PART 3 CONTRIBUTED PAPERS (Contd.)

SCS/82/CFE/CP-15

EQUIPMENT AND FACILITIES FOR COASTAL FISHPOND CONSTRUCTION, MAINTENANCE AND REPAIR¹

by

C.R. dela Cruz²

1. INTRODUCTION

The Philippines has a long history of coastal fishpond construction and operation. It was reported that the first fishpond in the province of Iloilo was built between 1898–1900 (Denila, 1980). There are about 176 000 ha of brackishwater fishponds for milkfish (Chanos chanos) and/or shrimp (Penaeus monodon) production. Through the years of fishpond development, the fishpond owners together with the coastal folks have developed the skill in the manual construction of fishponds as well as the kinds of construction implements. Where the use of heavy machinery becomes a limitation fishponds are continuously developed manually.

This paper presents a review and observation on the traditional and practical tools or equipment used in the Philippines in the manual construction of fishponds. Some scientific and practical equipment and facilities that have become common and necessary for pond management, maintenance and repair, are also given. For brevity, the name/kind of equipment or facilities are just enumerated with brief description or illustration and their uses.

2. POND CONSTRUCTION EQUIPMENT

2.1 Leveling equipment

Surveying equipment such as engineer's transit, level instrument, leveling or target rod, and measuring tape are commonly used in fishfarm planning, designing and construction works. A plain fishpond owner usually does not own these equipment. But he usually avails of the services of a surveying firm for the topographic mapping of his area. Planning, designing and construction may not necessarily be done by an engineer but by an experienced fishpond developer who has acquired the skill from his years of experience. Under this situation, most of the existing fishfarms have been constructed without using the standard surveying equipment. But fishpond developers have developed simple and practical techniques in checking elevations in the execution of construction works.

Examples of these techniques are the use of tidal water level and depth gauge for leveling pond bottom, and determining the volume of excavation to be done or the quantity of available soil for diking. Another is the use of plastic hose and water for checking the level height of dike.

2.2 Determining approximate volume of excavation by water level and depth gauge (After Denila, 1980)

Determination of the volume of soil to be moved can be determined from a prepared topographic map. However, an alternative method is being used which is done by manipulating the water level with the help of an ordinary wooden depth gauge (Fig. 1). The procedure is as follows:

The water level at the staff gauge or benchmark (Fig. 2) is adjusted to the zero datum. At this point, the waterline of all portions of the proposed pond that are exposed are staked out. The area of the exposed ground must be determined; this represents the excess elevation of the pond bottom and hence, must be removed by excavation. After staking out the exposed area, the water level is again raised up to the highest portion of the ground. Random measurement of water depths by the depth gauge within the limits of the exposed area follows in order to determine the average depth. The data obtained can be used in determining the average thickness of soil to be excavated and the volume of excavation.

The depth gauge is also being used to check the quality of finish of pond bottom during actual leveling work.

2.3 Staff guage for establishing benchmark

Prior to the actual construction, a reference point or station is established in which all measurements of elevations, such as the elevation of main gate, canal bottom, height of dike and pond bottom, are referred to. Such point is called benchmark. The benchmark can be made simple but must be stuck firmly into the ground. A piece of whole bamboo, lumber or any straight object is usually driven (Fig. 3) in front of the designated location of the main gate facing the river or sea, down to the hard portion of the subsoil. Another planed stake with graduation up to 300 cm above the zero mark and minus 30 cm below the zero mark is nailed to the upper end of the bamboo. The zero mark is the reference point in determining the different elevations of pond components during construction. The zero mark should coincide with the 0 datum or the lowest sea level in the project. It can be established by referring (a few times) to the tide table at a given date and hour, in which the graduated stake is nailed during the lowest low tide. With this method, the tidal range from lowest low, to the highest high tide can be determined.

¹ Contribution to the FAO UNDP-SCSP Consultation/Seminar on Coastal Fishpond Engineering, Surabaya, Indonesia, 4–12 August 1982.
² Dean, College of Inland Fisheries and concurrently Director, Freshwater Aquaculture Center, Central Luzon State University, Munoz, Nueva Ecija Philippines.

Fig. 1 A simple depth gauge (After Jamandre and Rabanal, 1975)

Fig. 2 Illustration of procedure in determining depth of soil above O tidal datum using water level, staff gauge and depth gauge

Fig. 3 Staff gauge as benchmark (After delos Santos, 1980)

2.4 Dike construction

2.4.1 Soil excavation and transport

Manual construction of dike is usually done by piling soil blocks that have been cut by a digging blade and transported to the site of dike. A soil block measures approximately 30 × 30 × 60 cm which is cut by a hand tool locally called "tagad" in the Visayas region (Philippines). The blade is made out of a flat bar, 9.5 mm thick, 5 cm wide near the wooden handle, 90 cm long and widens at the tip to 12 cm (Fig. 4). Another digging blade used in Luzon is called “osod”.

Fig. 4 Hand tools for excavation (After Denila,1977)

Fig. 5 Bamboo raft for transporting soil blocks in diking (After Denila, 1977)

The soil blocks are transported from the digging site to the path of dike by a bamboo raft, dugout boat or a flatboat. The bamboo raft, however (Fig. 5) has a much smaller load capacity than the flatboat. The flatboat (Fig. 6 and 6a) is presently considered the best method of hauling soil blocks because of the following advantages.

1. Does not require much effort to load;
2. Construction is simple:
3. Manueverable, easy to tilt and dump the soil (Fig. 7); and

4. Requires minimal maintenance — only periodic tar coating.

Fig. 6 A flat boat for transporting soil blocks during dike construction (After Jamandre and Rabanal, 1975)

Fig. 6a Details of a flatboat (After Jamander and Rabanal, 1975)

Fig. 7 Two ways of unloading flat boat (After Jamandre and Rabanal, 1975)

The daily output (8–9 hr/day) of one skilled worker who digs the soil and uses a flatboat depends also on the hauling distance is as follows:

For cut and fill (during leveling of pond bottom), the output is as follows:

When the source of soil is near the dike line, a sliding board is installed perpendicular to the dike. The workers throw the soil blocks on the board and allowed to slide (Fig. 8). This system saves hiring cost for two to three workers (Denila, 1977).

2.4.2 Investigating soil strata

In constructing the main or perimeter dike and water control structures, the respective location of each is properly staked out. The soil characteristics (stratification and texture) along the dike path or water gate foundation is determined by driving bamboo poles (with inner internodes removed) into the wet ground as deep as it could go. The bamboos are pulled out, together with the entrapped soil column inside. Splitting the bamboo poles longitudinally will provide the samples of soil column with undisturbed strata. This sample is used in determining the soil type and its relative load bearing capacity. A sandy loam soil is the type which can carry much load but is not a good diking material. A soft and deep muddly layer will require the use of pilings and wider base of dike to prevent creeping and cracking of soil as its height increases.

2.4.3 Compacting top of dike

To compact the soil on the top and sides of the dikes, a wooden mallet made of a log about 30 cm in diameter and 30 cm long, cut into a wedge of 45° angle and provided with a handle 1.8 m long will do the job (de los Santos, 1978). The device is manually raised and made to fall against the sides of the dike starting from top to the bottom. This is done by stages when dike is high. Proper soil moisture condition is observed when using the mallet, to make it work effectively.

Fig. 8 The sliding board method of moving soil blocks (After Denila, 1977)

2.4.4 Checking elevation of top of dike

In dike construction, it is very important to have uniform elevation of top of every dike. To have an accurate measure of this, a 12 mm plastic hose of 25 meters long is filled with water. One end is held by a man at the starting point or station and the other end held by another man. The water surface level at the two ends of the hose should be the same. This level is properly marked and is checked against the finish elevation of the top of dike. The same procedure is done in subsequent stations covering the entire length of dike.

The plastic hose with water is also used in laying out the grade line or longitudinal slope of a water supply canal of a fishfarm.

2.5 Clearing pond site

Clearing usually follows after the construction of main or perimeter dike is completed. Removal of trees and stumps prevents the soil and pond water turning acidic due to decaying roots and other parts, especially so if the vegetation are high in tannin such as Rhizophora, Nypa and Bruguiera (Jamandre and Rabanal, 1975).

Some machines are being used for clearing the trees and stumps out of the pond. A chain saw is used for cutting down the trees. Engine and winch combination together with jetting pumps, is also useful as a tree puller (Fig.9). For uprooting stumps, jetting pumps/hydraulic excavator and chain block are commonly used.

3. POND MAINTENANCE AND REPAIR

Dikes are made strong to avoid high maintenance cost. Puddled core trench is being provided to minimize seepage and piping of soil. Piping of soil induces boring of holes of rodents and crabs along the path of the tiny conduit.

Practically, the same implements are being used in making repairs as in construction works. For cutting vegetation or grasses on top of dikes, however, portable brush cutters with shoulder strap of 1.5 hp are being used including small (10–15 hp) tractor mowers.

4. POND MANAGEMENT EQUIPMENT

Some equipment composed of commercially manufactured and improvised ones are both being used in the management of fishfarms.

4.1 For insuring water availability and quality

4.1.1 Water pump — The present use of pump in brackish-water fishfarming are:

1. Providing total or supplementary source of water in order to maximize production;

2. In intensive culture of shrimps, dissolved oxygen becomes limiting hence a pump is used to effect water circulation and continuous or flow through system; and

3. Insuring supply of freshwater whenever necessary, especially in maintaining salinity level in ponds during dry season months when evaporation rate is high.

