A novel method for assessing evaporation in small water bodies: considering floating covers, water surface flows, and wind speeds

In small water reservoirs, the effectiveness of floating covers on evaporation reduction, especially with water surface flows and wind, remains uncertain, and a reliable theoretical framework for estimating evaporation in these conditions is lacking. This study seeks to fill this knowledge gap through modeling and experiments. The research setup includes a small water basin (1.14m2 surface area, 0.5m depth) for water storage, a pump to make water surface flows (2.5–11lmin-1), two fans to create wind speeds (0–2.2ms-1) aligned with the water surface flows, black and white floating balls to cover 75% of the water surface, and various measuring instruments (e.g., thermometer, heat flux sensor). The findings reveal that due to the thermal mixing of the layers, water surface flows reduce evaporation to a specific flow rate, maintaining this reduction until a certain wind speed (1.4ms-1). Beyond this threshold, the evaporation reduction flow rate starts to retreat so that it reaches its lowest value at a wind speed of 1.8ms-1. Further escalation in wind speed negates the reduction in evaporation, leading to increased evaporation rates across all water surface flows. The study highlights the significant role of floating covers in reducing evaporation, showing 55–66% efficacy under various water surface flows and wind speeds. A mathematical relationship is developed using dimensionless numbers and non-linear regression analysis to enhance the applicability of laboratory findings for estimating evaporation in real conditions, showing a good agreement with measurements in a small agricultural reservoir.

Subjects

Evaporation reduction | Floating balls | Water reservoir | Water surface flow | Wind speed

DDC Class

600: Technology

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A novel method for assessing evaporation in small water bodies: considering floating covers, water surface flows, and wind speeds