The town of Morgan on the River Murray in South Australia is a critical monitoring station for the operations of the Murray-Darling Basin. It is the end-of-valley site for the Basin Salinity Management Strategy (BSMS), with the Strategy setting an electrical conductivity (EC) target of less than 800 μS/cm for 95% of the time. Annual salt loads are reported as part of the BSMS, calculated using EC and flow data. Although EC is monitored continuously at Morgan, salt loads are calculated based on an average of the rated flows reported at Locks 1 (downstream) and 2 (upstream). Given the assumptions involved in using this method of salt load calculation, continuously monitored flow at Morgan is preferred for salt load calculations.
Resource Monitoring Services of the Department for Water (DFW) was engaged to establish a suitable monitoring site at Morgan using acoustic Doppler “Side-looking” technology. Exploratory work was conducted to identify an appropriate monitoring section downstream of Morgan, and a permanent installation was subsequently deployed. The low stream velocities encountered in the lower reaches of the Murray in recent times necessitated a prolonged flow averaging period of 15 minutes to be employed. An ultrasonic wind sensor was also included in the installation to aid in determining the impact of wind speed and direction on flow.
Commissioning of the station involved conducting a series of acoustic flow gaugings over a range of flow rates. Stationary gauging on a cross-cable was the preferred gauging method given the difficulty of controlling boat speed and direction when using the moving boat method at the low velocities encountered. The gauging results were compared with the continuous data obtained from the station, enabling the development of a viable Velocity- Index (V-I) rating for the site. The monitoring results revealed the dynamic behaviour of flow patterns in the reach, particularly with respect to the effect of wind on the flow. Statistical analysis of flow, water levels at locks and wind parameters indicated a complex relationship, particularly a delayed effect on flow on change in water level downstream of Lock 2.