Siting of the pond area as designed by the consultants, shown in the preliminary report on engineering aspects of planning, design and construction (Section 3.1.1) is good. The site is in an area with fine grained silty clay. Fifteen nursery ponds of one-fourth acre (0.10 ha) size and 25 culturing ponds of one acre (0.41 ha) each is adequate for the initial phase.
The rectangular shape of culturing ponds with opposite corners rounded-off to facilitate uniform dispersal of water during times of flooding and draining is practical, but the long axis of the ponds should be oriented parallel to the direction of the prevailing winds (northeast and southeast monsoons). The advantages are to increase water movement, provide more aeration and expose lesser length of dike per pond being exposed to erosion due to the wind action. The layout of ponds as submitted by the consultants (Fig. 1/3) in the preliminary report (Fig. 1) needs to be revised.
Based on the results of soil analysis, the pH of the soil within the proposed site were 5.8, 5.5, 5.2, 6.1 and 5.4 taken from boreholes, BH5, BH7, BH2, BH14, and BH6, respectively. Unfortunately, the borelogs did not indicate the depth from the ground surface where the samples were taken from. This is important because of the possibility of the presence of soil layer where the potentially acid soil can be traced.
Even though sulphate content of the above samples was nil except for BH6 sample which indicated a sulphate content of 15.9 ppm, yet an acid condition of the soil may develop due to the presence of iron (Fe+++) as well. Based on soil pH from the soil sample, it is evident that the soil in the proposed site is slightly acid.
More effort should be exerted into determining whether or not the soil is a potential acid sulphate soil. Potential acid sulphate soil does not become acid until oxidation has taken place. The extent and rate of acidification processes are regulated by chemotrophic bacteria. Determination of the potential acid sulphate condition of the soil can be conducted as follows:
Soil sample is made into 1 cm thick cake and sealed in a thin plastic bag. The bag preserves the soil moisture and is permeable enough to allow oxidation of the pyrite to proceed rapidly. If the soil is an acid sulphate soil, the pH of the soil should reduce to below 4.0 within one month (Potter, 1976).
If the project has to proceed in spite of soil acidity, special construction procedures should be adopted and the economics of this procedure has to be calculated to determine if such actions are advisable. Pond layout will have to be revised as it may be more economically favourable to use a bar-ditch type of construction1.
Improving or controlling soil acidity (Soil pH below 6.5) can be done by repeatedly drying and filling the pond until the red coloured scum from oxidized iron is removed. Lime can be used to control soil acidity. The cost of this treatment has also to be determined.
Since the soil at the proposed site shows a slightly acid condition, it is much better if the pond depth is reduced from 3 to 2 feet (0.90–0.60 m) with a peripheral canal of 1.5 feet (0.45 m) deeper than the general level of the central part of the pond. This will help to reduce the acidity of the pond water.
To facilitate harvesting, the pond bottom should be contoured to permit drainage of water to the outlet gate. The general elevation of the nursery and culturing pond bottom can be used as suggested by the consultants (+) 17 feet M.S.L. It is based on normal operational condition of the ponds with the average water level at Sungai Tumboh of (+) 15 feet M.S.L.
Dykes designed by the consultants (Section 3.2; Fig. 3/2) of the preliminary report are suitable. Test results carried out on samples for Atterburg Limits, particle size distribution, bearing capacity and shear strength indicate that the soil is suitable for dykes and other infrastructure requirement. Compaction tests were not conducted for the determination of optimum moisture content2. It is suggested that this should be done during construction. Maximum compaction and low soil permeability is attained when the moisture content of the soil is at “optimum” during compaction. This gives a physically stable dike with a low rate of percolation (Tables 1 and 2).
Dyke soil taken from areas with low pH values can be used for the core of the dykes. The outer surface can be covered with good top soil.
Permeability tests by the Constant Head Permeameter were carried out on two selected sites, undisturbed 1.2 -inch diameter samples of silty clay taken from boreholes BH9, and BH13 at depth of 5 feet (1.50 m) to 6 feet 6 inches (1.98 m). No permeability tests were conducted on the remaining 12 boreholes especially at places within the proposed pond site. It is suggested that this test be done.
The vertical profiles of boreholes BH1, BH2, BH3, BH4, BH5, BH6, and BH14 revealed the presence of a layer of well-graded, medium, grey sand at depth of 4–5 feet (1.20 to 1.50 m). BH2 and BH14 are located within the proposed pond site and this condition has to be looked into for positive water retention requirement.
As discussed under Section 3.1, the layout plan located the pond site within where the fine grained silty clay exists. Coefficients of permeability obtained from tests showed vertical “k” values of 1.8 × 10-4 cm/min and 6.3 × 10-5 cm/min on BH13 and BH9, respectively. These “k” values give a low rate of percolation and the water loss through the pond bottom would be small. If in the construction/excavation process, sandy layers are encountered, it might be better to leave the area undisturbed. Future pond sealing may be expensive, or may take time.
