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1\ TABLE 6. Changes in channel morphology resulting from alterations in stream flow and sediment vield" Indep..'ndem vanable Dependent variable Average Meander RallO of \alley Stream Sediment Channel channel wave Channel slope to channel discharge load width depth length scope slope + NC + + + NC + + NC + + + + NC + + + + + :t + :t + :t :t + + :t + :t + + :t :t + . Ratio of width to depth + + + ~ t f Jf , ~ I "NC = no change; + = direction of change is an increase; - = direction of change is a decrease; :t = direction of change is indeter- minant.(Modified from Schumm 1977.) TABLE 7. Change in width resulting from construction of a dam and reservoir." River Average width (m) Pre-dam Post-dam A verage annual peak discharge (m3.s.1) Pre-dam Post-dam Chanahoochee River, GA Jemez River, NM Arkansas River, CO Missouri River. MT Missouri River, ND Missouri River, SD Medicine Creek, NE Middle Loup River. NE Smoky Hill River, KS Republican River, KS Wolf Creek, OK North Canadian River, OK Canadian River. OK Red River, OK-TX Nueces River, TX Des Moines River, lA "Source: William and Wolman (1984). 69.2 213 152 272 568 707 53 33 39 127 223 52 369 255 106 168 where Q = the 1.5 yr annual flood flow in m3/s, Qs = the bed load in m3/s, Dso = the median particle size of the bed material (m), P = the wetted perimeter (m), R = the hydraulic radius (m), dm = the maximum flow depth (m), and S = slope. The Hay equations demonstrate that changes in channel geometry can result from changes in sediment loads, streamflow, or the size of the sediment load, and. not just streamflow alone. Lane (1955) gave the following equation to elucidate some of the possible changes. (22) QprvQw52 where Qs is the bed material load, Q... is the streamflow, D is the size of the bed material, and S is the slope of the stream. Use of hydraulic geometry equations for channel main- tenance should be restricted to water planning studies for the purpose of reserving flows from future consumptive uses, where the assumption is being made that the channel must remain the same as presently exists. These equations are not 26 70.6 46 45 315 727 826 56 77 40 140 31 28 357 268 126 177 660 160 560 770 3900 5200 530 58 320 290 240 280 3600 3000 I 100 1200 270 39 190 690 1 100 1200 13.5 53 135 150 35 44 740 950 800 800 appropriate for impact analyses and the management of reg- ulated rivers which will alter both flow and sediment trans- port. A further restriction is that the equations apply only to alluvial rivers, which means that the river bed and banks are composed of sediments and are not controlled by bed- rock. The alternative to maintaining the existing channel is to predict the channel characteristics resulting from the streamflows and sediment movement from specific water resources development. A basic assumption of physical process models is that the nature of a stream channel, including the bed material, is related to all the flows that occur in the channel and that the channel is in a continuous process of adjustment. Consequently, a new pattern of flows may produce a channel response even though the bankfull discharge may remain the same. The linking of physical fish habitat analyses to stream sedimentation processes modeling is of considerable impor- tance and a high priority subject for additional research if we are to have any influence upon how streams are to be ~