Aside from these uses, water pump is also useful in draining water from ponds during dike or gate construction.

Fig. 9 A tree puller (After Jamandre and Rabanal, 1975)

The popular pump in use in brackishwater pond operation is the low head-high discharge type or propeller/axial-flow type (Fig. 10). The axial flow pump can be driven by an engine or an electric motor. It can be installed vertically and along the slope of dike; hence, the latter is also called dike pump. The hydraulic head range of an axial flow pump is up to 6 m per stage and available in the market up to 500 000 gpm. In most brackishwater pond applications, a single stage of the axial flow pump is usually sufficient, considering active tidal fluctuations of only 1 to 2.5 m.

4.1.2 pH measurement — The pH of water is determined by using portable meter by some progressive farmers; others use lithmus paper (Fig. 11).

Fig. 10 An example of propeller (axial-flow) pump set up

Fig. 11 Instruments used for determining physico-chemical parameters of pond waters. (After delos Santos, 1978)

4.1.3 Salinity — The level of salinity is determined by refractometer (Fig. 11B2) which gives direct value of salinity. A hydrometer is also used wherein equivalent salinity in ppt is determined from a graph which shows the relationship among the water temperature, specific gravity and salinity. For practical purposes, an improvised salinometer (Fig. 12) serves as a substitute for indicating salinity in milkfish pond (IFP., 1974). The improvised salinometer is a narrow-mouthed rigid plastic bottle which will not break under field condition. The bottle need not be larger than about 100 cc capacity. To make the hydrometer, the bottle needs to be corked and fitted with a light stem such as a piece of split bamboo. Enough rocks should be put inside the bottle so the tip of the steam just floats vertically out of the water when the bottle is placed in freshwater, preferably rainwater. The point where the stem comes out of the water should be marked on the stem. Next, the bottle is floated in seawater. The new place where the stem comes out of the water is again marked on the stem. Half freshwater and half seawater are mixed and used to float the bottle and a locate a mark on the stem which corresponds to the 50–50 mixture of fresh and seawater. With the marks on the stem engraved, the bottle can now be used in any farm to determine the relative level of salinity. Best results are obtained when the temperature of the water tested is the same as the water used to make the reference marks.

Fig. 12 An improvised Salinometer (After IFP, 1974)

4.1.4 Water aeration — Mechanically or electrically operated aerators to maintain high dissolved oxygen level is not usually practiced in most ponds. However, a way of aerating water that is used by some is through manipulation of water gate, such as the one shown in Fig. 13.

Fig. 13 Aeration by manipulation of closure slabs (After delos Santos, 1978)

4.2 Fish food availability

4.2.1 Fertilizer platform — The accepted method of pond fertilization is a combination of organic and inorganic fertilizers. Fish food organisms in the form of “lab-lab” and plankton are recommended in milkfish pond production. In areas where water depth and salinity is better controlled, the use of “lab-lab” method is highly recommended. However, in areas where the pond bottom is not level and salinity fluctuates widely due to rainfall, the plankton method is practiced. Some grow “lab-lab” during dry months and shift to plankton as the rainy season comes (de los Santos, 1978).

When plankton method is practiced the nutrient from inorganic fertilizer should be kept in suspension for plankton growth. A fertilizer platform is a facility that has been found effective for this. The fertilizer is placed on top of the platform which is approximately 30 cm below the water surface (Fig. 14) and dissolves slowly, thus keeping the nutrients in suspension rather than being absorbed readily by the pond bottom when applied directly. Although originally practiced in freshwater ponds, brackishwater pond operators have also adopted the fertilizer platform in their farm management.

Fig. 14 Fertilizer platform (After delos Santos, 1978)

4.2.2 The Secchi disc — The Secchi disc (Fig. 11C) measures the depth of visibility or water transparency in the pond. It is a handy, cheap and practical device for indicating the relative abundance of plankton or food organisms in the pond. A Secchi disc reading of 20–30 cm. provided this is not due to silt, is an indication of good abundance of fish food organisms in the pond. The depth of visibility is maintained by following a regular fertilization programme. If the reading is less than 20 cm fertilization should stop momentarily. Secchi disc reading, however, should not be taken when the pond water is muddy or turbid due to colloidal suspension in the water.

4.3 Use of screens and water-sealed gates

The water gates of ponds are made water sealed by placing closure wooden slabs in two parallel rows starting from the bottom to a height which is in level to the desired water line to culture the fish. Mud is tightly packed between the slabs. When pipes or wooden culverts are used to allow water in, a pair of slabs are cut to fit and accommodate the pipe or culvert. Soil or mud is tightly packed around the pipe or culvert and two more slabs are added on top which are also filled with compacted soil. Fine-meshed nylon net or wire screen is attached to the pipe or culvert. Various arrangements of screening are shown in Fig. 15 to 16.

Fig. 15 Soil-sealed gates with screens (After delos Santos, 1978)

Fig. 16 Netting screens in water gates (After delos Santos, 1978)

5. REFERENCES

Delos Santos, C. 1980 Farm site selection and pond construction. In Vol. II. Technical papers. APDEM III.

Delos Santos, C. 1978 Pond site selection, design and construction. In: Modern Aquaculture for the Philippines. 1st ed. Yuhum La Defensa Press. Iloilo City, Phil. pp. 40–59.

Denila, L. 1980 Site selection and pond construction. In: Vol. II, Technical papers. APDEM III.

Denila, L. 1977 Improved methods of manual construction of brackishwater fishponds in the Philippines. SCS-SFDC/77/AEn/CP16. Joint FAO-UNDP/SCSP and SEAFDEC Regional Workshop on Aquaculture Engineering (with emphasis on small-scale aquaculture projects). Iloilo, Philippines.

Inland Fisheries Project (IFP). 1974 A simple salinometer. Fish Culture Leaflet No. 6. NSDB. 2p.

Jamandre, T.J. and H.R. Rabanal. 1975 Engineering aspects of brackishwater aquaculture in the South China Sea region. SCS/75/WP/16. 37p.

SCS/82/CFE/CP-4

MAINTENANCE AND REPAIRS OF ESTABLISHED COASTAL FISHPONDS¹

by

B.S. Ranoemihardjo²

1. INTRODUCTION

At present, aquaculture is receiving worldwide interest as a potential primary industry to produce animal protein. Many coastal fishponds in Asia for the culture of shrimp and finfish are constructed recently in selected coastal areas. Besides the need of proper site selection and pond construction, maintenance and repairs are also needed to increase production. Maintenance and repairs of dikes are very important because these provide the boundary of the pond system. Water supply canals should be kept deep enough, so that water flow into the ponds can be done easily. Sluice gates for water control should be maintained and repaired whenever necessary.

Techniques for maintenance and repairs are well known since the pond system is constructed by people. However, advance technology in maintenance and repairs requires much more efficient and better skills, and also pond management techniques. If the dikes, water supply canals and sluice gates are in good condition, it would make operation and management of the ponds much easier.

The yield of a pond can be classified by the fertility of the pond soil. Fertilization is therefore important to maintain the fertility of the pond soil to produce food for supporting the cultured biomass. Good soil for growing natural food is clay loam or silty clay loam.

Most brackishwater ponds are constructed on tidal lands adjacent to rivers or creeks near the coast and estuaries at or near sea level elevation. Buffer zones are required along the river or bay to protect the main dike from erosion. Buffer zones should be provided with vegetation for protection.

2. METHODS OF MAINTENANCE AND REPAIRS

2.1 Completion or modification of layout and structures

A brackishwater pond or “tambak” in its simplest form, common in West and Central Java, consists of a square or rectangular body of water, at about 1.0–2.5 ha in surface area. Mostly this traditional coastal fishpond has a small compartment for nursery and a large area for rearing. The nursery pond is usually located in the middle of the rearing pond, and without a sluice gate. Water level is controlled through the sluice gate of the rearing pond. This system is more difficult to manage, especially for nursery pond; and to maintain and repair the dikes and sluice gates.

Conditions in East Java differ from those in West or Central Java. Usually the brackishwater ponds in East Java are larger and this bigger size refers to the number of compartments jointly irrigated by a main gate.

After the structure has been modified, one unit of pond system has a main gate to control the water for the whole unit, and water supply canals including a catching pond, a secondary gate for the rearing or fingerling pond and a tertiary gate for the nursery pond. Thus, each compartment has its own sluice gate making it easier to operate without disturbing the other compartments. By modification of layout and structures, maintenance and rapair of each compartment are easier compared with the traditional pond system in West and Central Java. Usually repair of dike and sluice gate will be done during preparation between culture periods.

2.2 Maintenance and repairs of water control structures, gates, etc.

A water supply system consists of a number of water gates and canals at different levels and of different sizes. These enable the maximum utilization of tidal energy and gravitation for the control of the inflow and outflow of water in a given period of time required by the farm management system. In most cases, water supply system is also used for water drainage.

2.2.1 Main canal

Main canals should be widened and deepened at regular intervals to ensure enough tidal flow and to satisfy water management requirements for the individual ponds. At the narrow tidal range area where water intake and drainage are problems, siltation and construction of water passages further aggravate the situation, making shallow ponds which otherwise could be easily dewatered entirely difficult to drain. Silt and organic matter or sometimes sand that are carried from the sea and deposited in the main canals should be removed. Excavation by hands, which is commonly practiced by Indonesian fishfarmers, or by machine should be often carried out to deepen the main canals to increase volume of water that could pass through them.

