Influence of wetted perimeters variation of physical cover porosity on the evaporation suppression effect of plains reservoirs in arid zones

In arid and semi-arid regions, high evaporation losses from plains reservoirs pose a significant challenge to the effective management of water resources. The implementation of anti-evaporation materials (e.g., foam boards, PE floats, etc.) on the water surface can be an effective strategy to mitigate ineffective evaporation losses. However, the length of the contact line between the boundary of the cover and the water surface has been demonstrated to influence the rate of evaporation from the water surface. Investigating Evaporation Suppression Through Wetted Perimeter Theory and Porous Coverings. This study employed field experiments and an analytical model, based on the wetted perimeter theory, to understand how the pore characteristics of physical covers suppress water surface evaporation. Evaporation inhibition tests were conducted using evaporators near a reservoir dam. We utilized foam boards with identical coverage area and porosity, but varying numbers of equilateral triangular holes (1, 10, 20, 40, and 60). By monitoring water body solar radiation absorption and temperature distribution, alongside meteorological data, we thoroughly analyzed the impact of varying pore parameters on evaporation. The results of the study demonstrate that increasing the number of holes enhances evaporation and convective heat dissipation, consequently lowering water temperature; however, this effect was not significant. Crucially, the covering material significantly reduced the water surface mass transfer coefficient, thereby decreasing water evaporation. Notably, a non-monotonic relationship was observed between the wetted weeks length and evaporation suppression rate. During the experimental period, the suppression rates for covers with 1, 10, 20, 40, and 60 holes were 84.35 %, 83.33 %, 82.54 %, 81.88 %, and 81.21 %, respectively. This highlights the wetted perimeters as a key factor influencing evaporation suppression. Optimizing the pore structure of cover materials, by minimizing the contact between the material's periphery and the water surface during structural design, can more effectively suppress water surface evaporation and enhance water resource utilization efficiency. • Focusing on the wetted perimeter variation of physical water-surface covers, this (study) is more engineering-significant. • Taking the pore wetted perimeter of covers as the key, this study explores its impact on evaporation inhibition rates. • A new idea is proposed: optimize cover pore structure to improve evaporation inhibition.