zones of passage 



ANY BARRIER to migration and the free 

 movement of the aquatic biota can be 

 harmful in a number of ways. Such barriers block 

 the spawning migration of anadromous and cata- 

 dromus species. Many resident species make local 

 migrations for spawning and other purposes and 

 any barrier can be detrimental to their continued 

 existence. The natural tidal movement in estuaries 

 and downstream movement of planktonic orga- 

 nisms and of aquatic invertebrates in flowing fresh 

 waters are important factors in the re-population 



of areas and the general economy of the water. 

 Any chemical or thermal barrier destroys this 

 valuable source of food and creates unfavorable 

 conditions below or above it. 



It is essential that adequate passageways be pro- 

 vided at all times for the movement or drift of the 

 biota. Water quality criteria favorable to the 

 aquatic community must be maintained at all 

 dmes in these passageways. It is recognized, how- 

 ever, that certain areas of mixing are unavoidable. 

 These create harmfully polluted areas and for this 

 reason it is essential that they be limited in width 

 and length and be provided only for mixing. The 

 passage zone must provide favorable conditions 

 and must be in a continuous stretch bordered by 

 the same bank for a considerable distance to allow 

 safe and adequate passage up and down the 

 stream, reservoir, lake, or estuary for free-floating 

 and drift organisms. 



The width of the zone and the volume of flow 

 in it will depend on the character and size of the 

 stream or estuary. Area, depth, and volume of flow 

 must be sufficient to provide a usable and desirable 

 passageway for fish and other aquatic organisms. 

 Further, the cross-sectional area and volume of 

 flow in the passageway will largely determine the 

 percentage of survival of drift organisms. There- 

 fore, the passageway should contain preferably 

 75 percent of the cross-sectional area and/or 

 volume of flow of the stream or estuary. It is 

 evident that where there are several mixing areas 

 close together they should all be on the same side 

 so the passageway is continuous. Concentrations 

 of waste materials in passageways should meet the 

 requirements for the water. 



The shape and size of mixing areas will vary 

 with the location, size, character, and use of the 

 receiving water and should be established by 

 proper administrative authority. From the stand- 

 point of the welfare of the aquatic life resource, 

 however, such areas should be as small as possible 

 and be provided for mixing only. Mixing should be 

 accomplished as quickly as possible through the 

 use of devices which insure that the waste is mixed 

 with the allocated dilution water in the smallest 

 possible area. At the border of this area, the water 

 quality must meet the water quality requirements 

 for that area. If, upon complete mixing with the 

 available dilution water these requirements are not 

 met, the waste must be pretreated so they will be 

 met. For the protection of aquatic life resources, 

 mixing areas must not be used for, or considered 

 as, a substitute for waste treatment, or as an exten- 

 sion of, or substitute for, a waste treatment facility. 



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