Fish Hatchery Management - fisheries & aquaculture

HATCHERY REqUIREMENTS 29Sedimentation basins can take several forms. One is a modified concreteraceway, called a linear clarifier (Figrrres 12, 13, and l4). Water entering alinear clarifier should do so through a screen-preferablyof two or more screens-atthrough a seriesthe head end of the unit. Such screens, whichshould be more than 50% open area, distribute flow and reduce turbulencemuch better than dam boards, which cause turbulence near them and astronger surface than bottom flow.Perhaps the most common settling basins are outdoor earthen ponds or"lagoons." These can be of varying sizes and configurations. Obviously, thebigger the pond, the more effluent it can accommodate. Because of theamount of land settling ponds occupy, there usually are practical limitationson lagoon size.Several commerciallyproduced settling systems incorporate baffles andsettling tubes. These are quite efficient and require less space and retentiontime than either linear clarifiers or lagoons. However, they can be quiteexpensive.FIGURE 12. Effluent treatment system at the Jordan River National FishHatchery consists of two linear clarifiers (top), 30 ft x 100 ft with a water depthof 4 feet. The system will handle up to 600 gpm divided equally between the twobays. The bays are cleaned by drawing off the top water and moving the sludgewith a garden tractor to collection channels. The sludge is then removed with atruck-mounted vacuum liquid manure spreader (bottom). (FWS photos.)