|Langston University Aquaculture|
By Kenneth Williams
Location, soil type and design are critical to successful pond construction. Expertise and experienced consultation can be obtained at no charge from your county Natural Resource Conservation Service (NRCS) office. The NRCS can determine your soil type, suggest appropriate locations for ponds on your property, assist in pond design and survey the pond site before actual pond construction begins. NRCS provides current information on government cost share programs for pond construction. Most offices also have a list of reputable construction companies that build ponds. Consultation with the Natural Resource Conservation Service is the first step on the way to a long lasting, productive pond.
Determine state regulations that may apply to the proposed pond before work begins. This consideration becomes very important if pond construction will result in blocking a stream and/or affecting down stream water flow.
Before building the pond it is important to determine its primary use. Pond use may indicate need for specific design criteria.
A pond used for commercial aquaculture is usually constructed as a rectangle with a smooth sloping bottom and a depth of no more than 6-8 feet. Although conventional pond construction calls for all side slopes to be 3:1 ( 1 foot of drop in 3 feet); practical experience at Langston University suggests that a 4:1 slope is easier to maintain and may be more cost effective. Aquaculture ponds require a bottom drain and at least 1 pond dike that has an all weather road capable of supporting a semi truck.
Livestock ponds are best constructed with a freeze proof watering trough built below the dam. The pond should be fenced to force livestock to use the watering trough or at minimum, fenced enough to force animals to use a selected and prepared part of the pond. A heavily graveled drinking area constructed on a shallow sloping bank of the pond can help prevent erosion and other pond problems caused by livestock (fig.2.). Access can be restricted further using a floatable electric fence or other barriers.
To prevent erosion and a muddy pond keep livestock away from the pond until grass cover is well established.
Recreational fishing ponds
Recreational fishing ponds can be constructed with the requirements of fish and anglers in mind. Minimum size should be ˝ acre in surface area and 10 feet deep in about 1/4-1/3 of the pond. Brush or tire shelters can be placed strategically in the pond to encourage forage fish survival and reproduction and to attract larger predatory fish. Gravel spawning beds or boxes can be placed in the pond to improve bass and bluegill reproductive success. Berms, peninsulas and islands are often constructed in recreational ponds to improve fishing access or provide wildlife habitat (fig. 3). A bottom drain is an important fish and aquatic vegetation management tool. It should be installed in ponds that will be managed for quality fishing. Drains allow water level to be lowered for leak repairs, nuisance plant control and manipulation of fish populations.
Watershed and soil requirements
The watershed is the land area that ultimately drains into the pond. The amount of watershed needed to maintain each acre foot of pond water depends on annual rainfall, evaporation rate and soil type. A typical Oklahoma pond 1 surface acre in size contains about 4 acre feet of water. In parts of southeastern Oklahoma as little as 5 acres of watershed are needed per acre foot of pond. In far northwestern Oklahoma as much as 50 acres of watershed are required per acre foot of water. Ponds in central Oklahoma require 10-15 acres of watershed per acre foot of water. Too little watershed results in a pond that rarely or never fills to its proper level. Too much watershed and water is often flowing out the auxiliary spillway or even washing away the dam. It is usually unwise to attempt to dam flowing or intermittent streams.
Pond site selection
A pond situated near the home has many advantages. It can be viewed which is enjoyable and pond access is easier to control. Fishing and feeding the pond is more convenient as well. Ponds situated near the home also can be used for fire protection by constructing a dry hydrant.
For those interested in seclusion and wildlife, a pond located in a woodland may be the best choice.
Consider laws regarding "attractive nuisance" before locating the pond in an area with easy public access, especially access for children.
Consult with Natural resource Conservation Service personnel or other qualified engineers before damming streams or canyons. Fish populations are difficult to manage in ponds constructed by damming streams because many species of unwanted wild fish will invade the pond.
Do not locate ponds downstream from potential pollution sources such as animal feed lots, fertilized agricultural fields or surface mines. Excess nutrients from intensive animal operations or farming activity can cause eutrophication of the pond with resulting heavy algal and rooted aquatic vegetation growth. In extreme instances, most or all pond life may die.
