Background (Review)
The area of Sebec Lake is 10.27 sq. miles. The area of the watershed that feeds into the lake is 327 sq. miles. If all the water of a 1" inch rainfall landing on the Lake and its watershed arrived at the lake "instantaneously" the lake level would rise 33"! Obviously, this does not occur. First, not all the water landing on the watershed reaches the Lake (although anywhere from 20 to 90% of it does, depending on recent rainfall amounts and the time of year). Secondly, the rate which the watershed rain reaches the lake depends on the local terrain of the eighteen brooks and streams that feed into the Lake, recent rainfall amounts, and type of ground cover (forested, fields, etc.).
Per the July 1995 modification to the original 1983 operating agreement between Sebec Hydro (Swift River) and the Maine Department of Environmental Protection, the water levels in the lake are to be maintained as follows:
Memorial Day to the Monday after Labor Day: 323.3 - 322.8 (feet above sea level)
Monday after Labor Day to October 15th:
322.0 - 322.8 (feet above sea level)
October 15th to Memorial Day: 317.2 - 322.8 (feet above sea level)…
"…except as temporarily modified by inflows to the project area, or by operating emergencies beyond Sebec Hydro's control."
Traditionally, a set of 18" flashboards are used at the dam site to establish a pour-over level at 322.8 feet.
Some Rudimentary Considerations
Changes in the lake level are primarily determined by "sources" (all the feed-in brooks and streams, etc., and rainfall directly on the lake) and "drains" (water through each of the electricity generating turbines at the dam, water through other discharge gates, water spilling over the top of the flashboards, and of course, leakage through the boards, etc.). (Note: water loss from the Lake resulting from evaporation also occurs, but is minimal, and will be neglected in the discussion that follows.) If the total amount of water in a given time inter
