Moderate water level variations which follow a long term "normal" pattern are not as likely to have as much negative effect in this regard.ĭrawdowns have been used in some states to reduce dense populations of aquatic plants, especially nuisance exotic species, via desiccation and freezing damage. Drawdowns, which expose significant areas of fine sediment to drying, can result in release of phosphorus when the lake is re-filled and can expose previously stable sediments to wind and wave action, temporarily increasing turbidity and nutrient concentrations in the lake. Moderate amounts of shoreline erosion can promote growth of algae attached to rocks and plants, but usually this growth is more controlled by sunlight, amount of wave energy or disturbance, and the lakes' phosphorus and nitrogen levels. Siltation effects on plant growth are usually seen in coves and other protected areas and usually in less than 5-6 feet of water. Increased siltation along a lake shoreline is often a result of some new sediment supply, usually relatively nearby. This is especially true for fairly steep shorelines where erosion below this cobble layer undercuts bank stability. Major level fluctuations can actually aggravate shoreline erosion in some areas if wave or ice action is concentrated below the level where cobbles and boulders have accumulated over the years. This level should be chosen to avoid ice contact with unstable or sensitive shoreline but not so low as to cause problems with wildlife habitat or uses such as water intake pipes.
Ice damage can often be reduced by attaining a stable, slightly lower water level in the fall and actively managing the dam to keep at the target water level through the winter season and into the spring. Are drawdowns an effective way to control shoreline erosion, siltation, and aquatic plant growth?ĭrawdowns are usually not useful in controlling shoreline erosion unless they are the only way to prevent significant springtime ice damage, which aggravates the process of soil loss by root damage and scouring. Options usually considered by lake associations, towns and others who own dams are for variations of only a few feet at most. Most lakes are not suited to benefit by this technique. The ability to rapidly re-fill the lake with relatively low phosphorus water.The ability to drawdown the lake (dam capacity) sufficiently to export a large proportion of the lakes' water and thus much of its phosphorus in a short period of time, and.Very high phosphorus concentrations which peak at a specific time of year, typically late summer,.For such drawdowns to have a beneficial effect on water quality, the lake has to have: Some lakes are managed to reduce high phosphorus levels with significant (6 feet+) drawdowns, typically in September of each year.
What is the effect of drawdown on a lake? Is there a beneficial effect on the water quality? Here "drawdowns" (significant, rapid reduction in water levels, usually for a limited duration) are distinguished from more usual water level management, which targets a narrow range of water level over the entire year. They include effects on water quality of the lake and the area downstream of the lake, on wetland conditions, and on plant and animal species and their habitats. However, there are a number of environmental questions often asked, and here are some thoughts about them.Įffects of water level management on a lake can be numerous. This is often hard to answer, as the issues surrounding managing water levels can often more related to conflicts over use and other "social" issues than to environmental issues. The Lakes Assessment Program is frequently questioned about what water level is right for a particular lake. Related page: Hydropower and Dams (including petition to set water levels/minimum flows) Some Common Questions