Improving irrigation efficiency (IE) is an approach used globally to help meet competing demands for water and facilitate reallocation of water between sectors. In the Murray–Darling Basin in Australia, the Australian government has invested heavily in IE projects to recover water for the environment. However, this approach has been seriously questioned, out of concerns that improved IE would reduce irrigation return flows to rivers and therefore offset water recovery. In this study, we use a water balance model to assess the impact of the IE projects on return flows and highlight sensitivities and uncertainties. The model enables the impact on return flows to be assessed on specific IE projects and regional characteristics. Overall, reductions in return flows are estimated to be less than 20% of the total proposed IE savings. The history of IE in the southern MDB has meant that most of the current reductions are in ground return flows. Our estimate is much lower than two previous studies, mainly due to different assumptions being used on groundwater connectivity between irrigation areas and major streams. While the IE projects significantly reduce seepage to groundwater (with off-farm and on-farm projects reducing seepage by 19% and 53% of total savings respectively), not all seepage reductions will translate to a reduction in ground return flows to rivers. A lower estimate is consistent with existing monitoring and groundwater modeling studies. In this paper, the study results are discussed in a broader context of impacts of IE projects on volumes and salinity of streams and groundwater resources.

中文翻译：

---

评估澳大利亚东南墨累-达令盆地的灌溉效率项目对回流的影响

提高灌溉效率（IE）是一种全球性使用的方法，可帮助满足竞争的用水需求，并促进部门之间的水分配。在澳大利亚的默里-达令盆地，澳大利亚政府已在IE项目上投入大量资金，以回收环境用水。但是，由于担心IE的改进会减少灌溉流向河流的流量并因此抵消水的回收，因此这种方法受到了严重质疑。在这项研究中，我们使用水平衡模型评估IE项目对回流的影响，并强调敏感性和不确定性。该模型使得可以根据特定的IE项目和区域特征评估对回流的影响。总体而言，回流的减少估计不到提议的IE节省总额的20％。南部多边开发银行的IE的历史已经表明，目前的大多数减少都来自地面回流。我们的估算值比之前的两项研究要低得多，这主要是由于对灌溉区和主要河流之间的地下水连通性使用了不同的假设。尽管IE项目显着减少了地下水的渗入（非农场和农场内项目分别将渗漏减少了总节约量的19％和53％），但并非所有的渗漏减少都将转化为流向河流的地面回流的减少。较低的估算值与现有的监测和地下水模型研究一致。在本文中，将在更广泛的范围内讨论IE项目对河流和地下水资源量和盐分影响的研究结果。