Silver Lake Dam: Root Cause Report on the May 14, 2003 Operation of the Fuse Plug Spillway and Subsequent Channel Erosion Resulting in the Uncontrolled Release of Silver Lake

Silver Lake is located on Michigan’s Upper Peninsula, approximately 22 miles northwest of Marquette, Michigan. Silver Lake is the uppermost impoundment of the Dead River Hydroelectric Project (FERC Licensed Project No. 10855) and is used to store spring runoff for regulated releases and power generation later in the year. There is no power generation capability on Silver Lake; the power generation takes place at the downstream Hoist and McClure Hydroelectric Developments.

In 2002 Upper Peninsula Power Company completed upgrades to Silver Lake to increase its spillway discharge capacity to accommodate flows up to the Probable Maximum Flood (PMF). Included in these upgrades were the raising of the crest elevations of the existing dike structures, the removal of one of the dikes (Dike 2) and, in its place, the construction of a new fuse plug spillway.

On Wednesday May 14, 2003 the recently completed emergency fuse plug spillway at Silver Lake operated as a result of inflows from rain that was experienced in the area on Sunday and Monday, May 11 and 12. The fuse plug embankment washout introduced sustained flows to the
fuse plug spillway channel. As a result of these sustained flows, which reached approximately 5,000 cfs (prior to erosion of the channel), and which lasted several hours, the fuse plug spillway channel experienced erosion that extended well below the fuse plug embankment foundation. The final erosion channel extended downstream along the entire length of the spillway channel and upstream into Silver Lake. The extension of this erosion into Silver Lake resulted in the release of an additional volume of water, causing peak discharge flows out of Silver Lake to increase to between 30,000 and 32,000 cfs. The volume of water released from Silver Lake, approximately 25,300 acre-feet, was largely contained in the Dead River Storage Basin – the reservoir impounded by Hoist Dam, and whose presence attenuated the discharges downstream. Peak discharge flow rates from Hoist Dam reached approximately 7,600 cfs.

Washington Group International, Inc. (Washington Group) was retained to perform an evaluation of events leading up to and following the breach of the Silver Lake fuse plug spillway. The result of the evaluation is this report on the root causes of the operation of the fuse plug spillway and the release of Silver Lake.