Scour at Contracted Bridges (2006) / Chapter Skim
Currently Skimming:
Pages 127-299
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 127... ...
A-1 APPENDIX A - CASE STUDY REPORT #1 Pomme de Terre River at County Route 22 near Fairfield, Minnesota SITE OVERVIEW Swift County Road 22 over the Pomme De Terre River is a three-span structure supported by round concrete-pile bents. The site is located in a rural / agricultural area and is 18 miles upstream of the US Geological Survey (USGS)
|
From page 128... ...
A-2 Hydrologic Conditions Record snowfall and snowpack-moisture content, combined with excessive soil moisture conditions in much of North Dakota, South Dakota, and Minnesota led to severe flooding during April 1997. During the winter of 1996-97, precipitation amounts in nearly all of the west-central portions of Minnesota were equal to or in the excess of the 90th percentile based on the 30-year period 1961-1990.
|
From page 129... ...
A-3 Bridge Data The bridge is a new structure with wide shoulders and concrete guardrails. The bridge is angled about 15 degrees to the low-flow channel.
|
From page 130... ...
A-4 Table 3. Geomorphic data Geomorphic Characteristic Description Drainage Area 836 Slope in Vicinity (ft/ft)
|
From page 131... ...
A-5 Bed Material Data The boring logs of the site generally indicate the bed material to be sand with some loam layers with fine gravel in the sub-bottom. Bed material samples at the site were collected from the upstream bridge face on 10/28/2001 with a USGS BM-54 grab sampler.
|
From page 132... ...
A-6 Abutment Details The bridge has spill-through abutments set at the edge of the main channel. The abutments were protected by riprap and formed the banks of the main channel.
|
From page 133... ...
A-7 Table 6. Pier data.
|
From page 134... ...
A-8 PHOTOS Figure 4. Looking upstream from County Route 22 bridge deck during low flow.
|
From page 135... ...
A-9 Figure 6. Looking at scoured area on right upstream bank of County Route 22, during low flow.
|
From page 136... ...
A-10 Figure 7. Cross-section data collected from the County Route 22 upstream bridge face during the April 1997 flood.
|
From page 137... ...
A-11 Table 8. Abutment scour data ( -- , not available; ft/s, feet per second; cfs, cubic feet per second; Abut, abutment; Avg, average; US, upstream; DS, downstream)
|
From page 138... ...
A-12 Table 9. Contraction scour data ( -- , not available; ft/s, feet per second; cfs, cubic feet per second; US, upstream; DS, downstream; Avg, average)
|
From page 139... ...
A-13 Table 10. Comparison of observed to computed abutment scour at County Route 22 over the Pomme de Terre River in Minnesota.
|
From page 140... ...
A-14 Any questions regarding the CR 22 bridge over the Pomme De Terre River should be directed to the following points of contact: 1. David Mueller, U.S.
|
From page 141... ...
A-15 HWY220009.jpeg – Looking downstream at right fldpln, OP#4 HWY220010.jpeg – Looking downstream from roadway, OP#4 HWY220011.jpeg – same as 0010 HWY220012.jpeg – USGS employee collecting bathymetry data with scour board HWY220013.jpeg – Scour board collecting bathymetry data HWY220014.jpeg – same as 0012 HWY220015.jpeg – Looking downstream from bridge deck HWY220016.jpeg – same as 0015 HWY220017.jpeg – same as 0015 HWY220018.jpeg – Looking upstream from bridge deck HWY220019.jpeg – Upstream bridge face and area of scour along right bank HWY220020.jpeg – Looking upstream at channel and left overbank from deck HWY220021.jpeg – Looking at right abutment from US left bank HWY220022.jpeg – Looking at bridge from US left bank, in bend HWY220023.jpeg – Looking upstream at upstream bend from left bank HWY220024.jpeg – same as 0021 HWY220025.jpeg – Looking at DS right bank from left abutment HWY220027.jpeg – same as 0025 HWY220028.jpeg – Looking DS from left abutment HWY220029.jpeg – Looking US at right bank from left abutment HWY220030.jpeg – Looking US from left abutment HWY220031.jpeg – Upstream left floodplain, gravel pits HWY220032.jpeg – same as 0031 HWY220033.jpeg – Downstream left floodplain HWY220034.jpeg – Looking westward at upstream bridge face from roadway HWY220035.jpeg – Upstream left overbank HWY220036.jpeg – Looking eastward at upstream right overbank from roadway HWY220037.jpeg – Looking westward at bridge from roadway HWY220038.jpeg – Upstream bridge face / the source of 3 days of pleasant odors HWY220039.jpeg – Upstream right overbank from bridge deck CR22PDT.doc - MS Word summary of site, bridge and scour data CR22PDT.xls - contains the following worksheets cross sections are label by location upstream (us) or downstream (ds)
|
From page 142... ...
