6
To be profitable, an aquaculture pond must be sited properly and designed for efficiency. An inac- cessible location, leaks in the pond, poor seining conditions, or lack of good quality water will doom an aquaculture enterprise to failure. Ponds do not have to be built on land as flat as the delta regions of western Mississippi, southeastern Arkansas or northeastern Louisiana. There are more than 20,000 acres of catfish production in slightly hilly areas of Mississippi, Tennessee, Alabama, Georgia and Illinois. On rolling terrain the annual rainfall may be enough to completely fill and periodically recharge production ponds. Such watershed systems are not so dependent on ground- water. They also act as flood con- trol reservoirs and can greatly reduce erosion on land previously scarred with unsightly gullies. Watershed ponds are constructed by building dams across valleys to form reservoirs that store rainwa- ter (Fig. 1). Some aquaculture facilities have large reservoirs that, in turn, fill smaller ponds with captured runoff. Watershed ponds can be cheaper to build than levee ponds on flat land and they don’t require expensive wells. A disadvantage of deep watershed ponds is that they are prone to strati- fy. However, most aqua- culture production ponds are routinely aer- ated and adequate aera- tion will break up daily stratification. Water supplies Watershed ponds are usually filled by surface runoff from an area above the dam. This area, the watershed, can be estimated by draw- ing a line on a topo- graphic map that fol- lows the ridge lines forming the perimeter of the watershed (Fig. 2). The watershed area and pond acreage can be roughly estimated using a planimeter. Field engineers with the Natural Resources Conservation Service (NRCS) should be able to help landowners with this calculation. The entire watershed area of a proposed pond must be investi- gated to determine whether runoff might be polluted. Large chicken and hog farms, extensive areas of row crops, grazing live- stock, industrial sites and other water quality hazards in the watershed could preclude the VI PR September 2002 Revision SRAC Publication No. 102 Watershed Fish Production Ponds Guide to Site Selection and Construction Gregory N. Whitis* *Alabama Cooperative Extension System Figure 1. Watershed pond. 150 Figure 2. Determining the possibility of a potential pond site and its respective watershed. The dashed lines indicate the boundaries of the watershed. Numbers are elevations in feet.

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Page 1: Watershed Fish Production Ponds - Extension...in slightly hilly areas of Mississippi, Tennessee, Alabama, Georgia and Illinois. On rolling terrain the annual rainfall may be enough

To be profitable, an aquaculturepond must be sited properly anddesigned for efficiency. An inac-cessible location, leaks in thepond, poor seining conditions, orlack of good quality water willdoom an aquaculture enterprise tofailure.Ponds do not have to be built onland as flat as the delta regions ofwestern Mississippi, southeasternArkansas or northeasternLouisiana. There are more than20,000 acres of catfish productionin slightly hilly areas ofMississippi, Tennessee, Alabama,Georgia and Illinois. On rollingterrain the annual rainfall may beenough to completely fill andperiodically recharge productionponds. Such watershed systemsare not so dependent on ground-water. They also act as flood con-trol reservoirs and can greatlyreduce erosion on land previouslyscarred with unsightly gullies. Watershed ponds are constructedby building dams across valleys toform reservoirs that store rainwa-ter (Fig. 1). Some aquaculturefacilities have large reservoirsthat, in turn, fill smaller pondswith captured runoff. Watershedponds can be cheaper to buildthan levee ponds on flat land and

they don’t require expensivewells. A disadvantage of deepwatershed ponds is thatthey are prone to strati-fy. However, most aqua-culture productionponds are routinely aer-ated and adequate aera-tion will break up dailystratification.

