APPENDIX VIII
TECHNICAL REPORT ON THE NEW AQUACULTURE RESEARCH CENTRE AT NAVUA

1. INTRODUCTION

This appendix provides details on the new freshwater research - hatchery - fry rearing - training centre at Navua.

At present, while MAAF staff as a whole include many civil engineers (Department of Land and Water Resources Management) experienced in planning, construction and maintenance of earthworks and structures related to irrigation, no engineer experienced in freshwater fisheries is available. Thus this report attempts to explain what is expected of the facilities, and how they should be developed and operated to achieve the expected results. Emphasis is put on engineering aspects.

2. THE SITE

The site is located at the north of Navua town, about 1,5 km from the Suva-Navua main road on the right side, on the left bank of Navua river at the foot of hills bordering the valley on the north, between the main irrigation canal (marked McCo) and existing Viticorp fish farm.

The project area is 17.7 ha including 2.0 ha for staff recreational purpose, but excluding the residential area.

At the north the irrigation canal, at the west a natural depression (arm of the creek) and at the south a road close to the site. There is no natural or human made formation bordering the eastern side, but this may be the direction of future expansion.

2.1 Accessibility, link to infrastructure

The site is accessible on the left bank of the main irrigation canal from the Navua-Waiyanitu road. Distance is about 700 m.

The ground level on the site varies between 3.50 – 4.00 m amsl, but along the Wainakavika Creek it is only 2.00 m amsl.

Electric transmission line ends at Viticorp hatchery, about 1,100 m in distance.

Drinking water main is along the Navua-Waiyanitu road.

2.2 Soil

In the absence of soil investigation the classification made by Viticorp is available to describe soil characteristics. Accordingly the soil on site is classified as fair arable land with moderate limitations. Poorly drained flats with deep, moderately infertile Navua (red) clay.

Visual observation and experience already gained at the nearby Viticorp farms implies that the soil is good for pond construction, and no significant amount of seepage may be expected during operation.

2.3 Climate

The country is tropical, temperature range is between 18 – 31 °C. The cold drier season is in mid-year, while the hotter rainy season is at the end and beginning of each year.

The rainfall and temperature data in the Navua region are shown in

Table 8 are only available¹¹. Although temperature values indicate considerable evaporation, rainfall probably exceeds it.

Table 8. Meteorological data of Navua

¹¹ Source: Fiji Meteorological Service, Nadi. Meteorological station: Tamanoa - Navua.

3. FUNCTIONS AND PRODUCTION OBJECTIVES

The new aquaculture research centre at Navua will take over all functions of NRS. Accordingly, it will operate as a national

• research centre:

  • to conduct research on tilapia genetic, selective breeding and to maintain brood stock;

  • to conduct research on various fresh water species as problems are identified;

• tilapia, carp and freshwater prawn seed supply centre;

  • to adapt and develop new breeding, nursery and rearing techniques to local conditions;

  • to supply tilapia seed for subsistence farmers;

  • to produce Chinese carps juveniles for stocking into rivers and canals;

  • to produce freshwater prawn post larvae;

• human resource development (training) centre;

  • to ensure improvement in staff capability;

  • to organise training for private entrepreneurs; and

• development centre for processing and marketing.

Although the CDF programme identifies tilapia seed production for subsistence farmers only, it is recommended to consider the new centre as a seed supply source for commercial farms as well in future.

Capacity of the centre is specified on the basis of the objectives of CDF, but with continuous improvement of management, and mastering techniques of production, seed output may be even more.

Accordingly the initial production output is set to:

Number of ponds and other facilities are computed on the basis of figures presented in Appendix VI: “Basic data of technology applied at Naduruloulou Research Station”.

The production potential of the new research centre is higher than that required for the present, but this allows for future needs, and provides for increased operational capacity.

In the case of tilapia the proposed technology is based on the current method as a starting point for production. In order to meet the production target the current method must, however, be expanded to the collection of just-feeding larvae for further growing. As a following step, the collection of eggs and hatching in jars is proposed in order to achieve full control over the process.

Introduction of new carp breeding technology would be necessary if demand substantially increases. In such a case the hormone induced ovulation (current method) should continue in artificial egg fertilisation and hatching and rearing in vertical flow-through type incubator / rearing jars.

Prawn post-larvae production will be based on the clear-water system. The water for larvae rearing will be circulated through biofilters to maintain good water quality. This will reduce the amount of sea water to be transported to the site. While freshwater will only be used, no biofiltering would be applied: used water will continuously be replaced.