A-16 us0_4-5 us0_4-9 us0Q_4-5 us0Q_4-9 us0Q_7-15 lsrtww_4-9 - longitudinal section along the right wing wall lsp1p2_7-15 - longitudinal section between piers 1 and 2 ds0_4-4 ds0_4-5 ds0_7-15 dsfv_bp ds10_4-9 ds15_4-5 ds20_4-9 ds25_4-4 ds40_4-5 ds50_4-4 ds50_4-9 ds50_7-15 ds80_4-5 ds80_4-5(2) ds90_4-9 ds100_4-4 ds100_7-15 ds500_bp Q4-5-97- velocities from discharge measurement on 4-5-97 Q4-9-97 - velocities from discharge measurement on 4-9-97 Q7-15-97 - velocities from discharge measurement on 7-15-97 Hydrograph - hydrograph from nearest gage
|
From page 143... ...
A-17 CASE STUDY #2 U.S. Route 12 over the Pomme De Terre River near Holloway, Minn.
|
From page 144... ...
A-18 Table 1. Site information Site Characteristic Description County Swift Nearest City Holloway State Minnesota Latitude 45o16'58'' Longitude 95o58'45'' Route Number 12 Route Class US Stream Name Pomme De Terre Record or near-record amounts of snowfall occurred in most of the western portions of Minnesota during this period.
|
From page 145... ...
A-19 Bridge Data Structure #5359, at the time of the scour measurements, was an old truss bridge with a perpendicular alignment to the main channel. However, during the 1997 flood there was considerable skew as a significant amount of flow was coming from the left floodplain.
|
From page 146... ...
A-20 Figure 2. Plan view of U.S.
|
From page 147... ...
A-21 Figure 3. USGS topographic map of U.S.
|
From page 148... ...
A-22 Bed Material Data The bed material size distribution that is reported for the U.S. 12 bridge site are from information provided the Minnesota Department of Transportation (MnDOT)
|
From page 149... ...
A-23 Pier Details There were no piers associated with the U.S. 12 bridge over the Pomme De Terre river.
|
From page 150... ...
A-24 Figure 4. Pictures of the U.S.
|
From page 151... ...
A-25 PHOTOS Figure 5. Looking at the upstream U.S.
|
From page 152... ...
A-26 Figure 7. Looking upstream at U.S.
|
From page 153... ...
A-27 Figure 10. Looking downstream from replaced U.S.
|
From page 154... ...
A-28 floodplains because of heavy vegetation and submerged structures in the park located on the left overbank, upstream of the bridge. A plot of measured cross-section in the bridge opening is illustrated in Figure 12.
|
From page 155... ...
A-29 Table 8. Abutment scour data ( -- , not available; ft/s, feet per second; cfs, cubic feet per second; Abut, abutment; Avg, average; US, upstream; DS, downstream)
|
From page 156... ...
A-30 at 75 ft downstream. It was assumed that the 4/5/97 cross section could have been affected by the scour at the bridge section.
|
From page 157... ...
A-31 Table 9. – Contraction scour data ( -- , not available; ft/s, feet per second; cfs, cubic feet per second; US, upstream; DS, downstream; Avg, average)
|
From page 158... ...
A-32 COMPUTED SCOUR A calibrated HEC-RAS model of the site was developed to assess how accurately the scour for this flood could have been predicted. The pre-flood geometry of the bridge section was simulated with a HEC-RAS model utilizing the channel geometry from the original bridge plans and the low-flow survey conducted by BRW, Inc.
|
From page 159... ...
A-33 Table 11. Comparison of observed to model-computed contraction scour at U.S.
|
From page 160... ...
