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

Open-File Report 96-188

Prepared in cooperation with Vermont Agency of Transportation and Federal Highway Administration
By:
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Abstract

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-mi2 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 (D50 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.

Geospatial Extents

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Level II scour analysis for Bridge 28 (BRIDTH00440028) on Town Highway 044 crossing Plymouth Brook, Bridgewater, Vermont
Series title:
Open-File Report
Series number:
96-188
Year Published:
1996
Language:
English
Publisher:
U.S. Geological Survey
Description:
iv, 30 p.
Number of Pages:
35
Country:
United States
State:
Vermont
City:
Bridgewater
Other Geospatial:
Plymouth Brook