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CRC PUBLICATIONS |
Modelling the Effectiveness of Recharge Reduction for Salinity Management
Chris Smitt,
Mat Gilfedder,
Warrick Dawes,
Cuan Petheram
and Glen Walker
Publication Type:
Technical Report
This publication is hosted by the CRC for Catchment Hydrology
CRC Program:
Landuse Impacts on Rivers
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Publication Keywords:
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Abstract / Summary:
Modelling the Effectiveness of Recharge Reduction for Salinity Management: Sensitivity to Catchment Characteristics
Executive Summary
The objective of this report is to use modelling to investigate the sensitivity of groundwater and other characteristics on the effect of recharge reduction on salinity management. This is a continuation of the work on recharge increase by Gilfedder et al. (2003). The emergent properties of a groundwater system are examined using scaling arguments that combine the effect of aquifer properties into a single dimensionless groundwater system similarity parameter (G). This study will be based upon well-documented case studies used in the Australian Groundwater Flow Systems framework.
Dryland salinisation is recognised as a major degradation issue in southern Australia with rural and urban infrastructure, cropping and grazing lands, lakes, wetlands and rivers all directly affected. It has now become evident that management and control of salinity need to be developed and implemented so that this degradation of rivers and land does not continue to expand unabated. The effect of changes in land use on catchment yield or groundwater discharge is not instantaneous and there may be long time delays between any land use change and the subsequent changes in salinity. While the evaporated and runoff components may respond relatively quickly to a land use change, a reduction in recharge to a groundwater system may not express itself as a corresponding reduction in surface discharge for many years. The timing of effects of a large-scale land use change on catchment yield will be different for a range of groundwater systems within a catchment remains poorly understood. This timing is very important, especially when looking at the physical and economic viability of a range of possible management options, since groundwater discharge is the process, which mobilises salt to the land surface and to surface water bodies.
Strategies within this area of research have often been hampered due to a lack of measured data at catchment and regional scales, even in the well-studied parts of Australia's dryland regions. Therefore, any suitable approach that investigates the effect of land use change on groundwater discharge at this scale must be simple. One approach that offers a more rigorous estimate of a catchment's overall response to changes in land use for their component groundwater systems is to use a dimensionless similarity parameter (G) (Gilfedder et al. 2003). This allows the characterisation of a groundwater system to be simplified by combining transmissivity, specific yield, recharge, length and head. G can be visualised as the ratio of the system's ability to fill (tV) compared to its ability to drain (t H ). As such, G gives an indication of the state of balance of a groundwater system. Relationship between G and groundwater response times caused by a reduction in recharge can then be examined using the FLOWTUBE groundwater model.
A simple approach has been developed to generate normalised groundwater system response curves following an increase in recharge, by using the time to drain (tH) factor in combination with the amount of recharge change, to parameterise a simple discharge function. Predictions of groundwater response times are an essential part of predicting likely effects of land use change on stream salinity and salt loads into the future. In the absence of detailed hydrogeological and hydrological data at a regional scale, simple methods are needed. The G parameter provides a tool that can help simplify the investigation of catchment behaviour. It is not a 'silver bullet', but will help improve the initial prediction of groundwater system responses across large areas without the use of process-based models.
This report is available for downloading (see below).
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Centre Office:
CRC for Catchment Hydrology
Dept of Civil Engineering
Building 60
Monash University Vic 3800
Tel: +61 3 9905 2704
Fax: +61 3 9905 5033
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