Lakebottom Changes Please note there were many changes to the lakebottom and shorelines during the flood because of sediment that moved. While the lake is at its legal level, much of the bottomland and shoreline changed because of the impacts of the 2020 flood and shoreline erosion. Please read through last week's news flash regarding changes to the lakebottom. What Is the Sanford Normal ("Legal”) Lake Level and How Is It Measured? The Sanford legal lake level elevation is 630.2 ft (+0.3/-0.4 ft). We held the lake at its winter lake level of 627.2 ft, which is 3 ft below the summer level, for approximately two weeks. All four lakes’ elevations are based on the North American Vertical Datum of 1988 (NAVD 88), not NGVD29 which was used in the FERC licenses. The Four Lakes Legal Lake Levels The April 2019 Lake Level Study and the May 2019 circuit court order establishing State of Michigan normal (“legal”) lake level elevations match the exact same elevations in the Federal Energy Regulatory Commission (FERC) licenses that Wolverine Power (and then Boyce) were prescribed to operate under until 2020 when FERC revoked the Edenville hydropower license and issued an implied surrender order on the other three dams. This same level was set to prevent detrimental impacts to private property, including septic tanks, drain fields, sea walls, docks or other pertinent physical features. It was also to avoid detrimental impacts to the environment, including currently established hydrology, drainage, and natural resources. Each lake has a different elevation, managed by its respective dam, which extends throughout the lake. The reason for the different lake levels is that rivers run downhill, and elevations increase on the Tittabawassee River as you move upstream. At each lake, we will be looking at establishing a target elevation within the legal lake level range that is optimal for operating the dam and maintaining the lake. Normal Legal Lake Levels for the Four Lakes (NAVD88*)
The summer lake level can be maintained within 0.3 feet above and 0.4 feet below the normal legal lake level. The reason for the 0.7-foot range is that it allowed the hydropower operator to raise and lower the lake to generate power. The winter drawdown may begin December 15 and must be completed by January 15. The return to summer operating levels is required when surface water temperature reaches 39 degrees Fahrenheit. FLTF will operate the lakes as run-of-river, which keeps the level the same and adjusts the flow out of the dam to match the water entering the lake. Take a look at this short video which explains run-of-river operations: How Is the Elevation Measured? What Is a Vertical Datum?
A vertical datum is a reference surface that defines zero elevation – the baseline from which all heights and depths are measured. “Sea level” is a more general term and is usually a reference to vertical datum. *The North American Vertical Datum of 1988 (NAVD 88) is the official vertical control datum established in 1991 for surveying and mapping in the United States, Canada and Mexico. It fixed the height of a single primary tidal benchmark at Father Point/Rimouski, Quebec, Canada, to minimize distortions found in older systems. Since the dams have been around since the 1920s, you will see different elevation numbers used in historical documents, but with each new version, conversions are made from one datum to the next. The actual elevation does not change, just the reference point being used. This has confused property owners in the past when their deeds stated an elevation with a previous datum. Comments are closed.
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