ENERGY-BUDGET EVAPORATION RATES AT UPPER KLAMATH LAKE - AGENCY LAKE, KLAMATH COUNTY, OREGON

Reliable estimates of evaporation rates in a ground water-dominated basin provide important constraints in formulating ground water models for Upper Klamath Basin. Estimates of daily evaporation rates from Upper Klamath Lake – Agency Lake (at 1262.8 m stage total area is approximately 283 km² and mean depth is roughly 2.7 m) were determined by the energy-budget method from June 4 to October 9, 2003. Hydrometeorological data were collected at the surface of the lake and on-land stations in direct proximity. Two RUSS (Remote Underwater Sampling Stations) buoys allowed continuous measurement directly at the lake surface. Air temperature, relative humidity, and water surface temperature allowed calculation of temperature and vapor pressure differences necessary to calculate the Bowen ratio. Temperatures in the water column (1-2 cm, 30 cm, 60 cm, and 90 cm depths) observed at RUSS-7 were used in combination with daily lake stage measurements and lake bathymetry to calculate the change in energy stored in the water body. Incoming solar and atmospheric radiation were continuously recorded using a precision spectral pyranometer and a precision infrared radiometer (pyrgeometer), respectively. Daily net flux of energy to the lake from incoming and reflected solar and atmospheric radiation, as well as atmospheric radiation emitted from the water body, ranged from 241 W m^-2 to 7 W m^-2. Total daily flux of energy exiting the lake is considered primarily from Link River, A-Canal, and Keno Power Canal where discharge collectively ranged from 4.27E⁷ m³ day^-1 to 1.82E⁸ m³ day^-1 equating to energy losses ranging from 25 W m^-2 to 6 W m^-2. Stream discharge and temperature of the primary inlet to the lake (Williamson River) were monitored continuously from 6/1 to 10/14 and 6/1 to 8/11, respectively. Daily energy flux from the Williamson River ranged from 9 W m^-2 to 2 W m^-2. Water-advected energy to the lake from other sources – including Wood River, ground water, irrigation canals, and agricultural drainage – were calculated using temperatures recorded at Wood River and local springs; past water budget studies; and reliable estimates of ground water flux. Precipitation was considered negligible as a source of energy since the total mean rainfall during the study period amounted to less than 8 mm.