Figure 1. Status of U.S. Geological Survey bridge scour projects.
The U.S. Geological Survey (USGS) has worked in cooperation with the Federal Highway Administration (FHWA) and state highway departments for almost 50 years on research and data collection to design and maintain bridges that are resistant to the dynamic and often damaging processes of alluvial rivers (table 1). During this period, 37 USGS District offices have been involved in bridge scour projects (fig. 1). These projects have ranged from qualitative site assessments to detailed data collection with state-of-the-art instrumentation. The experience and innovation of USGS personnel in the collection and analysis of field data has put the USGS at the forefront of bridge scour research.
Table 1. Selected history of USGS projects associated
with the impacts of streams on highways [USGS, U.S. Geological
Survey; FHWA, Federal Highway Administration; DOT, Department
|Year||Description of Activity|
|1950s||USGS begins providing bridge site reports on the hydraulics and hydrology of selected bridge sites to several State Departments of Transportation. This activity is ongoing in several states.|
|1964||The USGS began a study of scour at selected bridge sites in Alaska (Norman, 1975). FHWA funds bridge scour research by USGS personnel at Colorado State University's hydraulic laboratory.|
|1969||The USGS in cooperation with the FHWA, Mississippi DOT, Alabama DOT, and Louisiana DOT began a 5-year study on backwater and discharge (Schneider and others, 1977).|
|1978||USGS publishes report on countermeasures for hydraulic problems at bridges (Brice and Blodgett, 1978).|
|1981||USGS publishes report on study of flood characteristics of the Sacramento River near the Gianella Bridge (Blodgett, 1981).|
|1986||USGS publishes report on pilot study for collection of bridge-scour data (Jarret and Boyle,1986). USGS develops backwater model with routines to compute backwater from bridges over waterways (Shearman and others, 1986).|
|1987||FHWA funds the USGS to initiate the National Bridge Scour Program.|
|1988||A model agreement for studies with USGS is included in the FHWA technical advisory and interim procedures to evaluate scour at brides in this advisory. Tennessee DOT initiates study with USGS to assess bridge-scour problems across the State. This is the first Level I - Assessment.|
|1989||USGS publishes first report on the use of geophysical techniques for assessing scour. This opened a new marketing area for geophysical equipment manufacturers (Gorin and Haeni, 1989).|
|1989-90||State DOT's fund the USGS in eight States to collect real-time scour data at selected bridges.|
|1990-93||State DOT's fund the USGS in 10 States to complete Level I - Assessments (modeled after the 1988 study initiated in Tennessee). State DOT's fund the USGS in 11 states to make hydrologic, hydraulic, and scour analyses at selected bridges for the 100-year and 500-year floods.|
|1991||FHWA funds the USGS to develop instrumentation for detailed scour measurements and for quick scour measurement to determine bridge safety.|
|1993||FHWA funds the USGS to collect detailed scour data utilizing state-of-the-art instrumentation.|
|1993-94||USGS demonstrates data-collection equipment and techniques to many State DOT's.|
|1994||First USGS national scour report receives Director's approval.|
|1996||USGS national bridge scour report published (landers and Mueller, 1996). The USGS national bridge scour data-management system is released for distribution (Landers and other, 1996).|
Historically, most of the research on scour at bridges has been
conducted in the laboratory with little or no validation by field
data. The lack of field data reflects the difficulty associated
with collecting hydraulic and sediment transport data during floods
in sufficient detail to study scour processes and to improve design
and evaluation methods. The USGS, in cooperation with the FHWA
and state highway departments have collected over 400 limited-detail
measurements of local pier scour (Landers and Mueller, 1996; Landers
and others, 1996).
Limited-detail measurements of scour consist of cross-sections
and water velocities collected from the bridge deck during flood
conditions. These real-time measurements are supplemented with
bridge geometry and bed-material data, usually collected during
low-flow conditions. The limited-detail measurements have been
used to evaluate published pier-scour prediction equations. Scour
observed in the laboratory appears to be consistently deeper than
scour observed in the field. The limited-detail measurements have
indicated potential differences between processes observed in
the laboratory and those observed in the field (Landers and Mueller,
1996; Mueller, 1996). Evaluation of contraction and abutment scour
typically requires detailed hydraulic and channel geometry data
collected in a reach extending upstream of to downstream of the
hydraulic influence of the bridge. Limited-detail data are good
for evaluating local pier scour but lack the spatial coverage
necessary for a good evaluation of contraction and abutment scour.
