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Otl1215 VII.8 Specifically, if the reservoir is deep and if evaporation must b~ estimated for periods of a month or less, energy advected to the reser- voir by inflow and outflow, and the change in energy storage within the reservoir should be evaluated, The water temperature would integrate the net advection. In this connection, the reader is referred to Geological Survey Professional Paper 298, "Water-loss investigations, Lake Mead"; also to Weather Bureau Research Paper 38, "Evaporation from pans and lakes." Under appropriate conditions, howeve:r, the ratio betl<<len pan' evaporation and reservoir evaporation can be relatively unifo~. For example, at the Pine Flat Reservoir, Oalifornia--a deep reservoir in mountainous terrain--observations by the CQrps of EIlgineers have disclosed the following regimen: (1) lnflow is largely cold snowmelt during the spring, (2) Owing to density currents in the head of the reservoir and to draft from low-level outlets through the dam, mOlltof the cold inflow water passes through the reservoir at depth. (3) Thus, even in spring the near-surface water in the reservoir is near the temperature of water in the land pan. (4) Under the autu,mn schedule of reservoir operation, draft is cOllJDlon1y through high-level o'Q.tleta; thus the near-surface water that has stored heat during the S~er is Boon drawn off and temperature of the surface layer in the reservoir again is near that of the land pan. Under this particular regimen, water temperatures at the .surface of the reservoir do not differ greatly from those in the land pan at any season. They are not, as had been anticipated, substantially lOwer in spring and substantially higher in autumn and winter. In general, therefore, coefficients for translating evaporation values from a land pan to a deep reservoir should be selected with due regard to the possiblility that water in the reservoir is stratified according to marked differenCes in density (temperature). In certain instances, measurements of land-pan evaporation adjacent to a reservoir may be biased by events in the operation of the (lam. At Pine Flat Reservoir, a flip-bucket spillway, whenever it 1'unctioned, greatly increased humidity tf the adjacent air. At times, the lIlass of super-humid air extended to and "blanketed" the adjacent land pan, sO that evaporation from the pan dilllinished. Periods of record so b;i.ased may be disclosed by plotting measured pan evaporation against its principal parameters, and examining apparently aberrant measurem'1nts for possible coincidence with unusual eVents in the operating schedule for the dam and reservoir.