A-34 pdt12-brgpln-siteplan.jpg is a site plan scanned from the bridge plans provided by MnDOT. The following photos/sketches were taken during the April, 1997 flood: pdt12-flood-us-bridge.jpg is a photo taken during the flood, from the right bank looking across the face of the bridge to the left floodplain.
|
From page 161... ...
A-35 CASE STUDY #3 Minnesota River at State Route 25 near Belle Plaine, Minnesota SITE OVERVIEW The study site is located on the Minnesota River .7 miles north of the town of Belle Plaine on State Highway 25. The site is approximately 7.5 miles upstream from the USGS gaging station near Jordan (05330000)
|
From page 162... ...
A-36 Table 1. Site information Site Characteristic Description County Scott Nearest City Belle Plaine State Minnesota Latitude 44o38'02'' Longitude 93o45'58'' Route Number 25 Route Class State Stream Name Minnesota River Hydrologic Conditions Above normal rains in early November 2000 followed by snowfalls later in the month resulted in precipitation totals that were well above historical averages for the month, particularly in the central and southwestern portions of Minnesota.
|
From page 163... ...
A-37 supported by 82 concrete pilings driven to elevations ranging from 665.96' and 654.96'. The south and north abutments are supported by creosoted piles driven to elevation 670.53' and 665.96', respectively.
|
From page 164... ...
A-38 The bridge is located in a sinuous reach of the river in between two small radius bends that flow directly across or even slightly up-valley. These bends are located immediately upstream of the bridge and appear to be actively migrating down-valley.
|
From page 165... ...
A-39 Figure 2. USGS topographic map of the CR 22 bridge scour site.
|
From page 166... ...
A-40 Figure 3. Grain size distribution for CR 22 bed material samples Abutment Details The bridge has vertical abutments set back 30-40 ft from the edge of the main channel.
|
From page 167... ...
A-41 Figure 4. Picture of the re-stabilization done to the left abutment of the S.R 25 bridge over the Minnesota River near Belle Plaine, MN following April, 2001 flood.
|
From page 168... ...
A-42 Table 6. Pier data ( -- , not available)
|
From page 169... ...
A-43 PHOTOS Figure 5. Looking at flow contraction from left floodplain and location of upstream left overbank scour hole from right upstream abutment of S.R.
|
From page 170... ...
A-44 Figure 7. Looking at turbulent flow and eddy fence attributed to severe contraction along the upstream left abutment of the S.R.
|
From page 171... ...
A-45 MEASURED SCOUR All bathymetry data were collected with a 600 kHz ADCP and horizontally referenced with a differentially corrected global positioning system (DGPS)
|
From page 172... ...
A-46 Figure 10. Bathymetric contour plot of Minnesota River in the vicinity of State Route 25 bridge, collected during April, 2001 flood.
|
From page 173... ...
A-47 The velocity reported for "at the abutment" is the maximum velocity observed in the area of the scour hole. The site characteristics pertinent to abutment scour are summarized in Table 8.
|
From page 174... ...
A-48 change in elevation throughout the bridge opening that is consistent with the reported contraction scour depth (see Figure 9)
|
From page 175... ...
A-49 model incorrectly predicted more scour at the right abutments. The HIRE equation, which includes the velocity at the tip of the abutment, most likely predicted the more scour at the right abutment due to the inability of the HEC-RAS model to accurately simulate the extreme velocity magnitudes that were measured in the field at the left abutment.
|
From page 176... ...
A-50 2. Chad Wagner, U.S.
|
From page 177... ...
A-51 CASE STUDY #4 State Route 37 over the James River near Mitchell, South Dakota SITE OVERVIEW The study site is located on the James River 20 miles north of the town of Mitchell on State Highway 37. The site is approximately 4.5 miles downstream from the USGS gaging station near Forestburg (06477000)
|
From page 178... ...
A-52 Hydrologic Conditions Greater than normal precipitation starting with late fall rains in 2000, greater than normal snowfalls, a delayed snowmelt, and above average rains in April, all contributed to the upper Midwestern flooding in the spring of 2001. The James River basin received a surplus of 10 inches of precipitation through the winter of 2000-2001 and the early part of spring 2001.
|
From page 179... ...
A-53 on the left, looking downstream, and consists of 3 separate 3.75 ft diameter cylindrical piles. Pier 2 is on the right and also consists of 3 separate 3.75 ft diameter cylindrical piles.
|
From page 180... ...