¹ Contribution to the FAO/UNDP-SCSP Consultation/Seminar on Coastal Fishpond Engineering. Surabaya, Indonesia, 4–12 August 1982.
² Chief of Culture Technique Division, Brackishwater Aquaculture Development Centre, Jepara, Indonesia.

2.2.2 Sluice gates, etc.

The main gate primarily controls the flowing in and out of water for the whole pond system. It may have more than one opening, depending upon the requirements for water of the whole system. Secondary gates are to control the in-and outflow of water for the rearing and fingerling ponds. It can be made of wood or concrete, about one meter wide. It may be single or multiple opening depending upon the elevation of the pond bottom. Tertiary gates are to control the water supply of the nursery ponds. These are smaller than the main and secondary gates. All sluice gates are provided with screens. The number of sluice gates depends on the number of pond compartments.

To prolong the life span of the wooden sluices, barnacles, oysters and polychaete tubes attached to the sides should be scraped regularly, at least once a month. The same should be done with the concrete sluices, to minimize water friction and help maintain a better volume of water flow.

Concrete gates that have sagged or tilted due to failure of the foundation is very expensive to repair because of its weight. Sometimes it would be cheaper to construct another gate instead. However, if the defect is due to crack, then routing and plastering can stop the leaks. Wooden gates are easier to repair especially when the plankings are exposed. The underwater portions are most affected by marine borers. The lowest tide is the best time to replace the planks and flooring. Preserved lumber with coal tar or creosote and copper oxide stay very much longer than untreated ones. Weak wooden gates are totally repaired including the coarse and fine screen before the beginning of the culture period to prevent or minimize predators and pests from entering the pond system. Repairing the sluice gate during culture periods needs embankment for blocking the water from flowing in and out of the pond.

2.3 Maintenance and repairs of dikes

Main or perimeter dike is one which is to confine a pond system. Secondary or partition dike is constructed between compartments inside the pond. It is usually smaller than the main dike and it can also serve as a wind-breaker. Tertiary dikes are constructed in the nursery and are smaller than the secondary dikes. These serve as partition in the nursery pond system.

Main dikes deteriorate from erosion caused by waves, winds, water and rains and trampling by man and animals. Exposed dikes especially those facing the sea are most expensive to maintain. Boulders, rocks, concrete, bamboos and tree trunks are used to prevent inundation of the dikes. Main dikes usually constructed on creeks, rivers and soft mud are vulnerable to leaks. During the drying period of pond bottom system, all dikes should be checked for leakages. Most often crustaceans and eels burrow through the base of dikes made of soft clay or silty clay. To eliminate burrowing aquatic animals such as crabs, traps may be installed, but some fishfarmers commonly use poisoned baits to kill these pests.

Repair of deep leaks is not an easy job. It is a dangerous job because slides often cause casualities to the workers. In repair work a trench is dugged at the side of the dike big enough to prevent slide and deep enough to reach the desirable level of the river bed. Usually the original soil is replaced by a better kind. If sand is available nearby, it can be mixed with the original soil. Palm fiber (Arenga fiber) can be used also as lining of the trench before filling. If these materials are not exposed to the air, they will last for many years.

The maintenance of secondary dikes involves placing pond bottom soil on the top and sides of the dike. Most of the eroded soil is beside the dike. Erosion is faster when there is no vegetation. The planting of grasses on the dike will minimize the losses of soil. However, grasses will not grow well on small dikes. Dikes with a base of 4 meters will easily grow grasses provided the soil is not acidic.

2.4 Repair and maintenance equipment

Many kinds of equipment are used in brackishwater pond operation, especially for digging of soil, carrying of soil, harvesting traps, etc.

Digging tools. In West and Central Java usually people use “cangkul” for digging. This is made of iron plate with wood as a handle. Another type is wooden spade with iron strip on its tip. In East Java, a digging blade is called “sarap” and is made of steel. The broad end as well as the sides are sharpened. It can slice through roots 5 cm in diameter or even more. These blades are used also for digging puddle trenches, deepening of canals, repairing of leaks besides for cutting out soil blocks for diking purposes. To maintain those digging blade is simple. The tools are cleaned after use and then rubbed with oil to protect them from rusting.

Mud scoop. Generally, it is made of aluminium or galvanized iron sheet and sometimes from wood. It is used for deepening the peripheral canal by taking out the mud and throwing it to the dike. Maintenance for these equipment are simple like the digging blades which have been mentioned earlier.

Boat. It is needed in various work in the coastal fishpond such as for repair of dikes or harvesting of fish. If a boat is not used, it is filled with water to protect is against the sun so it does not crack.

Pump. This is essential to fishfarms with small tidal water amplitude. It can be used in supplying water to a pond when tidal water cannot flow in or to drain water when the pond bottom is below the zero tide mark. Pump needs maintenance regularly to sustain long life.

Equipment usually used for harvesting, for instance, are the shrimp traps and bamboo screens. They are made of bamboo and rattan with nylon twine for tying. These equipment and nets are washed after use and stored away after air dried. Shrimp traps and bamboo screens are repaired by replacing the broken ones by new ones.

2.5 Maintenance of fishpond environment and adjacent watershed area

The distance of the main dike will depend on the steepness of the river bank. If it is of a moderate slope, the distance between the river bank and the base of the main dike should not be less than 10 meters. It is enough as a buffer zone for protecting the main dike. Since mangrove vegetation is the best protection of the main dikes, buffer zones are therefore very much required along the river or bay. Vegetation left undisturbed in wide belt counteracts the destructive action of the waves. The buffer zone also serves to maintain an ecological balance in the area. Sometimes the trees can be used as wind-breaker, and to maintain temperatures of the pond area during the dry season.

3. CONCLUSIONS AND RECOMMENDATIONS

Maintenance and repairs are essential to the operation and management of coastal fishponds. In addition to proper site selection, pond construction and pond management, they are essential components to successful fishpond culture.

Construction of berm along the foot of the dike or constructed broken dikes inside the pond can protect the dike from the adverse effects of wave action.

Grass can be planted on the top and slope of the dike for protection from erosion, as soon as the construction of dike is completed. It can be maintained by fertilizing and minimizing trampling.

To eliminate burrowing aquatic animals such as crabs, traps may be installed. Some fishpond operators use poisoned bait to eliminate pests.

A coat of oil is applied to each piece of metal equipment for protection against rusting. Equipment made of wood, bamboo and nylon such as nets should be cleansed and air dried before storage.

Buffer zones are required along a river or bay to prevent the erosion of the main dike. Mangrove vegetation grown in such an area often gives the best result.

Repairing the sluice gates and screens should be done during the preparation between culture periods to prevent or minimize predators and pest from entering the pond.

REFERENCES

Anonymous. 1980 Fishfarm engineering. In: Brackishwater Aquaculture Development and Training Project. BFAR-FAO/UNDP. Manila, Philippines, 1980. 85p.

Denila, L. 1977 Planning and designing of brackishwater fishpond for milkfish. Aquaculture Department, SEAFDEC, Tigbauan, Iloilo, Philippines, 1977. 50p.

Schuster, W.H. 1952 Fish culture in brackishwater ponds of Java. IPFC. Special Publ. No. 1, 1952. 143p.

SCS/82/CFE/CP-1

PUMPS FOR COASTAL AQUACULTURE¹

by

D.R. Jamandre²

1. INTRODUCTION

With the growing interest and emphasis on aquaculture, the main concern is maximizing production per unit area or per unit volume whether the production is in tanks, ponds or elsewhere.

Pumps³ are essential as support facilities for water supply management. Their use can play an important role in coastal fishfarm production. Due to the high cost of energy (fuel), pump efficiency is a very critical consideration if pumps are to be used. The cost of pump operation in relation to the crop being cultured and marketed must be carefully analyzed.

With intensive culture and maximum stocking densities, dissolved oxygen becomes one of the limiting factors. There is need for “low head-high volume” pump to continuously move water in a “flow-through” system in culture ponds. The same kind of pumps are used for aeration and circulation of the culture water supply. Since almost all aquaculture areas require pumps that are not only close to the water but which may also be within the tidal range, it is essential that the total dynamic head should be as low as possible and should be within the range of pumps designed for low head and high volume.

2. PUMPS IN AQUACULTURE

Wheaton (1979) has classified the four major types of pumps as 1) reciprocating 2) rotary 3) centrifugal and 4) airlift.

From studies of pumps, their capacities, energy requirements in relation to pond requirements. Jamandre (1977) made the following observations: 1) Pumps are devices that transfer energy from the prime mover to impeller to material (fluid) being moved; and 2) pumps are basically better suited to push rather than suck. Efficient installations are those with the least suction head of those with “zero” suction heads such as submersible or propeller pumps.

Three basic designs of pumps suitable for moving large volumes of water with low head are: a) radial flow, (Fig. 1). b) mixed flow, (Fig. 2), and c) axial flow. (Fig.3). These are briefly described below.

Fig. 1 Radial flow pump

¹ Contribution to the FAO UNDP-SCSP Consultation Seminar on Coastal Fishpond Engineering, Surabaya, Indonesia, 4–12 August 1982.
² Private fishfarm operator Jamandre Industries. Inc., Iloilo City, Philippines.
³ To provide better understanding of the technical descriptions and use of pumps, the technical terms commonly used are compiled in Annex A.

