Implementation of an Integrated Quantity and Quality Model for in-stream salinity in the Hunter Valley, NSW, Australia

Increases in in-stream salinity from dryland salinisation is a significant natural resource and environmental issue. An element of the NSW Salinity Strategy is to set end of valley and within valley targets for salinity management. The assessment of targets required prediction of future increases. Tools are available to estimate salt exports at point, hillslope and small catchment scales. However, to assess the contribution of tributaries to valley targets, an integrated river basin model is needed. The Integrated Quantity and Quality Model (IQQM) of the Hunter River provided a framework to meet this need. Salt loads and salinities were estimated for a number of tributaries, providing inputs to the IQQM from Glenbawn Dam (catchment area 1,300 km2) to Greta (17,500 km2). IQQM was calibrated on continuous observed data on the mainstream. A Current Conditions scenario applied river operations and development as at the year 2000 over the entire 1975 98 climatic period. The Current Conditions scenario was then used as a base case to compare future increases against. Salt loads from the tributaries for future conditions were based on hydrogeological analysis of groundwater level changes. The impacts of these changes on concentrations in the mainstream at key locations down the system were assessed. Results for IQQM calibration with observed data, current conditions base case, and changes are presented in this paper. There are some issues in the existing implementation of the Hunter IQQM that need to be addressed in the future to provide a more accurate representation of sources and magnitudes of salt. The future changes from dryland salinity only, produced a small increase from the base case mainstream salinities. The study highlighted the potential for salinity problems in some tributaries, although the extent is unknown due to lack of suitable data. The method used for modelling groundwater and surface water interactions created uncertainty in both current and future predictions that will be significant at lower flow ranges.