USGS Science⌕ Search

SEARCH · USGS Science

Results for “Engineering Structures”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources
USGS1997

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

This report provides the results of a detailed Level II analysis of scour potential at structure HUNTTH001007H on Town Highway 1 crossing the Cobb Brook, Huntington, Vermont (figures 1–10). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. In August 1976, Hurricane Belle caused flooding at this site which resulted in road and bridge damage (figures 7-8). This was approximately a 25-year flood event (U.S. Department of Housing and Urban Development, 1978). The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 4.20-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest upstream of the bridge. Downstream of the bridge is brushland and pasture. In the study area, the Cobb Brook has an incised, straight channel with a slope of approximately 0.03 ft/ft, an average channel top width of 43 ft and an average bank height of 6 ft. The channel bed material ranges from sand to boulders with a median grain size (D 50 ) of 65.5 mm (0.215 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 24, 1996, indicated that the reach was stable. The Town Highway 1 crossing of the Cobb Brook is a 23-ft-long, two-lane bridge consisting of one 20-foot concrete slab span (Vermont Agency of Transportation, written communication, June 21, 1996). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 2.8 ft deeper than the mean thalweg depth was observed along the left abutment during the Level I assessment. Protection measures at the site include type-1 stone fill (less than 12 inches diameter) at the downstream right wingwall, type-2 stone fill (less than 36 inches diameter) at the upstream right wingwall and the downstream end of the downstream left wingwall, and type-3 stone fill (less than 48 inches diameter) at the upstream left wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.2 to 1.3 ft. The worst-case contraction scour occurred at the incipient-overtopping discharge. Abutment scour ranged from 4.0 to 8.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 10. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 29 (HARDTH00310029) on Town Highway 31, crossing the Lamoille River, Hardwick, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HARDTH00310029 on town highway 31 crossing the Lamoille River, Hardwick, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province of north-central Vermont. The 64.4-mi 2 drainage area is in a predominantly rural basin. In the vicinity of the study site, the surface cover is pasture except for the immediate downstream channel banks and the downstream left overbank which are brush covered. In the study area, the Lamoille River has a sinuous channel with a slope of approximately 0.001 ft/ft, an average channel top width of 84 ft and an average channel depth of 4 ft. The predominant channel bed materials are cobble and gravel with a median grain size (D 50 ) of 36.1 mm (0.119 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 26, 1995, indicated that the reach was stable. The town highway 31 crossing of the Lamoille River is a 65-ft-long, one-lane bridge consisting of one 61-foot steel-beam span (Vermont Agency of Transportation, written communication, March 27, 1995). The bridge is supported by vertical, stone abutments with wingwalls. The right abutment has a concrete facing and a concrete subfooter. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 0 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 2.7 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 10.3 to 18.6 ft. The worst-case abutment scour occurred at the 100-year discharge at the right abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

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

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

Vermont↗
USGS1997

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

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

Vermont↗
USGS1997

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

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

Vermont↗
USGS2007

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

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

Scientific Investigations Map↗
USGS2014

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

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

Rhode Island↗
USGS2018

Fault displacement hazard for strike-slip faults

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

Conference Paper↗
USGS1996

Level II scour analysis for Bridge 45b (BRIDTH00040045b) on Town Highway 4, crossing an unnamed Dailey Hollow Branch Tributary, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH0004045B on town highway 4 crossing an unnamed Dailey Hollow Branch Tributary, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 2.47-mi 2 drainage area is in a predominantly rural and forested basin. Surface cover in the vicinity of the study site is variable. A gravel road is adjacent to the left bank with the immediate upstream left bank covered by grass and the immediate downstream left bank covered by shrubs and brush. The upstream right bank is densely forested; the downstream right overbank is covered by grass with trees and brush on the immediate channel bank. In the study area, this unnamed Dailey Hollow Branch Tributary has an incised channel with a slope of approximately 0.04 ft/ft, an average channel top width of 29 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel with a median grain size (D 50 ) of 47.0 mm (0.154 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 15, 1994, indicated that the reach was stable. The town highway 4 crossing of the unnamed Dailey Hollow Branch Tributary is a 62-ft-long, corrugated steel multi-plate arch structure. It is supported by concrete footings leaving natural stream bed exposed (Vermont Agency of Transportation, written communication, January, 1996). The road embankments are protected by stone fill, however, the size is unknown due to sand and grass covering the fill except for the upstream left embankment which has type-2 stone fill (less than 36 inches diameter). The downstream left bank is protected by type-3 stone fill (less than 48 inches diameter) extending 25 feet downstream of the culvert. The channel approach to the culvert has a mild s-curve bend with the opening skewed ten degrees to flow. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.1 to 1.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.7 to 11.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). 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↗
USGS1960