A-54 Figure 2. Geomorphic setting and channel alignment for the James River at SR 37 bridge near Mitchell, SD Table 3.
|
From page 181... ...
A-55 Figure 3. Bathymetric contour plot of James River in the vicinity of S.R.
|
From page 182... ...
A-56 Bed Material Data Bed material samples were collected at three locations in the main channel on 10/26/2001 with a BM-54H grab sampler; 150 feet upstream of the bridge, in the bridge opening, and 200 feet downstream of the bridge. The samples consisted primarily of a sandy clayeysilt and had a D50 = .02 mm.
|
From page 183... ...
A-57 Figure 6. Grain size distribution for the bed material sample collected downstream of the SR 37 bridge.
|
From page 184... ...
A-58 Roughness Coefficients A distribution of Manning's n values is provided in Table 4. Table 4.
|
From page 185... ...
A-59 Figure 8. Picture of the bank failure at the left abutment of the S.R 37 bridge over the James River near Mitchell, SD taken during low-flow survey following April, 2001 flood.
|
From page 186... ...
A-60 determined from the bride plans. A summary of the measured water surface elevations is presented in the Table 7.
|
From page 187... ...
A-61 Figure 11. Looking at downstream left floodplain from bridge deck Figure 12.
|
From page 188... ...
A-62 Figure 14. Post-flood conditions, looking at upstream left floodplain from S.R.
|
From page 189... ...
A-63 MEASURED SCOUR All bathymetry data were collected with a 1200 kHz ADCP and horizontally referenced with a differentially corrected global positioning system (DGPS)
|
From page 190... ...
A-64 Contraction Scour Inspection of the "approach" section (one bridge width upstream) revealed a large discharge relative to that of the contracted opening.
|
From page 191... ...
A-65 COMPUTED SCOUR A calibrated HEC-RAS model of the site was developed to assess how accurately the scour for this flood could have been predicted. The pre-flood geometry of the bridge section was simulated with a HEC-RAS model utilizing the channel geometry from the original bridge plans and the low-flow floodplain survey.
|
From page 192... ...
A-66 Table 11. Comparison of observed to model-computed contraction scour at S.R.
|
From page 193... ...
A-67 SR37(ADCP_Data) .xls - Excel file with multiple worksheets containing ADCP depth integrated velocities collected during April, 2001 flood.
|
From page 194... ...
A-68 CASE STUDY #5 State Route 35 over Conehoma Creek near Kosciusko, Mississippi SITE OVERVIEW The State Highway 35 crossing of Conehoma Creek is located in Attala County, approximately 3.7 miles south of Kosciusko, MS and 2.5 miles upstream from the confluence of the Yockanookany River (see Figure 1)
|
From page 195... ...
A-69 Scour estimates for both the 1979 and 2001 floods were also computed with the WSPRO simulations. A summary of the general site information on the site is found in Table 1.
|
From page 196... ...
A-70 floods, respectively. The estimated peak discharges for both of these floods were greater than the 100-year flood estimated using procedures outlined in the 1991 USGS report, "Flood Characteristics of Mississippi Streams." DISCUSSION OF CONTRACTED SITE The cross section surveyed at the downstream side of the bridge in June 1979, April 2001 and February 2002 indicate scour occurred at the bridge during the 1979 and 2001 floods The scour likely occurred as the flood was peaking and perhaps beginning to recede.
|
From page 197... ...
A-71 Geomorphic Setting Based on MDOT geotechnical reports in the area, the stream has very likely scoured down into or near the top of the Zilpha Clay formation during the floods of April 12, 1979, and the April 5, 2001. A 1997 MDOT geotechnical report for Yockanookany River at proposed State Highway 14 Bypass of Kosciusko, located about 1.9 mi northwest of this site, indicates that the top of the Zilpha formation possesses a cohesion of about 1,320 pounds per cubic foot (lb/ft3)
|
From page 198... ...
A-72 Figure 3. Aerial photo of the S.R.
|
From page 199... ...
A-73 Bed Material Data Bed samples collected by the USGS on October 27, 1994, indicated the channel material was fine sand with a D84 of 0.29 mm, D50 of 0.10 mm, D16 of 0.017 mm, and a gradation coefficient of about 4.1. A 1997 MDOT geotechnical report for Yockanookany River at proposed State Highway 14 Bypass of Kosciusko, located about 1.9 mi northwest of this site, indicates that the top of the Zilpha clay formation has a D84 of about 0.37 mm, D50 of 0.16 mm, D16 of 0.026 mm, and a gradation coefficient of about 3.8.
|
From page 200... ...
