The Commonwealth Environmental Water Holder (CEWH) was established under the Water Act 2007 to manage the water entitlements that the Commonwealth is currently acquiring for the purpose of protecting or restoring the environmental assets of the Murray-Darling Basin. On behalf of the CEWH, the Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), engaged RPS to examine the salinity impacts of current and potential future environmental watering activities in a manner consistent with the Basin Salinity Management Strategy 2001-2015 (BSMS) requirements of the Murray-Darling Basin Authority (MDBA).
The overall objectives of the project were to inform the CEWH of the salinity implications of environmental water application by:
Conducting an initial risk assessment of the salinity impacts of the 2008-09 and 2009-10 environmental watering programs under a range of different watering scenarios
Quantifying the potential salt mobilisation impacts of the 2008-2009 and 2009-2010 environmental watering programs
Investigating and quantifying the potential salt mobilisation under projected future environmental watering programs
Compiling and comparing information on analytical and modelling techniques applied in assessing salinity impacts at Morgan (South Australia), consistent with the BSMS requirements.
By using a risk assessment framework developed by RPS, each of the 2008-2009 and 2009-2010 watering sites were categorised into high, moderate or low risk classifications in terms of the potential for in-stream salinity impacts in accordance with the BSMS.
These salinity impacts were determined to be generated primarily from the intrusion of saline groundwater into the River Murray or its creeks and tributaries.
For the site considered to have either a ‘moderate’ or ‘high’ risk with sufficient site data, quantification of the salt load impacts and EC impacts at Morgan were assessed using the appropriate tools including MODFLOW, Hotspots2 and MSM-BigMOD.
This analysis confirmed that the relationship between groundwater elevation and the river level was critical to determining the likelihood of saline groundwater entering the river as the result of a watering event. This groundwater flux along with the groundwater salinity then determined the magnitude of the salinity impacts. The management implication was that in considering site selection for watering and for management of salinity impact, the antecedent groundwater levels are critical in determining the likelihood of salinity risks.