i) Essential aquatic habitat in and downstream from the 

 site 



ii) Unimpeded instream migrations 



iii) Maintenance of natural pool:riffle ratio; riffles should 

 be avoided except in the following situations: 



• In a long riffle, excavation may be acceptable near 

 the middle of the riffle 



• When more rapid site recovery is desirable 



• When the riffle is unproductive aquatic habitat be- 

 cause of cementation or infiltration by f i ne °sed iments 



• Where deepening the thalweg may reduce or eliminate 

 auf e i s development 



24 



II. SITE PLANNING 



