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 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. The water energy balance equation was linked to the energy balance of floating discs on the surface of reservoir to consider the effect of surface coverage and cover properties on radiative energy storage within the water body and surface heat fluxes. The modeling results demonstrated significant drop in evaporative losses from covered reservoirs where incoming radiative flux is primarily intercepted by the cover surface and released into the atmosphere in form of long wave radiation and sensible heat fluxes 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.