|Inland Aquaculture Engineering (1984)|
|DESIGN AND CONSTRUCTION OF FRESHWATER FISH FARMS|
|Chapter 6. Principles of Designing Inland Fish Farms|
|2. PREPARATORY WORK|
The layout of the site is governed by the combined requirements of operation and the particular site conditions. Prior to designing work, all information should be collected regarding technological requirements and the data particular to the site.
- Species of fish to be produced.
- Sequence of operations envisaged: production from hatching to market fish, or production of market fish alone.
- Method of fry production.
- Production quantities envisaged.
- Methods and possibilities of nutrient supply to the ponds, such as organic manure, duck farming, fertilizer application.
- Feed distribution (fish feed, grain feed, etc.).
- Transport management - method and means of in-farm and external transportation.
- Buildings required (operation, social-cultural amenities, grain store, equipment shed, repair shop, housing, etc.).
- Data on existing water uses affected.
- Data affecting water supply and drainage.
- Future development plans for the area.
- Data on other facilities (roads, railways, etc.)
- Property conditions and data.
Topographic surveys to the scale 1:500 to 1:5000 and with contour lines of 20-25 cm (perhaps 1 ft) vertical spacing are needed for the entire fish farm area, in order to permit designing complete pond drainage and earthwork volume estimates of the required accuracy.
On any existing earth structures (embankments, canals, etc.) cross sections should be taken at 50-100 m spacing, with points spaced sufficiently close to each other to plot the actual terrain with ± 20 cm accuracy on the cross sections of 1:100 scale.
Cross sections should be plotted at the sites of major structures (intakes, road crossings, etc.)
Cross sections at not more than 500 m intervals and continuous profiles are needed on the connecting stream or canal extending for the distance affected by the fish farm (e.g. to the backwater limit).
The topographic survey should be connected, especially as regards elevations, to the national survey network.
Where water is obtained from a natural stream, data must be acquired on the stages and flow rates to be anticipated at the diversion point in the periods of pond filling and for compensation of water losses. Water supply should be designed for a flow rate of 80 percent probability.
In the case of ponds through which floods must be conveyed, or the dikes which are required to retain floods on the stream, the designer will require also data on design flood levels and discharges. The probability of occurrence of the design flood is normally specified by the competent water agency. In the absence of such specification, the flood of 1 percent probability of occurrence (once in a hundred years) should be adopted as the design flood. In the case of minor ponds, where a dam failure would cause no other losses, a flood of say 3 percent probability might be adopted as the design flood. The retention capacity of upstream ponds is taken into account in estimating the design flood.
Data on the peak values of monthly evaporation and rainfall are needed for estimating the water demand.
Data on the monthly average and extreme temperatures are needed for selecting the species of fish for farming, for planning the necessary feed supply rates and for designing the holding and storage facilities of live fish.
The annual volume of sediment entering the ponds should be estimated.
Data are needed on the direction and highest speed of wind prevailing in the area in order to design wave protection.
The geotechnical explorations should be extended to the entire area of the fish farm, to provide data on the soil stratification in the pond area, under the dikes, along the canal traces and at the sites of structures.
The data obtained by soil explorations should be suited to estimate:
- seepage losses
- underseepage conditions and the hazard of piping failure
- stability of the dikes
- the required degree of compaction
- the allowable flow velocity in the supply canals, and
- the foundation of the structures.
The methods of exploration and laboratory testing, as well as the interpretation of the results are described in more detail in Chapter 5 on soil characteristics for aquaculture farms.
The water supplied to the fish ponds must not contain pollutants and toxic substances detrimental to fish life. The composition of the feed water should be subject to quality analysis, including the following:
- oxygen content
- pH value
- total salts content
- ammonia content
- free CO2 content
- phenols, oil and tar content.
The water quality analyses should be such as to enable prediction of the interactions between the soil and the feed water.