A WEIGHING LYSIMETER SYSTEM FOR CONDUCTING EVAPORATION STUDIES

rhe lysimeters are 3.1 m long, 2.2 m wide and 1.3 m deep. Each lysimet er is supported by four 4.5 Mg load cells and has a resolution of 0.1 mm over approximately 6.8 m2 surface. The supporting structure was des igned so that all load cells are accessible for maintenance and repair from the surface. The design eliminated the need for a counterweight mechanism and reduced requirements for excavation and underground stru ctures. Additional instrumentation included net radiometers to measure net solar radiation impinging upon the soil surface and thermocouples to measure the temperature as a function of depth. A dual-probe gamma radiation density gauge was used to monitor the vertical distribution of soil water. Unit cost for construction and installation of each ly simeter was approximately US$ 17,500 at the time of construction in 19 85. Design criteria, calibration curves and typical evaporation data a re reported.