| مستخلص: |
The annual evaporative loss from agricultural storages in many countries exceeds water gained from annual rainfall. Annual estimates of water lost to evaporation in subtropical Queensland from about 243,000 farm storages with a total surface area of 311,000 ha range from 1,320,000 ML to 2,880,000 ML. Evaporation reduction products may save water, reducing the uncertainty of supply at critical farm management times. However, the uncertainty of product efficacy and suitability for different storage conditions limits their adoption. The performance of five evaporation reduction product categories was characterised using published and supplier information on product design, mode of action, installation, operation, maintenance, and the evaporation reduction achieved. The technical and operational suitability of each product for water storages ranging in area from ≤ 2 ha to 100 ha was assessed for three water residence scenarios; full capacity, receding volume, and periodically dry. Suspended continuous covers and chemical films are suitable for all three water residence scenarios. The span loading, cable tensioning and anchorage needed to suspend the covers is most appropriate for storages ≤ 2 ha, and to reduce evaporation by 80% the fabric must reduce light transmittance by > 70%. Chemical films should only be applied when weather conditions enable the film to spread over the entire water surface. The number of application sites to achieve full coverage may limit the use of monomolecular films to storages ≤ 100 ha. The higher rate of application required for multimolecular films is best suited to storages ≤ 10 ha. The need for ballasting and tethering limits the use of continuous floating covers to storages ≤ 2 ha, managed at full capacity. Floating modules are best suited for storages ≤ 5 ha as the units must pack to cover > 60% of the surface to reduce evaporation by 80% |
