|Langston University Aquaculture|
Spillway Screen Construction
By Kenneth W. Williams
The spillway screen is one of the most important and least expensive tools used in pond management. It is of little benefit to stock, feed and manage ponds only to have fish leave the pond over the emergency spillway during the first heavy rain. The spillway screen also prevents unwanted or undesirable fish from entering the pond through the spillway. Fish are attracted to currents of water and will follow a current up or down stream. Green sunfish, bullhead catfish and other species have been found stranded in fields in less than an inch of water, far from the nearest pond or stream after heavy runoff rains. Loss of fish populations over emergency spillways during runoff rains is one of the most common events that upsets the balance and angling quality of otherwise well managed ponds. A well constructed spillway screen can protect your investment of time and money in pond management.
Spillway Screen Construction
1. Place the screen on the pond side edge of the spillway. The spillway should be relatively level and grass covered.
2. Dig a trench about 6-8 inches deep and about 6 inches wide across the spillway and 1-2 feet into each side of the spillway. The bottom edge of the screen will be placed in this trench.
3. Set "T" posts, 2-4 ft. in length in the trench and across the spillway.
4. Attach a water resistant mesh to the posts. The bottom of the screen should be below ground level. 1in. X ˝ in. plastic coated welded wire is an ideal material for this use. Do not use mesh sizes larger than 1in. X 1in. Or smaller than ˝ in. X ˝ in. Spillway screen height should be 18 - 36 inches tall. Extend the screen well into the sides of the spillway to anchor the structure and to prevent fish from going around the screen.
5. Attach a strip of 1/8 - 1/4 in. plastic or welded wire mesh to the bottom inside edge of the spillway screen. The mesh should be tall enough to extend 6-8 inches above ground level. The smaller mesh helps retain young fish and prevent larger numbers of small, "wild" fish from entering the pond.
6. Fill in the trench, making sure that the bottom of the screen is covered and below ground level.
Trash guards can be constructed to protect most spillways or drain pipes.
It may be necessary to construct a trash guard on the pondward side of the spillway screen. The trash guard can be positioned 1-2 feet in front of the spillway screen to catch large limbs, logs or other debris that may wash into the screen and cause damage.
Trash guards can be constructed of 3/8 in. or larger re-bar, iron pipe or other sturdy material.
Bars should be spaced about 2-3 inches apart and stand 1-2 feet above spillway level.
Screen All Water Inlets
It is often advisable to construct screens across small ephemeral or permanent streams that enter the pond. Even streams that only flow seasonally or during rains can provide an entry point for wild fish or an escape exit for pond fish.
Some ponds are filled through pipes from a larger reservoir. Fish from the reservoir, particular larval-sized and young fish, can swim through the pipes and enter ponds. If undesirable species are in the reservoir, they may become established in all ponds filled by the reservoir. Saran cloth (a fine mesh synthetic fabric) can be attached over pipe outlets to prevent entrance of undesirable fish. Saran cloth can be purchased from aquaculture supply dealers.
Spillway Screen Maintenance
Keep leaves, grass, branches and other debris from collecting on spillway screens and trash guards. Blocked screens can topple over during heavy rains allowing unrestricted fish movement; or prevent the emergency spillway from operating as designed.
A well constructed spillway screen should limit fish migration into and out of the pond for many years and add to the pond management tools that can be used to maintain optimum production in sport fishery and food production ponds.
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