Item talk:Q79621: Difference between revisions

      "name": "Level II scour analysis for Bridge 43 (SPRICYBRIG0043) on Bridge Street, crossing the Black River, Springfield, Vermont",

          "propertyID": "USGS Publications Warehouse IndexID",

          "value": "ofr97227",

          "url": "https://pubs.usgs.gov/publication/ofr97227"

          "propertyID": "USGS Publications Warehouse Internal ID",

        },

          "value": "10.3133/ofr97227",

          "url": "https://doi.org/10.3133/ofr97227"

      ],

      "inLanguage": "en",

      "abstract": "This report provides the results of a detailed Level II analysis of scour potential at structure \nSPRICYBRIG0043 on Bridge Street crossing the Black River, Springfield, Vermont \n(figures 1\u20138). A Level II study is a basic engineering analysis of the site, including a \nquantitative analysis of stream stability and scour (U.S. Department of Transportation, \n1993). Results of a Level I scour investigation also are included in Appendix E of this \nreport. A Level I investigation provides a qualitative geomorphic characterization of the \nstudy site. Information on the bridge, gleaned from Vermont Agency of Transportation \n(VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is \nfound in Appendix D.\n\nThe site is in the New England Upland section of the New England physiographic province \nin southeastern Vermont. The 191-mi2\n drainage area is a predominantly rural and forested \nbasin. In the vicinity of the study site, the surface cover consist of some grass, buildings, \nand pavement. The immediate banks are covered with trees, shrubs and brush. \n\nIn the study area, the Black River has an incised channel with a slope of approximately \n0.001 ft/ft, an average channel top width of 156 ft and an average bank height of 14 ft. The \nchannel bed material is predominantly cobbles with a median grain size (D50) of 90.7 mm \n(0.298 ft). The geomorphic assessment at the time of the Level I and Level II site visit on \nSeptember 19, 1996, indicated that the reach was stable.\n\nThe Bridge Street crossing of the Black River is a 123-foot-long, two-lane bridge consisting \nof one 119-foot steel-beam span (Vermont Agency of Transportation, written \ncommunication, March 30, 1995). The bridge is supported by vertical, concrete abutments \nwith wingwalls. The channel is skewed approximately 20 degrees to the opening while the \nopening-skew-to-roadway is 20 degrees. \n\nThe scour protection measures at the site were type-2 stone fill (less than 36 inches \ndiameter) along the downstream left bank and the downstream left wingwall. There was \nalso type-1 stone fill (less than 12 inches diameter) along right abutment and the \ndownstream right wingwall. There is a nine foot tall concrete wall along the downstream \nright bank to 89 feet downstream of the bridge. Additional details describing conditions at \nthe site are included in the Level II Summary and Appendices D and E.\n\nScour depths and recommended rock rip-rap sizes were computed using the general \nguidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). \nTotal scour at a highway crossing is comprised of three components: 1) long-term \nstreambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction \nin flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and \nabutments). Total scour is the sum of the three components. Equations are available to \ncompute depths for contraction and local scour and a summary of the results of these \ncomputations follows.\n\nThere was no computed contraction scour. Left abutment scour ranged from 9.9 to 11 ft. \nThe worst-case left abutment scour occurred at the 100-year discharge. Right abutment \nscour ranged from 6.5 to 11.2 ft. The worst-case right abutment scour occurred at the 500-\nyear discharge. Additional information on scour depths and depths to armoring are \nincluded in the section titled \u201cScour Results\u201d. Scoured-streambed elevations, based on the \ncalculated scour depths, are presented in tables 1 and 2. A cross-section of the scour \ncomputed at the bridge is presented in figure 8. Scour depths were calculated assuming an \ninfinite depth of erosive material and a homogeneous particle-size distribution. \n\nIt is generally accepted that the Froehlich equation (abutment scour) gives \u201cexcessively \nconservative estimates of scour depths\u201d (Richardson and others, 1995, p. 47). Usually, \ncomputed scour depths are evaluated in combination with other information including (but \nnot limited to) historical performance during flood events, the geomorphic stability \nassessment, existing scour protection measures, and the results of the hydraulic analyses. \nTherefore, scour depths adopted by VTAOT may differ from the computed values \ndocumented herein.",