Adaptation of clear-water system will need preliminary research to develop appropriate techniques of post-larvae production.

The facilities of the two hatcheries, the laboratory completed with the outdoor tanks and ponds will enable the staff to conduct various research programmes.

4. ENGINEERING ESTABLISHMENTS

The research station comprises various engineering establishments to provide optimum facilities to achieve the set objectives.

Pond pattern has been designed on the basis of a map scaled 1:5,000.

Hydraulic computation of water supply is based on elevation data of drawings of the main irrigation canal (marked as McCo) and of the reservoir. All maps and drawings have been made available by the Land and Water Resources Management Department of MAFF.

4.1 Administrative and ancillary buildings

The administrative centre of the compound is the office building. This building provides workspace for 10 staff members. There is also a meeting room, a tea room (for staff use) and a lecture room for about 20 persons with separate entry from the yard. Its floor area is 200 m²

For the effective operation of the research centre the erection of some additional buildings is planned.

The feed-processing unit of NRS is to be transferred to the new research centre. A separate feed store adjoins the feed mill.

An equipment store (120 m²) is to keep all fisheries gear and other equipment.

A workshop (70 m²) and open shed (100 m²) serve for machinery maintenance.

A dormitory of 200 m² accommodates about 20 participants of various training programmes.

Each building is of standard design according to local provisions:

• Foundation: concrete footing 500 mm below ground surface 400 mm width.

• Floor: 150 mm concrete on sandy gravel bedding with moisture insulation.

• Walls: concrete block 150 mm with two side plastering.

• Standard roofing: corrugated iron sheet, with heat insulation, and ventilation.

Internal division of each of the buildings is according to their specific functions, and they are equipped and furnished accordingly. The present documentation does not include detailed designs of these buildings.

4.2 The hatchery - laboratory block

The hatchery - laboratory block comprises one laboratory and two hatcheries - one for Tilapia and carps, and one for freshwater prawn respectively.

Basically, the laboratory accommodates the equipment and other tools of the laboratory of NRS, but with some upgrading or replacement of worn out ones.

4.2.1 Laboratory

The laboratory building is constructed according to local standards; foundation, floor, walls and roofing are similar to those of other buildings. Laboratory and sanitary installations (toilets for gents and ladies one each, cold and warm water supply, water heater min. 80 l storage capacity) are in accordance with respective standards of Fiji.

One main door (2,100 mm × 1,000 mm) and two doors to hatcheries (2,100 mm × 1,500 mm each) provide good access to other facilities. Windows on both longer sides of building ensure good ventilation.

The laboratory building accommodates a small office (about 7–8 m²), a store room for hatchery tools (10 m²) and a feed storage (10 m²).

A completely separated room with entry from the yard accommodates the air-blower and emergency diesel engine. The total laboratory area is 100 m².

4.2.2 Hatcheries

Propagation of the selected finfishes (tilapia, Chinese carps and Puntius) and propagation of Prawn require different facilities. Two separate hatcheries are, therefore, planned. Both are semi-closed sheds joining the laboratory building at its two ends.

With reference to architectural structures, the two hatcheries are the same. Foundation is similar to that of the other buildings. Floor level is 4.20 m amsl. Walls made of 100 mm concrete blocks, 2.30 m high with galvanised wire mesh up to ceiling level (7.60 m amsl) on two sides of the shed provide protection against wind. Roof structure is of wooden trusses with corrugated iron sheet cover on pine posts.

The research station accommodates facilities for various methods of propagation:

1. Natural spawning and hatching of Tilapia either in ponds or concrete (out-door) tanks,

2. Rearing of swim-up Tilapia fries in (out-door) tanks and jars,

3. Hatching and larval rearing of fertilised tilapia eggs collected from females,

4. Hormone induced spawning, hatching and larval rearing (Chinese method) in circular concrete tanks,

5. Hormone induced ovulation with artificial fertilisation of eggs, hatching and larval rearing in vertical flow-through jars of different size Induced ovulation, and

6. Clear-water system Prawn post-larvae production.

Some facilities can serve various purposes depending on the species. Combination of devices provides optimum use of all facilities either for mass production of seed or implementing research with some individual fish only.

Large space between units enables the staff to carry out different operations conveniently at each point.

