Functions Of Monk As Water Control Device In Fish Ponds

A = water surface area.

B = internal bund slope.

C = bund landfill geometric volume.

D = bund landfill volume, compensated (f = 1.43, where f = expansion factor for loose soil). E = number of hours of Caterpillar tractor use (86 HP) needed for construction.

F = number of hours of scraper tractor + number of hours of Caterpillar tractor needed for construction.

Fig. 8.10 Inlet system.

Key: a = collection point; b = transport channel; c = flow distribution.

Fig. 8.10 Inlet system.

Key: a = collection point; b = transport channel; c = flow distribution.

anchor blocks), with at least one fixing for every pipe section (typically 6 m). Special care should be taken to fix the pipe at bends, and at corner or 'T' joints, where pressure surges may shift the pipe or even spring open its joints. Protection should also be provided in busy areas, for example by using simple fences, guards or bollards or, where vehicle access is required, using a reinforced concrete or concrete slab cover. In such areas it may of course be simpler to bury the pipe. In all cases, access should be provided for cleaning out the pipe. Most pipe suppliers have simple access fittings with screw cap or other closing devices; alternatively, these can be adapted from basic pipe materials, or a simple concrete or brick access box may be constructed.

For both pipes and channel systems, a range of simple connection structures may be required to join flows from different sources, or to split them up to supply different parts of the farm or individual ponds. These are usually brick, concrete block, reinforced concrete or timber boxes, pinned into the substrate or set on a concrete foundation. Typically 0.8 to 2 m wide by 1 to 3 m in length, depending on the flows to be handled and the number and dimension of connecting pipes or channels, these may also have sluices or stop-logs to adjust or close off water flow in particular directions. FAO (1992) provides typical details.

Inlets are usually constructed once the main pond shape is formed, normally with short channel lengths or PVC pipes, which are more durable and flexible. These are generally installed in shallow trenches dug at a slope of 0.5 to 2%. The inlet system should allow flow adjustments into the ponds. An inlet box is shown in Fig. 8.10, where the water flow is controlled by wooden stop-logs. In pipes, flow adjustments are made by valves or sliding vanes. Alternatively, an inlet sluice may be cut through the pond bund, but these structures are usually much larger, heavier and more expensive, and are rarely justified. The inlet should be placed in the shallow end of the pond, directly or diametrically opposite the discharge point (New & Singholka 1985). Water should be introduced at least 0.3 m above the pond water surface; it may also be useful to place a deflector or baffle in the pond, to direct the inflow water downwards into the lower water column. Both techniques improve aeration. Mechanical filters in inlets are also useful to avoid introducing predators or competitors into the ponds. Lom-bardi (1998) gave a detailed scheme of filtration systems used in Brazil. Water filtering devices are also discussed in FAO Manuals (FAO 1992, 1996).

8.3.5 Outlets

Outlets are normally sited at the lowest construction level, and are built first. Alternatively, the pond bund can be cut through and the outlet constructed. There are two main objectives - to retain water at the desired level, and to exchange water through the pond, drawing from the most suitable level in the water column. Continuous water flow reduces concentrations of toxic substances produced by prawn metabolism and the decomposition of organic matter deposited on the bottom. Prawns are benthic and thus live on the pond bottom, where water quality is not so good. An efficient outlet system should therefore remove water from near the pond bottom, without changing the entire water column. Finally, at the end of the production cycle, the pond needs to be partially or completely drained for harvest and subsequent pond maintenance.

The most effective and widely used outlet system for Macrobrachium on-growing ponds is the monk (Figs 8.11

to 8.18). This is usually formed as a tall concrete, brick or wooden box, set in the lower end ofthe pond, in which one side (usually facing the pond) is open, with sets of grooves to contain one or two sets of stop-logs and at least one outside screen. At the base of the opposite side of the monk, a pipe is set through the pond bund, allowing the water to drain externally. The screen is placed in front of the stop-logs to prevent the stock from escaping during drainage. An extra pair of grooves can also be set into the structure to allow a spare screen to be used when the principal screen is being cleaned. Screens of 2.0 and 5.0 mm mesh are normally used during initial and final stage grow-out ponds, respectively. Flexible plastic screens are usually the most durable.

