wingwall and left abutment during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches) along the downstream end of the left abutment and upstream 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 recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 1.5. Abutment scour ranged from 8.4 to 15.1 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 29 (PUTNTH00210029) on Town Highway 21, crossing East Putney Brook, Putney, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure PUTNTH00210029 on Town Highway 21 crossing East Putney Brook, Putney, 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 10.3-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover consists of pasture and forest. In the study area, East Putney Brook has an incised, sinuous channel with a slope of approximately 0.009 ft/ft, an average channel top width of 33 ft and an average bank height (channel depth) of 3 ft. The channel bed material is cobbles predominantly with a median grain size (D 50 ) of 80.7 mm (0.265 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 stable. The Town Highway 21 crossing of East Putney Brook is a 35-ft-long, one-lane bridge consisting of one 29-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 40 degrees to the opening. Historical records show an opening-skew-to-roadway of 10 degrees but 20 degrees was computed using field survey data and used in this study. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on each abutment wall, the upstream right wingwall and the upstream right bank, and type-3 stone fill (less than 48 inches diameter) on the left bank upstream, the upstream left wingwall, and 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). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.9 feet. The worst-case contraction scour occurred at the incipient-overtopping discharge, which was less than the 100-year discharge. Abutment scour ranged from 6.1 to 18.4 feet. The worst-case abutment scour occurred at the 500-year discharge for the right abutment and the incipient overtopping discharge for the left abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A crosssection of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 4 (DANVTH00010004) on Town Highway 1, crossing Joes Brook, Danville, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure DANVTH00010004 on Town Highway 1 crossing Joes Brook, Danville, 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 northeastern Vermont. The 42.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture along the upstream and downstream left banks with trees and brush along the immediate banks. The upstream and downstream right banks are forested. In the study area, Joes Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 68 ft and an average bank height of 5 ft. The channel bed material ranges from gravel to bedrock with a median grain size (D 50 ) of 80.1 mm (0.263 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 22, 1995, indicated that the reach was stable. The Town Highway 1 crossing of Joes Brook is a 49-ft-long, two-lane bridge consisting of one 45-foot steel-beam span (Vermont Agency of Transportation, written communication, March 17, 1995). The opening length of the structure parallel to the bridge face is 45 ft.The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening and the computed opening-skew-to-roadway is 15 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. The scour hole also extends upstream and downstream of the bridge, along the right side of the channel. The 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 and along the entire base length of the downstream right wingwall. Type-3 stone fill (less than 48 inches diameter) is along the entire base length of the upstream right wingwall and type-5 protection (stone block wall) is along the upstream right bank. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995) 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 computed to be zero ft. Abutment scour ranged from 11.7 to 13.0 ft along the right abutment and from 6.6 to 9.4 ft along the left abutment. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich and Hire equations (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 8 (NEWFTH00010008) on Town Highway 1, crossing Wardsboro Brook, Newfane, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NEWFTH00010008 on Town Highway 1 crossing Wardsboro Brook, Newfane, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (Federal Highway Administration, 1993). Results of a Level I scour investigation also are included in appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in appendix D. The site is in the New England Upland section of the New England physiographic province in southestern Vermont. The 6.91-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 right overbank and downstream left and right overbanks. The surface cover on the upstream left overbank is pasture. In the study area, Wardsboro Brook has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 63 ft and an average bank height of 9 ft. The channel bed material ranges from gravel to boulders with a median grain size (D 50 ) of 95.4 mm (0.313 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 21, 1996, indicated that the reach was stable. The Town Highway 1 crossing of the Wardsboro Brook is a 32-ft-long, two-lane bridge consisting of a 26-foot concrete tee-beam span (Vermont Agency of Transportation, written communication, April 6, 1995). The opening length of the structure parallel to the bridge face is 26.7 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 45 degrees to the computed opening while the openingskew-to-roadway is 45 degrees. A scour hole 1.0 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. Scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) along the upstream right bank, and type-2 stone fill (less than 36 inches diameter) along the upstream left bank and the upstream ends of the upstream left and right wingwalls. A stone wall extends along the downstream right bank from the 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 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 3.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 11.1 to 12.9 ft. Right abutment scour ranged from 4.3 to 4.8 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 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.

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