Free communication between the hatcheries and the laboratory is provided through large double doors. The structural set-up provides good ventilation, but good protection against wind.

4.2.3 Technological facilities

Table 9: “. Water demand in the hatcheries” also includes the list of technological devices for the hatcheries.

Tilapia - Carp hatchery

Provided that fertilised Tilapia eggs are collected from females, hatching can be done in the small size jars (20 litre). Hatched larvae are further reared in troughs (75 litre) before they are put into fry rearing tanks. The troughs are also the place where first feeding is given, and, if applied, hormone treatment to obtain monosex population can be done.

In case of Carps, hatching of eggs and rearing of hatchlings take place in the vertical flow-through fibre glass incubators and rearing jars.

The jars and troughs are grouped on modular steel stands. The stands are manufactured from round steel bar with welded joints and should be protected against corrosion. The base frame holds the water distributing pipe and the fibre glass drain trough.

Additional elements are welded on the base frame to hold the 20 litre and 60 litre jars. The 200 litre jars have individual stands due to their weight.

The jars are connected to the inflow distribution pipe with flexible (e.g. rubber) pipe of 20 mm. The water current is adjusted by globe valves. Each unit is equipped with two additional globe valves to supply water for additional units if needed, or to take water for various purposes. One valve is for drainage.

The horizontal flow-through rearing troughs are the same size as that of drain troughs of the jars.

The jars and troughs are grouped in units as follows:

Each jar has a removable filter of fine mesh sieve (0.5 – 0.6 mm) fixed on plastic or fibre glass frame. The large filtering surface is to avoid overflow due to choking.

If Tilapia eggs are being hatched in jars, the filter sieve can be removed thus allowing hatchlings to leave into the drain trough, where they can be collected and put into rearing jars.

Five twin concrete tanks serve various purposes, such as holding brooders during propagation course, holding larvae before stocking and in case of medical treatment, etc.

Four of the five have the internal dimensions of 2 × 2.00 × 0.80 × 1.00m. The fifth one is larger and has the dimensions of 2 × 4.00 × 0.80 × 1.00 m. The bottom slopes toward the ID 50 (2") turn-down pipe. The inner surfaces of the small ones are possibly glaze-tiled for easy cleaning and sterilisation. The grooves are for wooden framed screens to segregate fish.

Freshwater prawn hatchery

The prawn hatchery accommodates all devices from NRS. The hatching - rearing tanks are made of fibre glass or plastic. The number of devices is as follows:

The concrete tanks serve primarily larvae rearing, and, therefore, each of them is complete with a simple biofilter.

Water circulation is ensured by air-lift pumps. When only freshwater is used, no recirculation of water is maintained. A central air-blower will serve both hatcheries, the laboratory and the out-door tanks.

Out-door tanks

The large rectangular out-door tanks serve primarily for the propagation of Tilapia, but can be used for other purposes, too. There are 24 in two groups. Each is filled and drained separately. Each has a water surface of 20 m² with about 1.00 m water depth. The only one circular concrete tank is for mass production of Chinese carp larvae.

4.2.4 Water supply to the hatchery - laboratory block

The hatchery - laboratory block is supplied with water from the reservoir: a diameter 200 mm PVC (pressure) pipe leads from the irrigation canal intake structure to an elevated reservoir (made of concrete) on the right bank of the canal. This tank always has the water level at the same level as that of the reservoir, and provides sufficient discharge to the hatchery - laboratory block.

Safe operation in the hatcheries requires a sufficient amount of water at each phase of the propagation process. The conveying capacity of the water supply system is, therefore, designed for peak water demand.

The normal water demand of devices is based on experience and does not equal to the mathematical mean value. It is assumed that the annual water demand equals to eight months continuous operation of all devices with the supply of normal water demand. (There may be days when certain devices operate on maximum level, while others are out of operation.)

From the elevated reservoir the water is conveyed to the two overhead tanks by gravity through diameter 150 mm pipes. The two overhead tanks, located at the two hatcheries serve only to provide balanced static water pressure and do not provide emergency reserves. Water inflow to overhead tanks is regulated by float ball type valves.

The water is distributed to the devices through diameter 100 mm PVC pipes. In case of any repair works, the system can be sectioned by gate valves. However, maintenance of the system should normally be done out of spawning season. Each block of devices is supplied with water through a diameter 50 mm pipe branching out from the main pipe. The distribution pipe of each block is connected to these.