All tree stumps in the path of the dykes should be removed. A berm should be provided on the inside of the dykes. The height should be slightly above the water surface in order to minimize the effects of wave action due to the wind on the side slope. This will also facilitate closer inspection of the cultured species if a platform (berm) is provided for technicians to walk on.
The size of the channels to carry water at the rate of 30 gallons (136 liters) per minute is adequate. A pond can be filled over a period of one day. The details of the supply channels as submitted by the consultants (Fig. 3/3) in the preliminary report are acceptable.
The design of earth-interconnecting drainage channels shown in Fig. 3/4 and its capacity as given under Section 3.4 of the consultant's report is suitable. It is advisable that water in the drainage channels be passed through the retention pond after retreatments. The suggestion presents a plan to reuse the drain water instead of wasting it directly into the river.
Spillweir, inlet, water control structures, and drainage structures as given under Section 3.5 of the preliminary report are well designed. However, to improve the water quality to the required level for aquaculture, a filtration unit in addition to sedimentation (retention) basin should be incorporated into this design.
The pond should have the long axis perpendicular to the direction of prevailing winds (northeast and southwest monsoons). The ratio of the long axis to the short one is 2:1. Depth is about 10 feet (3.04 m) to allow space for settled materials. It may be necessary to relocate the sedimentation (retention) pond to higher grounds, but if this is not done, the height of the peripheral dykes surrounding the basin shall be increased and the original pond bottom be allowed to build up in elevation as more sediments settle over the years.
Retention period depends on the discretion of the engineer, since it is a function of volume of flow and basin size. Minimum turbulence at inlet is attained by having a good inlet design. Overflow weirs should have overflow rates with less velocities at the outlet. Outlet channels and weirs should extend across the ends of the tanks for a distance of one-third or more of the side length.
Design should be of a continuous flow, if it is feasible. The amount of settled material can be estimated from test models. This is necessary for determining the space and the time interval between cleaning.
To facilitate mud removal, the bottom should be sloped to one or more sludge outlets with a grade of 2 to 5 percent at the deepest point of the inlet end. Hose outlets of 1.5 inches (3.81 cm) diameter should be provided for flushing, at pressure of not less than 50 psi (3.51 kg/sq.cm).
For the very highly turbid river as Sungai Tumboh, it is advisable to grow water hyacinths at the intake channel. A fence of bamboo strips will keep the plants within the designated area. Initial deepening of the channel at the pump sump will be necessary. The roots of the water hyacinths will provide mechanical filtering as well as biological filtering in reducing the solid materials and dissolved solid materials. Control of growth of the plants is done by the removal of the matured plants. The harvested plants may be used for feeds.
With possibly major bed modification at the river inlet channel, an SWS water filtration system may be adopted. It has been shown that a physically clean water can be provided using this system of sub-sand abstraction (Cansdale, 1979).
The water in Sungai Tumboh is very turbid and its very sluggish flow may have resulted to a heavy accumulation of mud at the river bed. Since the SWS system makes use of the natural bed of sand and gravel for its filter medium, the thick mud would make the proposed sump site unsuitable for such system. Further studies on this will have to be done.
It may be necessary to relocate the sedimentation (retention) pond to higher grounds, but if this is not done the height of the peripheral dykes surrounding the basin shall be increased and the original pond bottom be allowed to build up in elevation as more sediments settle over the years.
For thisparticular case, sedimentation alone is not sufficient to reduce the suspended solids and dissolved solids to the required level for aquaculture, if straight river water cannot be used. It is suggested that a gravity sand filter be incorporated into the system. The basic design of the filter is as follows:
The filter bed consists of a 30-inch (76.20 cm) thick sand bed. The sand must have a specified quality, effective size and uniformity coefficient1 (see Fig. 2). The gravel layer is about 24 inches (60.96 cm). Bed size could be determined from filtration rates which could be from 2 to 4 gallons per square foot (97.8 to 195.5 liters per m2) per minute with provisions for overload. The filter bottom is provided with underdrains for the collection of the filtered water and the distribution of wash water during the washing process. Wash water is supplied by gravity from an elevated storage tank of about 35 feet high. When at full capacity, it should have enough water to wash the filter for about 5 minutes (15 gal/sq.ft./min). Wash water may be obtained by pumping from the sedimentation pond and backwash flow is wasted to the stream. A wash rate control system may be incorporated into the filter plant. Filtration aids in the removal of colour, taste, odour, iron, manganese and also some of colloid materials.
Water have to be lifted from the inlet channel sump by pumping into the retention pond for settlement and for filtration, and distribution into the ponds. The total amount of water to be circulated is about 1 230 gpm (5 572 1/min). The size of pump required should be about 7 hp. Power required for the pump set would be about 6 KW. Two units should be installed, one for constant operation, and the other for stand-by.