A-74 Table 5. Abutment data Abutment Characteristic Description Left Station 1642+58 Right Station 1643+78 Left Skew (deg)
|
From page 201... ...
A-75 Surveyed Elevations Bridge data elevations were taken from MDOT plans, and are consistent with the 1929 National Geodetic Vertical Datum (NGVD) at the Conehoma Creek site.
|
From page 202... ...
A-76 Figure 4. Photos looking upstream from S.R.
|
From page 203... ...
A-77 Figure 7. Looking downstream through the S.R.
|
From page 204... ...
A-78 Contraction Scour The contraction scour at this site was diminished during the April 12, 1979 flood due to a reduction in discharge and velocities through the bridge as a result of a substantial amount of road overflow.
|
From page 205... ...
A-79 COMPUTED SCOUR A WSPRO model of the site was developed to estimate the peak flow during both the 1979 and 2001 floods and assess how accurately the scour for this flood could have been predicted using HEC-18 procedures. The pre-flood geometry of the bridge reach was simulated with the WSPRO model utilizing the channel geometry from the 1941 "asbuilt" plans and a 1977 inspection.
|
From page 206... ...
A-80 Table 12. Computed contraction scour depths at S.R.
|
From page 209... ...
A-83 SUPPORTING DATA WSPRO Model Files: ________________________________________ 1979post.prt – Model output file for simulation of April12, 1979 flood using scoured geometry. 1979post.wsp – Model input file for simulation of April 12, 1979 discharge using scoured geometry.
|
From page 210... ...
A-84 CASE STUDY #6 Bear Creek at U.S. 70 near Mays Store, North Carolina SITE OVERVIEW The U.S.
|
From page 211... ...
A-85 most of the major basins including the Neuse River Basin. The estimated peak discharge of 11,000 cfs for this flood was greater than the 500-year flood estimate of 8,480 cfs.
|
From page 212... ...
A-86 Geomorphic Setting Bear Creek is generally straight with the exception of two bends directly upstream of the U.S. 70 crossing.
|
From page 213... ...
A-87 Figure 3. – Aerial photo of the U.S.
|
From page 214... ...
A-88 Bed Material Data Streambed was collected from a location immediately downstream of the east bound bridge by the USGS on February 24, 2003. The size distribution of the bed material sediment is shown in Figure 4.
|
From page 215... ...
A-89 Roughness Coefficients A distribution of Manning n values used in the HEC-RAS analysis is provided in Table 5. Table 5.
|
From page 216... ...
A-90 Pier Details The piers are pile bents consisting of 11, 18-inch diameter concrete piles spaced 6.4 feet apart in a single line. The four piers are numbered from left to right, looking downstream.
|
From page 217... ...
A-91 PHOTOS Figure 5. Looking upstream at the east bound bridge abutment during low-flow.
|
From page 218... ...
A-92 Figure 7. Looking at the east abutment from the top of the west abutment.
|
From page 219... ...
A-93 Figure 9. West bound left pile groupwith temporary steel soldier piles.
|
From page 220... ...
A-94 opening (220 ft) is apparent in the measured scour pattern and locations of maximum scour depth.
|
From page 221... ...
A-95 Embankment Embankment Stage 1 Stage 2 Stage 3 Stage 4 Figure 10. Progression of geometric change at spill through abutments caused by scour.
|
From page 222... ...
A-96 Stage 5 Stage 6 Stage 7 Stage 8 Figure 10(cont'd)
|
From page 223... ...
A-97 Stage 9 Figure 10(cont'd)
|
From page 224... ...
A-98 channel geometry from the 1968 "as-built" plans and a 1986 inspection. The approach and exit sections used in the model were collected during the post-flood survey.
|
From page 225... ...
A-99 Figure 11. Velocity magnitudes from the 2-D model and significant features of post-flood assessment of the U.S.
|
From page 226... ...
A-100 Flow Profile 1 Profile 2 Profile 0 50 10 0 Graphic Scale (ft) N Figure 12.
|
From page 227... ...
