Prepared in cooperation with the South Carolina Department of Transportation The South Carolina Bridge-Scour Envelope Curves Scientific Investigations Report 2016–5121 Version 1.2, April 2021 U.S. Department of the Interior U.S. Geological Survey Cover. Little Pee Dee River at S.C. 917 in Horry County, South Carolina, April 20, 2007. Photograph by U.S. Geological Survey. The South Carolina Bridge-Scour Envelope Curves By Stephen T. Benedict, Toby D. Feaster, and Andral W. Caldwell Prepared in cooperation with the South Carolina Department of Transportation Scientific Investigations Report 2016–5121 Version 1.2, April 2021 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior RYAN K. ZINKE, Secretary U.S. Geological Survey William H. Werkheiser, Deputy Director exercising the authority of the Director U.S. Geological Survey, Reston, Virginia First release: 2016 Revised: January 2018 (ver. 1.1) Revised: April 2021 (ver. 1.2) For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://store.usgs.gov. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Benedict, S.T., Feaster, T.D., and Caldwell, A.W., 2016, The South Carolina bridge-scour envelope curves (ver. 1.2, April 2021): U.S. Geological Survey Scientific Investigations Report 2016– 5121, 96 p., https://doi.org/10.3133/sir20165121. ISSN 2328-0328 (online) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................2 Description of the Study Area ............................................................................................................2 Previous Investigations........................................................................................................................3 The South Carolina Pier-Scour Envelope Curves .....................................................................................4 Clear-Water Pier-Scour Envelope Curve ..........................................................................................5 South Carolina Clear-Water Pier-Scour Field Data ................................................................5 Clear-Water Pier-Scour Envelope Curve .................................................................................8 Live-Bed Pier-Scour Envelope Curve ................................................................................................9 South Carolina Live-Bed Pier-Scour Field Data .....................................................................9 Live-Bed Pier-Scour Envelope Curve .....................................................................................11 Comparison of the South Carolina Pier-Scour Envelope Curves With Other Data ..............................13 The PSDb-2014 Database ..................................................................................................................13 South Carolina Clear-Water and Live-Bed Pier-Scour Field Data .....................................13 Screened Laboratory and Field Data ......................................................................................16 Verification Data ........................................................................................................................16 Skewed Piers ..............................................................................................................................16 The PSDb-2014 Pier-Scour Envelope Curve ...................................................................................17 Envelope Curve for the PSDb-2014 Screened Laboratory Pier-Scour Data ....................17 Extending the Envelope Curve With the PSDb-2014 Screened Field Data .......................17 Verifying the Envelope Curve With the PSDb-2014 Unscreened Field Data .......................19 Review of Field Data That Exceed the Envelope Curve .......................................................19 Flow Recurrence Intervals for Data Used in the PSDb-2014 Pier-Scour Envelope Curve .............................................................................................................22 Comparison of the South Carolina and PSDb-2014 Pier-Scour Envelope Curves ......................22 Relative Increase in Theoretical Pier Scour Associated With the 100- to 500-Year Flows .............24 Theoretical Pier-Scour Data .............................................................................................................25 The 500-Year Flow Adjustment Coefficient .....................................................................................25 Application and Limitations of the PSDb-2014 and South Carolina Clear-Water and Live-Bed Pier-Scour Envelope Curves ................................................................................26 Evaluating Scour Depth at Pier Widths Less Than or Equal to 6 Feet .......................................26 Clear-Water Pier Scour on the Flood Plain............................................................................27 Live-Bed Pier Scour in the Main Channel .............................................................................27 The PSDb-2014 Pier-Scour Envelope Curve ..........................................................................27 Evaluating Scour Depth at Pier Widths Greater Than 6 Feet ......................................................28 iv The South Carolina Clear-Water Abutment-Scour Envelope Curves .................................................28 South Carolina Clear-Water Abutment-Scour Field Data ............................................................30 Field Conditions That Influence Clear-Water Abutment-Scour Potential .................................31 Clear-Water Abutment-Scour Envelope Curves With Respect to Embankment Length ........33 Piedmont Clear-Water Abutment-Scour Envelope Curve ...................................................33 Coastal Plain Clear-Water Abutment-Scour Envelope Curve ............................................35 Clear-Water Abutment-Scour Envelope Curves With Respect to the Geometric-Contraction Ratio ....................................................................................................35 Piedmont Clear-Water Abutment-Scour Envelope Curve ...................................................37 Coastal Plain Clear-Water Abutment-Scour Envelope Curve ............................................37 The Modified Clear-Water Abutment-Scour Envelope Curves ...................................................37 Comparison of the South Carolina Clear-Water Abutment-Scour Envelope Curves With Other Data ..............................................................................................................................41 Comparison of the Clear-Water Abutment-Scour Field Data to Laboratory Data ...................43 Discrepancies in the Upper Bound of the Clear-Water Abutment-Scour Laboratory and Field Data ...................................................................................................43 Comparison of the South Carolina Abutment-Scour Envelope Curves to Other Abutment-Scour Field Data ......................................................................................45 Relative Increase in Theoretical Abutment Scour Associated With the 100- to 500-Year Flows ...................................................................................................................48 Theoretical Abutment-Scour Data ...................................................................................................48 The 500-Year Flow Adjustment Coefficient .....................................................................................48 Application and Limitations of the South Carolina Clear-Water Abutment-Scour Envelope Curves .............................................................................................................................49 Selecting a Reference Surface ........................................................................................................50 Estimating the Embankment Length and the Geometric-Contraction Ratio .............................50 Selecting the Appropriate Clear-Water Abutment-Scour Envelope Curve ..............................50 Original Clear-Water Abutment-Scour Envelope Curves ....................................................50 Modified Clear-Water Abutment-Scour Envelope Curves ..................................................51 Single-Bridge Openings ............................................................................................................51 Multiple-Bridge Crossings .......................................................................................................51