The elevation of the pond bottom in relation to the normal water level is such that economic water management is possible only with a pumped supply system. Installation of three as proposed under Section 4.5.1 is good; two would be duty pump set, while the third unit is stand-by, providing 50 percent of stand-by capacity. The duty pump set designed to cater for a regular circulation flow of 30 gallons (136 liters) per minute is enough.
The office and laboratory could be in the same building. It is good to be near the nursery ponds. The structure could be a single storey building of masonry and wood construction. For the initial phase, the 3 700 sq ft (344 m2) of the floor area as proposed by the consultants is reasonable.
The location of the staff quarters is good as they are located along the main and access roads and are near the pond complex. The number of quarters and the respective building types as indicated under Section 4.2 are adequate for the initial phase.
Other buildings like storehouse, guardhouse, garage are necessary for the project. Their size and materials for construction as suggested by the consultants are acceptable. Field shelters and field storehouses for collecting organic fertilizer should also be provided. The former serve as a rest area for the field workers and also can be used as guard posts at night, while the latter can be used for storing the organic fertilizer which might be abundant in a certain period of the year. These shelters are light wood construction which are easily dismantled and reassembled at any desired location.
It is suggested that a separate building for the processing and storing of feeds be included.
The proposed site is 32 miles (51.48 km) from Ipoh. The nearest town of Tanjong Tualang is about 9 miles (14.48 km). The journey to the site from Ipoh or Tanjong Tualang is over a well-paved highway. There is an existing earthen road which runs from the highway along the western boundary of the site. This road is used by lorries and trucks hauling timber from the inner forest areas. The road is in a bad condition, and could not be used by cars during the rainy season.
The internal road network in the office area and quarters area as designed by the consultants under Section 4.4.1 is acceptable. The top width of the road embankment is 12 feet (3.65 m) with side slopes of 1.5:1 and turfed to prevent erosion. Road culverts and drains should be provided where necessary for the proper and efficient drainage of the area.
Surface water from Sungai Tumboh is the only water available for the ponds. Sungai Tumboh is a fairly large river. Its watershed area comprises about 33 acres (13.35 ha) of swamp and waterlogged areas. The stream flood flow discharge is about 3 135 cu ft/sec (88 783 liters/sec). Dry season discharge gives about 12.6 cu ft/sec (356.8 liters/min). During a ten-year frequency, it was observed that flood water level rose to +23.00 feet above M.S.L. At normal flows, the water level is +15 feet M.S.L. Dry season flows give water surface elevation at +10 feet M.S.L. The water in the Sungai Tumboh is very turbid. According to Mr. Donald Lovett's report (1979), the turbidity of the water is 260 NTU, the colour is 45 HU, COD is 6.6 mg/l. Dissolved oxygen is 2.20 mg/l, iron is 3.3 mg/l, total alkalinity is 13 mg/l, pH is 6.0, total coliform bacteria count is 35 000 colonies per 100 ml. Five-day BOD is less than 1 mg/l. The turbidity of the water river is mainly due to suspended solids and dissolved solids. The concentration of the former varies from 10 to 405 mg/l while the latter lies between 105 to 225 mg/l.
Unfortunately, there are no available data on the level of zinc in the river water. In amounts of as little as 0.4 ppm, zinc is lethal to the Macrobrachium larvae as well as young juveniles. The authors strongly recommend that the level of zinc in the water of Sungai Tumboh especially in the vicinity of the project site should be determined.
A visit to the site near a stagnant pool by the river bank revealed the presence of clear water. This indicated that in its quiescent state, the particulates have settled at the bottom. According to Lovett (1979), when a water sample was collected, a fraction of the particulate matter quickly settled, but the water still remained turbid after standing overnight. The observation revealed the fact that 24 hours is not enough for all particulates to settle. The colour of the water may be its true colour which generally is such for waters from swamps or humic streams, which leads such question like whether this water is fit for aquaculture and if so, at what stocking density.
Ground water studies were not undertaken and no information are available. The drilling of a well is advised as an interim measure for water supply during the season of low stream flow and when there is a heavy load of silt in Sungai Tumboh. If favourable tests are noted on yield and quality, a plan should be prepared to evaluate this feasibility of a partial well supply for the project.
As mentioned in the consultants' report, water supply could be tapped from the Jabatan Kerja Raya main along the Tanjong Tualang/Telok Anson Road with the approval of Jabatan Kerja Raja. If it is possible, tap water should be a good water supply for the daily use of both office and laboratory.
Supply of electric power could be obtained from the supply mains with the appropriate contributions and prior approval from Lembaga Letrick Negara (LLN) (Federal Electric Institute). Power could be supplied to all the buildings and lamp posts would also be erected at the pond complex, road junctions, office compound and quarters. A space has been allocated for the provision of an LLN sub-station.
Sewerage system, as suggested by the consultants, is practical.