Fig. 1A Performance curves of radial flow pump
a. Head curve is relatively flat
b. Head decreases as flow increase
c. BHp increases gradually overflow range

Fig. 2 Mixed flow pump

a) Radial flow pump (Fig. 1A). In this type of pump, the liquid enters parallel to the shaft and is thrown to a 90° angle towards the wall of the bell. The energy or force imparted to the liquid is all centrifugal. Of the three types listed, this type delivers the higher head, but less volume for the same power. Normally operated at speeds of 3 600 RPM, this speed if generally higher than the speeds at which the two other pumps operate.

Fig. 2A Performance curves of mixed flow pump
a. Head curve is steeper than radial flow
b. Shut-off head is usually 150%–200% of design head
c. BHp remain fairly constant over flow range

b) Mixed flow pump (Fig. 2A). For this type of pump, liquid enters the pump parallel with the shaft. The liquid is then thrown at an angle from 40° to 80° to the angle of the shaft. Energy imparted is a combination of centrifugal and displacement energy. The hydraulic head ranges from 10 to 150 feet (3 to 45 meters) and these pumps are available with capacities of over 30 000 RPM. Normal operating speed is usually 1 760 RPM. The pump's power is usually provided by an electroc motor which makes it quite convenient if one has to install this type of pump where electric power is available.

Fig. 3 Axial flow propeller pumps

c) Axial flow pump (Fig. 3A). For this type of pump, liquid enters parallel to the shaft and is discharged in the same direction. All force of energy imparted to the liquid is 1 to 20 feet (0.3 to 6.4 meters) per stage. Ideal operating speed is about 1 600 RPM or higher.

Fig. 3A Performance Curves of axial flow pumps
a. Head increase drastically near shut-off
b. BHp increase drastically near shut-off

2.1 Centrifugal pumps

A centrifugal pump consists of a set of rotating vanes enclosed within a housing or casing used to impart energy to a fluid through centrifugal force (Fig.4). A power unit such as an electric motor drives the pump shaft, causing the impeller to rotate. Vanes on the impeller direct the flow of water and help impart energy to it. Impeller rotation causes any particle on the impeller surface to accelerate outward as a result of centrifugal force. If the inlet and the pump cavity are filled with water (i.e. primed) the outward movement of water on the impeller lowers the pressure at the impeller centre causing additional water to be drawn into the inlet.

Impeller rotation imparts a high velocity to water at the periphery of the impeller. As this water leaves the impeller the velocity is rapidly reduced and the velocity (dynamic head) is converted to static pressure head. Thus, the pressure change from inlet to outlet on a centrifugal pump is dependent on characteristics of the pump.

Fig. 4 Centrifugal pumps

The stuffing in the stuffing box forms a seal around the shaft to prevent water from leaking out around the shaft. There are many types and designs of stuffing and stuffing boxes used on centrifugal pumps.

2.1.1 Volute pumps

This type of pump derives its name from the spiral shaped casing surrounding the impeller (Fig.5). This casing section contains the liquid discharged by the impeller and converts velocity energy into pressure energy.

A centrifugal pump volute increases in area from its initial point until it encompasses the full 360° around the impeller and then flares out to the final discharge opening. The wall dividing the initial section of the discharge nozzle portion of the casing is called the tongue of the volute or the “cut water”.

Volute pumps are used when pumping from surface sources and in general when the total head exceeds approximately 45 feet (14 m). Such pumps are available in many types such as vertical or horizontal shaft and suction, bottom suction, double suction with semi-open or closed impeller and so on. These pumps are mounted in dry pits when located below grade and on slabs or floors when located above grade.

Figure 5. Mixed flow volute type pumps

Volute pumps are commonly used because of their simplicity and ability to handle fluids containing a reasonable amount of solids. Impellers with curved vanes are commonly used because they provide less turbulence and circulation within the pump thus improving pump efficiency.

2.1.2 Self priming centrifugal pumps

For self priming centrifugal pumps (Fig. 6) a check valve on the suction side of the pump permits the chamber to be filled with water prior to starting the pump. When the pump is started, the water in the chamber produces a seal which enables the pump to draw air from the suction pipe. The air and water flow through into the chamber where the air and water flow through the discharge, and the water flows down through another channel to the impeller. This action continues until all the air is exhausted from the suction line and water enters the pump. When the pump is stopped, it will retain its charge of priming water indefinitely.

This type of pump is often used in instances where the pump must be set above the surface of the water to be pumped.

Fig. 6 Self-priming volute pumps

2.2 Propeller pumps

A simple propeller pump consists of a boat propeller placed inside a pipe and a motor to drive the propeller. Since propeller pumps (Fig. 7) mechanically lift the water by the pitch of the propeller in each revolution, the thrust bearing must absorb the entire accelerating force created by the impeller.

Fig. 7 General design of propeller or vertical pumps

Speed on propeller pumps is limited by the cavitation at the propeller tips. Since the tip velocity increases with the diameter, the larger the propeller diameter, the slower it must turn. Large pumps commonly operate in the 100 to 300 RPM range, too slow for direct coupling to an electric motor.

Propeller pumps are best used for conditions of low head and high discharge. The head capacity and efficiency curves tend to be flatter for the propeller pump than for the centrifugal pump. Power requirements increase as discharge is decreased and head is increased. It is therefore important that these pumps should be choked at the outlet to reduce discharge.

2.3 Airlift pumps

Airlift pumping systems consisting of a pump and air compressor are particularly useful when pumping gritty or corrosive liquids. Since there are no moving parts in the well, wear and corrosion will not occur as rapidly as in the deep well turbine pumps. Since the air compressor is at the surface and readily accessible at all times, it is never in contact with the corrosive water, proper operation and maintenance are generally easy.

An airlift pump (Fig.8) consists of an open ended pipe or tube into which air is injected; part of the tube being submerged below a free liquid surface. The percentage of the pump submergence varies with the application. Airlift pumps operate because a difference in specific gravity exists between the water outside the tube and the air-water mixture within the tube. The injection of air into the tube lowers the specific gravity of the air and water mixture in the column.

Fig. 8 Airlift pump

The most important points in the design of an airlift pump installation are the selection of i) the rate of discharge, ii) the size of the pipe, iii) the capacity of the air compressor, and iv) the pressure against which the compressor must work.

The determination of the rate of discharge may depend on discharge desired or the capacity of the existing well. In either case, the discharge and corresponding draw-down should be known accurately.

Compared to other pumps, the airlift pump will probably have higher power costs but lower repair costs. The economical life of airlift equipment is sometimes quite short owing to changing water levels and reduced efficiency from that cause.

3. SUCTION SUMP DESIGN

Propeller pump performances are affected to a large degree, by the flow in the suction sump. These are due to high relative velocities, short impeller passages, few vanes and limited guiding action from the suction bell. It is necessary to consider: a) strainer and trash racks, b) spacing of several units, c) sump intake or flow distribution, d) submergence, and e) clearance from floor to walls (Figs. 9 and 10).

Fig. 9 Suction sump design showing proper spacing

Submergence is selected with regard to cavitation limits. Minimum submergence limits are set to prevent vortices in the suction sump. It is ideal to set the lower edge of the suction bell at five feet (1.5 m) or lower. The minimum allowable should be the diameter of the suction bell which should not be less than twice the impeller hub or eye to keep the pump self-priming at all times that it is operational.

Fig. 10 Various correct and incorrect designs for suction pumps

In sump design, it is important that the amount of turbulence and entrained air (Fig. 11) be kept to a minimum. The inlet end of the suction line should be 3 to 6 feet (0.9–1.8 m) below the minimum water level. Baffles are used for vortex protection. Figure 12 can be used as a guide for minimum submergence. Figure 13 illustrates baffle arrangements for vortex protection.

Floor clearances are the free areas between the suction bell and the sump floor. This distance should be at least equal to the area of the bell itself. Figure 14 shows some clearance dimensions for sump installation.

Fig. 11 Correct and incorrect sump designs for minimum entrained air into suction line

Fig. 12 Minimum suction pipe submergence, h feet for pipe flow velocity, ft/sec
(Source: Goulds pumps manual)

When the intake sump or pit is supplied by a tube, the diameter of the supply tube should be at least twice that of the sump column diameter with the absolute minimum being 1.5 times that size.

Fig. 13 Baffle arrangement for vortex prevention

4. INSTALLATION

Some precautions must be observed in planning a pump installation. Such items as sump design, suction piping design, and discharge pipe size must be carefully considered.

Both the suction and discharge lines should be independently supported so that no strains will be thrown on the casing. The suction line should never be smaller than the suction connection of the pump and may be one size larger. Suction lines must be as short as possible. Any elbow must have long radius. For pumps operating with a suction lift, no valves other than a foot valve should be used. Suction lines should be airtight and high spots at which dissolved gases or air might separate out and destroy the vacuum must be avoided. Inspection with a flame is recommended in that air leakage will draw air into the opening. The elbow next to the pump suction line must be vertical.

Fig. 14 Types of sump installations

Fig. 15 Types of propeller pump installations

A check valve and a gate valve are usually placed in the discharge line. The gate valve regulates the flow and the check valve prevents backflow into the pump. The check valve is placed between the gate valve and the pump.

5. OPERATING DIFFICULTIES

To avoid operating difficulties, the following precautions must be taken into account:

1. The foot valve may become jammed and cannot open fully. This results in insufficient suction head.

2. The foot valve may become jammed with leaves, aquatic plants, etc. The suction line may be clogged. Periodic inspection is necessary. The sump may have to be redesigned.

