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<br />. <br /> <br />(\#\ <br />1.~ <br /> <br />.1 <br /> <br />Sedimentation of McHillan Resco"evoi.r <br />---------~---- ~ ------ <br /> <br />A ~tudy was made to de~;81'r:::'ne -t~fJ nurlber of years required <br />for McMillan Reservoil' ';,0 become cornpleteJy filled with sediment up <br />to the normal wa';,er surface under conditio~s of sediment inflow that <br />would prevail subsequent to the construction of the water salvage <br />channel and floodway. A second study was made to determine the resid- <br />ual capacity of the reservoir at the end of the sama period of time <br />u~der nresent conditio~s of sedimant inflow where about 80 percent of <br />the sediment passing the A::-tesia gagir!g station is retained by the <br />native vagetation in the delta ~ea.. <br /> <br />The inflow to the reservoir in both studi..es >Tas considered to <br />be represented by the a~nual flows of the Peccs Rival' near Artesia for <br />the period of 1905 thr~ugh 1953 that wculd have occurrad had Alamogordo <br />Reser-voir bee!l i!l oper-ation during the e!ltire period. Uaing these <br />inflo,lS, the annual total sediment inflow at Artesia for each year was <br />computed from the studies of total sedime~t load made for the channel <br />and floo<hlay design studies. The trap efficiency of the reservoir was <br />determined by the 9rur.e method, <br /> <br />These studi.es show that under the conditions of sediment <br />inflow to McMillan Reservoir that would prevail after the beginning of <br />ope~'ation of the proposed project works, the reser-voir would be com- <br />pletely filled with sedime;1t up to normal wa>,er 8u.'face elevation in <br />abOI~ 36 years. If the present conditions of sediment inflow should <br />continu.e, the reoi_du.al capacity of i-IcJ1illan Rese~"voir at th." e~d of <br />the 36..year period would be abolJt 21,400 acre~feet, Conseq'.lently on <br />this basis t.I1e increaaed r".te of s~diment il1.flow to the flJC:l.lillan <br />Reservoir would represent a!l j.~'~;'"me!ltal J.oss of reservoir capacity of <br />about 21,400 a~re...feet over the estimated 36-year period, <br /> <br />VALUE OF ~jATER SALVAGED <br /> <br />M0tnod of Analysis <br /> <br />Ample opportunity exists for irr!.gation use of all of the <br />waters whi,ah could be salvaged under the proposed plan, However, <br />specific assignment of the salvageable waters is impracticable at this <br />time. The determination of net water savings that would be consi.d- <br />ered salvage water under the terms of the Pe00s River Compact is the <br />responsibility of the Pecos River Commission which will need to estab- <br />lish procedures for determining the amount salvaged, apportioning it <br />to users in the two states, and recording the u3'e made, Consequently, <br />in order to determine the value of water fo:,' irrigation, which is <br />indicated by the benefits that would result from its use, a farm budget <br />analysis was made using data from the Carls bad Project on the basis of <br />the following concluBions: <br /> <br />(a) The val ue of irrigation water per acre~foot for the <br />production of crops on the Carlsr.ad Project is reasonably applicable <br />to the principal irrigated areas of the basin, <br /> <br />14 <br />