A-101 0 2 4 6 8 10 12 14 16 -50 -40 -30 -20 -10 0 10 20 30 40 50 Station (ft)
|
From page 228... ...
A-102 0 2 4 6 8 10 12 14 16 18 -50 -40 -30 -20 -10 0 10 20 30 40 50 Station (ft)
|
From page 229... ...
A-103 Table 10. Contraction Scour Data Contraction Scour Depth Date Observed (ft)
|
From page 230... ...
A-104 CASE STUDY #7 Old Glenn Highway (State Route 1) over the Knik River near Palmer, Alaska SITE OVERVIEW The Old Glen Highway (State Route 1)
|
From page 231... ...
A-105 Figure 1. Location of study site and map of collected data points.
|
From page 232... ...
A-106 Hydrologic Conditions The hydrologic events responsible for the measured floods were typical summer glacial melt runoff from the Knik glacier. The peak discharge that was measured during the 1999 survey was 23,000 cubic feet per second (cfs)
|
From page 233... ...
A-107 The new structure (#539) consists of three continuous composite steel box girder spans supported by two concrete webbed piers, and spill-through abutments (type III contracted opening)
|
From page 234... ...
A-108 Figure 4. USGS topographic map of Old Glenn Highway (S.R.
|
From page 235... ...
A-109 conveying flow. An aerial photo of the site taken in 1996 is shown in Figure 5.
|
From page 236... ...
A-110 Table 4. Manning's n values for the Knik River at the Old Glenn Highway bridge.
|
From page 237... ...
A-111 Table 6. Pier data ( -- , not available)
|
From page 238... ...
A-112 PHOTOS Figure 7. Looking downstream at the Old Glenn Highway (S.R.
|
From page 239... ...
A-113 Figure 9. Looking from right bank to left bank between the two Old Glenn Highway bridges (new bridge is on the right)
|
From page 240... ...
A-114 Figure 11. Looking along downstream face of the new Old Glen Highway bridge over the Knik River, field crew and survey boat are in shown in the foreground.
|
From page 241... ...
A-115 Figure 12. Looking downstream at location of ADCP cross-sections on the Knik River at Old Glenn Highway (S.R.1)
|
From page 242... ...
A-116 Pier Scour Scour at pier #3 of the old bridge is a concern of the AkDOT and therefore it has been protected with riprap. None of the measured scour is associated with pier scour.
|
From page 243... ...
A-117 Figure 14. Schematic of survey data for bridge 539 at Knik River near Palmer, AK, collected during 2001-scour survey (Coordinate system is UTM Zone 6, NAD27 Alaska datum)
|
From page 244... ...
A-118 Figure 15. Plot of average bed elevation change (across the entire bridge opening)
|
From page 245... ...
A-119 Roughness values of 0.08 for the overbanks and 0.03 for the channel were initially selected and the channel values were adjusted to as low as .027 and as high as 0.037 to calibrate the modeled water surface elevation to the observed. Using these values the modeled water surface elevations are equal to the observed for sections EXIT2, EXIT1, and APPR1.
|
From page 246... ...
A-120 Table 10. Summary of selected model parameters used for the level 2-scour analysis of the new Old Glenn Highway bridge.
|
From page 247... ...
A-121 SUPPORTING DATA 1999 Level 2-scour analysis files: File name File description and software 539_knik_ics.txt 539_knik_printed Raw data files from the data logger in Northing, Easting, Elevation (ics) and full information formats.
|
From page 248... ...
A-122 2001 Survey Files: File name File description and software finalTable.txt All bathymetry, topo and bride survey data from 1999 survey, in a text file format. gps points.txt Summary of all bathymetry, topo and bride gps data from 1999 survey, in a text file.
|
From page 249... ...
A-123 Description of Photos taken in 2001: Photo Name Description Knik_002 Downstream view to bridge piers Knik_003 Upstream view to bridges Knik_004 ADCP/GPS mount Knik_005 Tributary, US Right bank above spur dike Knik_006 Old bridge pier Knik_007 Right bank to left bank downstream of bridges Knik_008 Downstream right bank from new bridge Knik_009 Downstream channel from new bridge Knik_010 Right bank to left bank from new bridge Knik_011 Right bank to left bank between bridges Knik_012 Old bridge from new Knik_013 Left bank downstream of bridges Knik_014 Right bank to left bank under new bridge Knik_016 Tributary from end of right bank spur dike Knik_017 Right bank to left bank under old bridge Knik_018 Upstream from right bank spur dike Knik_019 Upstream view to bridges Knik_020 Right bank approach to bridge Knik_021 Upstream left bank Knik_air1 Aerial view of bridges looking downstream Knik_air2 Aerial view of bridges looking downstream Knik_air3 Aerial view of bridges looking downstream
|
From page 250... ...