The water flows through the jars vertically, entering at their bases and leaving them through an upper outlet point. The shape of the jars produces smooth, vortex-free flow. Used water is collected in a trough and conveyed to floor drains.

In the rearing troughs and concrete tanks the water flows horizontally. The supply valves (diameter 25 mm) are about 100 mm over the edge (approx. 200 – 300 mm over the water). In case of concrete tanks, drainage is through a turn down pipe to the floor drain.

Table 9. Water demand in the hatcheries

Table 10. Water demand for out-door tanks

It is assumed that one out-door tank is charged 12 times annually, and 10 % of storage capacity is changed (replaced) daily. Daily change is considered for 300 days per year thus resulting in the annual total water demand for replacement. Daily change in terms of current equals to (rounded) 1 litre per second.

Water demand expressed in terms of current is required for computing network capacity, while the annual water demand is required to be specified in order to secure it from the reservoir.

Thus, for hatchery purposes, the rounded

Total annual rounded water demand

Brine for the prawn hatchery will be regularly brought from a carefully selected site of the nearby shore. Mixing of brine and fresh water will be done on site to reach the desired level of salinity.

The floor drain collects water and evacuates it from the hatcheries. It is made of cement concrete with light reinforcement and covered with steel grate.

Toilets are available for the staff in the laboratory building. Sanitary installations and plumbing in the toilets need no detailed explanations. Sewage from the toilets is disposed in septic tanks separately from the drained water of the hatchery system.

In addition to the fresh water supply system, the prawn hatchery is installed with a secondary supply system for salt water supply. Salt (sea) water is stored in an overhead tank, and distributed to the devices through pipes. The distribution system is very similar to that of the fresh water system, but with less capacity.

Collection of salty water and evacuation from site need careful operation and care to protect the environment. In this respect salty water may only be drained to the creek if well diluted and salinity does not exceed the relevant environmental standards. The research centre must not be a source of any environmental contamination.

Devices in the prawn hatchery are of mainly circular plastic tanks. They are filled in the same way as the concrete tanks described above. Their drainage is through a pipe fixed in the axis of the tank. The upper edge of pipe regulates the water level in the tank. Complete drainage needs the removal of the centre pipe.

The outdoor tanks receive water from the irrigation canal branching out at Section 1=400. The irrigation canal bottom elevation is between 4.80 and 5.00 at the outlet to the research centre which provides good options for gravity water supply.

4.3 The ponds

4.3.1 Pond pattern

Details on pond characteristics are given in Table 11: “. Schedule of ponds” on page 48, but an extract is given below in Table 3.

Pond pattern is developed to fully satisfy the production objectives. Their layout is designed with the use of (i) a 1:5,000 scale map and (ii) detailed drawing of the (abandoned) irrigation system made available by the Land and Water Resources Management of MAAF.

The number of ponds is 78 with total water surface of 5.81 hectares.

The ponds are operated according to defined schedules. Each pond is assigned to a specific function, but on the basis of detailed management plans ponds may be used for other purposes, too. Their size is defined according to the operating requirements. They must be filled and drained separately.

Table 3. List of ponds at Navua (extract)

The ponds are earthen with natural soil base. Ponds assigned to carp production have a water depth of 1.5 m, while all other ponds are only 1.00 m deep. Each pond outlet is accessible by small trucks on the dike.

The brood, spawning and nursery ponds are located close to the hatchery shed to decrease transport distance.

The dikes are designed to be homogeneous, and their cross-sections follow uniform dimensions; slopes on each side are 1:1.5, crest width is 3.00 m on the contour dikes, but where drainage structures exist the crest width is 4.00 m to allow for the traffic of small trucks. Crest width of separation dikes is 2.50 m.

Crest level is uniformly 4.50 m amsl. Following detailed site levelling prior to the preparation of final designs, adjustment of crest levels should be done and accordingly, the water and bottom levels regulated to reduce the quantity of earthwork.

Free board over operational water level is 0.5 m everywhere. The drainage structures serve as harvesting places, and therefore should be accessible by small trucks. The pond bottoms have 200 mm slope running from the pond inlet to the drainage structure.

4.3.2 Water supply of ponds

Water for pond filling is taken from the irrigation canal at branching out at Section 1=400. A check dam will increase the water level to the desired level in the irrigation canal. Since the irrigation canal runs along the toe of the hill, the elevation of its bottom is between 4.80 and 5.00 m amsl at the intake to the compound, which provides good options for gravity water supply.