Water suppliesWatershed ponds areusually filled by surfacerunoff from an areaabove the dam. Thisarea, the watershed, canbe estimated by draw-ing a line on a topo-graphic map that fol-lows the ridge linesforming the perimeterof the watershed (Fig.2). The watershed areaand pond acreage can

be roughly estimated using aplanimeter. Field engineers withthe Natural ResourcesConservation Service (NRCS)should be able to help landownerswith this calculation.The entire watershed area of aproposed pond must be investi-gated to determine whetherrunoff might be polluted. Largechicken and hog farms, extensiveareas of row crops, grazing live-stock, industrial sites and otherwater quality hazards in thewatershed could preclude the

VIPR

September 2002Revision

SRAC Publication No. 102

Watershed Fish Production PondsGuide to Site Selection and Construction

Gregory N. Whitis*

*Alabama Cooperative Extension System

Figure 1. Watershed pond.

150

Figure 2. Determining the possibility of a potential pondsite and its respective watershed. The dashed lines indicatethe boundaries of the watershed. Numbers are elevations infeet.

Page 2: Watershed Fish Production Ponds - Extension...in slightly hilly areas of Mississippi, Tennessee, Alabama, Georgia and Illinois. On rolling terrain the annual rainfall may be enough

operation of a watershed pond.Good watersheds contain well-established, undisturbed vegeta-tive cover such as timber or grass.A buffer zone of grass or sodshould surround the pond, espe-cially if there are croplands, con-centrated feed lots, or largedenuded areas in the watershed. Springs or streams can be used asa water source. Large streamsflowing through watersheds mayrequire some kind of diversiondevice. Streams can be contami-nated with wild fish or man-made pollutants, so it’s a goodidea to get the water tested beforeconstruction begins. Also, largeinflows of soft water in acid soilsmay hinder any long-term reme-dial effects of liming.

Proper site selectionWhen choosing a pond site, con-sider the soil type, topography,characteristics of the watershedand, of course, safety. A powersupply for aeration equipmentmust also be available.

Soil type

The suitability of a pond site ismostly dependent on whether thesoil will hold water when com-pacted by heavy machinery dur-ing the construction process. Soilcomposition ranges from puresand to heavy clay. Soil type canvary drastically within a singlesite. The pond area should con-tain a relatively impervious layerof clay or silty clay soils. Coarsesoils containing large amounts ofsand and/or gravel are unsuit-able. If the soil can be formed intoa tight ball that maintains itsshape or is moldable, it is suitablefor pond construction. A rule ofthumb is that soil must contain atleast 20 percent clay.If there is poor soil over a portionof the pond, large amounts of claymay have to be trucked in tomake it impervious, and thatcould make construction costs toohigh. Also beware of limestoneareas. They may have sinkholesor caverns just beneath the sur-face. Ponds built in limestoneareas have been known to draincompletely overnight!

The type of soil in the dam area isespecially critical for safety rea-sons. Dam seepage can lead todangerous dam failures. TheNRCS and some private agricul-tural and civil engineers havehydraulic probes that can samplesoils several feet down. A backhoeswipe also will help in analyzingsoil. Cutoff trenches and damcores must be located where soilhas a high clay content so theywill remain structurally soundduring the life of the pond.

Topography

The objective is to locate a pondwhere the largest storage volumeis obtained with the least amountof earth fill needed for the dam.Locating a dam between two gen-tly sloped ridges in front of abroad section of valley is ideal.The less pond excavation needed,the more feasible the site and thelower the construction costs.

Safety

Do not locate large dams wheretheir failure could cause loss oflife, injury to people or livestock,damage to buildings, or the inter-ruption of the use of railways,highways or public utilities.Aquaculture ponds are not asdeep as public reservoirs and damfailures are rare. However, if thesite involves some degree of riskto the public, a professional engi-neer with experience in dam con-struction should be consulted.Almost every state has a damsafety law. Contact an Extensionfisheries specialist or aquaculturistfor more information.The location of buried pipelines,electrical lines or telephone wiresshould be researched before anyconstruction begins. Breaking afiber optic communication cablewill put most pond constructionbudgets into the red!

