Selecting Flow Frequency Distributions for Designing a Small Low-Head Dam Removal Cofferdam

Abstract

One of the first steps in removing a dam is the construction of a cofferdam so that demolition activities can proceed safely. The time necessary for removing a small low-head dam is often on the order of a few months. To minimize the cofferdam construction cost, these dams are generally removed during the low flow months of the year. Therefore, design of cofferdams should be based on river flow series during the dam removal period, rather than the entire year. In this study, available hourly and daily average records at the recently removed Marmot Dam on the Sandy River, Oregon are analyzed for four dam removal periods, varying from 1 to 4 months (July through October).