3. The water level may decrease and the depth of submergence becomes inadequate. This may result in air getting into the suction lines. Under this condition, the flow may be reduced or stopped entirely on account of cavitation, resulting to possible mechanical destruction due to vibration of the unit.

4. Air may leak into the suction lines or at pump casings. This leakage may occur at the joints or at the packing boxes. The leaks are located by holding a flame near the joints.

6. ACCESSORIES AND OTHER DEVICES

For pumps that are not the self-priming, propeller or submerged types there is a need for foot valves. For the selfpriming pumps, the valve is in the pump body itself necessitating very little priming. In some volute centrifuge pumps, priming handpumps and/or tanks are integrated with the pump system during construction.

For the propeller pumps, one of the accessories is the “gear drive” which does three things:

1. Changes the direction of the drive from vertical to horizontal to accommodate most prime movers;

2. Serves to change input RPM to the desired or designed pump RPM; and

3. provides auxillary horizontal drive where there already is a vertical electric motor drive.

Gear drives are also used to change direction of rotation but these gear drives at times cost as much as the pump itself if not more. It is also possible to install pumps at a slanting position and have them driven directly by the use of cross joints or shafts.

An angle drive can be made out of surplus differentials by permanently immobilizing one side of the differential (Jamandre, 1977). Different horsepowers can be accommodated as well as different gear ratios because of the wide variety of available differentials from cars, trucks and tractors.

In most cases drive shafts and cross joints, chains and other flexible couplings are chosen over pulley and belt systems especially for permanent high horsepower installations where prime movers and pump's R P M are matched.

For coastal water applications, corrosive effects of saltwater have to be taken into consideration. In some places, pump columns are made of either wood or concrete. Because cast iron is less affected by saltwater than steel, propeller pumps are usually of cast iron construction.

Fiberglass and ferrocement have been used, and in some propeller pump fabrication, the whole assembly is thickly coated with zinc which makes it quite durable and rust resistant. There are also asphalt and epoxy paint jobs available at the option of the customer. Figure 15 represents some propeller pump installations.

7. PRACTICAL APPLICATIONS

So far, pumps have been discussed in their capacity for moving water into ponds. Jamandre (1977) designed a pump to move water in and out of the pond, regardless of the tide conditions in the supply rivers (Fig. 16). Being able to drain and fill ponds at will gives the operator of the pond certain advantages:

1. He can harvest his crop when prices are good while other operators will have to wait for ideal tide situations.

2. He can discharge low oxygen water and replenish the pond with new high oxygen water.

3. He can have higher stocking densities and be more flexible with pond management procedures.

With pumps, it is possible to operate swamplands that previously could not be utilized because they were elevated or submerged. Pumps can remove the oxygen deficient water or totally drain these ponds for harvesting.

8. OTHER CONSIDERATIONS

Selection of the correct pump for a particular application requires knowledge of the pump characteristics of the various types of pumps. The system requirements in terms of total head and discharge and the characteristics of the fluid that must be pumped in addition to these requirements should be known.

The initial decisions required in pump selection require knowledge of at least the following:

1. Total head required
2. Discharge required
3. Suction lift required
4. Liquid to be pumped and its characteristics
5. Whether the service is to be continuous
6. Types of power to be used
7. Space, weight and similar limitations

8. Special requirements.

The selection of the materials for pump construction is at best a compromise between the cost of manufacture and the anticipated maintenance costs. Many pump installations start out with a low service factor and through operating experience are gradually upgraded in materials until an acceptable and scheduled replacement programme is achieved. It must be anticipated that for the more corrosive services, modifications and replacements of the parts that are in direct contact with water will be necessary during the life of the pump.

A pump selection study should always be made, but before initiating such a study, all previous studies made to determine the total pumping requirements or station capacity, pertinent water surface elevations, terrain, utility locations, proposed station or well location, points of discharge and the proposed method of operation should be reviewed. Also to be considered is the experience of the personnel that will be responsible for the operation and maintenance of the installation.

The number of pumps ultimately used should be consistent with the demand of the project (Annex B). If during the pump selection process it is found that the rated horsepower of the prime mover exceeds the maximum horsepower requirements by a considerable amount, the contemplated number of pumps should be increased or decreased provided the change results in a better horsepower match without increasing the overall cost of the installation (Annex C).

The prime movers used in drainage and irrigation installation are electric motors, diesel and gas engines. The one to be used in any particular situation must be determined before the pump can be selected. The following guidelines can be considered.

a. Electric motors - Electric motors are the most economical installations and should be used when a reliable source of electric power is available and when the cost of bringing it into the pumping station is not unreasonable.

All motors should be full voltage starting unless it is specified by the electric power company that reduced voltage starting is necessary. Devices to automatically start and stop the pump can be attached to the installation.

b. Engines - Engines run by fuel energy are used to drive pumps when it is not feasible to use electric motors. They are more expensive than electric motors but reliable if properly maintained and serviced. There are also variable speed drives that should be operated at constant speeds whenever possible. The requirements of most installations can be met with constant speed operation. However for those that cannot, the number of speeds should be held at a minimum.

Fig. 16 Main tidal gate - with auxiliary pump for electric & diesel engine drive

The following checklist is supplied for use when considering materials for pump usage.

8.1 Impellers

For most water and other non-corrosive services, bronze satisfies this criterion on an evaluated basis. Cast iron impellers are used to a limited extent in small, low cost pumps. The factors to consider are: (i) corrosion resistance. (ii) abrasive wear resistance, (iii) cavitation resistance. (iv) casting and matching properties, and (v) cost.

8.2 Casings

For most pumping applications, cast iron is the preferred material when evaluated against initial cost. For single stage pumps, cast iron is usually of sufficient strength for the pressure developed. For casings, the following factors are considered: (i) strength, (ii) corrosion resistance, (iii) abrasive wear resistance, (iv) casting and machining properties, and (v) cost.

8.3 Shafts

The endurance limit is the stress below which the shaft will withstand an infinite number of stress reversals without failure. Since stress reversal occurs every revolution, the shaft would never fail if the actual maximum bending stress in the shaft is less than the endurance limit of the shaft material.

In actual operation, the endurance limit is substantially reduced because of corrosion and stress raisers such as threads, keyways, and shoulders on the shaft. In the evaluation and selection of the shaft, material consideration must be given to the corrosion resistance of the material in the fluid being pumped as well a the notch sensitivity.

8.4 Deciding on suitable pump arrangement

The final selection of the pumping arrangement to be used in a given installation and the particular bid to select in accordance with this arrangement usually depends upon an economic study of the various alternatives available. Such a study may also dictate the replacement of an existing pump or pumping arrangement which appears to be giving satis-factory service.

The total cost of the pump end driver is made up of the purchase price plus the annual charges required to keep them in operation. Annual charges include the cost of power, taxes, and so on.

9. MAINTENANCE

The working schedules of the semi-annual and annual inspection programmes should be entered on individual pump maintenance cards which contain a complete record of all the items requiring attention. Space for comments and observations on conditions of the parts to be repaired or replaced must also be provided.

In all cases, a log showing a complete record of the cost of maintenance and repair should be kept for each individual pump, together with a record of its operating hours. A study of these records will generally reveal whether a change in materials or even a minor change in construction may not be the most economic course of action.

10. SUMMARY AND RECOMMENDATIONS

The following pumps, in order of preference, are suitable for use in coastal aquaculture:

1. Self-priming volute pumps
2. Mixed flow volute pumps
3. Radial flow propeller pumps
4. Mixed flow propeller pumps

5. Axial flow propeller pumps.

Selection of pumps should be made on a case to case basis depending on the characteristics of the area where the pump is to operate and the conditions under which it is to operate.

Peurifoy (1970) states that even before selecting a pump for a given job, it is necessary to analyze all information and conditions that will affect the selection. The most satisfactory pumping equipment will be the combination of pump and pipe for the period that it will be used with an appropriate allowance for salvage value at the completion of the project. In order to analyze the cost of pumping water, it is necessary to give certain information such as:

1. Rate at which water is pumped
2. Height of lift from the existing water surface to the point of discharge
3. Pressure head at discharge, if any
4. Variations in water level at suction discharge
5. Altitude of project
6. Height of the pump above the surface of water to be pumped
7. Size of the pipe to be used if already determined

8. Number, sizes and types of fittings and valves in pipelines.

11. LIST OF REFERENCES

Church, A.H. 1944. Centrifugal pumps and blowers. Robert E. Krieger Publishing Co., Huntington, N.Y. 1972.

Department of State Agency for International Development. 1963 Village Technology Handbook.

Jamandre, T.J. 1977 Pumps for brackishwater aquaculture. Joint SCSP/SEAFDEC Workshop on Aquaculture Engineering, SCS/GEN/77/15.

Karassik, I.J., W.C. Krutzch, W.H. Frazer and J.H. Messina. 1979 Pump handbook. McGraw Hill, New York, N.Y.

Olson, R.M. 1961 Essentials of engineering fluid mechanics. International Textbook Company, Scranton, Pennsylvania.

Peurifoy, R.L. 1970 Construction, planning, equipment and methods. International Student Edition. McGraw Hill Book Co., New York, N.Y.

Turneaure, F.E. and H.L. Russel. 1940 Public water supplies: requirements, resources and the construction of works, 4th Ed., John Wiley and Sons, Inc., New York. U.S.A.

