Because of the liability involved with dams, most aquaculturists should confer with a person experienced in the design of commercial aquaculture ponds.
The Natural Resources and Conservation Service, a federal agency, offers technical assistance in pond design in most states.
This agency designs ponds that incorporate exact safety standards, well-established design criteria, and the latest conservation practices.
They are almost always approved by a professional engineer or the NRCS approval authorities. However, the NRCS can’t always respond to requests quickly because of its small staff.
Private engineers or consultants may be available for a fee. Be sure to get referrals and check any state codes for pond construction before paying for the services of a consultant. A good site survey and layout design will contain the following information:
- Location, top width, slopes, earth fill requirements, and elevation of the dam
- Emergency spillway location and size
- Shoreline dimensions
- Soils investigation report
- Dimensions of the cutoff trench and core
- Location, dimensions and elevations of the riser and barrel pipes
- Estimate of the total cut and fill in cubic yards (This figure will account for most of the expense in pond construction.)
- Watershed area and characteristics
- A bill of materials needed, including valves, concrete and lumber for the pipe ballast, pipes, vegetative materials (seed, fertilizer, lime), and any diversion pipes or valves
Pond sizing and depth:
The size of a watershed pond should be based on the availability of water from the watershed. The water should be deep enough to compensate for evaporation and seepage. Even during summer drought the water should be at least 3 to 4 feet deep. Ideally, the average water depth in a commercial watershed pond should be 4 to 5 feet.
The maximum depth should be 8 to 10 feet because of the limited size of commercial seines. Ponds that can be seined without releasing water are called “seine-through” ponds. Catfish ponds in the southeastern United States are seldom drained for harvest.
Other design features:
Since catfish and most other finfish ponds are always seined for harvesting, pond bottoms should be smooth and almost flat. Stumps and other natural obstructions should be removed. Watershed ponds need not be rectangular or square in shape.
Curvilinear shorelines will work as long as the maximum width of the pond doesn’t exceed the length of the seines used for harvesting. Most seines used by custom seiners and processing plants are 1,000 to 1,500 feet long. Ideally the seine will have some slack or curvature, so maximum pond widths should be about 700 to 1,000 feet.
The dam should have a minimum inside slope of 3:1, 4:l if economically feasible. A 4:1 slope makes easier and safer to position emergency aerators and load and unload boats. It also reduces wave erosion and makes for better seine contact with the bottom at the inside toe of the levee. However, 4:1 slopes are more expensive because there must be more earth fill.
The outside slope can be 3:1. This slope will allow for maintenance duties such as bush hogging and driving around emergency aeration equipment with pickup trucks. Occasionally it is necessary to drain a pond to capture large, seine-wary fish, repair drains or renovate banks.
Pond bottoms should be graded toward the drain at a 0.1 to 0.3 percent fall to ensure complete drainage and allow fish to concentrate in the deeper end.
Pond construction :Contractors
Pond contractors run the gamut from “fly-by-night operators” to companies that have their own engineers and use laser devices for leveling. It is always a good idea to get references for work already completed. If possible, get competitive bids from several contractors, check out their references, and then decide.
Be sure establish specifics about what is be done by whom, the quality of material and workmanship required and payment details. Some companies prefer to do turn-key jobs, from building the pond to planting the dam with grass.
Contractors are usually paid by the number of cubic yards of dirt moved so a good estimate of earth fill is needed. A welder will be needed to fabricate the drainage structures so be sure to negotiate who will be responsible for this phase of construction.
Author:
Gregory N. Whitis
