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<br />001443
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<br />(I) The word "depleted" here refers to natural losses, sinoe by
<br />definition there v.ere no man-made "depletions" under virgin 0 onditions,
<br />and might better read "reduoed" or "diminished."
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<br />(2) A "growing stream" down to the Black Canyon section does
<br />not mean that natural losses are absent above that point, or may be ignor-
<br />ed as in the Report. On the contrary it means only that inflows to the
<br />main river. or oontributions from tributary streams and areas, are great-
<br />er in amount than the quantities of water lost in conveyanoe. Similarly,
<br />a losing river in the desert region does not mean that there were no
<br />tributary oontributions under virgin conditions, or that they may be dis-
<br />regarded. Instead, it means that natural losses from the main-river
<br />channels were greater in amount than the tributary inflows (except at
<br />times of flood).
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<br />(,) Hith "virgin flOWS" of 2.282,000 acre-feet at Phoenix and
<br />1.271,000 acre feet at Dome, the oonveyanoe loss would be 1.011,000 acre
<br />feet plus all the virgin tributary inflow to the river section.
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<br />(4) The indioated net gain from Lee Ferry to Laguna Dam. ao-
<br />oording to the above table, is 180,000 acre feet. Since tl~ contribu-
<br />tions reported from rattle Colorado and Virgin Rivers together amount to
<br />648,000 acre feet, the table implies that ne,tural losses under virgin
<br />conditions were 468,000 ac['e feet. Colorado questions the acouracy of
<br />the estimates for the two reported tributaries, and says that miscellane-
<br />ous tributary drainage areas were ignored. Under so-called virgin condi-
<br />tions the tributary contributions between Lee Ferry and lAguna. Dam (as
<br />estimated by Colorado engineers) averaged 495,000 acre feet from the Little
<br />Colorado River, ,92,000 acre feet from the Virgin River, 41,,000 acre feet
<br />from miscellaneous drainages between Lee Ferry and Boulder Dam, and 200..000
<br />acre feet from miscellaneous streams (including Williams River) and areas
<br />bet\-.eell Boulder Dam and Laguna Dam. Assuming that total figure of 1,500,000
<br />ac['e feet, of the net gain between Lee Ferry andLaguna Dam is 180,000 acre
<br />feet, as shown in the above tab Ie., the natural conveyance loss would aver-
<br />age 1.,20,000 acre feet annually along that river section under virgin
<br />conditions.
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<br />(5) From the instances above mentioned it is apparent that
<br />natural conveyance losses in the Colorado River Basin involve substantial
<br />quantities of water, and it seems self-evident t'hat such losses under so-
<br />called "virgin conditions." when streamflows were ,.laximum and wholly un-
<br />regulated, would have been greater than those observed and calculated
<br />from records during the historic period. Colorado suggests that estimates
<br />of natural losses should be made by the Bureau of Reolamation, and should
<br />appear in the Report, covering so-called virgin conditions, or the condi-
<br />tions of the period of record, or both. As estimated by Colorado engi-
<br />neers during the period 1908-1942 (when man-made depletions averaged
<br />1.952,000 acre feet per year above Lee Ferry, and 2,911,000 acre feet be-
<br />low Lee Ferry. and when the recorded flow at the International BOUndary
<br />averaged 12.68,,000 acre feet annually), the natural oonveyance losses
<br />averaged 870.000 acre feet above Lee Ferry, and 2.640.000 acre feet below
<br />Lee Ferry. or totalled ,.510,000 acre feet annually in the Colorado
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