The Winter Draw-Down – Sanford Lake
Foreword: For compliance with their FERC license, Boyce Hydro monitors the reservoir pool level (as mentioned in the following article) at the Sanford dam. Lake levels upstream may be higher since there is a natural North to South flow due to the active river that runs through the lake. When the lake levels are impacted by strong winds, actual levels observed may be different. Sanford Lake is defined as an impounding reservoir. Minimum flows must be maintained and are outlined in the FERC license.
The annual winter draw-down of Sanford Lake is common for dams in Michigan and other Northern States according to the DNR and FERC. The primary driver, historically, was continued electrical production through the winter where the water flow is slowed down as most of the precipitation is tied up as ice and snow. Running in the spring with a reduced lake level enables the capture as much runoff as possible to maximize energy generation and minimizes spillage (lost electrical production). Before the dam was regulated by FERC, Wolverine Power would lower the lake level by as much as 5 feet or more.
Today the dam is regulated under FERC (starting in 1987), under a license, originally issued to Wolverine Power, transferred to Synex International when they owned the dam and now to Boyce Hydro, the current owners. A rehearing and amending license order was issued in Oct. 1998, where Article 411 defines the operating lake levels including the winter draw-down.
Normal Dam Operations
For normal operating conditions (typically from mid -spring to Dec) the normal pool elevation is to be maintained by Boyce Hydro at 630.8 feet (USGS/NGVD) and cannot fluctuate more than 0.3 foot above or 0.4 foot below the normal pool elevation, measured at Sanford Dam.
Temporary modification of the required reservoir level is allowed for emergencies and for short periods for project maintenance purposes, upon mutual agreement between the Licensee and the Michigan Department of Natural Resources.
Winter Draw-Down Operations
Under article 411, Boyce Hydro is allowed to draw down the lake between December 15 and January 15. The amount of the draw down is determined by Boyce each year, but cannot exceed 3 feet or a pool level of 627.8 feet (USGS/NGVD). In addition Boyce cannot fluctuate the level more than 0.7 feet in 24 hours.
Boyce has to completely refill the reservoir, thus ending the winter draw-down period, prior to the surface water temperature of the reservoir reaching 390F.
Safety Note: A second item is the condition of flow in the reservoir during the winter months when the drawdown is in effect. To maintain a given flow during the draw-down period, the water velocity is increased. This higher velocity inhibits the formation of a good ice layer and can lead to areas of thin ice that may not be safe to travel on, especially in the shallow areas of the lake. Take heed when electing to venture onto the lake surface during winter months.