Wheaton, F.W. 1977 Aquacultural Engineering. John Wiley and Sons, New York, N.Y.

ANNEX A
DEFINITIONS OF TERMS USED ON PUMPS

1. Suction lift exists when the source of supply is below the centre line of the pump. It is the vertical distance. Static suction lift is the vertical distance from the centre line of the pump from the free level of the liquid to be pumped.

2. Suction head exists when the source of supply is above the centre line of the pump. Static suction head is the vertical distance from the centre line of the pump to the free level of the liquid to be pumped.

3. Static discharge head is the vertical distance between the pump centre line and the point of free discharge or the surface of the liquid in the discharge tank.

4. Total static head is the vertical distance between the free level of the source of supply and the point of free discharge of the free surface of the discharge liquid.

5. Friction head is the head required to overcome the resistance to flow in the pipe and fittings. It depends on the size of pipe, type of pipe, flow rate and nature of liquid.

6. Velocity head is the energy of a liquid as a result of its motion at some velocity V.

7. Pressure head must be considered when a pumping system either begins or terminates in a tank which is under some pressure other than atmospheric.

8. Total dynamic suction lift or the static suction lift plus the velocity head at the pump suction flange plus the total friction head in the suction line. It is the reading of a gauge on the suction flange, converted to feet of liquid minus the velocity head at gauge attachment.

9. Total dynamic suction head is the static suction head minus the velocity head at the pump suction flange minus the total friction head in the suction line.

10. Total dynamic discharge head is the static discharge head plus the velocity head at the pump discharge flange plus the total friction head in the discharge line.

11. Total dynamic head is the total dynamic discharge head minus the total dynamic suction head or plus the total dynamic suction lift.

12. Vortex is the movement of a liquid in a circular motion.

13. Cavitation is an undesirable condition that causes noise, vibration and even pump damage. It occurs when conditions within the pump cause cavities to form due to local pressure drop.

14. Capacity is the volume of liquid pumped, per unit of time measured in gallons per minute or in cubic meters per hour.

15. Efficiency is the ratio of pump energy output to the energy applied (input) to the pump shaft. The degree of hydraulic and mechanical perfection of a pump is judged by this criteria. Efficiency is governed by impeller design, impeller to case clearance, back flow, channel and sump design, speeds, cavitation, construction and guide vanes, among other considerations.

16. Performance curves the variations of head with capacity at a constant impeller speed. A complete characteristic includes (i) efficiency, (ii) brake horsepower curves, and (iii) head variations. The variations in head, capacity, brake horsepower and speed follow established values known as “affinity laws”. In general, capacity varies directly with speed. Head varies directly with the cube of the speed.

ANNEX B
PUMPS IN SERIES OR PARALLEL COMBINATIONS

For a given capacity, the total head is the sum of the heads added by each individual pump, the resulting characteristics curves being similar to that obtained by multi-staging on a single shaft.

When two or more similar pumps are in parallel, the total capacity is increased to two or more times the capacity of each individual pump for the same head.

In the figure below, one pump will operate at point A, and two pumps will operate at point B, depending on the pump combinations as series of parallel.

In the above figures, one pump will operate at point A and two pumps will operate at point B. In the series combination, the head will double; in the parallel combination, the capacity will double.

ANNEX C
PUMP SIZE AND HORSEPOWER REQUIREMENT
(After C.A. Kulman, Nomographic charts, McGraw-Hill N.Y. 1951:108–109)

ABSTRACT

Preliminary selection of pump and drive motor size may be made using this nomograph.

TOOLS AND MATERIALS

Straight edge for nomograph

DETAILS

For preliminary sizing of a pump used to lift liquid to a known height through simple piping, follow these steps:

1. Determine the quantity of flow desired in gallons per minute. 8.33 = 1 gallon.

2. Measure the height of the lift required (from the point where the water enters the pump suction piping to where it discharges).

3. Choose a pipe size, so that velocity through it will be about 6 feet per second (see entry on “Velocity of water in Pipe”).

4. Estimate the pipe friction loss “head” (10 foot “head” represents the pressure at the bottom of a 10 foot high column of water) for both suction and discharge piping, using the following table.

Average friction loss for water flowing through pipe when velocity is 6 ft/second.

Any bends, valves, constrictions and enlargements (such as passing through a tank) add to friction. The equivalent pipe length of such “fittings” in the pipe line should be added to the pipe length used in the friction loss equation. A separate handbook entry gives a quick and easy estimate of equivalent lengths. For friction loss when velocity is greater than 6 feet per second.

Obtain “Total Head” as follows:

Total Head = height of lift + friction loss head

Using a straight edge connect the proper point on the “Total Head (ft)” line with the proper point of the “Discharge U.S. gallon per minute” line. Read motor horsepower and pump size (diameter of discharge outlet), choosing the printed values just above the straight edge.

Note that water horsepower is less than motor horsepower. This is because of friction losses in the pump and motor. The nomograph should be used for rough estimate only. For an exact determination give all information on the flow and piping to the pump manufacturer. He has the exact data on his pump for various applications. Pump specifications can be tricky especially if suction piping is long and the suction lift is great.

EXAMPLE

Desired — to pump 100 gallons per minute 50 feet high, no fittings

Pipe Size — 3" (for 6 feet per second) reference: Handbook entry “Velocity for Water in Pipes”

Friction loss head — about 3 feet
Total head — 53 feet
Pump Size — 2"
Motor horsepower — 3 hp

If you plan to use human power for the pump, figure that a man can generate about 0.1 hp for a reasonably long period and 0.4 hp for short bursts. From this and the total head, you can predict the flow you should design the hand pump for.

EVALUATION

Tables and Nomographs are heavily used by U.S. engineers.

SCS/82/CFE/CP-18

WATER PUMPS USED IN SHRIMP FARMS IN THAILAND¹

by

P. Tharnbuppa²

1. INTRODUCTION

Shrimp farming requires considerable management inputs in dealing with water quality, irrigation and maintenance. In Thailand, particularly in the Gulf of Thailand coast, water supply is an important problem because of narrow tidal fluctuations throughout the year. Water pumps have to be employed to provide mechanical aid to control this problem.

In the past, pumps were of the simple types designed for small-scale shrimp farming. Shrimp farming has since developed and considerable technological progress has been attained resulting in increasing large-scale investments. Accordingly, pumps used in aquaculture have been improved and there are new types of pumps currently commonly in use in Thailand.

In the main, there are four types of pumps used in coastal aquaculture. These are described in the following Sections.

2. DRAGON WHEEL PUMP

This is a simple type of water pump which is still in use in some shrimp farms. The delivery rate of this pump is low since water is drawn through wooden buckets or troughs. The merit of this pump is that it can be used under any tidal situation.

Sometimes this type of pump can be run by windmill, but recently engines powered by diesel fuel has come up for more general use. The main part of the pump comprises a diesel engine which drives the wheels to draw water into the pond. The following summarizes the specifications of a typical unit.

3. PUSH PUMP DRIVEN BY DIESEL ENGINE

In the past decade, shrimp farmers especially in Samut Prakarn. Samut Sakhorn and Samut Songkram provinces of the inner part of the Gulf of Thailand where shrimp farms are concentrated, have been using the push pump, designed by a Thai mechanic. Before this, most shrimp farmers used the afore-described conventional dragon wheel pump, which is a much less efficient pump. This did not enable the farmers to raise their yield since the production of shrimp farms depends mainly on the amount of water delivered into the pond. As the traditional type of shrimp farming in Thailand is solely concerned with the grow-out of wild seeds, the more water pumped into the pond the greater is the number of shrimp stock.

The push pump has rapidly become popular among shrimp and finfish farmers in the coastal areas of Thailand.

The push pump delivers water in large volume and high pressure through an asbestos pipe to a concrete water conveyor. It is estimated that the volume of water pumped through the system using a 120 hp engine is 5 196 m³/hr approximately.

3.1 Installation

3.1.1 Engine installation

The site for the installation of the pump should be on firm ground and above high tide level to avoid flooding. The angle formed by the conveyor pipe and the bottom of the receiving canal should not exceed 20°. The smaller this angle the better the efficiency (Fig. 2). The discharge head of the pipe must be installed on the bottom of the water conveyor canal. The smaller the length of the pipe the lower the height and the better the working efficiency of the pump system. The direction of the propeller should be set inside and near the suction head of the pipe (Fig. 2). The direction of the propeller shaft should be in alignment with the engine gear to the centre of the pipe (Fig. 2). Theoretically, the propeller shaft must be laid inside and in line with the engine and the pipe.

¹ Contribution to the FAO/UNDP-SCSP Consultation Seminar on Coastal Fishpond Engineering, Surabaya. Indonesia, 4–12 August 1982.
² Senior Fisheries Biologist. Brackishwater Fisheries Division. Department of Fisheries, Bangkok. Thailand.

Fig. 1 Dragon wheel pump

3.1.2 Water conveyor installation

The pump unit consists of five main parts and accessories:

A water conveyor is used to bring water directly into the pond(s). It is made of concrete or bricks in rectangular shape of about 2 m high. 6–8 m long and 1 m wide (Fig. 1).

3.2 Main parts and accessories

The pump unit consists of five main parts and accessories: a diesel engine (usually a used truck engine); a propeller shaft. with length of 6–8 m; a propeller (2 or 3 bladed); a pipe (usually defective asbestos pipe); and a propeller shaft joint (or joints). Data on the use of this type of pump are shown in Table 1.

