Drawdown
Reviewed • Standard Hydrology Definition • WaterLakeLevel
# Drawdown
A drawdown is the physical lowering of a waterbody's surface elevation. Drawdowns occur through two distinct mechanisms:
Dam authorities intentionally open spillway gates or hydroelectric penstocks to release water downstream. Common reasons include:
- Winter Flood Preparation: Lowering the lake in autumn to catch winter runoff.
- Aquatic Weed Control: Exposing shoreline vegetation to winter freezing temperatures to kill invasive milfoil or hydrilla.
- Infrastructure Maintenance: Permitting shoreline residents to repair seawalls, inspect dock pilings, and dredge boat slips.
Occurs when evaporation and municipal releases exceed watershed rainfall over extended periods.
The deliberate or natural reduction of a lake or reservoir water surface elevation.
What Is a Lake Drawdown?
A drawdown is the physical lowering of a waterbody's surface elevation. Drawdowns occur through two distinct mechanisms:
1. Intentional Operational Drawdown
Dam authorities intentionally open spillway gates or hydroelectric penstocks to release water downstream. Common reasons include:
- Winter Flood Preparation: Lowering the lake in autumn to catch winter runoff.
- Aquatic Weed Control: Exposing shoreline vegetation to winter freezing temperatures to kill invasive milfoil or hydrilla.
- Infrastructure Maintenance: Permitting shoreline residents to repair seawalls, inspect dock pilings, and dredge boat slips.
2. Drought-Induced Drawdown
Occurs when evaporation and municipal releases exceed watershed rainfall over extended periods.
Explore Other Hydrology & Boating Terms
Acre-Foot
A volumetric water unit representing the amount of water required to cover one acre of land to a depth of one foot.
Conservation Pool
The volume of water stored in a reservoir dedicated to beneficial uses such as drinking water, power, and recreation.
Datum
A reference surface or mathematical baseline from which vertical elevations or geographic coordinates are reckoned.
Dead Pool
The critical low-water elevation below which water cannot flow downstream through gravity outlets.
Evaporation Loss
The invisible volumetric loss of water from a lake surface into the atmosphere caused by heat, sun, and dry winds.
Flood Pool
The temporary storage capacity above full conservation pool designed to capture floodwaters and prevent downstream damage.