Evaporation Reduction with Floating Granular Materials

Investigations were conducted to determine the feasibility of reducing evaporation from open water surfaces with white, floating granular materials which cool the water by reflecting incoming shortwave radiation. Studies were conducted on buried 7.2-m diam tanks where almost all energy exchange occurred through the water surface. Materials evaluated were calcium carbonate dust, silica sand, polystyrene beads, chopped styrofoam, and perlite. Evaporation reduction for 1 week ranged from 21% for water repellent sand to 64% for chopped styrofoam. Polystyrene beads reduced evaporation 39% for a 6-month period. Tests on a 400 sq m pond showed that perlite was self-spreading when wind speed was below 1 m per sec. White dust saved water over a 45-day period at a cost of 53 cents per 1,000 gal. Use of reflective granular materials is feasible for reducing evaporation of expensive water form small, steep-sided reservoirs.