The water enters the filter pool where undesirable aquatic organisms are removed. The water is filtered through a horizontal wall filter, filled with stone chips of various size, and collected in a tank for further transport to the compound. The filter material must be changed regularly.

Distribution of water to ponds and tanks is through four pipelines of diam 200 mm each. The four lines will serve four groups of ponds separately. This set-up has the capacity to fill all ponds within 12 days continuous operation.

The water is distributed to ponds through pipes; inflow water can be regulated by gate valves. In order to increase aeration, a perforated steel plate is fixed at the end of the pipe to spread the inflow water. The end of the pipe should be 250 – 300 mm above operational water level in the pond. Under the inflow the dike is protected against erosion. Outlets to ponds are of diam. 100 mm pipes branching from the mains.

Taking 4 weeks as an average period of time between two stockings (including cleaning and other maintenance works), the number of production cycles for one tank is about 10 to 12.

Water demand for pond filling is computed with the assumption that ponds will be filled twice annually. Since some ponds will only be filled once, the total water demand will make possible the filling of some ponds several times.

Replacement of losses due to evaporation is not considered, because annual rainfall¹² in the region is 3,556 mm. Though no data on evaporation exist, this is assumed to be less then the annual rainfall, so the balance will be positive. Even more, excess water may be expected.

Seepage loss may be considerable at the very beginning of operation only.

Thus the total annual water demand

¹² Source: Fiji Meteorological Service, Nadi. Meteorological station: Tamanoa - Navua. Period covered: 30 years.

4.3.3 Drainage

The ponds are drained through drainage structures of monk type. A double set of wooden control board is used to allow the operator to control the pond water level in 250 mm steps (the depth of each board) and allows the release of surface water when draining is needed.

The drainage structures are constructed at the opposite sides to the inlets to ensure flow-through the ponds.

The ponds are deepest at the drainage structures and should be able to be fully dewatered by gravity. The drainage structures ensure rapid dewatering and control of water surface levels, and allow for release of excess water automatically.

At the drainage structures the pond base drops an additional 200 mm to form a pit or sump which is essential for collecting the fish at harvesting.

Harvesting takes place at the drainage structures. To make harvesting easier a certain area around the structure is covered by cement concrete slabs on a sandy gravel bedding.

The structures are connected to the drainage canals via a pipe. There is a 100 mm fall along the pipe from the structure to the drainage canal. There is thus 0.5 m difference between the pond base level at the pond inlet end, and the pipe outlet in the drainage canal.

The water is collected and evacuated from the site in drainage canals. The side slope of drainage canals is 1:1.5. In general lining of canals is not required, but around the drain pipe outlet, a lining is used to avoid erosion in the drainage canal. Its length is 1.60 m. Since the water level in the canals will not exceed 0.60 – 0.70 m in the most unfavourable conditions (e.g. more ponds are drained at once), the height of the lining is a maximum 1.00 m (3 rows of 300 × 300 3 80 mm slabs).

The lined sections in the canals as well as in the ponds should be bordered with a c.c. beam. The bottom of the drainage canals is 0.50 m. The bottom slope should be hydraulically dimensioned. Flow of drainage water should be neither too slow nor too rapid. There are some crossings on the canals, and culverts should therefore be constructed. Drainage canals also collect seepage water from ponds, and evacuate the rainwater from the site. Drainage canals discharge into the Wainikavika Creek, which joins Navua River. Environmental protection issues must be given due care in operation.

4.3.4 Distribution pipes

The distribution pipes conveying water to the ponds may be either placed on the crest or on the slope over the water level. They must be fixed to the dike body by buttresses at tees, turnings and at 30–40 m intervals of straight sections.

4.3.5 Pond structures

The drainage structure of ponds is the traditional monk. The monk is a structure which is U shaped in plan, open at the front, facing the pond. Its internal dimensions are 0.40 m wide, 1,00 m deep, and 1,80 or 2,30 m high depending on the pond. The water is conveyed to the drainage canal through plastic pipe of internal diameter 300 mm.

The slope of the dike around the structure is 1:1.5, and the structure is placed at the toe of the slope. A widened foundation slab is provided to avoid overturning. The opening area is spread out to provide better flow towards the drainage part. The monk outlet is designed specifically to prevent the pipes sliding apart.

The length of the pipe basically depends on the distance between the axis of the dike and the axis of the drainage canal.

