McNary Lock and Dam Temporary Spillway Weir (TSW) II

摘要

The Value Engineering (VE) analysis was conducted in August 2007. The TSWll contract was under BCOE review at the time of the study. The McNary project staff reviewed requirement to install new upper leaf sections of the operating gates, with the potential to rehabilitate existing gates to perform the same function. It was determined feasible and cost effective. Team meetings were held, the new scope was verified with the team and the design changes were implemented by the project delivery team. Impacts to dam safety have been discussed and are considered easier to resolve with the recommended action described herein than under the original design. The original design of this project was developed using a regional expert review process with the concept to utilize minimal components for the weir structures. The intent of the testing was to install low-cost and short-term weirs meant for 'temporary' use to gather performance information on the surface bypass flow they provide. The cost to redevelop a TSW design was anticipated to cost more in redesign than could be recovered in reduced initial costs. The intent of the prototype work was also to gather biological performance data as quickly as possible. Any conceivable design changes would result in additional regional consultation, physical modeling and demonstrations, adding substantial time and defeating the purpose of the project. Therefore, this study focused on the most costly element of the project, the fabrication of two new upper leaf gate sections. This function was to 'close flow' over the TSW, and it was determined this function could still be accomplished using existing gates, rehabilitated to maintain functional reliability, and modified to shift the seals to fit to the new TSW crest.