Lake Drawdown Methods

A lake drawdown is a method of reducing the water level of a lake or reservoir for needs including power generation, irrigation and aquatic weed control. Lake drawdowns are designed to expose aquatic weeds to extreme temperatures that damage and can eventually prove fatal to aquatic weeds.

  1. Water Level

    • A lake drawdown is usually planned months in advance. and some states require permits from local and state authorities to complete the process. The level of the water is lowered over a long period of time, which allows the non-problematic plant and animal life of the lake to become accustomed to the changing water level. This process is usually completed in fall to winter when the lake or reservoir is used little by humans and animals and when plants are over wintering.

    Plants

    • The control of aquatic weeds is one of the most common uses of the lake drawdown technique, in which aquatic plants that do not have the ability to over winter successfully are exposed to freezing temperatures. Aquatic weeds, such as the Eurasian Watermilfoil, have no over wintering parts, such as viable seeds and tubes, meaning freezing temperatures can damage the root system of the plant and cause the removal of the plant from an exposed area. The exposure of a lake bed also exposes sediment and removes moisture from the lake bed causing damage to targeted aquatic weeds.

    Use

    • Drawdown's is often carried out in lakes and reservoirs with equipment capable of lowering the water level, such as dams used for flood control and power generation. During periods of drawdown, maintenance can be completed on lake equipment, such as docks and boat launches, however these periods can cause economic problems because of the reduction in the use of boat launches and docks. Lake drawdown methods often attempt to raise the level of water in a lake or reservoir to the recommended level by the summer months for ecological, economic and aesthetic reasons. A lake drawdown must be carried out on a regular basis to maintain levels of aquatic weeds. If drawdowns are not completed regularly, aquatic weeds can reestablish colonies in control areas.

    Problems

    • Using lake drawdown methods to control aquatic weeds can cause problems for colonies of aquatic plants and animals that are not targeted for control, according to the New Hampshire Department of Environmental Studies. Freeze damage to non-targeted plants through exposure to low temperatures, along with damage to animals, such as frogs and mussels that spend winters in exposed areas of a lake. Other problems caused by lake drawdown methods include blooms of algae that can occur when the lake or reservoir is brought back to its usual level after a drawdown.