Use of Physical and Biological Covers for Decreasing Evaporation Loss from Small-Scale Water Storage

Abstract

Evaporation is one main factor leading to water loss, especially in the case of small ponds located in various areas of Thailand. A study on effective methods to reduce the rate of evaporation is necessary to reduce the water loss. Covering the surface of water is a widely used method to decrease the rate of evaporation. The objective of this study was to investigate two techniques utilizing physical and biological covers to reduce evaporation loss from small-scale water storage. Floating covers, i.e., plastic balls and reused plastic bottles, were selected as the physical covers, whereas duckweed was used as the biological cover. Three concrete ponds were constructed for the study. Three experiments were then conducted; each experiment consisted of a pond with no surface covering, which served as the control pond. In the first experiment, evaporation reduction via complete coverage of the pond with plastic balls was compared with that via 70% coverage using the same plastic balls. Uses of plastic balls and duckweed covers were compared in the second experiment. Finally, plastic balls and reused plastic bottles were used to fully cover the water surface. Results revealed that reused plastic bottles exhibited the highest efficiency (64%) for evaporation reduction. Use of plastic balls with 100% coverage showed the efficiency of 55%. Duckweed coverage exhibited the lowest efficiency of only 18%. Use of reused plastic bottles could reduce the evaporation rate by about 3.25 mm/day or 1,185.34 mm/year. However, study on material costs for evaporation reduction revealed that plastic balls presented the highest cost of 584 Baht/m²; this was followed by reused plastic bottles, with the cost of 15 Baht/m². There was no cost of duckweed itself but the labour cost for occasionally changing duckweed needed to be considered.