The monk operates as follows:

1. There are three grooves on the structure: the outer one is for the steel screens and the two inner ones are for the control boards.

2. The control boards are placed in the grooves in a double row as high as the desired pond water level.

3. The space between the two rows of control boards is filled with some impermeable material (e.g. clay) to minimise seepage.

4. The dimension of control boards allow 0.25 m steps in water level. Excess water automatically overflows the top board.

5. When the water level is to be decreased, the upper boards should be removed. After dropping the water level 0.25 m, the next pair of boards should again be removed. This procedure ensures gradual draining of ponds and limits erosion of dikes due to rapid dewatering.

6. As the water level decreases the fish move together in front of the drainage structure, where the water is the deepest. This can be helped by using nets to move the fish towards the outlet.

Good and watertight closure of control boards is an important factor in minimising seepage loss at the structures. The grooves are lined with steel channels of 25 × 25 × 5 mm. They must be made with steel bar fixing pins, set at appropriate distances. These are concreted into the structure. The control boards should be individually fitted and numbered by structure and groove.

The steel screens are to prevent the escape of fish through the drainage structure. If the gap between the bars is too wide for small fish and larvae, an additional net of suitable mesh size must be attached.

4.3.6 Culverts

There are some crossings on the drainage canals, and culverts should therefore be constructed. The internal diameter of culverts is 0.60 m and is constructed of prefabricated cement concrete pipes. This diameter is required to avoid choking. To keep the pipe assembly together, both the inlets and outlets are constructed on site on a blinding concrete bed which has a concrete key deepened into the soil base.

4.3.7 Outdoor tanks

The large rectangular out-door tanks serve primarily for the propagation of tilapia, but can be used for other purposes, too.

There are 24 in two groups. Each is filled and drained separately. Each has a water surface of 20 m², and is 1.00 m deep. Each rectangular tank has a dimension of 7.00 × 3.30 × 1.20 m. The walls are made of concrete blocks placed on reinforced concrete slab, with reinforcement and watertight plastering inside and outside.

The only one circular concrete tank is for mass production of Chinese carp larvae. Internal diameter is 8.00 m, height is 1.20 m. The wall is made of concrete blocks placed on reinforced concrete slab, with reinforcement and watertight plastering inside and outside. Both types of tanks are drained through turn-down pipes of 50 mm diameter.

4.3.8 Others

The (i) check dam on the irrigation canal, (ii) the diversion sluice to the compound and (iii) the culvert on the irrigation canal at the road crossing are standard designs of the Land and Water Resource Management Department of MAAF and need no detailed explanations.

4.4 Quarantine facilities

The quarantine facilities comprise six rectangular concrete tanks with separate water supply and drainage. Their structural design is the same as that of the out-door tanks at the hatchery and needs no separate explanations.

4.5 Internal transport

Harvesting takes place at the drainage structures and they must be accessible by transport vehicles (e.g. pick-up trucks). At the dikes where drainage structures are located the crest width is 4.00 m to allow vehicle access.

5. GENERAL RECOMMENDATIONS FOR FURTHER DESIGN

The present state of designs, while correct in outline is incomplete as there is some further information to be obtained. In particular, soil and land surveys should be completed before the final designs of the pond components are detailed. The present drawings, however, give ample guidelines for this work.

5.1 Land and soil survey

In general the ponds should be partly excavated and dikes partly filled. Although an orthophotomap exists (scaled 1:5,000) about the site, a land survey before the finalisation of the designs is necessary. The land survey should give details on:

• the elevation of ground surface plotted on the map at 0.20 or 0.25 m contourline intervals;

• the boundary of the site and any natural formation which may influence pond pattern;

• geodetical identification marks, north direction;

• existing dikes, trenches and natural depressions with appropriate details on their longitudinal and cross sections for consideration in design;

• structures, buildings;

• trees and other vegetation which are to be preserved;

• connection to transport facilities;

• electric, telephone and drinking water supply lines;

Elevation data and cross sections of the existing irrigation canal (marked McCo) should be verified. The same applies to Wainikavika Creek since this is planned to be the receiver of all drained water.

The soil survey must be prior to design works, and should follow the respective standards of Fiji. In general, prescriptions for compaction and foundation of structures (incl. buildings) should be based on well detailed soil investigation.

