Irrigation & Drainage Systems Engineering

The rate of evaporation in dry climates is a concern and needs to be assessed and quantified for planning in water management activities. The main objective of the study was to investigate evaporation rate of a bare ground in Masvingo district in Zimbabwe using a class ‘A’ evaporation pan. Specific objectives include calibrating the pan using the FAO-Penman Monteith (P-M) method and obtaining typical evaporation rates for the area which could be extended to represent areas of relatively similar climates. To achieve these objectives an evaporation pan was installed on a wooden grid platform near a weather station that recorded wind speed, air temperature, humidity, maximum and minimum temperatures. Considering fetch dimensions the pan results were correlated against P-M method results to give pan calibration coefficient and the slope of the curve gave a Kpan of 0.91 and changes in water depths with respect to pan dimensions gave average evaporation rates of 5.1 mm/day at mean maximum temperature of 24.9°C. The evaporation rates obtained were not sustainable in the long term if water harnessing and conservation strategies are not employed.