Assessing opportunities for Managed Aquifer Recharge at regional catchment scale
In northern Australia, with such high intra-annual variability in rainfall, it is potentially feasible to store excess surface water in wet seasons for later use, in dry seasons. Traditionally, dams are used for this purpose. However, suitable dam sites are relatively infrequent, especially in terrain with low relief.
A complementary form of storage, managed aquifer recharge (MAR), uses aquifers instead of valleys to store water below ground, protected from evaporation.There are many potential benefits of conjunctive use of surface water and groundwater as this increases flexibility and expands the options for water resource management. In general terms, a suitable aquifer for MAR is one that can accept a sufficient volume of water at a desired recharge rate and recover water of a suitable quality at a desired rate, in order to be economically viable.
To identify areas with better potential for MAR development within very large areas (catchment or basin-scale, for instance), a form of pre-feasibility regional-scale assessment must be conducted to focus further investigations. This pre-feasibility level of assessment, referred to as 'MAR opportunity mapping', is a key first step.
A data-driven approach to regional scale MAR opportunity assessment
A unified method for MAR opportunity assessment at the regional scale was applied to the Fitzroy (Western Australia), Darwin (Northern Territory) and Mitchell (Queensland) study areas.
MAR opportunity maps were developed initially from gridded estimates of soil permeability, topographic slope, and regolith thickness (as an indicator of superficial aquifer thickness). Areas were further refined by considering the proximity to sources of water for recharge.
This pre-feasibility opportunity assessment identifies prospective areas for MAR and provides guidance for proponents regarding the additional information required to assess the feasibility of a specific MAR scheme in accordance with the Australian MAR guidelines.
Targeting prospective areas for detailed assessment
We defined four categories of MAR opportunity relating to permeability and slope (after filtering by suitable aquifer type and where regolith thickness was <10 m) were defined.
Based on these characteristics, across the Fitzroy catchment there was 21,900 km2 (23% of the catchment) of area with opportunity for MAR, across the Darwin catchments there was 18,400 km2 (62% of the catchment), and across the Mitchell catchment there was 16,400 km2 (23% of the catchment).
MAR is most suitable in proximity to non-perennial rivers, which are dominant in the three study areas.
In each catchment, the length of non-perennial rivers within the MAR opportunity area was at least 600 km (based on major watercourses). This suggests that there are multiple sites (>100) where the feasibility of small-scale MAR schemes could be considered in detail. Assessment of the surface water available for harvest from non-perennial river reaches would be required in the feasibility assessment.
The results of the MAR opportunity assessment for the Mitchell River catchment are shown in below, similar maps were produced for the other study areas.
The majority of the area identified as having MAR opportunities had high or moderate permeability soils on low slope (classes 1 and 3). A maximum distance of 5 km from major rivers was assumed the economic limit for channelling or pumping water to a MAR scheme. Limiting areas to within 5 km of major rivers reduced the areas of opportunities to 9,100 km2 (13% of the catchment).
Further analyses of MAR technical feasibility and economic viability was made using case studies. These were located in areas identified by the regional scale MAR opportunity assessment where suitable aquifers were within 5 km of major river reaches, focusing on non-perennial sections and the potential locations of dam sites.
Scheme options included a range of infiltration-based methods including reservoir release, recharge weir, and infiltration basin techniques, and also considered well injection methods for a specific site in the Finniss River catchment (Northern Territory).
For a Western Australian case study, read more about the Groundwater Scenario Modelling for Myalup Managed Aquifer Recharge Project. This project was completed for the Department of Department of Primary Industries and Regional Development, WA.