Evaporation Investigation at Elephant Butte Reservoir Using Energy-Budget and Mass-Transfer Techniques

摘要

Three basic methods for evaluating evaporation losses at Elephant Butte Reservoir have been reviewed in this investigation. They are: (1) Energy budget; (2) Mass transfer; (3) Cummings radiation integrator. The energy-budget technique requires, from the first law of thermodynamics, that a balance of energy exist between the loss or gain of heat at the surface of the reservoir. The mass-transfer method relies on the upward transport of water through the process of eddy diffusion. The method uses the principle that the forces involved in turbulent diffusion of momentum apply to the diffusion of water vapor and heat. This implies that a similarity exists between the wind profile and the humidity and temperature profiles. A thermally-insulated evaporation pan, known as a Cummings Radiation Integrator (CRI), was tested as a possible instrument for measuring net incoming radiation. Incoming net radiation obtained from the CRI was statistically compared to that using the pyrheliometer and flat-plate radiometer, the square of the correlation coefficient being 0.987. Lake evaporation, using the computed CRI net radiation, was only four per cent higher than that obtained from radiation instrument data. (Author)