leHJMMfo ol wat&i witkdMUuwU 



PROJECTIONS OF FUTURE USE 



In order to adequately and uniformly assess the potential effects of water 

 withdrawals on the many aspects of the present study, projections of specific 

 levels of future withdrawals had to be made. The methodology by thich this was 

 done is explained in Report No. 1 in this series, in which also the three pro- 

 jected levels of development, low, intermediate, and high, are explained in 

 more detail. Summarized in appendix A, these three future levels of development 

 were formulated for energy, irrigation, and municipal water use. Annual water 

 depletions associated with the future levels of development were included in 

 the projections. These projected depletions, and the types of development 

 projected, provide a basis for determining the level of impact that would occur 

 if these levels of development are carried through. 



YELLOWSTONE RIVER 



If flow reductions under the low, intermediate, or high level of develop- 

 ment would be sufficient to alter the present dynamics of channel morphology 

 through changes in sediment and bedload transport, those species which nest on 

 islands in the river would probably be adversely affected. If the dominant 

 discharge (that high flow recurring about every \h to 2 years which, through 

 a combination of magnitude and frequency, accomplishes the most geomorphic 

 work in a channel over time) were reduced to the point that the rates of island 

 erosion and formation were altered (Koch 1976b), nesting goose and loafing 

 waterfowl populations would be reduced through stabilization of bars and islands 

 and the resultant encroachment of vegetation. Channel changes which cause loss 

 of island separation from other land masses and the reduction in width and 

 depth of channels would result in lower nesting success of Canada geese, ducks, 

 and mergansers through increased accessibility of these areas to predators. 

 Water withdrawals resulting in flows at Miles City below 255 to 283 m 3 /sec 

 (9,000 to 10,000 cfs) during the early part of goose nesting could result in 

 poor goose reproduction. Based on flow data from Miles City in 1975 and 1976, 

 312m3/sec (11,000 cfs) maintained during the early nesting period would be 

 most conducive to successful goose nestina. Should alterations in the flow 

 regime and channel morphology reduce ice scarification in any section of the 

 river where it has been active most winters, plant succession on some ice- 

 gouged sites could accelerate, lowering goose nesting success on those sites. 

 Flow reductions sufficient to alter channel morphology could result in 

 abandonment of some heron rookeries if the flow in the channels near the 

 rookery were cut off as the main channel changed course. 



Short-term reductions in flow could benefit pelican, cormorant, heron, 

 merganser, and other piscivorous bird populations through concentrations of 

 fish and stranding of fish in receding backwaters. Flow reduction for an 

 extended period, however, would probably cause loss of fish habitat and a 



71 



