Federal Highway Administration, indicated that about million was expended annually up
to 1973 to repair roads and bridges that were damaged by floods. This cost does not include
the additional indirect costs to highway users for fuel and operating costs resulting from
temporary closure and detours and to the public for costs associated with higher tariffs,
freight rates, additional labor costs and time.
Rhodes and Trent (1999) document that
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.2 billion was expended for restoration of flood
damaged highway facilities during the 1980s. They state that this amount is conservative
because it (1) only includes the amount funded by the U.S. Government which ranges from
75 to 100 percent of the total restoration costs, and (2) the funds were only for disasters
related to very large floods and do not include the hundreds of smaller events that occur
every year. They also demonstrate that the added cost of operating a vehicle over a detour
and time lost traveling when a bridge failed (only part of the indirect costs) exceed by several
times the direct cost of bridge replacement or repair.
7.1.3 Bridge Scour Evaluation Program
The U.S. Department of Transportation, Federal Highway Administration (FHWA) in 1988
issued Technical Advisory T5140.20 (superseded by T5140.23 in 1991) requiring the States
to conduct a scour evaluation program. This program resulted from the failure of the I-90
bridge over Schoharie Creek in upstate New York which killed ten people (NTSB 1988 and
Richardson et al. 1987). The evaluation is to be conducted by an interdisciplinary team of
hydraulic, geotechnical and structural engineers who can make the necessary engineering
judgments to determine the vulnerability of a bridge to scour. As of February 2001, the
481,313 bridges over water in the National Bridge Inventory have been screened as to their
scour vulnerability (100 percent).
The evaluation program in the U.S. is on schedule and scour countermeasures are being
implemented on bridges that have been identified as scour susceptible or scour critical.
Replacement bridges are being constructed as rapidly as funds can be provided. Scour
countermeasures include riprap protection, scour monitoring before, during and after a flood
and the inspection program (Richardson and Davis 2001, Lagasse et al. 1997, 2001a, and
2001b, Schall et al. 1997a and 1997b).
7.1.4 Comprehensive Scour Analysis
This chapter presents background knowledge on scour analysis. Earlier chapters give a
comprehensive overview of fluvial geomorphology, sediment transport, and flow in alluvial
channels and stream stability fundamentals needed to understand streams, stream instability
and scour. The comprehensive procedure for scour and stream instability analyses and
countermeasures to control them are given in the FHWA publications HEC-18, HEC-20, and
HEC-23 (Richardson and Davis 2001; Lagasse et al. 2001a, 2001b). The interrelationships
and procedures recommended in the three documents are shown in the Figure 7.1.
7.2
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