Determining an adequate watershed area

The amount and quality of waterentering the pond from the sur-rounding watershed is dependenton several factors—slope, soiltype, vegetative cover and theamount of precipitation. There are

no set criteria for determiningwhether a watershed is sufficientfor a given size pond, but thereare some general rules.Watersheds containing mostlypasture with heavy clay soils maysupply 1 acre of water for every 5acres of land. At the otherextreme, timberland on sandy soilmay require a ratio of 30 acres ofland to 1 acre of water. Excessively large watersheds canbe just as problematic as limitedwatersheds. Too much water maydilute water amendments such aslime and salt, allow valuable fishto escape during floods, and makeit necessary to install expensiveflood or diversion devices. Pondswith excessive watersheds alsomay fill in faster with sediments,requiring frequent and costly ren-ovations. An undersized water-shed may cause pond water toremain shallow, allowing weedsto get a foothold and preventingthe use of emergency aerationdevices when fish becomestressed.

Pond design and layoutBecause of the liability involvedwith dams, most aquaculturistsshould confer with a person expe-rienced in the design of commer-cial aquaculture ponds. TheNatural Resources and Conser-vation Service, a federal agency,offers technical assistance in ponddesign in most states. This agencydesigns ponds that incorporateexact safety standards, well-estab-lished design criteria, and the lat-est conservation practices. Theyare almost always approved by aprofessional engineer or the NRCSapproval authorities. However,the NRCS can’t always respond torequests quickly because of itssmall staff. Private engineers orconsultants may be available for afee. Be sure to get referrals andcheck any state codes for pondconstruction before paying for theservices of a consultant. A good site survey and layoutdesign will contain the followinginformation:1. Location, top width, slopes,

earth fill requirements, and ele-vation of the dam

Page 3: Watershed Fish Production Ponds - Extension...in slightly hilly areas of Mississippi, Tennessee, Alabama, Georgia and Illinois. On rolling terrain the annual rainfall may be enough

2. Emergency spillway locationand size

3. Shoreline dimensions4. Soils investigation report5. Dimensions of the cutoff trench

and core6. Location, dimensions and eleva-

tions of the riser and barrelpipes

7. Estimate of the total cut and fillin cubic yards (This figure willaccount for most of the expensein pond construction.)

8. Watershed area and characteris-tics

9. A bill of materials needed,including valves, concrete andlumber for the pipe ballast,pipes, vegetative materials(seed, fertilizer, lime), and anydiversion pipes or valves

Pond sizing and depth

The size of a watershed pondshould be based on the availabili-ty of water from the watershed.The water should be deep enoughto compensate for evaporationand seepage. Even during sum-mer drought the water should beat least 3 to 4 feet deep. Ideally,the average water depth in a com-mercial watershed pond shouldbe 4 to 5 feet. The maximumdepth should be 8 to 10 feetbecause of the limited size of com-mercial seines. Ponds that can beseined without releasing water arecalled “seine-through” ponds.Catfish ponds in the southeasternUnited States are seldom drainedfor harvest.

Other design features

Since catfish and most other fin-fish ponds are always seined forharvesting, pond bottoms shouldbe smooth and almost flat.Stumps and other natural obstruc-tions should be removed.Watershed ponds need not be rec-tangular or square in shape.Curvilinear shorelines will workas long as the maximum width ofthe pond doesn’t exceed thelength of the seines used for har-vesting. Most seines used by cus-tom seiners and processing plants

are 1,000 to 1,500 feet long. Ideallythe seine will have some slack orcurvature, so maximum pondwidths should be about 700 to1,000 feet. The dam should have a minimuminside slope of 3:1, 4:l if economi-cally feasible. A 4:1 slope makes iteasier and safer to position emer-gency aerators and load andunload boats. It also reduces waveerosion and makes for better seinecontact with the bottom at theinside toe of the levee. However,4:1 slopes are more expensivebecause there must be more earthfill. The outside slope can be 3:1.This slope will allow for mainte-nance duties such as bush hog-ging and driving around emer-gency aeration equipment withpickup trucks. Occasionally it is necessary todrain a pond to capture large,seine-wary fish, repair drains orrenovate banks. Pond bottomsshould be graded toward thedrain at a 0.1 to 0.3 percent fall toensure complete drainage andallow fish to concentrate in thedeeper end.

