Using Hydrology to Target Salinity

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Impacts of Land Use Change in Non-irrigated Upland Catchments on Stream Salinity and Salt Loads

Background

The Basin Salinity Management Strategy (2001) (BSMS) differs from the 1987 Salinity and Drainage Strategy, mainly in that it incorporates impact within tributaries due to diffuse non-irrigated impacts. As part of this process, the BSMS has required the use of end-of-valley targets. These targets are intended to encourage land-use change for salinity control, as well as reminding different jurisdictions to meet their obligations to neighbouring catchments. However it is the in-valley targets that better represent the key assets within the valley that maybe impacted by salinity.

At the heart of the BSMS is a modelling framework that is used to monitor a program of actions and how the outcome of this compares with the targets. Thus, there is an expectation that there will be an ability to model the impacts of cumulative actions around the MDB. The development of such a modelling capability will necessarily involve different groups contributing to different aspects.

This project looks at the impacts of actions in non-irrigated upland catchments. Before this project, there were no models that could be used over large areas that included groundwater processes and also integrated the effects of water yield and salt loads.

Objectives

• Determine the impact of land use changes on salt loads and stream salinity, developing linkages between surface hydrology and salt loads for remobilisation and delivery of salts to streams in local to intermediate groundwater flow systems
• Defining technically how we can attain end-of river targets and do this on the case study within the catchment characterisation project – this does not involve linkage with economics
• Identify relationships between groundwater discharge and stream salt loads and salinity for the high-risk catchment types.

Findings

• For the non regulated upland catchments studied, (a) the flow/salinity relationship could be adequately represented by a straight line on a log:log plot; (b) majority of salt export occurred at high flows; (c) flow weighted mean salinity was most sensitive to rainfall.
• Following land use changes these relationships remained the same, but the values (mean flow weighted salinity, slope of flow vs EC line) changed over time.
• Groundwater response time to a change in recharge can be modelled simply yet robustly using the physical attributes of the aquifer (Three store model)
• The BC2C tool can help users understand the trade-offs between in-valley stream flow and salt load changes as a result of land-use change (including Groundwater Response Times).

Lemon Creek stream flow versus salt load summary graph. Data are broken into 5-year blocks and fitted separately. Clearing occurred in 1976/77 and groundwater reached the land surface in 1988. (Ruprecht and Schofield, 1991)

Publications

Dawes W, Gilfedder M, Walker G, Evans WR, Stenson MP, Dowling TI, Austin J & Best A (2004) BC2C Technical Documentation, Technical Report 36/04, CSIRO Land and Water, Brisbane. (PDF, 1.4 MB)

Dowling T, Dawes W, Evans WR, Dyson P, Walker G (2004) Prioritising upland catchments in the Murray-Darling Basin with respect to salinity benefits from afforestation, CLW Technical Report 15/04. CSIRO Land & Water: Canberra. (PDF, 32 MB)

Evans WR, Gilfedder M, Austin J (2004) Application of the Biophysical Capacity to Change (BC2C) model to the Little River (NSW), CLW Technical Report 16/04. CSIRO Land & Water: Canberra (PDF, 999 kB)

Permission to publish CRC-CH Technical Reports granted by David Perry for the CRC-CH