Fig. 2 Push pump and installation

Table 1
Some features of diesel powered push pump

* 1 Rai = 1 600 m²
** More than 220 hp

4. PUSH PUMP DRIVEN BY ELECTRIC MOTOR

This a new type of water pump utilized in shrimp farms with supply of electricity. The performance and the method of installation of this pump are like those of the engine push pump. This new push pump uses power from an electric motor instead of a diesel engine. At least, a 20 hp motor is required.

5. COMBINATION PUMP (Fig. 3)

Fig. 3 Combination pimb

This is the newest type of water pump modified from the engine push pump by using the engine air compressor together with that from an air compressor to the engine, for pushing up underground waters for two purposes: first, for mixing with the seawater to reduce water salinity in the pond, and second, for household use.

When the pump is operated, underground water will be lifted by the effect of pressure generated from the air compressor.

5.1 Installation

5.1.1 Engine installation

The site preparation and procedures for installation of this pump are the same as those for the push pump.

5.2 Air compressor installation

The main pipe of 3–4 inches (7.6–10.2 cm) in diameter is driven down to underground below water table where fresh-water may be available. Inside this pipe, a concentric inner pipe of 1–2 inches (2.5–5.8 cm) in diameter for water uptake is inserted down to the water table, and connected to the ponds or water storage tank. The air exhaust pipe of the air compressor engine, 0.5 inch (1.2 cm) in diameter, is then connected to the main pipe of 3–4 inches (7.6–10.2 cm) in diameter.

6. COST OF DIFFERENT PUMPS

The costs of the four different types of water pumps are briefly listed in this sub-section.

7. CONCLUSIONS AND RECOMMENDATIONS

In all types of the aforementioned pumps, there are two sources of driving the unit-engine drive and motor drive. The motor-driven pump has been modified and used since the last two years. Some of the push pumps driven by used truck engines are also combined with water well unit and the air compressor of the unit will airlift freshwater from underground. The usage of any specific type depends on the locality and suitability.

The advantages of push pumps are as follows: (i) greater volume of water delivered; (ii) save time in pumping water during spring tide; (iii) increase in number of wild seed collected; and (iv) possibility of attaching freshwater airlift pump.

At present all the motor-driven pumps are used directly without gear attachment so that driving speed cannot be adjusted as desired. Hence, the pump unit should be improved.

SCS/82/CFE/CP-11

PADDLEWHEEL AERATOR FOR EMERGENCY POND AERATION¹

by

P. Menasveta² and P. Leeviriyaphanda³

1. INTRODUCTION

Severe oxygen depletion in the fishponds poses a major fish culture management problem to many aquaculturists. It usually occurs in ponds which have been used for fish, shrimp or prawn culture for a period of time. In the case of the culture of the giant freshwater prawn (Macrobrachium rosenbergii), oxygen depletion usually occurs after four to five months of culture. Green, et al (1977) reported that 45 percent of the giant prawn reared in an experimental pond were killed within three days resulting from severe oxygen depletion in the pond water during the night time. The responsible factors include the over-fertilization of pond water by feed residue degradation, bottom turn-over due to heavy rains and an algal bloom.

It is therefore sometimes necessary to the pond water aeration to prevent fish or prawn mortality when dissolved oxygen concentrations are low. This paper reports the design of a paddlewheel aerator for emergency aeration of the culture medium. It should be noted that the present design is a modification of the paddlewheel aerator manufactured by Clark Livingston Machine Shop, Greensboro, Alabama.

2. DESIGN AND EXPERIMENTAL PROCEDURE

The aerator (Fig. 1) consists of two paddlewheels mounted on the axles of the Austin van differential. The wheels are rotated by a drive shaft connected to a diesel engine by a belt. Twelve paddles each 35 cm long by 15 cm wide, are attached to each wheel. The diameter of each wheel is 35 cm. The shaft is 5.3 m long and it is placed on three ball bearing spots of a chassis. The chassis is placed on the leveling devices attached to an axle of the tires. On operation, the paddlewheel aerator was positioned in the pond so that paddles on the under size of the wheels extended 25 cm into the water. The 12 hp diesel engine was operated at 1 900 rpm. The paddlewheels could splash large volumes of water into the air and set up a strong circulation pattern in the pond.

Fig.1 The Thai-made paddlewheel aerotor towed by on “E-Tan” tractor

A pond of 0.32 ha (40 m × 80 m × 1.5 m deep) belonging to the Golden Claw Prawn Co., Ltd. was utilized for the feasibility study of the aerator. The pond has been used for giant prawn culture for six months. The experiment was carried out for two nights. This was done to prevent the addition of oxygen by photosynthesis. The pond was not aerated on the first night but it was aerated in the second night from 0000 to 0800 hours. Certain water quality parameters were checked in four positions of the pond at every two hours starting from 0000 hr and the weather conditions were recorded.

3. RESULTS AND DISCUSSIONS

The average values of certain water quality parameters, including dissolved oxygen (DO), pH and temperature, of the non-aerated night and aerated night are shown in Table 1. It is interesting to note that only DO concentrations showed significant variation. Weather conditions of the two nights were similar; there was neither wind nor breeze in both nights.

Table 1
Average values of certain water quality parameters of the non-aerated pond and aerated pond

a. Non-aerated, October 22, 1981

¹ Contribution to the FAO/UNDP-SCSP Consultation Seminar on Coastal Fishpond Engineering, Surabaya. Indonesia, 4–12 August 1982.
² Associate Professor. Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
³ Farm Manager, Golden Claw Prawn Farm, Klong 8. Rangsit, Pathumtani, Thailand.

b. Aerated, October 23, 1981

The DO concentrations of the non-aerated night decreased from 3.15 mg/l at 0000 hr to 1.80 mg/l at 0600 hr. The latter level of DO is very near the critical level. It has been observed that the giant prawn starts to die when DO decreases to 1.50 mg/l. On the aerated night, DO did decrease from 3.37 to 2.50 mg/l during the initial period of aeration (0000-0200 hr). However, the aeration could maintain DO at the latter level, and it started to level up later in the night (Fig. 2).

Fig.2 Dissolved oxygen in non-aerated and aerated ponds

From this study, it can be concluded that the paddlewheel aerator could more or less maintain the DO concentrations in the pond at safety levels throughout the night.

The design of this aerator differs from the Greensboro design at two points. First, the present aerator is equipped with the level devices; therefore, it is easier to set the position of paddles in pond water. Second, the shaft is belt-driven, instead of the direct drive from a power-take-off of a farm tractor. Our diesel engine is 12 hp when compared with the farm tractor which has more than 50 hp; therefore, the operational cost is less. Fuel consumption of this aerator was 1.5 liter/hr. If the whole period of aeration was calculated (8 hrs) the fuel consumption would be at 12 liters. The total cost for manufacturing this aerator in Thailand excluding a diesel engine was US$300.

Emergency aeration is expensive but oxygen depletion may cause extensive fish or prawn mortality and farms must have such equipment available to mechanically aerate oxygen deficient waters.

REFERENCES

Green, J.P., T.L. Richards and T. Singh. 1977 A massive kill of pond-reared Macrobrachium rosenbergii. Aquaculture 11:263–272.

SCS/82/CFE/CP-12

WIND AND WAVE ACTION IN COASTAL PONDS¹

by

B. Tiensongrusmee²

1. INTRODUCTION

Wind and wave action against the coastal ponds has long been recognized as a problem by fishfarmers. However, engineering concepts and principles have only been recently incorporated into the design of ponds and its adjacent shoreline to minimize wind and wave effects.

2. WIND AND WAVE ACTION AGAINST SHORE FACILITIES

The most natural and effective form of wind and wave breaks of coastal ponds near the shoreline is the mangrove buffer zone. Foreberg (1971) and Chapman (1971) suggest that the devastating effects of the 1970 tidal wave which struck Bangladesh would have been less severe if the coastal belt of mangrove forest had not been converted into the paddy fields. A belt of mangrove at a distance of between 100–400 m from the coastline can serve this purpose. Where ponds are not located in a mangrove area, wave and wind breaks can be designed to protect the pond against erosion and destruction of dikes and shoreline. Size and types of the structures vary according to the conditions for which they are constructed. Breakwaters commonly employed are described below.

2.1 Riprapping (Fig. 1)

Fig. 1 Rubble-stone breakwater

Riprapping is composed of rubble stones, concrete blocks or concrete slabs placed on the face of dikes or leavees to prevent erosion by wave action. It is important that the stone be placed on a berm built into the dam to prevent slippage of the riprap. The berm area should be covered with 20–50 cm of crushed stone before the riprap is placed on top. The crushed stone prevents waves from eroding the soil around and beneath the riprap.

2.2 Floating breakwater

A floating breakwater can be designed to reduce the wave action to protect the aquaculture system. The breakwater can be either a rigid type or made of flexible floats.

2.2.1 Rigid type

A pontoon is typical for this type of floating breakwater. This type of breakwater has an excellent damping effect but is difficult to anchor due to the strong stress on mooring ropes and on the sides of the float.

2.2.2 Flexible float

The simplest form of this type of floating breakwater is floating plates (Fig. 2). The tension applied to the mooring cable is small. When the wave meets the floating part, the wave energy is reflected by the plate, part is transformed into energy as water flowover and part of it is absorbed by the plate and its support.

