Evaporation suppression and energy balance of water reservoirs covered with self-assembling floating elements

Abstract

Abstract. The growing pressure on natural fresh water resources and projected climate variability would expand the need for water storage during rainy periods. Evaporative losses present a challenge to efficient water storage reservoirs, especially in arid regions with chronic water shortages. Among the various methods for suppressing evaporative losses, the use of self-assembling floating elements offers 10 a simple and scalable solution especially for small reservoirs. The use of floating elements is not new, yet the science behind the design and the resulting performance including other effects on the water body remain empirical. We propose a systematic approach for modeling the energy balance and fluxes from covered water surfaces considering element geometry, radiative properties and local conditions. 2 yielding much higher Bowen ratio over covered relative to uncovered water reservoirs. The theoretical approach provides a scientific basis for an important water resource protection strategy and a predictive framework for design purposes.

Evaporation Suppression From Water Bodies Using Floating Covers: Laboratory Studies of Cover Type, Wind, and Radiation Effects

“…The water and cover surface temperatures were computed from 1D considerations ignoring thermal feedbacks between water and air temperatures that could affect surface water temperature in the gaps between the covers. In Aminzadeh et al (), the temperatures of the surface water in the gaps and evaporation rates were obtained simultaneously by accounting for lateral heat exchanges between cover and water (still within an essentially 1D‐surface energy balance formulation). In this study, we apply a simpler approach by considering coupling between surface energy balance of water and floating cover elements.…”

“…Assouline et al (, ) provided several insights into estimating evaporation suppression, demonstrating that evaporation losses are typically higher than the uncovered area fraction, especially as the gaps in the cover become smaller (for the same total uncovered area). In a recent numerical study of evaporation from water reservoirs, Aminzadeh et al () demonstrated that for gaps between floating elements of centimeter size, the expected evaporation suppression with maximal floating covers was about 80%, supporting the potential of self‐assembling floating elements as an effective evaporation suppression method. Interestingly, estimated evaporation suppression was similar for black and white covers despite the effect of color on radiation and energy partitioning.…”

“…Various measures for reducing evaporative losses from small water reservoirs have been proposed including the use of windbreaks (Hipsey & Sivapalan, ), the application of environmentally innocuous surfactant monolayers (Barnes, ), continuous plastic covers and structures (Gallego‐Elvira et al, ), and the use of self‐assembling floating elements (Aminzadeh et al, ; Assouline et al, , ; Cooley, ). The economic efficiency of evaporation suppression solutions depends on reservoir geometry (volume/surface considerations), climate conditions, costs of the cover, the performance of the cover as measured by effective water saving, and cost of (available) alternate source of water (Aminzadeh et al, ). Among the various evaporation suppression solutions the use of self‐assembling floating covers offers a scalable, cost effective, reliable and long‐lasting solution especially for small reservoirs (<0.1 km 2 ), with relatively low maintenance requirements and high potential for evaporation suppression efficiency.…”

“…Some early studies of evaporation suppression using floating covers assumed that maximizing the covered water surface area would result in evaporation reduction in proportion to covered area (Cooley, ). However, complexities due to surface energy balance feedbacks, geometrical effects on vapor diffusion, and wind‐cover interactions may give rise to nonlinear effects that often reduce the cover efficiency (Aminzadeh et al, ; Assouline et al, ; Ruskowitz et al, ). Additional factors such as piling up of cover elements under windy conditions, lateral heat exchange with the surrounding for small reservoirs, and ecological considerations may lower evaporation suppression efficiency.…”

Integration of PV floating with hydroelectric power plants

“…This reduction is very relevant if we are in arid zones or for example for waste water basins where an adequate water coverage can save from 10,000 to 20,000 m 3 per ha. Several calculations have been done using Penman model [19] and experimental findings of several authors (see for example [27] and [28]) support this rough estimate. However, in the case of HPP, saving water is not the main concern so this is mentioned for completeness but not a major factor compared to the potential increase in energy production from FPV.…”