On-site visual observation indicates that the site is of red Navua clay with no permeable layer embedded within the depth of 1–1.5 m. In order, however, to avoid unexpected seepage, it is proposed to take samples along the proposed contour dike area and along the major inner dikes at an interval of 50 – 75 m.

In case of structures of ponds, the safe bearing capacity of soil is usually sufficient. Local standards may, however, set specific requirements, which should be fully satisfied. In case of buildings and the elevated reservoir, the requirements of soil properties are as in other civil engineering works. Consequently, the respective local standards are fully applicable.

5.2 Water quality

Good quality of water is a pre-condition of successful hatchery and pond operations.

Since the reservoir water is undisturbed and is free of any human pollution, it is not likely to have an inappropriate oxygen content.

In order to ensure good quality of water to the centre, it is, however, important to carry out water quality measurements regularly.

Accordingly, water sample from the reservoir water should be taken at the irrigation canal inlet structure

• at 0.5 m and 2.0 m below water surface,

• at 06:00 and 14:00 hours,

• at an interval of 3–4 weeks

starting as soon as possible, and continuing measurement until construction is completed.

Water quality measurements should include oxygen content, temperature, pH, transparency (with Secchi disk) suspended solids, chemical and other physical characteristics. The air temperature should also be recorded at each sample taking. A regular plankton analysis for practical purposes is also essential.

5.3 Design

5.3.1 Buildings

The present design gives only details on items which are necessary for their specific functions. Completion of architectural designs shall, therefore, be necessary prior to implementation. These will be based on local regulations and standards.

5.3.2 Earthworks

The present designs made an attempt to create a balance of excavation and filling. On the basis of the results of the recommended site survey, the amounts of excavation and filling should be checked. If any major differences occur, elevations should be rearranged. As a guideline, no excavation may be done below the receiver's bottom level.

According to the available site map, there is a gentle slope of ground surface towards the direction of East. Should this slope be verified by site survey, the pond elevations may be adjusted to follow ground surface and thus reduce the volume of dike construction.

As a general rule, the pond water levels, bottom levels, drainage canal bottom levels must fit between the operational water level of the irrigation canal and the bottom level of the Wainikavika Creek.

Existing trees are not marked on the maps. It is, however, important to take them into consideration and save them. Should a tree fall within a certain pond, this pond should be placed on area designated for future extension.

It is intended to place drainage canal on the line of existing trenches and natural depressions. Following the completion of site survey, reconciliation of planned and real locations of involved trenches should be made.

5.3.3 Structures

The drawings of pond structures are to demonstrate their required shapes and dimensions, and any adaptation to local customs should be made with professional care. In case of reinforced concrete a simple reinforcement of 10 mm diameter steel bars, centre to centre, 200 mm in both direction is usually satisfactory.

5.3.4 Hydraulic computation

Following the site survey and pond pattern verification or adjustment, hydraulic computation of water supply system must be checked and modified, if required.

5.3.5 Energy supply

Energy requirement should be recalculated when specification of electrical appliances are final.

5.3.6 Protection against predators

This is an important factor in pond operation. Predators may be either aquatic organisms or birds. Filtering the inflow water provides good protection against wild fishes of different size, including their eggs and larvae, but, for example, against frogs additional protection must be provided.

5.4 Construction

Before commencing excavation at any portion of the site, all vegetation (except trees to be saved) roots and trees must be cleared. The top soil should also be removed and deposited. If unfit material is found (not being suitable for dike construction) it should be removed from the site. This kind of material may be used for levelling areas, or to refill unused depressions to minimise the formation of swampy areas.

Excess soil material can be carefully laid at the toes of dikes to form berms between dikes and drainage canals.

Any top soil removed, after completing the dike construction should be laid on dike slopes and on the pond bottom.

The dikes should be well compacted by mechanical rollers, rammers, vibrators or other approved means so as to produce a minimum dry density not less than 95% of the maximum dry density determined in accordance with “AS 1289”. The compacted fill should consist of approved material spread and compacted in layers approximately horizontal and of uniform thickness not exceeding 200 mm with a slight outward slope.

The terrain correction and land levelling prescribed in the plan should be accomplished with ± 50 mm tolerance and the same should be applied for the pond bed correction.

The surface upon which dikes are to be placed should be cleared and all depressions backfilled in layers of appropriate soil. The area must then be scarified prior to placing the dikes.

Phasing of construction may be considered. The pond layout allows reorganisation of functions while construction is completed.

Table 11. Schedule of ponds