Evaporative loss and environmental impact of covers on water storages: A review

Commercial products to reduce evaporation from water storages have been developed since the 1960s. Categorised as suspended and floating continuous covers, floating modular covers, and monomolecular (monolayer) and multimolecular chemical films, product adoption by agricultural water managers is low. The role of evaporation reduction in improving water use efficiency is well established, but information on the suitability of product categories for farm water storages is lacking. We reviewed the environmental and operational performance of commercial evaporation reduction products using published and supplier information on design, mode of action, installation, operation, maintenance, the evaporation reduction achieved, and the impact on water quality, to analyze the suitability of the five product classes for water storages ranging in size from <= 2 to 100 ha. Span loading, cable tensioning and anchorage limit continuous covers to storages <= 2 ha. The cover fabric must reduce light transmittance by 80%, to reduce evaporation by 71%. Ballasting, tethering, and removal during dry times limit the use of continuous floating covers to storages <= 2 ha, managed close to full capacity. Floating modules must cover 88% of the surface to reduce evaporation by 70%, limiting their use to storages of <= 5 ha. Monolayer application is more flexible, but smart product selection and automated application strategies are required to improve performance. The number of application sites required to achieve full surface coverage limits monolayer use to storages <= 100 ha. Higher rates of application and poor self-spreading may limit multimolecular films to storages <= 10 ha.