Ground-water areas and well logs, central Sevier Valley, Utah

Between September 1959 and June 1960 the United States Geological Survey and the Utah State Engineer, with financial assistance from Garfield, Millard, Piute, Sanpete, and Sevier Counties and from local water-users’ associations, cooperated in an investigation to determine the structural framework of the central Sevier Valley and to evaluate the valley’s ground-water potential. An important aspect of the study was the drilling of 22 test holes under private contract. These data and other data collected during the course of the larger ground-water investigation of which the test drilling was a part will be evaluated in a report on the geology and ground-water resources of the central Sevier Valley. The present report has been prepared to make available the logs of test holes and to describe in general terms the availability of ground water in the different areas of the valley.

Utah↗
USGS1997

Level II scour analysis for Bridge 22 (WALDTH00180022) on Town Highway 18, crossing Coles Brook, Walden, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WALDTH00180022 on Town Highway 18 crossing Coles Brook also known as 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 site is in the New England Upland section of the New England physiographic province in northeastern Vermont. The 12.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly forested while the downstream left bank is shrub and brushland. In the study area, the Coles Brook has an incised, sinuous channel with a slope of approximately 0.004 ft/ft, an average channel top width of 54 ft and an average bank height of 4 ft. The channel bed material ranges from gravel to bedrock with a median grain size (D50) of 124.1 mm (0.407 ft). The D 50 was taken from a pebble count in the downstream channel, because the upstream channel is primarily bedrock. The geomorphic assessment at the time of the Level I and Level II site visit on August 8, 1995, indicated that the reach was stable. The Town Highway 18 crossing of the Coles Brook is a 46-ft-long, one-lane bridge consisting of one 44-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 41.4 ft. The bridge is supported by a vertical, concrete abutment with wingwalls on the left and by a vertical, stone abutment with stone wingwalls with a concrete cap on the right. The channel is skewed approximately 5 degrees to the opening while the computed opening-skew-to-roadway is 10 degrees. The only scour protection measure at the site was a stone wall along the upstream left bank and type-2 stone fill (less than 36 inches diameter) along the entire base length of the upstream left wingwall, left abutment, and downstream left wing wall. 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-year 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 0.0 ft. Abutment scour ranged from 6.4 to 7.9 ft at the left abutment and from 11.8 to 14.9 ft at the right 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”. 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↗
USGS2016

Rotational seismology

Rotational seismology is an emerging study of all aspects of rotational motions induced by earthquakes, explosions, and ambient vibrations. It is of interest to several disciplines, including seismology, earthquake engineering, geodesy, and earth-based detection of Einstein’s gravitation waves. Rotational effects of seismic waves, together with rotations caused by soil–structure interaction, have been observed for centuries (e.g., rotated chimneys, monuments, and tombstones). Figure 1a shows the rotated monument to George Inglis observed after the 1897 Great Shillong earthquake. This monument had the form of an obelisk rising over 19 metres high from a 4 metre base. During the earthquake, the top part broke off and the remnant of some 6 metres rotated about 15° relative to the base. The study of rotational seismology began only recently when sensitive rotational sensors became available due to advances in aeronautical and astronomical instrumentations.