Pond construction

Contractors

Pond contractors run the gamutfrom “fly-by-night operators” tocompanies that have their ownengineers and use laser devicesfor leveling. It is always a goodidea to get references for workalready completed. If possible, getcompetitive bids from several con-tractors, check out their refer-ences, and then decide. Be sure toestablish specifics about what is tobe done by whom, the quality ofmaterial and workmanshiprequired and payment details.Some companies prefer to doturn-key jobs,from buildingthe pond toplanting thedam withgrass.Contractors areusually paid bythe number ofcubic yards ofdirt moved so

a good estimate of earth fill isneeded. A welder will be neededto fabricate the drainage struc-tures so be sure to negotiate whowill be responsible for this phaseof construction.

Construction costs

Pond construction costs can behighly variable. On a per-acrebasis, large ponds are muchcheaper to build than small ones.Data at the Alabama Fish FarmingCenter in Greensboro indicate thatwatershed ponds larger than 15acres cost less than $1,000 per acreto build in ideal locations. Thisincludes clearing, earth fill, exca-vation, pipe and valve, concrete,seeding and dam gravel. Pondssmaller than 10 acres may cost asmuch as $1,800 per acre. Ponds onpoor sites, i.e., on sites that aresteep and require large dams toimpound relatively smallacreages, may cost $10,000 ormore per acre. The largest cost of building apond is earthmoving. All othercosts are relatively minor.Contractors in commercial catfishareas currently charge $.70 to$1.25 per cubic yard of dirtmoved. Costs will no doubt con-tinue to rise as machinery, fueland labor costs increase.

Equipment needed

Pond construction equipment mayinclude the following: large andsmall bulldozers for clearing andfinal dressing of levees; self-load-ing scrapers or tractor-pulledpans; laser leveling and weldingequipment; backhoes andhydraulic excavators; farm trac-tors with soil implements such ascultivators or discs; and a sheeps-foot roller (Fig. 3).

Figure 3. Farm tractor with pan.

Page 4: Watershed Fish Production Ponds - Extension...in slightly hilly areas of Mississippi, Tennessee, Alabama, Georgia and Illinois. On rolling terrain the annual rainfall may be enough

Soil moisture and compaction

Good compaction requires suit-able moisture and compactiveeffort. The dam must be builtgradually in layers of 6 to 8 inchesand each layer packed with heavyequipment or sheepsfoot rollers.The soil used in the dam must befree of all vegetation, roots andlarge rocks. Soil moisture is criti-cal. Soil too wet or too dry willnot adequately compact no matterhow many times it’s run over. Ifthe soil is so dry it can’t be handmolded, stop construction or addwater with large tank sprayers. Ifthe soil is so wet that it adheres toconstruction equipment, stop or, ifpossible, find drier material. Mostdam seepage problems occurbecause dams were built duringdrought conditions.

Constructing the pond area

Water depth at the shorelineshould be at least 3 feet, with aminimum 3:1 slope. This willeliminate most aquatic weedproblems and allow for emer-gency aeration anywhere in thepond. The bottom should be leveland graded to the lowest point infront of the dam where the barrelpipe will be located. The bottomshould also be pulverized with adisc harrow and then leveled. Ifagricultural lime is required,spread it before filling the pondwith water.

Building a watershed pond

Following the pond design, beginby flagging the dam, emergencyspillway, contours for the top ofthe riser, top of the dam, and theemergency spillway elevation.(Fig. 4) The contour for the top ofthe riser will become the actualshoreline. The dam will be built atthe same elevation as the top ofdam contour around the pond. The first step in actual earthmov-ing will be site preparation. Thisinvolves clearing trees, removingstumps and roots, and stockpilingthe topsoil which can be used todress the dam later. Trees, stumpsand roots should never be buried

