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Lecture 3: pond design: 

Lecture 3: pond design MARI-5432 Dr. Joe M. Fox

POND DESIGN CRITERIA: 

POND DESIGN CRITERIA Screened inflow gates at shallow end of pond Screened harvest gates at deep end Slope to harvest basin (0.5-1.0%) Water depth 1.25  2.00 M Feeding tray piers Rounded or square corners, steps or ramps for entry Primary dikes wide enough to accommodate vehicles

Slide4: 

GENERAL DESIGN, INTENSIVE POND HARVEST GATE HARVEST BOX FILTER BAG HARVEST BASIN SLOPE 1 SLOPE 2 SLOPE 3 DIKE DIKE DIKE DIKE DISTRIBUTION CANAL INFLOW GATE PRIMARY FILTER PADDLEWHEEL AERATOR RECIRC CANAL DIKE DIKE DIKE DIKE

POND DIKEWORKCONSTRUCTION CRITERIA: 

POND DIKEWORK CONSTRUCTION CRITERIA Dikes are typically constructed by D6- (Catepillar) sized bulldozers Construction is first undertaken on ponds nearest the sedimentation basins and pump station Bulldozers push earth up to create general form of the dike walls Follow stakes set along the length of the pond Smaller dozers used to put on finishing touches Smaller ponds can be constructed using pay scrapers.

POND DIKEWORKDESIGN CRITERIA: 

POND DIKEWORK DESIGN CRITERIA Heights determined by pond bottom elevation, tidal amplitude Perimeter dike often required for protection in flood areas Dikes trapezoidal with slopes 1:2 for high clay, 1:3-4 low clay Dike crown width varies with use Width of crown: 5 m (driving), 3m (walking) Crown is sloped to reduce puddles on dike top Once formed, dikes are sprigged with grass to reduce erosion

POND DIKEWORKCONSTRUCTION CRITERIA: 

POND DIKEWORK CONSTRUCTION CRITERIA Erosion is the main problem in maintaining dike slopes Source: both rainfall and wave action Solution: plant salt-resistant vegetation (local grasses or Salicornia sp.) as soon as possible via sprigging Pond sides receiving wind could be reinforced with rocks (contracted service) Tops of dikes definitely need layer of rocks, especially if high clay content

Typical Cross-section of Pond Dike: 

WIDTH=4 TO 5 M POND SIDE 4.0 CANAL SIDE 2.0M 1.5M CUT-OFF TRENCH Typical Cross-section of Pond Dike 2.0M 3.0

PREVENTING DIKE LEAKAGE: 

PREVENTING DIKE LEAKAGE Minimize amount of loss due to seepage - Proper compaction - Core trenching - Vertical plastic membranes - Vegetative coverage Remove burrowing animals Optimal clay content Construction during dry season

POND BOTTOM WORKCONSTRUCTION CRITERIA: 

POND BOTTOM WORK CONSTRUCTION CRITERIA If detailed pond bottom slopes are required, usually accomplished by scrapers Small 4-6 m3 earthmovers towed by 4X4 tractors, laser-guided (see video) Bottom slope from upper end to lower end of pond usually 1m:250-500m or 0.4-0.2% for large ponds In simple ponds, follows natural slope to estuary Must insure at least 20 cm height of harvest gate above high tide elevation (varies considerably by site)

POND BOTTOMWORKPOND BOTTOM DESIGNS: 

POND BOTTOMWORK POND BOTTOM DESIGNS crown canal canal canal canal plateau plateau

Pay Scrapers: 

Pay Scrapers Started in the 30’s and 40’s as scrapers being pulled behind bulldozers By the 1990’s hydraulic articulated units with motorized units were considered state-of-the art Now-a-days most units are pulled by 4WD tractors (cheaper and lower HP) Contractors started to see that the rest of their equipment couldn’t keep up with scrapers pulled by tractors Cost: about $400,000 for tractor + two scrapers

Pay Scrapers: 

Pay Scrapers Tractors with pull-behind scrapers are cheaper, unless moving material more than one mile (motorized units are faster) Motorized units typically have a 21 cubic yard capacity bed, but scrapers pulled behind a tractor can load 17 cubic yards each Equates to half the labor costs

POND BOTTOM ELEVATION: 

POND BOTTOM ELEVATION Primary design criterion Based upon tidal amplitude Above the freshwater table Above mean high tide Determines canal/dike height Pond should be drainable at all times

Pond Bottom vs. Tide: 

Pond Bottom vs. Tide WHERE SHOULD YOU BE????

WATER CONTROL STRUCTURESINFLOW GATES: 

WATER CONTROL STRUCTURES INFLOW GATES Used for control of pond water exchange Concrete structures with screen/bag filters on both sides of dike Dual primary screens for pre-filtration (1/4" to 1/2“) Secondary filtration screen bag eliminates potential predators (250-500 µM) Flashboards for controlling flow rate of water entering pond Multiple gates in larger ponds

POND GATE CONSTRUCTION: 

POND GATE CONSTRUCTION Cut gap in pond dike using excavator Add clay substrate to bottom of gate, tamp down with mulesfoot build wooden framework construct rebar frame add internal wooden framework, including screen slots pour concrete finish with slick glaze Time required: 2 weeks

Slide22: 

CONCRETE APRON PRIMARY FILTER DIKE CROWN DIKE SLOPE DIKE SLOPE FLASH BOARDS WING WALL BAG FILTER CORRUGATED PLASTIC TUBES PLAN VIEW OF TYPICAL INFLOW GATE

Slide23: 

