Securing low flows - a trial project to install low flow devices on existing farm dams

A steady increase in the number of farm dams has been experienced over the last 4 decades in South Australia's Mount Lofty Ranges as well as in other high water-demand zones. Dams provide the community with water security for stock, domestic, irrigation and other purposes and are critical to the region's economic and social well-being. However, the cumulative impacts of dam development and water use practises have significantly altered the natural flow regime across catchments. One of the key impacts is on the low-flow characteristics of watercourses; flow understood to be vital for the ecological health of these ephemeral systems. The passing of low flows is a fundamental principle underlying the science behind Water Allocation Plans (WAPs) adopted in South Australia. The assumption for the consumptive limits set in WAPs is that flows are returned (not captured) at or below the threshold flow rate (TFR) for (i) existing licensed dams and watercourse extractions and (ii) non-licensed dams with a capacity of 5 ML or greater. Catchment modelling was undertaken to derive these TFR estimates. The South Australian Government is implementing a program called 'Securing Low Flows' that aims to improve the timing, duration and volume of low flows within catchments in the Mount Lofty Ranges. These low flows are planned for reinstatement to improve measurable outcomes in the health of water-dependent ecosystems, while ensuring the system remains viable for economic and social use. The 'Low Flow Trials Project forms part of this larger program and aims to test the performance of low flow devices at dam scales. Trial sites were chosen based on a series of hydro-ecological and feasibility criteria. Key objectives of the project include to (i) install and test a range of different devices in various settings, (ii) learn about construction and management challenges (iii) monitor hydrological performance (iv) inform larger, catchment-scale implementation programs. Solutions have been tailored to individual situations using a 'tool kit' of approaches due to differing local conditions (topographic and wider catchment features). 11 trial sites were established in 2015-16 to test these devices to pass environmental flows from farm dams. A comprehensive, telemetered monitoring program is in place at the sites to study the effectiveness of the systems and enables fine-scale monitoring of dam water balance components. The data can also be used to validate existing catchment modelling, with preliminary data indicating that the modelled TFR estimates are realistic.