Development and evaluation of clear-water pier and contraction scour envelope curves in the Coastal Plain and Piedmont Provinces of South Carolina

Abstract

P r e p a r e d i n C o o p e r a t i o n wi t h t h e S o u t h C a r o l i n a D e p a r t me n t o f T r a n s p o r t a t i o nD e v e l o p me n t a n d E v a l u a t i o n o f C l e a r -Wa t e r P i e r a n d C o n t r a c t i o n S c o u r E n v e l o p e C u r v e s i n t h e C o a s t a l P l a i n a n d P i e d mo n t P r o v i n c e s o f S o u t h C a r o l i n a V e r s i o n 1 . 1 , A u g u s t 2 0 1 6 S c i e n t i f i c I n v e s t i g a t i o n s R e p o r t 2 0 0 5 -5 2 8 9 Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Development and Evaluation of Clear-Water AbstractThe U.S. Geological Survey in cooperation with the South Carolina Department of Transportation collected clear-water pier-and contraction-scour data at 116 bridges in the Coastal Plain and Piedmont Physiographic Provinces of South Carolina. Pier-scour depths collected in both provinces ranged from 0 to 8.0 feet. Contraction-scour depths collected in the Coastal Plain ranged from 0 to 3.9 feet. Using hydraulic data estimated with a one-dimensional flow model, predicted clear-water scour depths were computed with scour equations from the Federal Highway Administration Hydraulic Engineering Circular 18 and compared with measured scour. This comparison indicated that predicted clear-water scour depths, in general, exceeded measured scour depths and at times were excessive. Predicted clear-water contraction scour, however, was underpredicted approximately 30 percent of the time by as much as 7.1 feet.The investigation focused on clear-water pier scour, comparing trends in the laboratory and field data. This comparison indicated that the range of dimensionless variables (relative depth, flow intensity, relative grain size) used in laboratory investigations of pier scour, were similar to the range for field data in South Carolina, further indicating that laboratory relations may have some applicability to field conditions in South Carolina. Variables determined to be important in developing pier scour in laboratory studies were investigated to understand their influence on the South Carolina field data, and many of these variables appeared to be insignificant under field conditions in South Carolina. The strongest explanatory variables were pier width and approach velocity. Envelope curves developed from the field data are useful tools for evaluating reasonable ranges of clear-water pier and contraction scour in South Carolina. A modified version of the Hydraulic Engineering Circular 18 pier-scour equation also was developed as a tool for evaluating clearwater pier scour. The envelope curves and modified equation offer an improvement over the current methods for predicting clear-water scour in South Carolina.Data from this study were compiled into a database that includes photographs, measured scour depths, predicted scour depths, limited basin characteristics, limited soil data, and modeled hydrau...

The South Carolina bridge-scour envelope curves

“…Such conditions commonly occur on the flood plains of South Carolina streams as illustrated by Benedict and Caldwell (2006; fig. 3).…”

“…The U.S. Geological Survey (USGS), in cooperation with the South Carolina Department of Transportation (SCDOT), investigated historical scour at 231 bridges in the Piedmont and Coastal Plain Physiographic Provinces of South Carolina (Benedict, 2003;Benedict and Caldwell, 2006. (In this report, the Piedmont and Coastal Plain Physiographic Provinces will be referred to simply as Piedmont and Coastal Plain.)…”

“…To assist engineers in developing and applying such judgment, the data collected from the South Carolina field investigations were organized into regional bridge-scour envelope curves that displayed the range and trend for the upper bound of observed scour for each scour component, including clear-water abutment, contraction, and pier scour, as well as live-bed contraction and pier scour. The application and limitations of the South Carolina bridge-scour envelope curves were documented in four reports (Benedict, 2003;Benedict and Caldwell, 2006, with each report addressing different components of bridge scour. A primary objective of the current investigation (2016) was to synthesize the findings of these previously published reports into a single guidance manual providing an integrated procedure for applying the South Carolina bridgescour envelope curves.…”

Assessing potential scour using the South Carolina bridge-scour envelope curves

“…The application and limitations of these envelope curves were documented in four reports (Benedict, 2003;Benedict and Caldwell, 2006, 2009, 2012. Because each report addresses different components of bridge scour, it was recognized that there was a need to develop an integrated procedure for applying the envelope curves to help assess scour potential at riverine bridges in South Carolina.…”

“…It is rare, however, that such data are available at or near a site of interest, making the evaluation of predicted scour as compared to field data difficult if not impossible. Realizing the value of historic scour measurements, the U.S. Geological Survey (USGS), in cooperation with the South Carolina Department of Transportation (SCDOT), conducted a series of three field investigations (Benedict, 2003;Benedict and Caldwell, 2006, 2009, 2012 to collect historic scour data with the goal of understanding regional trends of scour at riverine bridges in South Carolina.…”