Fig. 2 Floating plate

2.3 Wooden type breakwater (Fig. 3)

Fig. 3 Wooden-type breakwater

¹ Contribution to the FAO UNDP-SCSP Consultation Seminar on Coastal Fishpond Engineering, Surabaya, Indonesia, 4–12 August 1982.
² Senior Aquaculturist Team Leader of Institutional Support for LKIM Aquaculture Development Project (FAO/UNDP/MAL/018), Tingkat 7. Wisma PKNS, Jalan Raja Laut, Kuala Lumpur, Malaysia.

Bamboo, coconut trunk, pine trees, palm trunks and mangrove poles can be driven in two lines in front of the shoreline at some distance. The piles are held together by stakes to increase the strength. The space between the lines is filled with twigs and branches of trees. The barrier acts as an energy absorber and dissipates wave energy before the waves reach the shoreline.

2.4 Worm out tires (Fig. 4)

Fig. 4 Worn-out tires breakwater

Worn out tires can be tied together in a pyramid and arranged to from an elevated barrier.

2.5 Secondary levee

To absorb wave pressure against the main dike, a secondary levee is often constructed. It is a low dike or block-mound breakwater which is submerged in front of the main levee.

2.6 Wave deflectors

Concrete wave deflectors may be designed to serve as wave breaks in areas facing the wash wave. The most common one is the six leg type placed on the bottom in front of the shoreline.

3. WAVE AND WIND ACTION AGAINST THE COASTAL PONDS

On large ponds the wind often creates waves large enough to severely erode the surface of the dike above and below the water level. This action on new ponds is often so severe that a foot or more of the dike is washed out in one day. Wave height created by wind in a brackishwater pond is a function of fetch which is the unobstructed straight line distance from the furthest point in the pond. Wave height can be related to fetch by the equation:

Wave action in ponds is caused by wind blowing across the surface. One cannot totally control wave action in ponds although it can be minimized. To minimize the wind and wave action against the dike, the following features can be incorporated into the design.

3.1 Proper orientation of the pond with respect to the direction of the prevailing wind

Every location is subject to the prevailing winds. Monsoons for instance, northeast monsoon blows from one direction over part of the year and southwest monsoon from the opposite direction over the remaining part of the year. Trade winds generally come from the east, prevails during the rest of the year when the monsoons are weak (Fig. 5).

Fig. 5 Wind direction in Southeast Asia

If pond layout can be oriented to reduce the length of the exposed area, it will lessen the side length of dike exposed to wave action. For instance, the longer pond dimension should be positioned somewhat parallel to the direction of the prevailing wind (see Fig. 6). This orientation of pond compartments will also have some advantageous effect in pond management.

Fig. 6 Layout of pond compartments oriented to the prevailing wind direction

3.2 Fetch length reducer (Fig. 7)

Fig. 7 Fetch reducer and wave absorber berm

Reducing the fetch length also minimizes the height of waves. This can be done by a submerged dike within the pond. Such submerged dikes can be small and short constructed at intervals across the direction of wind/wave.

3.3 Wave absorber berm

The pond dike has a gradually sloped front which reduces the wave pressure caused by the incident standing wave. To absorb wave pressure against the dike, a small berm can be incorporated in the design (Fig. 7).

3.4 Riprapping the dike

A log can be placed along the face of the dike to break waves and to prevent dike erosion. Bamboo poles 10–20 cm in diameter and approximately 6 m long are held in position along the surface of the dike by driving stakes along each side. The bamboo should be lapped so that there are no gaps between the poles. A system of this type allows a certain amount of fluctuation of water level and also gives good protection.

3.5 Pneumatic barrier (Fig. 8)

Fig. 8 Air bubble curtain

A continuous stream of bubbles emitted from a sunken hose perforated at intervals through which compressed air is released can reduce the wave height generated by the wind. This method also increases the oxygen content in the pond.

3.6 Planting trees and/or a farm crop along perimeter dikes to reduce wind action

To prevent erosion of the dike by heavy rains and strong winds, a suitable crop can be used to cover the entire surface area of the dikes. This practice is efficient and done in Central Java. Growing farm crops on the dikes maximize the utilization of land and prevents erosion of dikes due to wind and wave action. The crops that can be grown on the dikes are pumpkin (Lenenaria leucantha), spinach (Amaranthus), cassava (Manihot utilissima), maize (Zea mays) and chilli (Capsicum annum).

4. CURRENT BREAKERS

Current breakers commonly employed are green belt buffer zones, jetties and riprapping.

4.1 Green belt buffer zone

Mangrove not only protects the coastline, embankment and dikes from currents but also acts as a stabilizer to settle the suspended organic load brought by the current. In the central parts of west coast of Peninsular Malaysia, the rate of accretion has been rapid due to mining activity. Substantial amounts of fine sediments derived from the mining and deforested areas are carried out to sea by rivers. These sediments subsequently settle on the shore through tidal and wave action. Dixon (1959) noted changes along a stretch of the coast over a period of thirty years and found a net gain of new land. Acceretion resulted in the formation of 3 860 acres (1 560 ha) of new forest, while erosion resulted in the loss of 1 620 acres (650 ha) during the same period.

In areas where the mangrove are scarce, the mangrove can be planted. From the silvicultureal point of view, the mangroves are easy to farm. Rhizophora spp can be planted by sticking foot long fruits into mud which take roots rapidly. White and White (1976) reported the almost complete natural regeneration in 10 years of several sites in Papua New Guinea cleared for oil drilling operations. In Thailand mangrove planting along the river banks of Klong Wan Fishery Station, Prachuabkirikhan and also at Bang Chan Fisheries Station at Chantaburi Province provide good examples of the effort. After 5 years, the mangroves grow big enough to protect the river bank from erosion by current. The reforestation programme in the Tumpang seri ponds at Ujung Krawang and Tangerang district of West Java are additional examples. From 1976–1979, about 2 355 ha were reforested (Poernomo, 1980).

4.2 Jetties (Fig. 9)

Fig. 9 Jetties

Current can erode river banks and endanger fishponds in the vicinity. To prevent this, jetties made of bamboo or coconut trunks set in the from of an inverted V towards the bank are installed. Branches and twigs are placed inside to slow down the current and allow colloidal suspension to settle at the bottom.

4.3 Riprapping

Riprapping as discussed in section 2.1 can be designed to reduce the current action against the river bank.

5. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

Coastal breakwaters widely used in coastal fishponds to protect wind and wave action against shore facilities are mangrove buffer zones, riprapping, floating breakwaters, wood barriers, worn out tires, secondary levees and wave deflectors. To protect from wind and wave action in coastal ponds, the proper orientation of the coastal pond in relation to the direction of the prevailing wind is important to minimize the fetch or length of exposed area to wind. Other ways are by providing a wave absorber berm, riprapping the dike, installation of a pneumatic barrier and planting trees or farm crops along the dike. The effective structures for current breakers are green belt buffer zones, jetties and riprapping.

Since there are many types of breakwater that can be used to protect from wind, wave and current action against shore facilities and coastal fishponds, it is necessary to evaluate the available types as to their feasibility, their relative effect in dampening wave energy, durability, life span and economics. The structure must be checked and modified properly by applying the most advanced analytical methods and verified by model tests.

6. REFERENCES

Chapman, V.J. 1971 Mangroves v. tidal waves. Biol. Conserv. 4:39

Dixon, R.G. 1959 A working plan for the Matang mangrove forest reserve Perak (First revision report, 1959), Perak, Malaysia. Forest Department, 173p.

Foreberg, F.R. 1971 Mangroves v. tidal waves. Biol. Conserv. 4:38–39.

Poernomo, A. 1980 Status of the tumpang-seri system of brackishwater pond. FAO/IPFC working party on aquaculture and environment, Indonesia, 7p.

White, K.J. and A.E. White. 1976 The effects of industrial development on mangrove forests in the Gulf province of Papua New Guinea. Ecol. Prog. Rep. Off. for Port Moresby (3): 13p.

SCS/82/CFE/CP-27

ECONOMIC CONSTRAINTS OF SMALL/MEDIUM SCALE SHRIMP HATCHERY INDUSTRY (CASE OF P.T. BENUR UNGGUL, INDONESIA)¹

by

Z. Iskandar²

ABSTRACT³

P.T. Benur Unggul, a newly established company in 1981, under P.T. Bahana Pembinaan Usha Indonesia (Venture Capital Company) is engaged in shrimp hatchery with the main aim to provide shrimp fry to fishfarmers to meet the shortfall of supply. It is categorized as a small/medium scale industry due to the fact that the total cost of the project is less than Rp 200 million (US$317 000). The management of the hatchery including manpower requirement and the annual production target of shrimp fry are explained. In marketing the production as of the present moment, there is an indication that hatchery produced seeds are not preferred by fishfarmers for the reason of high mortality and slower growth. To cope with these problems, attention will be given to marketing promotion taking into consideration the role of “tengkulak” (middlemen).

The layout and design of the hatchery is described and the investment costs and the estimate of annual operating costs are given.

¹ Contribution to the FAO/UNDP-SCSP Consultation Seminar on Coastal Fishpond Engineering, Surabaya, Indonesia, 4–12 August 1982.
² Manager, Business Development, P.T. Bahana Pembinaan Usha Indonesia, (government-owned, Development Financing Corporation), Jakarta; Project Supervision Manager, P.T. Benur Unggul (shrimp hatchery industry), Besuki, East Java, Indonesia.
³ Abstract only, full paper with author.