TOP OF DIKE CANAL SIDE POND SIDE BAG FILTER ATTACHMENT SLOT FLASHBOARDS FILTER SLOT PRIMARY FILTER CULVERT PIPE CROSS SECTION OF TYPICAL INFLOW GATE

WATER CONTROL STRUCTURESHARVEST GATE: 

WATER CONTROL STRUCTURES HARVEST GATE concrete w/harvest basin in pond number/size of gates depends on speed of harvest required screen to retain shrimp, mesh changed with size of shrimp various slats for flashboards canal side often modified for harvest pump

Slide27: 

DIKE CROWN DIKE SLOPE DIKE SLOPE HARVEST BASIN WING WALL FILTER SCREEN FLASH BOARD CULVERT TUBES PUMP BOX NET SLOT DRAINAGE CANAL PLAN VIEW OF HARVEST GATE

Harvest Gate: inflow: 

Harvest Gate: inflow

Harvest Gate: outflow: 

Harvest Gate: outflow

Harvest Gates: outflow: 

Harvest Gates: outflow

Harvest Gates: multiple: 

Harvest Gates: multiple

Gate Construction: 

Gate Construction

Slide38: 

Gate Construction

Excavators: 

Excavators Consists of backhoe and cab situated on top of a pivot This sits on top of an undercarriage with a track (similar to bulldozer) Uses include: digging canals and trenches, loading, brush cutting, demolition, grading and landscaping, lifting of heavy equipment, dredging Weight: 180,000 lbs Bucket size: max of 4.5 cubic meters

POND AERATION/OXYGENATION: 

POND AERATION/OXYGENATION level determined by oxygen demand pumping vs. artificial aeration used for oxygenation and solids mobilization efficiency of devices varies paddlewheels: 2.13 kg o2/kwh (sotr) propeller/aspirator: 1.58 diffusors: 0.97

Typical Aerators: 

Typical Aerators paddlewheel

Paddlewheel Critical Control Points: 

Paddlewheel Critical Control Points horsepower/rpm number of paddlewheels gear reducer composition of shaft shaft connection to wheel number of blades on wheels orientation of holes in wheels float material

Slide47: 

air injector

Air Injectors: 

Air Injectors typically more expensive much quieter some injectors are more efficient Guatemala trial problem: burning up motor inject air by aspiration air bubbles sheared by “egg beater” finer bubbles = better transfer efficiency, longer hydraulic entrainment

Multiple Aeration Units: 

Multiple Aeration Units

Estimating Oxygen Requirement: 

Estimating Oxygen Requirement This applies to paddlewheel aeration and high density culture Usually estimated on the basis of feed application to pond 1 kg of feed = 0.2 kg oxygen consumed via respiration 300 kg feed = 60 kg oxygen consumed/day Caveat: only a portion of the oxygen consumed is by shrimp/fish, high proportion by primary productivity

Estimating Paddlewheel Requirements: 

Estimating Paddlewheel Requirements

Additional Paddlewheel Guidelines: 

Additional Paddlewheel Guidelines Use high quality switch boxes and adequate guage wire Orient paddlewheels to reduce “dead” spots in ponds (usually placed in corners); don’t change orientation during a run More paddlewheels (e.g., 1.0 hp units) = fewer dead spots but higher cost in wire and units Buy units having as much stainless steel as possible (i.e., shaft is connected directly to paddles) Pay attention to electrical demand and quality of electricity (less motor repair)

ELECTRICAL SUPPLY: 

ELECTRICAL SUPPLY Demand increases with level of technology Semi-intensive ponds need electricity for ice production, living accomodations, perimeter lighting, laboratory, fry acclimation facility Usually provided by diesel generators (more dependable and, therefore, cheaper in the long run) Intensive and super-intensive operations have large energy demand (aeration is about 90% of demand)

ELECTRICAL SUPPLY: 

ELECTRICAL SUPPLY Production accomplished by large diesel powered generators (e.g., 500 kVA or higher) Distribution via high tension line with 20-50 kVA step-down transformers situated throughout the farm Demand could be as high as 50 kVA per ha 300 ha intensive farm could have 3,000 one hp paddlewheels = 2.5 megawatt demand Electrical distribution system could cost well over $1 million

ARTIFICIAL SUBSTRATES(POND LINERS): 

ARTIFICIAL SUBSTRATES (POND LINERS) used in areas where soil quality is poor (percolation/toxicity) also used to reduce effluent solids via erosion of pond bottom and drainage canal cost now $0.25/m2 long-term viability and uv resistance use at least 30 mil thickness don’t install yourself, unless very good at it

Pond Liners: 

Pond Liners

Slide64: 

20 and 30 mil HDPE 45 mil EPDM For liners, 1 mil = 1/1,000 of an inch, not 1 mm, must be able to drive on and must be UV resistant

Soil-Cement Liners: 

Soil-Cement Liners Made from 1:6-8 mixture of cement and sand Pond raked down to 3” Cement added to achieve ratio Watered and smoothed via 3,000 lb roller compactor Rate: 1ha/wk Cost: $0.25/square meter

Harvesting Considerations: 

Harvesting Considerations The key to efficient harvesting is proper pond design This means: accessibility, proper gate design (harvest net or harvest pump?) Well-designed ponds typically have ramps down to harvest gate Harvest pumps are typically used on small ponds Pumps move product, not water (300 rpm, low capacity, big impeller) Operated by hydraulic motor or PTO

Harvest Pumps: 

Harvest Pumps

For Next Time:: 

For Next Time: Hatchery site selection