Lessons learned from past ice-jam floods concerning the challenges of flood mapping

Delineation of flood hazard and risk on maps is useful as a means of public education and as a basis for measures aimed at lessening future flood damages. In many northern countries, rivers and streams are prone to ice-related flooding that often results in higher water levels and more extensive damages than open-water events. Procedures and standards for analysing ice-related flooding, however, are much less common than well-established standardized approaches for the open-water events. Nonetheless, the inherent flood hazard along many northern and mid-latitude rivers is not fully represented on flood-plain, flood-hazard, and flood-risk mapping if the possibility of ice-jam floods is ignored. Fortunately, the biophysical, past-flood, and flood-envelope approaches for flood hazard can be readily applied to ice-related floods, and hydrotechnical approaches based on an improved understanding of river-ice processes have been developed. In this paper, the nature and severity of ice-jam flooding, the present status of delineating ice-related flood events, and challenges to delineating ice-related floods are discussed.