Book chapter↗
USGS1996

Level II scour analysis for Bridge 37 (BARTUS00050166) on U.S. Route 5, crossing Barton River, Barton, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BARTUS00050166 on U. S. Route 5 crossing the Barton River, Barton, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the New England Upland section of the New England physiographic province of north-central Vermont in the town of Barton. The 65.2-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the banks have a combination of dense woody vegetation coverage, brush, and field grasses. In the study area, the Barton River has an incised, sinuous-to-meandering channel with a slope of approximately 0.0065 ft/ft, an average channel top width of 58 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel (D 50 is 75.6 mm or 0.25 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 19, 1994, indicated that the reach was stable. The U. S. Route 5 crossing of the Barton River is a 126-ft-long, two-lane bridge consisting of one 60-foot steel beam span with two steel-beam approach spans (Vermont Agency of Transportation, written communication, August 4, 1994). The bridge is supported by two concrete piers. The left bank has a concrete retaining wall that is attached to the US face of the left pier; consequently this pier functions as an abutment for the analysis because no flow occurs to the left of the pier. For the purposes of computing scour, this pier was considered an abutment. The channel is skewed approximately 40 degrees to the opening while the opening-skew-to-roadway is 25 degrees. A scour hole 0.5 ft deeper than the mean thalweg depth was observed along the right pier during the Level I assessment. Scour protection measures at the site consist of type-1 stone fill (less than 12 inches diameter) along the entire base length of both piers. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.1 to 2.4 ft. Abutment-type scour was computed for the left pier; scour ranged from 9.1 to 11.3 ft. Abutment scour at the right abutment ranged from 6.1 to 11.3 ft. Pier scour, computed for the right pier, ranged from 31.3 to 33.3 ft. The severity of the pier scour was directly related to the attack angle of 25 degrees. The worst-case scour in all computations 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 108 (STJOUS00020108) on U.S. Highway 2, crossing the Moose River, St. Johnsbury, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure STJOUS00020108 on U.S. Highway 2 crossing the Moose River, St. Johnsbury, 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/White Mountain sections of the New England physiographic province in north-east Vermont. The 117-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture on the upstream right bank, forest on the upstream left bank, shrub and brush on the downstream left bank, and forest on the downstream right bank. In the study area, the Moose River has an incised, sinuous channel with a slope of approximately 0.008 ft/ft, an average channel top width of 96 ft and an average channel depth of 6 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 94.1 mm (0.309 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 14, 1995, indicated that the reach was stable. The U.S. Highway 2 crossing of the Moose River is a 103-ft-long, two-lane bridge consisting of three spans with a maximum 57-foot concrete T-beam span (Vermont Agency of Transportation, written communication, March 28, 1995). The bridge is supported by two piers, and vertical, concrete abutments with no wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 0 degrees. The scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) at the upstream and downstream channel banks. There is also type-3 stone fill (less than 48 inches diameter) at both the upstream and downstream ends of 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 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 0.4 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 9.3 to 12.2 ft. The worst-case abutment scour occurred at the left abutment 500-year discharge. Pier scour ranged from 8.3 to 15.7 for both piers. The worst case pier scour occurred at the left pier, for the 100-year discharge analysis. Additional in formation 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 42 (BENNCYSCHL0042) on School Street, crossing Walloomsac River, Bennington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BENNCYSCHL0042 on the School Street crossing of the Walloomsac River, Bennington, 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 southwestern Vermont. The 30.1-mi 2 drainage area is a predominantly rural and forested basin. The bridge site is located within an urban setting in the Town of Bennington with buildings and residences on all overbanks. In the study area, the Walloomsac River has a straight channel with constructed channel banks downstream of the bridge. The channel is located on a delta and has a slope of approximately 0.02 ft/ft, an average channel top width of 37 ft and an average bank height of 6 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 132 mm (0.435 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 6, 1996, indicated that the reach was stable. The School Street crossing of the Walloomsac River is a 36-ft-long, two-lane bridge consisting of one 33-foot concrete span (Vermont Agency of Transportation, written communication, December 13, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately zero degrees to the opening and the opening-skew-to-roadway is also zero degrees. Scour countermeasures at the site include type-2 stone fill (less than 36 inches diameter) along both upstream banks and upstream wingwalls. Downstream banks are protected by stone walls extending from the downstream wingwalls to more than 100 feet 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). 