Because the dike material is considered to have fair to good clay content and the tide amplitude (about 2.2 m) is considered of medium range, it is decided to adopt a ratio of 1:1 on the dike side slope (Figs. 10, 11 & 12). This means an angle of 45o between ground plane to crown. The crown width will depend on the use, position and location of the dike and the amount of excess soil it should accommodate. The berm will be wider on the wind side. The main canal has provision for expansion if the project is to be expanded to utilize the whole area of 80 ha and also to provide for flooding that may occasionally occur. The elevations used in the drawings are all based on “0.00” of the tide table.
The dike elevations (V) are compacted or finished elevation. Allowance for shrinkage would be given during construction. These are estimated to be 20 percent on perimeter dikes and 15 percent on the secondary and tertiary dikes. All are computed on the vertical height, no allowance on the horizontal part of the dike as the slope ratio can only improve (angle lessened) as the dike shrinks vertically.
Puddle trenches shall mostly be shallow and narrow except the northern dike on the mangrove edge which shall not be less than 50 cm wide and 50 cm deep. A 20-cm deep cut by one pass of a dozer blade can suffice for all the other puddle trench requirements. Puddle trenches may be done away with where the dike base exceeds 7 m in width.
In rearing pond construction, it is suggested that 5 to 8 cm of the surface be scraped by dozer and piled in strategic sections to allow easy spread back on the final levelling after excavation is done. The top portion is usually “rich” soil and is well worth the expenses and effort to scrape, pile and re-spread.
All pond bottoms shall be canted towards the gates. All the ponds shall have shallow transverse canals as well as peripheral canals. This will facilitate harvesting, drainage, drying, provide fish and shrimp shelters, and easy pest eradication.
At the chosen site at Diego Suarez, it has been noted that there is no skilled pond construction labour available. Mechanized construction can be done only by one company - The French Salt Company. There are no contractors that may have the capability or the equipment. On the other hand, the salt company has been doing earth moving and land forming jobs in the swamps for the last 20 or so years. This company has an array of equipment ranging from bulldozers, excavators, dump trucks and trailers, scrapers, grader and a host of other earth-moving equipment. Also, the company has a good supply of parts and is backed by a well-managed shop that can support all maintenance requirements of the mechanized fleet. Because of the above conditions, the-usual work contract through bidding may not work. Instead, a negotiated contract may be desirable. With proper negotiations, the salt plant may consent to do the work at cost. Work may be contracted by the machine hours, the volume of soil moved or by total overall contract.
The area has been observed to have a prevalent east wind that is rather strong and averages about 21 km per hour on a yearly basis. Because of this, it would be very advantageous to the project to harness this available wind power through windmill and use it to pump water into the ponds. It is estimated that there is no less than 1 HP net (actual - after efficiency and friction adjustment) continuously available, meaning a pumping capacity of 600 cubic meters per 24 hours at 2.5 m total dynamic head (TDH). Calculations are based on 21 km per hour with 5 m blade diameter at 10 m blade centre height. A wind pump will greatly enhance the project in that it can drive a freshwater pump to regulate salinity, especially during dry season.
The road to the project area is good. Eight hundred meters of the 2 km has very well laid stones on it and can be considered an all-weather-road. The remaining 1 200 m need grading and gravelling.
The Government's electric plant is planning to approve the salt plant's application for power. If this materializes, it will be very easy for the project to connect with only 2 km of transmission lines necessary.
With power to the project, pumps and aerators can later be used for intensive culture of fish and shrimps. A drawing of a two-channel gate (1 m per channel) is submitted by the writer with the set of plans (Fig. 14). It is suggested that this type of gate be constructed in place of the ordinary two-channel gate. This suggested gate has provisions for a vertical propeller pump if and when the project is expanded and would be geared for intensive culture, especially when electric power can be brought to the project area.
The selected project site will have a great socio-economic impact as it is near a well-populated village. There are houses scattered within an 800 m radius of the project area.
Other pertinent data obtained around Diego Suarez are presented. Although these can change with time, these are the prevailing costs during the survey.
| A. | Labour cost | |||
| Common labourer | 12 000 | fmg/month | ||
| Skilled labourer | 30 000 | fmg/month | ||
| Supervisor | 50 000 | fmg/month | ||
| B. | Fertilizer prices (N-P-K) | |||
| 11-22-16 | 95 | fmg/kg | ||
| 12-24-12 | 90 | fmg/kg | ||
| 13-13-21 | 84 | fmg/kg | ||
| 15-15-15 | 80 | fmg/kg | ||
| 12-12-12 | 100 | fmg/kg | ||
| 40-0-0 (Urea) | 80 | fmg/kg | ||
| C. | Fish and beef prices | |||
| Smoked fish | 500 | fmg/kg | ||
| Fresh fish | 300 | fmg/kg | ||
| Beef | 450 | fmg/kg | ||
| D. | Construction materials | |||
| Cement (50 kg/bag) | 1 070 | fmg/bag | ||
| Nails | 280 | fmg/kg | ||
| Steel bars | 130 | fmg/kg | ||
| Lumber (hard) | 45 000 | fmg/m3 | ||
| Planks | 37 000 | fmg/m3 | ||
| Galvanized sheets (2.5 m × 1 m) | 2 900 | fmg/sheet | ||
| Concrete blocks (10 × 20 × 40) | 70 | fmg/piece | ||
| Concrete blocks (20 × 20 × 40) | 130 | fmg/piece | ||
| E. | Equipment rental (at cost) | |||
| Fiat bulldozer, 60 to 80 HP | 2 500 | fmg/hr | ||
| Tracked front loader, 60–80 HP | 2 500 | fmg/hr | ||
| Wheeled tractor, 60–80 HP with hydraulic trailers or scrapers | 2 400 | fmg/hr | ||
| Hydraulic tracked excavator, 600 liter bucket capacity | 4 000 | fmg/hr | ||
| Tracked dragline, 10 m boom, 600 liter bucket capacity | 3 200 | fmg/hr | ||
| Bulldozing (economical distance only - dry) | 100 | fmg/m3 | ||
| Excavation by hydraulic tracked excavator and loading on trailers on dry ground | 75 | fmg/m3 | ||
NOTES: (1) FMG = Madagascar Franc
US$1.00 = 215 Francs at time of visit, March 1979
(2) Information on capacities are on good soil conditions. Allowance should be given for swamp conditions. Estimates given by Mr. R. Caisso.