Surface mining operations can pollute ponds with acidic water lethal to many aquatic organisms or contaminate them with heavy metals.
Salt water from abandoned oil wells also has the potential, when water tables are high, to spill into streams and watersheds. Salinity levels in ponds affected by well leakage can reach levels lethal to fish and other aquatic organisms.
Avoid constructing ponds underneath power lines. An errant cast could lead to angler electrocution. Also, before construction, check for buried cables or pipelines.
Dig the pond or construct the dam in a location that requires the least amount of excavation. Moving earth can be expensive.
Ponds should be constructed in soils containing at least 20 percent clay. Ponds constructed in sandy or gravel laden soils often leak and consequently will not maintain an adequate water level. Rock outcroppings also are a major source of leaks in ponds. Water travels through cracks and fissures in the rock and can quickly lower pond water level. Soil tests before pond construction can measure clay content and usually determine if potential geological problems exist. Conserve all good, on-site clay for lining the pond.
Always conserve topsoil during construction to re-spread over bared earth surfaces after the pond is completed. Topsoil will help to quickly re-establish vegetative cover and prevent erosion.
Watershed ponds in Oklahoma are constructed to have a depth of at least 10 feet in about 1/4-1/3 of the pond area. This depth allows the pond to maintain an adequate water supply during hot summer months and is deep enough to prevent winter kill from ice and snow cover in the winter. Greater pond depths are needed if the pond is to be used extensively for irrigation. Evaporation rates in Oklahoma can exceed 60 inches annually with most evaporation occurring during the summer .
A well constructed dam will contain an earthen core. The core is a trench dug the length of the dam and deep enough to reach into subsurface clay or other water impervious stratum. It should be 8 feet wide at the bottom of the trench and have sloping sides no steeper than 1:1. The core is filled with clay. The clay is put down in approximately 8 inch layers and compacted.
Dam width and slope
Top width of the dam depends on dam height. Minimum top width for dams 10 feet high or less is 6 feet. Minimum top width increases with dam height (table ). Dam top width should be at least 16 feet if it is to be used as a road.
Side slopes on the dam should be at minimum, 3:1 for most soil types. All slopes inside the pond should be about 4:1 with no shallow areas less than 3 feet deep to help prevent excessive aquatic vegetation growth.
Soil settling will occur during most types of pond construction. Amount of pond foundation settling depends on soil type and how well the soil in the dam was compacted. Allow about 5% for compacted soils and 10% for ponds that have not been roll compacted. For example, a small dam with a desired height of 10 feet should be constructed 11 feet tall to allow for soil settling. Also construct top width to 18 feet if desired width is 16 feet. Pipes and trickle tubes will also settle.
Freeboard is the distance from the water elevation to the top of the dam. Freeboard for most small ponds, (less than 660 feet long), should be at minimum 1 foot to prevent overtopping the dam from wave action or other causes. At least 2 feet of freeboard is required for ponds up to one-half mile long. Contact your county NRCS office for safe design criteria.
A trickle tube is installed through the dam during construction. The tube acts as the primary pond spillway, draining away excess water from common storm events, spring flow or seepage. Hooded-inlet trickle tubes are the least expensive and most commonly used type of trickle tube design. A disadvantage of the hooded-inlet design is that it can not be used as a drain.
The hood of the pipe is formed by angling the cuton the inlet side of the pipe. Flow efficiency can be increased by attaching a vertical metal plate to the pipe opening to prevent vortex formation.
Pipe diameter is extremely important and is determined by estimating needed discharge capacity and total head. Consult with Natural Resource Conservation Service personnel if unsure of the proper diameter for your application. A trickle tube too small in diameter will allow water to flow out the emergency spillway too often and drain excess water from the pond too slowly resulting in potential spillway erosion and premature dam failure. Trickle tubes that are larger than necessary efficiently remove water but unnecessarily increase construction cost.
