An Illustrated Guide for Monitoring and Protecting Bridge Waterways Against Scour

This report is a well illustrated and practical guide intended to aid engineers and engineering technicians in monitoring, maintaining, and protecting bridge waterways so as to mitigate or prevent scour from adversely affecting the structural performance of bridge abutments, piers, and approach road embankments. The scour processes affecting the stability of these components of bridge waterways are described and illustrated. Methods for monitoring waterways, and the various methods for repairing scour damage and protecting bridge waterways against scour are described. This report focuses on smaller bridges, especially those in Iowa. Scour processes at small bridges are complicated by the close proximity of abutments, piers, and waterway banks, such that scour processes interact in ways difficult to predict and for which reliable design relationships do not exist. Additionally, blockage by woody debris or by ice, along with changes in approach channel alignment, can have greater effects on pier and abutment scour for smaller bridges. These considerations tend to cause greater reliance on monitoring for smaller bridges. This guide is intended to augment and support, as a source of information, existing procedures for monitoring bridge waterways. It also may prompt some adjustments of existing forms and reports used for bridge monitoring. In accord with increasing emphasis on effective management of public facilities like bridges, it includes an example report format for quantitative risk assessment applied to bridge waterways. Quantitative risk assessment is useful when many bridges have to be evaluated for scour risk and damage, and priorities need to be determined for repair and protection work. It is expected that bridge inspectors will implement this guide as a concise, handy reference available back at the office. It also likely may be implemented as an educational primer for new inspectors who have yet to become acquainted with waterway scour. Additionally, it may be implemented as a part of the process to check whether existing bridge-inspection forms or reports adequately encompass bridge-waterway scour.