The overall purpose of the South East Regional Water Balance Project was to address a number of gaps in the conceptual model of the overall water balance of the Lower Limestone Coast Prescribed Wells Area (LLC PWA) and bring together all existing and new knowledge into a prototype model that, with future work, will enable assessments of risks to groundwater resources and wetlands from changing climate, land use and water management practices.
Phase 1, completed and reported on in November 2013, comprised a series of preliminary investigations into various components of the water balance of the LLC PWA, and development of the framework for a regional scale numerical groundwater flow model.
Phase 2 consisted of three main tasks:
The aim of Task 1 was to develop a regional groundwater flow model of the Lower Limestone Coast Prescribed Wells Area (LLC PWA), including both major aquifers, with the following primary objectives:
Longer-term objectives of the regional model were to:
The regional groundwater flow model developed in Phase 2 covers the entire regional groundwater flow system that includes the LLC PWA. As such, it covers the Tertiary Gambier Basin, extending east into Victoria, as well as part of the south-western Murray Basin to the north of the LLC PWA. Task 1 also included a number of activities aimed at improving the outcomes of the regional groundwater flow model. These included:
In Task 2, a new MODFLOW net recharge package was developed to incorporate the results of an unsaturated zone model through a lookup-table approach. This has the benefit of being able to incorporate the effects of shallow water tables on recharge, as well as changing rainfall and land use, with much lower model run-times than a fully-coupled unsaturated-saturated zone model. As rainfall recharge is a major input to the water balance for the South East, this activity was designated as a separate task in Phase 2 of the project, with the following objectives:
Future water allocation policy exercises in the LLC PWA will need to evaluate potential impacts on wetlands and other groundwater-dependent ecosystems. However, by necessity, the regional groundwater flow model was developed at a coarse spatial scale (1 km by 1 km cells) relative to the size of most wetlands in the region (a few km2 or less). Thus, the aim for Task 3 was to develop a complementary approach to the regional model to help evaluate potential impacts of future changes in climate, land-use and water allocation policy on wetland water level regimes. To achieve this, Task 3 had three objectives:
The three wetlands selected for the field study were hypothesised to represent a regional recharge (Deadmans Swamp), flow-through (Bool Lagoon) and discharge wetland (Lake Robe) along a regional hydrogeological system.
The South East Regional Water Balance Project has delivered the following outcomes to support water resource management for the South East:
A spatially continuous net recharge dataset for the period 2001 to 2010. For the 10 year period 2001-2010 the areal average net recharge was found to be 40 mm/yr.
An assessment of factors controlling net and gross recharge.
A regional scale numerical groundwater flow model that:
Estimates of the regional water balance for the LLC PWA that are based upon the best available data and knowledge, and a new understanding of how this water balance changes over time.
Recommendations for the areas of the conceptual model that require further investigation (critical knowledge gaps) and for the direction of future modelling activities.
A better understanding of the dynamics of rainfall recharge in the South East, and a range of new tools that enable the representation of the depth to water table dependence of this process in groundwater flow models.
A new lookup-table based approach that uses a newly developed MODFLOW package (the NetR package) to incorporate the effects of depth to watertable on recharge and evapotranspiration into MODFLOW regional groundwater flow models. A lookup table has been developed for the study area in the South East, and the methodology has been tested with the regional groundwater flow model, however, further calibration is required. Once fully validated this approach will be applicable to any area with shallow water tables.
A conceptual model for the geological factors determining groundwater-surface water interactions for South-East wetlands.
An evaluation of regional and local factors controlling groundwater – surface water interactions at three high value wetlands (Lake Robe, Bool Lagoon and Deadmans Swamp.
A new methodology for assessing the risks to wetland water leve regimes from changes in regional groundwater levels.