The USGS has developed equipment and techniques for collecting
detailed data sets needed to characterize and study the processes
associated with scour at bridges. A complete detailed data set
should include three-dimensional velocity measurements, channel
bathymetry, bed-material load, bed-material samples, water-surface
elevation, water-surface slope, water temperature, and discharge.
Although the methods for accurately measuring bed-material load
are still lacking, new technology, improvements in existing technology,
and application of instruments used in hydrographic surveying
and oceanographic research have made the collection of the bathymetric
and hydraulic data feasible. Portable scour-measuring systems
consist of the following four components: (1) a method to measure
the horizontal position of the data collected, (2) the instrument(s)
for making streambed-elevation and water-velocity measurements,
(3) a deployment system, and (4) a data-storage device.
Brice, J.C., and Blodgett, J.C., 1978, Countermeasures for hydraulic problems at bridges: Federal Highway Administration Report FHWA-RD-78-162.
Gorin, S. R., and Haeni, F.P., 1989, Use of surface-geophysical methods to assess riverbed scour at bridge piers: U.S. Geological Survey Water-Resources Investigations Report 88-4212, 33 p.
Jarret, R.D. and Boyle, J.M., Pilot study for collection of bridge-scour data: U.S. Geological Survey Water-Resources Investigations Report 85-4004, 46 p.
Jones, J.S., Alqalam, Kamel, Gratton, Buddy, and Summers, Brian, 1995, Effect of the 1994 Southeast flooding on the highway system in Georgia: Handout from presentation at the 1995 American Society of Civil Engineers Water Resources Engineering Conference, San Antonio, Tex.
Murillo, J.A., 1987, The scourge of scour: Civil Engineering, American Society of Civil Engineers, v. 57, no. 7, p. 66-69.
Landers, M.N., and Mueller, D.S., 1996, Channel scour at bridges in the United States: Federal Highway Administration Report FHWA-RD-95-184, 140 p.
Landers, M.N., Mueller, D.S., and Martin, G.R., 1996, Bridge-scour data management system user's manual: U.S. Geological Survey Open-File Report 95-754, 66 p.
Mueller, D.S., 1996, Local scour at bridge piers in nonuniform sediment under dynamic conditions: Fort Collins, Colorado State University, Ph.D. dissertation, 212 p.
Norman, V.W., 1975, Scour at selected sites in Alaska: U.S. Geological Survey Water-Resources Investigations Report 32-75, 160 p.
Rhodes, Jennifer and Trent, Roy, 1993, Economics of floods, scour, and bridge failures in Shen, H.W., Su, S.T., and Wen, Feng, eds., Hydraulic Engineering '93: New York, American Society of Civil Engineers, p. 928-933.
Shearman, J.O. Kirby, W.H., Schneider, V.R., and Flippo, H.N., 1986, Bridge waterways analysis model; research report: Federal Highway Administration Report FHWA-RD-86-108, 112 p.
Schneider, V.R., Board, J.W., Colson, B.E., Lee, F.N., and Druffel, L., 1977, Computations of backwater and discharge at width constrictions of heavily vegetated flood plains: U.S. Geological Survey Water-Resources Investigations Report 76-129, 64 p.
MUELLER, DAVID S.,|
U.S. Geological Survey,
Currently serves as the national coordinator and technical support contact for bridge-scour projects in the U.S. Geological Survey and is a member of the Acoustic Doppler Current Profiler workgroup. Work experience includes 7 years at the U.S. Army Corps of Engineers Waterways Experiment Station and 6 years with the USGS in Louisville, KY. Areas of interst and work include physical and numerical modeling of channel morphology and sediment transport, field data collection and instrumentation development.