HATCHERY REQUIREMENTS 



29 



Sedimentation basins can take several forms. One is a modified concrete 

 raceway, called a linear clarifier (Figures 12, 13, and 14). Water entering a 

 linear clarifier should do so through a screen — preferably through a series 

 of two or more screens — at the head end of the unit. Such screens, which 

 should be more than 50% open area, distribute flow and reduce turbulence 

 much better than dam boards, which cause turbulence near them and a 

 stronger 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, the 

 bigger the pond, the more effluent it can accommodate. Because of the 

 amount of land settling ponds occupy, there usually are practical limita- 

 tions on lagoon size. 



Several commercially produced settling systems incorporate baffles and 

 settling tubes. These are quite efficient and require less space and retention 

 time than either linear clarifiers or lagoons. However, they can be quite 

 expensive. 



Figure 12. Effluent treatment system at the Jordan River National Fish 

 Hatchery consists of two linear clarifiers (top), 30 ft x 100 ft with a water depth 

 of 4 feet. The system will handle up to 600 gpm divided equally between the two 

 bays. The bays are cleaned by drawing off the top water and moving the sludge 

 with a garden tractor to collection channels. The sludge is then removed with a 

 truck-mounted vacuum liquid manure spreader (bottom). (FWS photos.) 