The dimensions of monks depend on the pond size and depth, typically 1.0 to 2.0 m in height and 0.6 to 1.2 m in width and depth. If more sets of boards and screens are required, the depth usually needs to be greater to accommodate the grooves, which are usually placed about 50 mm apart. For widths of more than 0.8 m, it becomes more difficult to keep stop-logs from twisting and becoming difficult to move. The monk can be placed internally (Figs 8.11 and 8.12) or externally (Fig. 8.13) in the ponds. External monks

Monk Outlet Valve

Fig. 8.11 Internal monk outlet system.

Key: a = plateau; b = discharge channel; c = discharge box.

Fig. 8.11 Internal monk outlet system.

Key: a = plateau; b = discharge channel; c = discharge box.

Fig. 8.12 Concrete monk during the drainage of a Brazilian Macro-brachium pond. (Reproduced with permission of Julio Vicente Lombardi.)

have all four sides closed, with the boards set inside and a screen placed over the intake pipe on the inside of the pond. This makes access to the boards more difficult than with the open-sided internal monk. Valenti (1996) noted that internal monks can be an obstacle to seining. However, Huet (1986) pointed out disadvantages for external monks, including their vulnerability to theft and acts of vandalism. Another advantage of internal monks is the possibility of removing water from the upper water column, which is sometimes necessary to eliminate algal blooms in flushing operations. Internal monks usually have a larger screen surface, which helps to reduce clogging.

The stop-logs (Fig. 8.14) can be set so that drainage water overflows at the desired pond level (Fig. 8.15). The set next to the screen can be arranged with an opening lower down in the water column to allow lower-level water

Prawns Pond Outlet System

Fig. 8.13 External monk outlet system.

Key: a = screen; b = discharge pipe; c = monk; d = discharge channel.

Fig. 8.13 External monk outlet system.

Key: a = screen; b = discharge pipe; c = monk; d = discharge channel.

Fig. 8.14 Details of a concrete monk in a Brazilian Macrobrachium pond. (Reproduced with permission of Julio Vicente Lombardi.)

to be drained from the pond. This is particularly useful for removing excess nutrients. Stop-logs should be made from light, durable and water-resistant materials, typically using timber suitable for boat building. However, some twisting and warping may occur, and leakage between the boards is a common problem. Leakage can be reduced using a simple rubber or plastic flap attached to the lower edge of each board so that this covers the gap between it and the board below. For more long-lasting leakage control, mud or clay can be packed between the two sets ofboards. Where this is used, a third set of boards on the open side of the monk may be used to control the level from which the pond drains. A brick bund can be an alternative to replace wooden gate boards. In this type of monk, drainage flow control is done by means of removable caps on the end of the drainage pipes (Fig. 8.16).

Ideally, monks should be built in the early stages of the pond's construction, and set on a secure foundation so that the structure does not move. Critical design and construction aspects include attaching the exit pipe securely to the monk box, securing the pipe well through the pond bund, and preventing seepage around the pipe. In addition, the base of the pond around the monk and the sides of the bund may need to be strengthened with cobble or a light concrete cover or wooden piling, to protect them from erosion caused by water flow or harvesting activities. The foundations of the monk are typically at least 0.3 to 0.5 m wider than the monk area, usually made of lightly reinforced concrete on a bed of graded rock, or on simple wooden piles. A 20 m2 concrete foundation platform of 70 mm thickness is set below the ground level (as shown in Fig. 8.11a). This is also useful to avoid the deposition of mud around this area, and facilitates harvesting. Discharge pipes are typically 0.15 to 0.3 m diameter concrete, PVC or ABS. Concrete pipes usually need to be jointed at several points through the bund width, while single lengths of plastic pipe may be feasible for smaller bunds. Joints need to be carefully made and the pipe particularly securely fixed at these points, to avoid shifting and subsequent leakage. The foundations are usually extended below the outlet pipe, at least half of the pipe diameter in thickness (Wheaton 1977). Figure 8.17 shows a 0.35 m discharge pipe placed over a 0.18 m thick concrete base.

