Highway infrastructure damage caused by the 1993 upper Mississippi river basic flooding.

This report contains the findings of a study of the effects of the 1993 flooding of the Mississippi River Basin on bridge and related transportation infrastructure. Records of the types of facilities that were damaged are included, along with a damage classification system that can be applied to future natural disasters to aid in data collection and reporting. The contents of this report will be of immediate interest to bridge and structural engineers, hydraulics engineers and hydrologists, and others concerned with the effects of flooding on highway infrastructure. The Mississippi River Basin experienced substantial flooding in 1993 because of heavy rainfall. The flooding surpassed record levels in many areas and resulted in significant damage to the highway infrastructure. Although similar damage has been documented before, the 1993 catastrophe presented the opportunity to catalog the damage in multiple states in a way that may be useful for planning, mitigation, and remediation efforts related to future flood events. Designing bridges for flood events historically has been problematic for bridge engineers, especially from the perspective of determining suitable design loads associated with debris and hydrodynamic forces. The AASHTO `Standard Specifications for Highway Bridges’ states, "All piers and other portions of structures that are subjected to the force of flowing water, floating ice, or drift shall be designed to resist the maximum stresses induced thereby." Unfortunately, this is the extent of the guidance provided in the specifications for determination of debris or drift forces in bridge design. Accordingly, NCHRP Project 12-39, a six-task effort called `Design Specifications for Debris Forces on Highway Bridges’, was initiated with the objective of developing practical design specifications and supporting commentary for the determination of impact, drag, and hydrostatic forces on bridge piers and superstructures due to debris. The 1993 flooding occurred while NCHRP Project 12-39 was being conducted. The Federal Highway Administration and NCHRP decided to cooperatively fund a seventh research task to (1) conduct field surveys of flood-related highway bridge damages and losses for a sample of representative sites and for classes of problems and failures; (2) conduct in-depth evaluations of the actual mechanisms for bridge-related failure and damage due to extreme flood events for the sample sites and classes of problems and failures; and (3) interact with federal and state damage survey teams and disaster assistance teams and coordinate assessments, data, evaluations, and conclusions where practical. Task 7 of NCHRP Project 12-39 is the basis for this report. The research was performed at the University of Louisville, in Kentucky, and included a comprehensive field investigation of flood-damaged transportation structures, development of a damage classification scheme for the documentation of such damage, and analysis of apparent mechanisms of damage. This report summarizes the findings from that study and includes sections describing hydrodynamic loads on bridges, general bridge damage from the flood, scour around bridge abutments and piers, and damage to embankments and (to a lesser degree) pavements. The data for flood damage in multiple states are catalogued in an appendix to the report. The research observed that the damage from the 1993 flooding was significant and widespread. Substantial damage to bridge supports was noted, along with several structural failures. Although determination of the cause of failure was not always possible, scouring of the river bed near bridge supports and water and debris forces on bridge super- and substructures appear to be the primary reasons. The research provided a classification scheme to document which structures were damaged, the type of damage, the apparent cause of damage, and the cost estimates of the damage. The classification system can be used to document future flood events. Finally, the research provides recommendations for future activities related to flood-induced damage to transportation facilities. (A)