| |
CRC PUBLICATIONS |
Impact of Increased Recharge on Groundwater Discharge
Mat Gilfedder,
Chris Smitt,
Warrick Dawes,
Cuan Petheram,
Mirko Stauffacher
and Glen Walker
Publication Type:
Technical Report
This publication is hosted by the CRC for Catchment Hydrology
CRC Program:
Landuse Impacts on Rivers
|
Publication Keywords:
|
Abstract / Summary:
Impact of Increased Recharge on Groundwater Discharge: Development and Application of a Simplified Function Using Catchment Parameters
Executive Summary
The objective of the present report is to develop a simple approach towards estimating the response of groundwater systems to changes in recharge that arise from changes in land use. The emergent properties of a groundwater system are examined using scaling arguments, by combining the effect of aquifer properties into a single dimensionless groundwater system similarity parameter (G).
The expansion of areas of saline land, and rising river system salinities is occurring in many parts of Australia. Such environmental change has increased the need for an ability to predict the effects of salinity into the future. Without this predictive capability, management strategies will continue to try to treat symptoms caused by salinity rather than develop preventative and more effective management solutions.
The timing of salinity changes in response to land use changes is not well understood. While changes in land use may cause relatively rapid changes in surface run-off and evapotranspiration, the time lag between recharge to groundwater systems and their subsequent discharge to surface water can be much longer. Since groundwater discharge is the main pathway by which salt is moved into streams, understanding the time lags between management change and groundwater change is paramount. Unfortunately there is a lack of detailed measured data at catchment and regional scales, even in the well-studied parts of Australia's dryland regions. This fact alone means that any suitable approach at this large scale must be simple.
A dimensionless similarity parameter (G) is introduced in this report, which simplifies the characterisation of a groundwater system by combining transmissivity, specific yield, recharge, length and head. G can be visualised as a measure of the ratio of the system's ability to fill (Vt) compared to its ability to drain (Ht). As such, G gives an indication of the state of balance of a groundwater system.
A simple approach incorporating G is used to estimate groundwater system response times for five case studies under different increased recharge scenarios.
This approach offers an important step towards a more rigorous estimate of catchment's overall response to changes in land use for their component groundwater systems. This approach had three main steps: 1. The time to drain (tH) factor was scaled to give a baseline response (i.e. where no surface discharge occurs) to an increase in recharge. 2. G was then used to obtain an estimated response, by scaling this baseline response. For G < 4, the groundwater response time was faster than the baseline response (because surface discharge allowed faster change to a new equilibrium). 3. The estimated response was then converted into a 50% response time (which was then used to parameterise the discharge function in Eq. 21). This correction process relied on the good correlation (r squared = 0.92) between the estimated response and modelled FLOWTUBE predictions for several case study catchments.
This report is available for downloading (see below).
 |
1 Download(s) |
|
|
|
|
|
|
|
|
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
|
|
|
