Bottom Screening - Benthic Barriers - An Aquatic Plant Management Method

The Western Aquatic Plant Management Society

Description of Method

A bottom screen or barrier covers the sediment like a blanket, compressing aquatic plants while reducing or blocking light. Materials such as burlap, plastics, perforated black Mylar, and woven synthetics can all be used as bottom screens. There is also a commercial bottom screen which is specifically designed for aquatic plant control.

Texel A heavy, felt-like, polyester material.

An ideal bottom screen should be durable, heavier than water, reduce or block light, prevent plants from growing into and under the fabric, be easy to install and maintain, and should readily allow gases produced by rotting weeds to escape without "ballooning" the fabric upwards.

Even the most porous materials, such as window screen, will billow due to gas buildup. Therefore, it is very important to anchor the bottom barrier securely to the bottom. Unsecured screens can create navigation hazards and are dangerous to swimmers. Anchors must be effective in keeping the material down and must be regularly checked. Resource agencies prefer that natural materials, such as rocks or sandbags, be used as anchors.

The duration of weed control depends on the rate that weeds can grow through or on top of the bottom screen, the rate that new sediment is deposited on the barrier, and the durability and longevity of the material. For example, burlap rots within two years, and plants can grow through window screening material. Regular maintenance can extend the life of most bottom barriers.

Bottom Screening Material In this photo, bottom screening material is being prepared prior to installation around a boat dock.

Bottom screens can be installed by the home owner or by a commercial plant control specialist. Installation is easier in winter or early spring when plants have died back. In summer, cutting or hand-pulling the plants first will facilitate bottom screen installation. Bottom screens may also be attached to frames rather than placed directly onto the sediment. The frames may then be moved for control of a larger area.

Advantages

Installation of a bottom screen creates an immediate open area of water.
Bottom screens are easily installed around docks and in swimming areas.
Bottom screens control 100 percent of aquatic plants.
Screen materials are readily available and can be installed by homeowners or by divers.

Disadvantages

Bottom screens are suitable only for localized control.
Harvesters, rotovators, fishing gear or boat anchors may damage bottom screens.
Bottom screens must be regularly inspected and maintained.
Improperly anchored bottom screens may create safety hazards for boaters and swimmers.
Swimmers may be injured by poorly maintained anchors used to pin bottom screens to the sediment.
Some bottom screens are difficult to anchor on deep muck sediments.
Bottom screens may not work well in swimming areas when placed over soft sediments. Swimmers tend to push the screen into the sediment when they walk on it.
Bottom screens interfere with fish spawning and bottom-dwelling animals.

Permits

States have different permitting requirements. Permits are required for many types of projects in lakes and streams. Check with your state and local jurisdictions before proceeding with a bottom screening program.

Costs

Barrier materials cost $0.22 to $1.25 per square foot. The cost of some commercial barriers includes an installation fee. Commercial installation costs vary depending on sediment characteristics and type of bottom screen selected. It costs up to about $750 to have 1,000 square feet of bottom screen installed. Maintenance costs for a waterfront lot are about $120 each year.