Cofferdam Risk Review Assessment for River Management at the Keeyask Generating Station in Northern Manitoba, Canada

摘要

The proposed Keeyask Generation Project is a 695 megawatt hydroelectric generating station (GS) to be constructed at Gull Rapids on the Lower Nelson River. This project is located about 725 km northeast of Winnipeg, Manitoba. It will involve the construction of nine cofferdams and two rockfill structures to facilitate river management for the construction of the Keeyask GS. One aspect to consider in the design of these temporary structures is the selection of a reasonable flood magnitude, designated as the Construction Design Flood (CDF), which could occur during their service lives. In this study, an approach was taken to apply the concept of risk management to assist in identifying the optimum design flood for each structure. This approach seeks to minimize the total probable cost of the structure (including construction cost and probable damage costs/losses). The analysis takes into consideration the construction feasibility, and incremental costs that would be incurred to build these temporary structures to higher (or lower) design levels, and the damages and likelihood of incurring these damages should these design levels be exceeded. It also considers possible options to allow the timely raising up of the cofferdam crest if sufficient warning can be provided in advance of high flood events. This type of risk informed approach is becoming more common in the hydropower industry, not only in the assessment of temporary river structures, but also in the evaluation and selection of final Inflow Design Floods for a project.