inside the pond or near the dam.Some landowners have usedportable saw mills to recoup someof the costs of removing valuabletimber. Check with a local powersaw shop for names. The next step is dam construction.A cutoff trench is excavated alongthe centerline of the dam; itextends up each abutment as faras there is any pervious materialthat might allow seepage (Fig. 5).Any potential seepage must beprevented to avoid water loss andfailure of the dam. The bottom ofthe trench should be at least 8 feetwide with sides no steeper than1:1. Old stream channels runningthrough the dam should becleaned out. All stones, gravel,sand, sediment or anything else

that would prevent bonding of theearth fill and dam foundationmust be removed. Before filling the cutoff trenchwith the best available clay soil,the trench may have to bepumped out and lightly scarified.The clay fill should be compactedtightly as each layer is added tothe trench. If properly compacted,the clay will strengthen the dam.Eventually the trench will be filledand then the remaining dam corewill be constructed above ground.The core of the dam must be ashigh as the permanent water ele-vation. Allow 5 to 10 percent forsettlement.

Emergency spillway contour

Dam

Riser pipe/ shoreline contourWatershed

Top of the dam contour

Figure 4. Pond contour examples.

Barrel Pipe

ValveConcrete Ballast

Pond Surface

Turnscrewfor valve

Trash Rack

Cutoff TrenchAnti-SeepCollar

Core

Existing GroundSurface

Riprap outletprotection

Freeboard

3

1

Top of Dam

31

Emergency SpillwayFlow Elevation

Emergency SpillwayElevation

Riser

Pipe

Figure 5. Typical cross-section of dam at the pipe.

Page 5: Watershed Fish Production Ponds - Extension...in slightly hilly areas of Mississippi, Tennessee, Alabama, Georgia and Illinois. On rolling terrain the annual rainfall may be enough

Installing the drainage pipe

Typically, the barrel pipe withanti-seep collars attached isinstalled after the dam core hasbeen partially constructed aboveground (Fig. 5). The dam core istrenched down to the bottom ofthe pond and a barrel pipe withanti-seep collars is laid in thetrench. Anti-seep collars arerequired because water will seekthe path of least resistance. This ismost likely to be alongside astraight barrel pipe. Anti-seep col-lars are simply steel plates weldedvertically and completely aroundthe barrel pipe to provide the nec-essary resistance to laminar flow.The connection must be water-tight. If the dam is taller thanfourteen feet, more than one collarwill be needed. And be sure thebarrel pipe has a slight fall to theoutside of the dam so the pondcompletely drains.Compaction around the barrelpipe is extremely important. Thisis the weakest area of the damand the cause of most dam fail-ures. The fill should be compactedwith power tampers to ensuregood compaction against the pipeand the collars. Manual com-paction should continue untilthere is at least 2 feet of materialover the pipe. Riser pipes can be located insideor outside of the pond area.Locating pipes inside the pondarea reduces the chance of van-dals tampering with drains. Onedisadvantage of locating theminside the pond, however, is thatit will interfere with seining. Adisadvantage of locating the riseroutside the pond is that the riserand barrel pipe are hydraulicallycharged or pressurized at all timesso all the welds must be good orleaks will develop and cause thedam to fail. Risers placed outsideof the pond area will have to belarger because of the reducedhead pressure on the pipe open-ing. The dam’s freeboard mayhave to be increased also, addingto the expense. Large watershedsmay preclude the outside place-ment of the riser for safety rea-sons. In colder, northern climates

outside risers may freeze. Riserplacement should be a carefullyengineered consideration. A canal gate or alfalfa valve isinstalled to regulate discharge.

Concrete ballasts

If an inside riser is installed, theremust be a concrete ballast tocounteract buoyancy forces of thewater on the riser pipe. Steelpipes, like battleships, have a ten-dency to float. Buoyant forces arecreated when any object is sub-merged in water, whether or notthe object is heavier than water.When an object is submerged inwater, a force equal to the weightof the water displaced actsupward on the object. A 24-inchriser 10 feet tall will have a buoy-ant force of 1,372 pounds. Inorder to counteract this force, 0.6cubic yards of concrete must bepoured around the base of theriser. This amount of concreteweighs 2,430 pounds in the airbut only 1,419 pounds underwater (again because of the buoy-ant force on the concrete).Without a ballast, constantupward forces on the riser pipewill weaken any joints over timeand may crack welded seams.Also, water flowing through thepipe causes vibrations and move-ment. The ballast acts as adamper, adding longevity to thepipe system.

