Improving irrigation efficiency by identifying methods to reduce evaporation losses from on-farm storages in the Granite Belt

Improving irrigation efficiency by identifying methods to reduce evaporation losses from on-farm storages in the Granite Belt

Evaporation across the Granite Belt is approximately 1,680 mm per year with approximately 66% occurring over the summer period (Oct-March). A total loss of 1,680 mm of evaporation equates to 16.8ML over a 1 ha surface area.

Baillie et al (2010) assessed the likely water losses from storage dams (evaporation and seepage), distribution channels and infield irrigation losses in the Stanthorpe Water Management Area. The assessment suggests 60% of total on farm losses are through storage evaporation which equates to 586 ML/yr1.
This desktop assessment and review identifies that evaporation losses can be minimized using a range of products and strategies, however not all methods are suitable for widespread use in the Granite Belt. The table below considers the suitability of each evaporation saving method in the context of the type and usage of water storages in the Granite Belt.

Shade cloth systems have a potential to save between 70% and 85% of evaporation at a cost of between $675/ML/yr and $1,252/ML/yr. Floating cover systems have a potential to save between 85% and 100% of evaporation at a cost of between $787/ML/yr and $1,515/ML/yr. Modular systems are very expensive, have a potential to save between 75% and 90% of evaporation at a cost of between $2,745/ML/yr and $4,118/ML/yr. Monolayer systems (chemical covers) have a potential to save between 0% and 30% of evaporation at a cost from $123/ML/yr to well in excess of $6,572/ML/yr. Performance of monolayer systems on a commercial scale is largely unknown and impacted by many factors, hence the wide spread in potential cost. Raising the wall height or incorporating a cell wall has varying cost depending on the proposed design. For a small 1ha dam the strategy of raising the wall will be relatively expensive ($852-$1487/ML/yr). For larger dams of 10ha the additional earthwork costs are supported by large evaporation savings at relatively low cost ($204-$355/ML/yr).

Baillie et al (2010) shows that generally irrigators are seeking practical and low capital evaporation and seepage mitigation strategies to gain water savings. While the Stanthorpe Water Management Area shows high percentage uptake across all storage management technologies there are still options for savings that should be investigated. A list of research and extension works have been proposed in Section 9 of this report

NCEA Publication 1004863.