In summary, the split channel system is one that contains a relatively 

 large quantity of gravel material, but its narrow floodplain with stable 

 islands and banks restricts the areal extent where gravel can be easily 

 obtained. Use of vegetated areas will directly affect terrestrial organisms 

 by either complete removal or displacement to undisturbed areas. Similarly, 

 the tendency for localized widening of the floodplain will reduce lateral 

 stability of channels, facilitate the possible formation of a braided chan- 

 nel pattern, decrease water velocity, increase sedimentation rates and, 

 perhaps, increase water temperature. These changes will affect aquatic 

 organisms by increasing secondary productivity, by changing benthic com- 

 munity structure, by providing rearing areas for some species of fish, and 

 perhaps by affording situations conducive to fish entrapment (Table 40). 



Meander i ng 



A meandering river winds back and forth within the floodplain. The 

 meandering channel shifts downval ley by a regular pattern of erosion and 

 deposition. Few islands are found in this type of river and gravel deposits 

 typical ly are found on the point bars at the insides of meanders 

 (Figure 95). Sediment transport in meandering systems is usually less than 

 for braided and split-channel river systems of equivalent size. 



The size of individual gravel deposits in a meandering river depends 

 on the size of the river. On a large river, point bars can be quite ex- 

 tensive wh i le on sma I ler rivers the point bars are char acter i st i ca I ly smal- 

 ler. The areal extent of these gravel bars determines, to a large extent, 

 the degree of change which gravel extraction has on a meandering system. For 

 example, if a large point bar is used to supply gravel for a sma I I project, 

 the operation of a material site may cause little change to the river sys- 

 tem. However, when projects with large gravel requirements are situated 

 close to a sma I I meandering river or where the gravel requirements exceed 

 that available on a large point bar, potential effects to the river system 

 increase greatly. The alternative mining procedures are to completely remove 

 the point bar, use several point bars, or remove vegetated deposits back 

 from the channel. In al I cases, varying degrees of impact can be expected, 

 but all will depend on the manner in which the gravel is extracted. 



340 



