Lake drawdown schedules
Every autumn the lake pages here fill up with falling numbers, and every autumn people ask whether their lake is in trouble. Usually it is not. A drawdown is the scheduled lowering of a reservoir, and on most flood-control lakes it happens on the same calendar every year.
Why lakes are drawn down
A flood-control reservoir is only useful if its flood pool is empty when the flood arrives. Spring is the wettest season across most of the country, so operators lower the lake through autumn and hold it at a winter pool, leaving the maximum space above it. Some lakes have a second reason: a lower winter level reduces ice damage to docks and shoreline, and exposes the bank for repairs. Hydropower lakes may be drawn down to generate through winter demand peaks. The lower target is written into the rule curve and does not change from year to year without a public process.
Summer pool and winter pool
Most Corps lakes publish a summer pool and a winter pool rather than a single full pool. Where the agency feed gives both, the lake page uses the summer target as full pool. The difference between the two is the seasonal drawdown: about 2 ft at Table Rock, 5 ft at Lake Cumberland, 15 ft or more on some Pennsylvania and New England flood-control lakes that are essentially dry-bed reservoirs in winter. The pool elevations table on each page lists the bottom of the conservation pool so you can see the total planned range.
The autumn schedule
Drawdown usually begins between early September and mid October. Releases are increased above inflow by a set amount, the lake falls at a steady rate, often a tenth to a quarter of a foot a day, and levels off when the winter pool is reached, typically by December. The refill in spring is the mirror image: releases are cut, the lake rides up on inflow, and the summer pool is reached by May or June. On the one-year chart on each lake page this shows as a sawtooth.
Maintenance and special drawdowns
Occasionally a lake is drawn down further than the rule curve for a specific job: dam or gate repairs, dredging, aquatic weed control by exposing plants to frost, or a fish habitat project. These are announced in advance by the operating agency, last one season, and take the lake to elevations that normal operations never reach. If the level on a page is far below the bottom of the conservation pool and falling on schedule, look for a maintenance notice on the agency link.
Telling a drawdown from a drought
Three checks. First, timing: a drawdown starts in autumn on schedule; a drought decline can be under way in July. Second, the cause: during a drawdown the outflow figure on the lake page exceeds inflow because the agency is releasing on purpose; during a drought inflow has simply dried up and outflow is at its minimum. Third, the stopping point: a drawdown ends at the winter pool; a drought keeps going. A lake 8 ft down in October and holding at the winter pool is normal; a lake 8 ft down in July and still falling is not.
What it means for boating
Ramps and docks are built for the summer pool. As the lake drops, shallow ramps close first, marinas move floating docks out, and coves that were navigable in August become mud flats. Agencies publish the closing elevation for each ramp; compare it to the current level on the lake page. On lakes with a large seasonal range, plan autumn and winter trips around the main-channel ramps.