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The classification of river zones is helpful in comparing studies of the 

 ecology of different rivers and is useful in fishery and river management. 

 Most attempts at river classification have been instigated by the needs of 

 fishery management. With an increasing need for conservation of water quantity 

 and quality, a system of river-zone classification is invaluable in predicting 

 the likely effect on the ecology of the river of project management policies 

 such as water removal and flow regulation. 



River zonation studies began at the end of the last century with German 

 biologists who developed a system of classifying river zones on the basis 

 of the dominant fish species present, after which they named the zones- 

 trout, grayling, barbel, and bream. Similar methods of classification were 

 developed in other regions. Subsequent studies carried out throughout the 

 world to establish whether the German zonation scheme was generally applicable 

 attempted to characterize the different zones more precisely in physiographical , 

 physiochemical , and biotic terms (Whitton 1975). 



Carpenter (1928), an early British researcher influenced by the earlier 

 German workers, attempted to classify the mountain streams of North Wales- 

 She described a typical river as arising from several sources at high altitude 

 and forming a stream characterized by swift current, steep gradient, and 

 extensive erosion. Downstream, as the gradient decreases, the current slows, 

 and the stream deeDens and widens. With the reduction in current, stones, 

 gravel and sand are successively deposited on the streambed. Still farther 

 downstream, current is further reduced, the river widens and meanders, and 

 the bed is covered with deposited silt. Carpenter's classification of streams 

 included a taxonomic list of the flora and fauna of each zone. High altitude 

 zones included headstreams, trout becks, and minnow reaches. Lowland stream 

 zones included upper and lower reaches. 



Huet (1949, 1954), using European stream data, refined the European system 

 which recognized four zones, each identified by key fish species. The trout 

 zone had a steep gradient, fast current, cool temperatures, and oxygenated 

 water. The grayling zone was deeper and had less gradient, a gravel bottom, 

 cool temperatures, and oxygenated water. The barbel zone had moderate gradient 

 with an alternating riffle-pool morphology and few trout still present. The 

 bream zone was characterized by slight current, high temperatures, and deep 

 turbid water. The four zones represent two fish faunistic regions—an upper, 

 cool water region containing salmonid fish, and the lower, warmer waters 

 containing cyprinids. From lonqitudinal profiles of many European streams, 

 Huet concluded that the fish fauna was directly related to the gradient 

 of the stream, and that, in nearly all rivers of comparable size, streches 

 with similar gradients have similar fish faunas. From these conclusions he 

 formulated his slope rule: in a given biogeographical area, rivers or 

 stretches of rivers of like breadth, depth, and slope have nearly identical 

 biological characteristics and similar fish populations. 



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