To control seepage and avoid possible local erosion, metal or concrete anti-seep collars should be firmly placed along the pipes, perpendicular to the line of the pipe (Fig. 8.18). These should be at least 0.05 m wider than the pipe but preferably at least 50% greater than the pipe diameter, and more if the pond soils are loose and easily eroded. As the bund is built up around the pipe, soils should be well compacted around the collars and along the pipes. Once the whole pipe is covered, the rest of the bund may be built up, though care has to be taken in using machinery over the pipe area. Alternatively, the bund may be constructed normally, and then cut through to provide the route for the pipe. After placing the pipe, the soil removed from the bund should be replaced and well compacted. The success of this method depends on the type of soil and the care in construction.

Sluice gate structures built through the lower pond bund can also be used for drainage. These are much larger and more expensive than monks for an equivalent size, and so are less commonly used. However, for very large ponds which require a substantial drainage flow, they may be a practical solution, as large monks with very large pipes, or multiple pipes may be just as expensive. Sluices are also far more accessible for cleaning and repair.

For smaller ponds, a pipe outflow may be used to drain water. In its basic form, this is simply a pipe (typically 0.060.15 m diameter) run from the interior base of the pond, through the lower pond bund, with a cap or valve at the

The Main Diagram Pond Monk

outer end. As with the monk drain, the pipe should be fitted with one or more collars to restrict seepage. A common variant uses a 90 degree angle fitting on the outside, holding a vertical pipe extending up to the maximum intended level of the water inside the pond. This 'swinging arm' pipe can then be swivelled down to the required level, or dropped down completely to drain the pond. Both these systems need careful protection against leakage or accidental damage. Additional protection can be provided by connecting a vertical pipe on the inside of the pond. Sometimes, particularly for small ponds, outlet structures may not be used at all; in these cases either a small pump with a simple net screen is set up with its intake at a suitable drainage point, or the outer bund is simply cut through to let the pond drain down.

Where conventional outlets are used, a discharge channel (Fig. 8.11b) takes the water to a level below the ponds. Immediately below the discharge pipe a brick, concrete or timber frame and board box can be constructed (Fig. 8.11c)

to buffer the water impact force and prevent erosion in the discharge channel. In fish ponds, similar boxes may be placed inside the pond to collect fish during total harvesting (Bard et al. 1974; Huet 1986). However, placing these boxes outside the pond is better for freshwater prawn harvesting. Such boxes are typically 1.0-2.0 m wide x 1.53.0 m long, depending on the size of the pond and the quantity of harvest stock to be held. The discharge channel, usually dug into the site soils, would normally be set at a 0.1 to 0.5% slope (i.e. 0.1-0.5 m per 100 m) along its length. Topographic study (section 8.1.2) should indicate the best route for waste disposal, commonly downstream of the water supply. Channels dug in open soil need constant maintenance to de-silt, remove vegetation and repair surface erosion. Underground pipes can also be used, if dimensioned according to the maximum system discharge, though provision should be made for access to flush out or scrape clean the pipe interior. Pipes of these dimensions, typically 1 m in diameter or more, can be expensive.

Monk Outlet Valve
Fig. 8.16 Monk sluice gate in brick bund. Key: a = screen; b = discharge pipe; c = PVC pipes with caps to control flow rate; d = PVC pipes with caps to be used during emergency situations (flushing pond).

8.3.6 Other features

A number of other technical features may be incorporated into pond systems for Macrobrachium production, depending on the management approach, the intensity of produc tion and local environmental conditions. Some of the more common elements are described as follows:

Waste treatment, in some cases enriched water and waste solids may need to be treated to prevent adverse effects on receiving waters, or to permit some or all of the pond water to be reused at various stages, pumped back for the same ponds or drained into other systems downstream. Solids removal is the main form of treatment, usually based on sedimentation, in settling ponds. Aeration may be used to increase oxygen levels, and algal growth in the settling ponds may help to remove nutrients. Power supplies: where aerators are to be used, electrically driven pumps operated, overhead lighting installed, or for various items of field equipment, a power supply network may be required. Cables may be laid below surface, with suitable protection, or run overhead using power lines, ensuring that they are not at risk from damage. Live cables dropping into water can be extremely dangerous, and external lines should be protected ifpossible with an earth leakage circuit breaker. Sockets should be of suitable external rating, or else placed in secure, waterproof housings.

