tailieunhanh - Small-scale freshwater fish farming - Chapter 3,4

Fish farming ponds Different pond types Depending on the site, there are two different types of fish ponds to choose from: diversion or barrage ponds Diversion ponds (figure 3) are constructed by bringing water from another source to the pond. | 3 Fish farming ponds Different pond types Depending on the site there are two different types of fish ponds to choose from diversion or barrage ponds. Diversion ponds Diversion ponds figure 3 are constructed by bringing water from another source to the pond. Figure 3 Diversion pond A stream B water intake C diversion canal D inlet E outlet Bard et al. 1976 Fish farming ponds 13 Below are the different types of diversion ponds figure 4 A Embankment ponds The dikes of an embankment pond are built above ground level. A disadvantage of this type of pond is that you may need a pump to fill the pond. B Excavated ponds An excavated pond is dug out of the soil. The disadvantage of this type is that you need a pump to drain the pond. C Contour ponds Soil from digging out the pond is used to build the low dikes of the pond. The ideal site has a slight slope 1-2 so the water supply channel can be constructed slightly above and the discharge channel slightly below the pond water level. Since natural gravity is used to fill and drain the ponds no pump is needed. Figure 4 Different types of diversion ponds Viveen et al. 1985 A embankment pond B excavated pond C contour . Pump 2. Drainage canal 3. Inlet pipe canal 5. Overflow pipe Barrage ponds Barrage ponds figure 5 are constructed by building a dike across a natural stream. The ponds are therefore like small conservation dams with the advantage that they are easy to construct. However it is very 14 Small-scale freshwater fish farming difficult to control this system it is difficult to keep wild fish out and a lot of feed added to the pond will be lost because of the current. A properly built barrage pond overflows only under unusual circumstances. Figure 5 Barrage pond. A stream B inlet C dam D outlet pipe E spillway and overflow F monk One of the most common pond draining structures. It consists of a vertical tower with boards to regulate the water level a pipeline to discharge the water and a screen to .