Laserfiche WebLink
Table 3. Possible river morphology adjustments caused by sustained decreases in flow on Alaska's Beaver Creek. <br />Feature <br />Adjustment <br />Comments <br />Average width <br />decrease <br />hydraulic geometry relationships <br />Average depth <br />decrease <br />hydraulic geometry relationships <br />Meander length <br />decrease <br />hydraulic geometry relationships <br />Gradient <br />increase <br />hydraulic geometry relationships <br />Pools <br />fill <br />Heede (1976) <br />Point bars/beaches <br />decrease in size <br />stream tries to increase efficiency <br />Riffles <br />increase in number <br />stream tries to increase efficiency <br />Width /depth ratio <br />increase slightly <br />hydraulic geometry relationships <br />Bank stability <br />increase <br />lower stress on high banks <br />Velocity <br />decrease <br />hydraulic geometry relationships <br />Sloughs <br />decrease <br />less adjustment and rejuvenation <br />2. Loss of Peak Flows <br />Another classic case of an altered flow regime comes with the development of a large upstream dam and <br />storage reservoir. Most significantly, this creates a loss in peak flows as well as a loss in sediment, each of which <br />can cause a number of morphological or vegetational adjustments. <br />The Bill Williams River in Arizona provides a useful example (see Figures 19 and 20). The initial result of the <br />development of an upstream dam was severe downcutting of the channel immediately downstream due to the lack <br />of normal sediments. In addition, there was significant aggradation (channel choking) much farther downstream as <br />tributaries deposited sediments that the decreased main stem flows no longer had the ability to move. Both kinds <br />of changes can have important implications for recreation on similar river systems. In particular, the downcut areas <br />may lose beaches for camping or picnicking while the aggraded areas become choked with sediment and may <br />become unboatable. Impacts on the fishery can also be significant, as the sediment loading areas may smother <br />spawning or rearing habitat or cause declines in macroinvertebrates upon which fish feed. <br />Williams River, Arizona. <br />W <br />on the Bill Williams River. <br />