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 computed for all modelled flows was 0.0 ft. Computed left abutment scour ranged from 9.4 to 10.2 ft. with the worst-case scour occurring at the 500-year discharge. Computed right abutment scour ranged from 2.7 to 5.7 ft. with the worst-case scour occurring at the incipient roadway-overtopping discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 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 (BENNCYDEPO0043) on Depot Street, crossing the Walloomsac River, Bennington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BENNCYDEPO0043 on the Depot Street crossing of the Walloomsac River, Bennington, 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 southwestern Vermont. The 30.1-mi 2 drainage area is a predominantly rural and forested basin. The bridge site is located within an urban setting in the Town of Bennington with buildings and parking lots on overbanks. In the study area, the Walloomsac River has a straight channel with constructed channel banks through much of the reach. The channel is located on a delta and has a slope of approximately 0.02 ft/ft, an average channel top width of 48 ft and an average bank height of 6 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 108 mm (0.356 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 5, 1996, indicated that the reach was stable. The Depot Street crossing of the Walloomsac River is a 46-ft-long, two-lane bridge consisting of one 40-foot concrete span (Vermont Agency of Transportation, written communication, December 13, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 5 degrees to the opening and the opening-skew-to-roadway is 15 degrees. Scour countermeasures at the site include type-2 stone fill (less than 36 inches diameter) at the upstream end of the upstream right wing wall and type-1 stone fill (less than 12 inches diameter) along the base of the upstream left wing wall. Downstream banks are protected by concrete and stone walls. The upstream right bank is protected by alternating type-2 stone fill and masonry walls. 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 computed for all modelled flows ranged from 0.0 to 4.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Computed right abutment scour ranged from 2.9 to 13.4 ft. with the worst-case scour occurring at the 500-year discharge. Computed left abutment scour ranged from 5.6 to 16.3 ft. with the worst-case scour also occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 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 49 (BENNCYHUNT0049) on Hunt Street, crossing the Walloomsac River, Bennington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BENNCYHUNT0049 on the Hunt Street crossing of the Walloomsac River, Bennington, 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 southwestern Vermont. The 34.1-mi 2 drainage area is a predominantly rural and forested basin. The bridge site is located within an urban setting in the Town of Bennington with buildings and parking lots on overbanks except for the downstream left bank which is covered by trees and brush. In the study area, the Walloomsac River has a straight, incised channel. The confluence of the Walloomsac River and Roaring Branch is 140 feet downstream. The channel has a slope of approximately 0.01 ft/ft, an average channel top width of 54 ft and an average bank height of 6 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 76.8 mm (0.252 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 31, 1996, indicated that the reach was stable. The Hunt Street crossing of the Walloomsac River is a 51-ft-long, two-lane bridge consisting of one 49-foot steel span (Vermont Agency of Transportation, written communication, December 13, 1995). The bridge is supported by vertical, concrete abutments. The right abutment has a spill-through slope along its face. The channel is skewed approximately 25 degrees to the opening and the opening-skew-to-roadway is 20 degrees. Scour countermeasures at the site include type-2 stone fill (less than 36 inches diameter) on the spill through slope on the right abutment and along the base of the left abutment. Type- 2 stone fill also protects the channel banks upstream and downstream of the bridge for a minimum distance of 17 feet from the respective bridge faces. 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 computed for all modelled flows ranged from 0.9 to 5.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Computed left abutment scour ranged from 15.3 to 16.5 ft. with the worst-case scour occurring at the incipient roadway-overtopping discharge. Computed right abutment scour ranged from 6.0 to 8.7 ft. with the worst-case scour occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 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↗