Measuring evaporation from soil surfaces for environmental and geotechnical purposes

There are many reasons for the need to assess rates and quantities of evaporation or evapotranspiration from natural soil surfaces, the surfaces of deposits of mine or industrial waste, or soil-covered waste surfaces. These include assessing water balances for near-surface soil strata, landfills, tailings dams and waste dumps and suitable deposition or application intervals for hydraulic fill tailings dams, or for the disposal of liquid wastes on land. The surface energy balance is probably the most widely used method for assessing evaporation, although other methods are also available. The surface energy balance method is studied in this paper. The surface energy balance is by no means a new method (it was proposed by Bowen in 1926), but appears to be almost unknown to civil engineers, and in particular to those engaged in geotechnical engineering or waste management. The aim of this paper is to draw attention to this useful technique and to show how it can be applied in many aspects of environmental geotechnics and waste management. The paper describes the measurements made to assess the surface energy balance as well as its analysis, and presents the results of typical measurements. It also presents numerical values of the parameters and constants needed for the analysis. The experimental difficulties of the analysis are described and examined, and the method's accuracy is assessed by means of laboratory and field measurements. The paper is intended to be both informative and a practical guide to measuring evaporation in the field.