Sizing riser and barrel pipes

The characteristics of the water-shed and the typical rainfall in thearea are used to size riser and bar-rel pipes. Riser pipes are larger indiameter than barrel pipes. Theyare welded together in a “tee.”Riser pipes are usually designedfor 5-year storms, or rainfalls thatoccur normally once every 5 yearsfor a 24-hour period. For the westcentral area of Alabama, this isabout 5 to 6 inches of rain. Ofcourse, the larger the pond andwatershed, the larger the risermust be. Barrel pipes are similari-ly sized. It is obviously better tooversize pipes than to undersizethem.

Emergency spillways and damfreeboards

Emergency spillways are required,particularly if ponds are locatedon large watersheds. Spillwayscan discharge large volumes ofwater around the dam. If properlydesigned, they will prevent waterfrom overtopping the dam.Spillways are designed largeenough to handle a 25-year storm.This size storm also establishesthe top-of-the-dam elevation thatincludes adequate freeboard—thedistance between the designedflow of the emergency spillwayand the top of the dam. This criti-cal dimension is a minimum of 1foot (Fig. 5). There should be avertical drop where the spillwaydischarges into a natural water-course to discourage wild fishfrom entering the productionpond. The spillway should betransversely flat, shallow, andgrassed to minimize any channel-ing of water by erosion. The prop-er sizing of emergency spillwaysshould be determined by qualifiedpersons, especially if dams arelocated in potentially hazardousareas.

Establishing vegetation

Some new pond owners pay a lotfor pond construction and thenneglect to finish the project.Unless the soil is protected it maywash into the bottom of the pond.Gullies and rills can develop withthe first rainfall, making mainte-nance difficult and even jeopar-dizing the integrity of the dam. To prevent this, vegetation shouldbe established as quickly as possi-ble. If surface soil was stockpiledbefore construction, use it to topdress banks and dams. This willpromote quick and stable vegeta-tive cover. Soil on slopes shouldbe roughed up with a disc orspike harrow. This encouragesrainfall to soak in instead of run-ning off and reduces erosion.Distribute lime, fertilizer, seed andmulch at recommended rates.Depending on the season, plantwarm or cool season grasses.Check with your countyExtension office for recommenda-tions.

Page 6: Watershed Fish Production Ponds - Extension...in slightly hilly areas of Mississippi, Tennessee, Alabama, Georgia and Illinois. On rolling terrain the annual rainfall may be enough

All-weather gravel roads to andon the dam are necessary forchecking water quality, operatingand maintaining aerators, andcarrying out stocking and har-vesting operations. If banks havegood sod cover, it shouldn’t benecessary to have gravel com-pletely around the pond. A trash rack should be installedon top of the riser if it is locatedinside the pond. This keepsdebris from entering the pipe andclogging it.

For more information on water-shed pond construction pleasecontact the NRCS office and theExtension aquaculture specialistin your area.Material for this publication waspartially derived from NRCSinformation, the publication“Pond Building: A guide to plan-ning, constructing, and maintain-ing recreational ponds” (ANR-114, Alabama CooperativeExtension System, by Chris Hydeand Perry Oakes), and “Channel

Catfish Culture,” edited by C. S.Tucker. The author thanks Bill Kyser ofKyser Catfish Farms, WilmerPenner of Penner PondConstruction and Bill Hemstreetfor critically reviewing the manu-script, and Mickey Barton, GayleBarnette and Bruce Dupree fortheir assistance with the draw-ings.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Centerthrough Grant No. 00-38500-8992 from the United States Department of Agriculture, Cooperative StateResearch, Education, and Extension Service.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering Committee. Fact sheets arerevised as new knowledge becomes available. Fact sheets that have not been revised are considered to reflect the current state ofknowledge.