A-124 CASE STUDY #8 Cedar River at U.S. 218 near Janesville, Iowa SITE OVERVIEW U.S.
|
From page 251... ...
A-125 Table 1. Site information Site Characteristic Description County Bremer Nearest City Janesville State Iowa Latitude 42°39'13" Longitude 92°27'52" Route Number 218 Route Class US Stream Name Cedar River Hydrologic Conditions The peak discharge that was measured during the 1999 flood was approximately 42,200 cfs on July 23, 1999.
|
From page 252... ...
Figure 1. USGS topographic map (1984)
|
From page 253... ...
A-127 Table 2. Bridge data Bridge Characteristic Description Structure Number F 218-8(20)
|
From page 254... ...
A-128 Geomorphic Setting The Cedar River streambed is composed of sand, gravel, and rock and has narrow floodplains in the vicinity of the U.S. 218 bridge.
|
From page 255... ...
A-129 Figure 4. Grain size distribution for the bed material sample collected upstream of US 218 in the Cedar River near Janesville, IA.
|
From page 256... ...
A-130 Roughness Coefficients A distribution of Manning's n values is provided in Table 4. Table 4.
|
From page 257... ...
A-131 Surveyed Elevations Water surface elevations at the site were measured from the upstream and downstream sides of the US 218 bridge during the real-time scour measurements on July 23, 1999. The measurements were made at the beginning and end of the data collection and revealed that the river stage was falling throughout the day (Table 7)
|
From page 258... ...
A-132 PHOTOS Figure 5. Looking west across upstream face of US 218 bridge over the Cedar River near Centralia, WA on 7/23/1999.
|
From page 259... ...
A-133 Figure 7. Looking downstream from downstream US 218 bridge deck, 7/23/1999.
|
From page 260... ...
A-134 Figure 9. Looking upstream from upstream US 218 bridge over the Cedar River, 7/23/1999.
|
From page 261... ...
A-135 Figure 11. Looking upstream at right guide bank, floodplain and drainage ditch from upstream US 218 bridge over Cedar River during low flow, 8/10/99.
|
From page 262... ...
A-136 Figure 13. Looking downstream at right overbank and Pier 5 of US 218 bridge over Cedar River during low flow, 8/10/99.
|
From page 263... ...
A-137 channel elevation in uncontracted sections further upstream and downstream (Figure 2)
|
From page 264... ...
A-138 Table 9. Contraction scour data ( -- , not available; ft/s, feet per second; cfs, cubic feet per second; US, upstream; DS, downstream; Avg, average)
|
From page 265... ...
A-139 Table 10. Summary of computed and observed contraction scour for U.S.
|
From page 266... ...
A-140 Photos: DCP00172.jpg - DCP00207.jpg - photos taken during 1999 flood DCP00252.jpg-DCP00344.jpg - photos taken during after 1999 flood receded. DSCN0123.jpg-DSCN0138.jpg - photos taken during low-flow/floodplain survey (2000)
|
From page 267... ...
A-141 CASE STUDY #9 Galvin Road Overflow Bridge for the Chehalis River near Centralia, Washington SITE OVERVIEW The Galvin Road Overflow bridge is approximately 2.5 miles northwest of the town of Centralia, WA and serves as a relief opening on the east floodplain of the Chehalis River during high-flow events (Figure 1)
|
From page 268... ...
A-142 the FEMA 100-yr flood (56,000 cubic feet per second (cfs)
|
From page 269... ...
Figure 1. Location and topographic map of Galvin Road Overflow bridge site.
|
From page 270... ...
A-144 Figure 2. Sketch of flow patterns and HEC-2 model sections through Galvin Road overflow bridge during February 1996 flood.
|
From page 271... ...
A-145 Table 2. Bridge data Bridge Characteristic Description Structure Number 112 Length (ft)
|
From page 272... ...
A-146 Figure 3. Aerial photo of the Gavin Road Overflow bridge site taken in 1990.
|
From page 273... ...
