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Publication Number: FHWA-RD-03-052
Date: May 2005

Field Observations and Evaluations of Streambed Scour At Bridges


The Bridge Scour Data Management System (BSDMS) was developed to support the preparation, compilation, and analysis of bridge scour data.(22) Bridge scour data are stored in the BSDMS as data sets that are defined for each bridge scour site in the database. Each data set contains more than 200 site and measurement attributes of the channel geometry, flow hydraulics, hydrology, sediment, geomorphic setting, location, and bridge specifications. The BSDMS provides interactive storage, retrieval, selection, editing, and display of bridge scour data sets; it was originally programmed in FORTRAN and was available in both DOS and Unix® versions.

Changes to the structure of the database were difficult, which restricted adapting the database to different types of data and adding new parameters as research evolved on scour at contracted bridge openings. The capabilities of the BSDMS for extracting data from the database and putting the data into tables for subsequent analysis were also limited. It was determined that the BSDMS would be more efficient and useful if it were ported to a commonly used database engine, such as Microsoft® Access, rather than to try to adapt the FORTRAN code to meet the changing requirements of the BSDMS. Microsoft Access provides a much more flexible database structure with user-friendly methods for querying and extracting data. The use of Microsoft Access will also allow future versions of the BSDMS to be served on the World Wide Web.

The enhancement of the BSDMS and the serving of the data on the Internet are an ongoing effort that has received subsequent funding from the National Cooperative Highway Research Program (NCHRP) Project 24-14. As of 2000, all data from the original BSDMS had been ported to Microsoft Access and the transferred data checked for any errors in conversion. Most variables of the original BSDMS have been retained and some new variables added to better characterize bed material and contraction and abutment scour. Some features, such as entry of hydrographs and cross sections and all graphics capabilities, currently are not supported directly by the database. Hydrographs and cross sections can be stored as individual files and referenced in the files section of the database. This simplifies the database, and the files section provides the capability of including many different types of data, such as Acoustic Doppler Current Profiler (ADCP) data, xyz topography data, digital photographs, scanned bridge plans, maps, and satellite imagery. Data are easily extracted into tables so that the user may construct ASCII data tables and import those tables into the graphics or statistical software of their choice.

Corrections and enhancements to existing data were made during the data transfer and validation process. The data from Alaska, reported in Norman, provided only the D90 and D50 grain sizes.(16) The data set in the original BSDMS included D90 as D95 and noted this in the comments; this has been changed in the new BSDMS. The D95, D84, and D16 are computed from the data provided. The D84was interpolated from the D90 and D50 by use of a log-probability interpolation. The gradation parameter (Sigma) was computed as D84/D50 (although this parameter could also be computed as D50/D16 or (D84/D16)0.5), and the D95 and D16 were computed from the following equation:

Equation 1. Equation. D subscript I is the grain size of which I percent is finer. D subscript I is equal to the median grain size of the bed material (D subscript 50) multiplied by the coefficient of gradation superscript K subscript I, which is the standard normal deviate of I.       (1)

where Di is the grain size of which i percent is finer;
D50 is the median grain size of the bed material; and
ki is the standard normal deviate of i, defined as follows:

Di Ki
D10 -1.282
D16 -0.994
D35 -0.385
D50 0
D65 +0.385
D84 +0.994
D90 +1.282
D95 +1.645
D99.99 +3.72

The limit on the number of bed material samples that could be entered for a given site in the old BSDMS did not allow full presentation of the data for sites in Ohio. The new BSDMS does not have this restriction, and all the bed material data are included from a very extensive sampling program used in the Ohio bridge scour study.(42) The database now contains 557 bed material samples collected at bridge scour study sites.

New sites and additional data at existing sites were also added to the database. Landers et al. reported 384 local pier scour measurements at 56 bridges located in 14 States.(22) This has been expanded to 493 local pier scour measurements, 18 contraction scour measurements, and 12 abutment scour measurements. The database now contains data from 79 sites located in 17 States. Some of the contraction and abutment scour data sets are not complete, but they represent the best available information and should prove useful to other researchers working on abutment and contraction scour.

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