A pond drain is a valuable addition to any pond. Drains can be used to:
A drain pipe can be part of a drop-inlet trickle tube as shown below or can be a separate pipe extending through the dam. A separate drain pipe and trickle tube has the disadvantage of increasing construction cost and increasing the possibility of leaks through the dam along pipes.
A swivel riser pipe is adequate for small ponds. The riser pipe can be lowered from the surface to the bottom of the pond to remove some or all of the water .
A riser with capped outlets at several levels can be constructed at the toe of the dam on the downstream side (fig. ). This configuration has the advantages of easy maintenance and operation, however, provision must be made to prevent unintentional pond draining.
The drain is a valuable pond management tool. Lowering pond water level by about 4 feet in late summer can be very beneficial. Aquatic vegetation is exposed and killed back reducing the need for herbicide or other control measures. Cattails, water lilies and other hard to control species are easier to dig out on dry exposed soil after pond water level is lowered. Allow pond to begin refilling in late October.
Also the draw down forces forage fish out of vegetative cover and into open water where they are more likely to be eaten by bass or other predatory fish. This improves bass growth and helps sends them into the winter months in a healthy condition. Bluegill or other forge fish numbers are reduced which helps prevent over population and stunting.
During drought years it may not be advisable to lower pond level if the pond is filled only from water shed runoff. Look to weather trends to determine when this management practice can be used effectively.
Install antiseep collars to prevent seeps from forming along the length of trickle tubes or drain pipes going through dams. Water channels can form along unprotected pipe and cause serious leaks or even failure of the dam. Antiseep collars are plates that extend at least 24 inches perpendicular from the centerline of the pipe . For dams less than 15 feet high, 1 antiseep collar is sufficient. Use 2 or more equally spaced antiseep collars for dams higher than 15 feet.
The emergency spillway is constructed at one end of the dam and guides flood water around and away from the pond dam. It is designed to handle peak flows from storms. The amount of water the spillway must be designed for is based on storm frequency and duration, pond storage capacity, trickle tube capacity, watershed size, and dam height. For dams less than 20 feet high and draining fewer than 20 acres, the spillway is designed to handle the water from a storm that is likely to last 24 hours and occur at about 10 year intervals. Larger dams and drainage areas require greater capacities to handle less frequent 25 or 50 year storm events. The spillway should be designed by NRCS personnel or experienced contractors.
A spillway screen can be erected across the emergency spillway to prevent loss of fish during periods of overflow. See LU fact sheet "Spillway Screen Construction". For details.
Emergency spillways should be gently sloped from the inlet side up to the level area of the spillway. Beyond the level area, the spillway slopes around and beyond the dam. Allowable degree of slope is determined by soil type and vegetative cover. Poor cover and erodible soils require a flatter slope to reduce water velocity and prevent spillway erosion.
The spillway should be constructed to divert water away from the dam. Wing dikes are sometimes necessary to divert water flow and protect the dam .
Re-vegetating pond spillway, dam and banks
Seed or sod the spillway as soon as possible after construction. A dense stand of grass is the best protection from erosion. In Oklahoma, rye or wheat can be sown and established quickly in fall and winter. In spring, seed or sprig Bermuda grass. Fertilize and water the grass to establish a dense healthy stand over the entire spillway. Do not plant or allow trees or shrubs to become established on the pond dam. Tree roots open channels in the dam that can eventually result in leaks or dam failure; especially as old roots die and rot.
The dam slopes and top as well as any bare areas of soil around the pond also should be seeded or sodded to prevent erosion. A pond that is not revegetated can be seriously damaged or destroyed by even moderate rainfalls. The spillway and dam can be eroded and soil in the watershed can be washed into the pond, refilling much that was excavated. Re-vegetation is one of the most important steps in successful pond construction.
Construction cost depends on several variables:
Average cost of a 1 acre pond in Oklahoma is $2,000 - $5,000, based on moving an average of 3,000 cubic yards of earth at a cost of $1.10/cubic yard. Earth moving cost can be as much as $1.60 / cubic yard. Actual cost depends upon factors listed above. Ponds built on gently sloping pasture land are usually less expensive per surface acre than ponds constructed in steep forested terrain.
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