THE EFFECT OF SURFACE ALBEDO AND GRAIN SIZE DISTRIBUTION ON EVAPORATION LOSSES IN SAND DAMS

Abstract

Sand dams are very useful in arid and semi arid lands (ASALs) as facilities for water storage and conservation. Soils in ASALs are mainly sandy and major water loss is by evaporation and infiltration. This study investigated the effect of sand media characteristics, specifically surface albedo, grain size and stratification on water table recession using experimental model. Tanks of 220 litres capacity and 0.9 m depth were set as evaporation media at the JKUAT weather station in Kenya. Experimental media investigated were; fine ballast, fine sand, coarse sand, in situ sand and stratified combination. Surface albedo were varied by painting top sand media with colours such as white, grey and natural brown sand colour as a control. Albedo were indexed using luminance factor. The study concluded that evaporation losses are inversely proportional to the albedo of the evaporating surface measured in terms of luminance factor. The relation between water table recession in porous medium and pan evaporation is an exponential decay curve. The study showed that stratification of media have significant influence on water loss particularly, if the overlying material is courser than the underlying layers.