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MARCH 1973 H, J, MOREL-SEYTOUX AND F, SAHELI 1) and the control (San Juan zones 3 and 4), 336 TABLE 10. Optimal combination of stations in the target (San Juan Mountains Gage Drainage Weight CSU Location elevation area factor number Station name (Basin) (ft) (mi') X Stations in target (area 1 in Fig, , 1076920 Piedra River near Piedra 30 6530,00 371.00 1.0 Piedra 1075830 Los Pinos River near Los Pinos 30 6501.51 692,00 1.0 Bayfield Stations in control (areas 3 and 4 in . 1) 1371520 Uncompahgre River at Uncompahgre 30 6318,8 437,00 0,810 (near) Colona 1272445 San Miguel River near San Miguel 26 7096,44 308.00 0,705 Placerville 1277200 Dolores River at Dolores 30 6924,91 556.00 1.161 Dolores 1073448 Hermosa Creek near Animas 29 6705,08 172,00 4,543 Hermosa l Minimum number of years with optimal X's is 6 years, Minimum number of years with all X's= 1 is 13 years, The percentage increase in precipitation was con- servatively assumed in the calculations of this paper to be 10%. Thus, one can say with some confidence and optimism that the chance of significant evaluation (based on runoff) for the pilot project is at least 50%. That probability is most likely to be greater as it increases rapidly as the percentage increase in precipita- tion exceeds 10%. For example, for the case summarized in Table 9, the power of the test which is essentially 50% for a 4-year period increases to 84% for the same period if the precipitation increase is 15%. On the other hand, if the precipitation increase is only 10% as assumed in this paper, and because the test procedure CSU number Station name Location (Basin) was optimiz~~J one must unfortunately add that this is the best tliit can be done under the circumstances. ; ~ A cknmvlectrJnents. This work was supported by the Bureau of ;f-eclamation, Division of Atmospheric Water Reso~rces Management, under Contract 14-06- D-6597, in c~nection with the SKYWATER program. The help of tle Bureau is gratefully acknowledged. The opti~ation technique was supported by funds provided by ijJ.e U. S. Department of Interior, Office of Water Resoutces Research, as authorized under the Water Resoti~es Research Act of 1964; and pursuant to Grant A~ement 14-:31-0001-3506 (OWRR Project A-Oll-Color"4o). Gage elevation (ft) Drainage area (mi') Weight factor X 1076420 1077400 1078000 1371520 1272445 1277200 1073448 TABLE 11. Optimal combination of stations in the target (San Jl~n Mountains zones 1 and 2) and the control (San Juan Mountains zones:$ and 4). "J Number~ existing y~s of recordf within, (1939-6Sl Piedra River near Piedra San Juan River at Pagosa Springs East Fork San Juan River above Sand Creek near Pagosa Springs Target stations areas 1 and 2 Piedra 30 " 6530,00 371 San Juan 30 7052,04 295,00 San Juan 30 ;', 7597,63 86,9 Control stations areas 3 and 4 Uncompahgre River at (near) Colona San Miguel River near Placerville Dolores River at Dolores Hermosa Creek near Hermosa Uncompahgre San Miguel Dolores Animas 30 26 30 29 6318,18 7096.44 6924.9 6705.08 437 308 556 172 Number of years with optimal X's=4,9",5 years, N urn ber of years with all X's = 1 is 22 years. 1.613 0,086 2,010 -0,313 0,689 0.895 4,543 -I