Seasonal Variation of Evaporation Suppression Efficiency in Water Reservoirs Covered with Floating Elements

Since the dawn of civilization water reservoirs have been used to support irrigation and livestock in many arid regions of the world [1]. Evaporative losses diminish reservoir storage efficiency; hence, different means such as floating covers have been proposed to reduce losses. While laboratory and field studies have evaluated effects of cover properties (e.g., geometry, thermal, and radiative characteristics) on Evaporation Suppression Efficiency (ESE) [2-4], the influence of seasonal climate variability on ESE remains understudied. We conducted long-term field measurements in two identical water reservoirs (area: 25 m2, depth: 2 m) in a dry region to investigate how seasonal variations in atmospheric conditions affect ESE. We compared the evaporation rate and water temperature profile in a reservoir covered with Styrofoam discs (D: 50 cm, H: 5 cm) with those in an uncovered reservoir. For 90% surface coverage, measurements indicate that ESE varied from nearly 80% in summer to about 60% in winter. Temperature variations and radiative energy storage within the reservoirs show that the opaque and thermal insulating characteristics of the Styrofoam discs and their effects on wind-induced mixing lead to thermal stratification and formation of a seasonal thermocline in the covered reservoir. These affect the exchange of accumulated summer heat with overlying air resulting in a slower reduction in evaporation rate compared to the uncovered reservoir in cold seasons. The study sheds new light on thermal regimes and ESE in partially covered multiuse reservoirs under different climatic conditions.

Subjects

evaporation

water reservoirs

DDC Class

551: Geology, Hydrology Meteorology

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Seasonal Variation of Evaporation Suppression Efficiency in Water Reservoirs Covered with Floating Elements