Dam and Levee Safety Risk during Remedial Construction

Structural modifications to dams and levees can create life safety risks during the construction period. It is important for all parties involved to understand the potential risk, evaluate methods to mitigate risk, and consider the risk when making decisions. Most importantly, it is critical to always strive to “do no harm” and prevent activities that could potentially increase risk. This case history will provide examples of conditions that can lead to increased risk during construction including excavations that lower the crest of a dam or levee, excavations at the toe of an embankment, rapid embankment construction, blocked bypass tunnels, spillway modifications, excavations for outlet culverts, and damage from grouting. A key component of many construction projects is a temporary cofferdam to protect the work area from flooding. Cofferdams have a high potential to create risk during construction. An important step to help prevent increasing risk during construction is to have multiple constructability reviews during the development of the project design. If the potential for construction risk is properly identified, the risk can often be mitigated or reduced. Decision-maker involvement is necessary to assure risks are understood and proper decisions can be made. Several case histories are presented to demonstrate how risks during remedial construction are evaluated and incorporated into decision-making.