Roadways and access paths: these need to be constructed in most farm systems, to allow for everyday operations, to move materials and to collect harvested stock. Depending on the soil characteristics, the road or pathways may need to be reinforced, either with simple piling, with a suitable

Fish Hatchery Pond Monk


Fig. 8.18 Disposition of anti-seep collars along monk discharge pipe.

depth of stones and cobbles or, in some cases, using a light concrete surface or a brick-lined road bed. Suitable drainage ditches will be needed to allow water to drain from the road surfaces. Simple bridges and culverts may also need to be constructed.

• Feeding devices and storage facilities: simple tray feeders madefromnetting,wood,orplastic,typically0.5 x 1.0m and placed every 10-20 m, are sufficient for most systems. Suitable provision needs to be made for the storage and efficient delivery of feeds to the pond side.

• Aerators: aeration is discussed in Chapter 13.

• Integrated cropping: the integration of freshwater prawn culture and crop-livestock production is discussed in Chapter 11.

8.3.7 Landscaping and site finishing

At the end of the pond construction stage, grass should be planted on the bund free-board slopes and crests to avoid erosion. Pieces of turf are preferable to seeding, and can be transplanted from other areas in the farm or from neighbouring areas. The topsoil, which was scraped and set aside before pond construction, can be used as soil cover where grass is to be planted. Other areas of the site may need to be moved and shaped to redistribute surplus soils, to improve site drainage, prevent erosion, ensure effective lines of sight for security purposes or improve the visual quality of the site. In some cases, the planting of shrubs and trees may be required for visual protection or shelter. Fencing and erection of windbreaks may be required for site security purposes. Finally, the site should be cleared up and made safe and secure.

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  • Lete Kifle
    What monk in fish pond?
    2 years ago
  • JENS
    What is the function of monk in fish pond?
    2 years ago
  • paul
    Which is simplest and least expensive pond draining method sluice gate or stand pipe?
    2 years ago
  • elbert
    How to discharge water from a concrete fish pond?
    2 years ago
  • katja
    What are the functions of inlet,outlet,monk,board.?
    2 years ago
  • Adelgrim
    What type of pond can the monk be used?
    2 years ago
  • uta
    How does the monk function as a pond drainage?
    2 years ago
  • abraham rodriguez
    What are roles of monk in a pond?
    2 years ago
  • hessu larnia
    How to construct monks in the fish pond?
    1 year ago
    What is inlet in fish pond?
    12 months ago
    What is monk construction in pond?
    11 months ago
    What is monk in fishponds?
    11 months ago
    What is the work of a monk in a pond?
    11 months ago
  • jeffrey
    What is monk fishering farming?
    11 months ago
  • SABA
    What is the function of a monk in fisheries?
    11 months ago
  • Samira Ali
    What is monk in fishery and its function?
    9 months ago
  • marigold
    What is monk in fishpond?
    8 months ago
  • amanuel
    What is a screen of a fish pond?
    8 months ago
  • marigold
    Does a monk control seepage?
    6 months ago
  • Claudio
    What is monk in aquaculture?
    5 months ago
  • jennifer
    What is a monk in a fish farm?
    4 months ago
  • wolfgang
    What is 'monk' in fishing activities?
    3 months ago
    What is the meaning of monk in agriculture?
    3 months ago
  • Nicole Sloan
    What is the meaning of monk in concrete pond?
    2 months ago
  • zemzem brhane
    How to construct monk in earthen pond?
    22 days ago
  • Yohannes Kidane
    Why pipes are used in concrete fish pond?
    3 days ago

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