A-147 Table 3. Geomorphic data Geomorphic Characteristic Description Drainage Area (mi2)
|
From page 274... ...
A-148 Table 5. Abutment data Abutment Characteristic Description Left Station 68+05.04 Right Station 64+22.96 Left Skew (deg)
|
From page 275... ...
A-149 Table 6. Pier data ( -- , not available)
|
From page 276... ...
A-150 Table 7. Surveyed high-water mark elevations and corresponding modeled discharges modeled at the Galvin Road overflow bridge.
|
From page 277... ...
A-151 Figure 5. Looking east at Pier 10 (foreground)
|
From page 278... ...
A-152 Figure 7. Looking downstream (north)
|
From page 279... ...
A-153 Figure 9. Looking east at failed pier #9 following the February 1996 flood.
|
From page 280... ...
A-154 Abutment Scour No measurement of abutment scour was made at the Galvin Road overflow bridge. Contraction Scour The contraction at this site is most notably attributed to the severe constriction in the floodplain flow width created by extending the western approach fill 146 feet to accommodate the new shorter Galvin Road overflow bridge.
|
From page 281... ...
Figure 11. Plan and profile plots of scour hole location at Galvin Road overflow bridge for the Chehalis River, Centralia, WA.
|
From page 282... ...
A-156 COMPUTED SCOUR A HEC-2 model of the site was developed as part of a post-scour analysis of the Galvin Road overflow bridge to determine the cause of the scour at this site and suggest mitigation procedures. A discussed previously, from the high-water marks the HEC-2 model predicted that 45,000 – 50,000 cfs remained in the Chehalis River channel and 25,000 – 30,000 cfs passed through the overflow bridge.
|
From page 283... ...
A-157 POINTS OF CONTACT Any questions regarding the Galvin Road overflow bridge for the Chehalis River should be directed to the following point of contact: 1. Chad Wagner, Hydraulic Engineer U.S.
|
From page 284... ...
A-158 Photo8.jpg - Looking downstream at piers 8, 9 (the pier that failed) and 10 following the February 1996 flood.
|
From page 285... ...
A-159 CASE STUDY #10 Chariton River at State Route 129 near Prairie Hill, Missouri SITE OVERVIEW The study site is located on the Chariton River at mile 11.73 of State Route 129, about 9 miles north of the town of Salisbury (at the intersection of State Route 129 and U.S. Route 24)
|
From page 286... ...
A-160 A step-backwater hydraulic model (WSPRO)
|
From page 287... ...
A-161 Figure 1. Streambed cross-sections at the downstream face of the SR 129 bridge over the Chariton River near Prairie Hill, MO.
|
From page 288... ...
A-162 Figure 2. – Looking upstream at the remnants of the debris raft formed in front of the middle pier (#2)
|
From page 289... ...
A-163 Figure 3. – USGS topographic map of S.R.
|
From page 290... ...
A-164 Bed Material Data Bed material samples were collected in the main channel and on the left overbank with a grab sampler at low-flow. The sample in the main channel was sand with a D50 = .32 mm.
|
From page 291... ...
A-165 Figure 5. Grain size distribution for the bed material sample collected on the left overbank upstream of the SR 129 bridge over the Chariton River.
|
From page 292... ...
A-166 Table 5. Abutment data Abutment Characteristic Description Left Station 0 Right Station 264.75 Left Skew (deg)
|
From page 293... ...
A-167 Surveyed Elevations Bridge data elevations were taken from MoDOT plans, but are consistent with gage datum (elevation 632.05 feet above sea level)
|
From page 294... ...
A-168 Figure 7. Looking at upstream S.R.
|
From page 295... ...
A-169 Figure 9. Looking along upstream S.R.
|
From page 296... ...
A-170 Pier Scour Scour is reported only at the middle pier (#2) for all of the scour measurements made at the S.R.
|
From page 297... ...
A-171 Table 9. Contraction scour data ( -- , not available; ft/s, feet per second; cfs, cubic feet per second; US, upstream; DS, downstream; Avg, average)
|
From page 298... ...
A-172 Table 10. Pier scour data Measurement Number Pier ID Date Location Scour Depth (ft)
|
From page 299... ...
A-173 Table 11. Comparison of model-computed and measured scour at S.R.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.