The hydrogeology of the Macquarie Catchment has been studied extensively in the past 20 years, but there are still many gaps in our understanding of the groundwater systems and river-aquifer interactions. These gaps in our knowledge limit our capacity to manage water resources throughout the catchment. This document captures our current understanding of the hydrogeology of the catchment and provides a multidimensional spatial analysis of the groundwater standing water level data. Based on the finding recommendations for further research are then presented.
Abstraction of groundwater for the purposes of irrigating cotton and other crops started in the Macquarie Catchment in 1967, and expanded until the turn of the century. To monitor the impact of groundwater usage NSW State water management departments installed monitoring bores in the zones with significant groundwater usage. The groundwater monitoring data are publicly available on the Pinneena Groundwater Monitoring CD. This report presents all the hydrographs for the Macquarie Catchment, and examines the spatial and temporal trends displayed in these data. The primary goal of this project was to provide a graph of all the groundwater hydrographs in the catchment. A printout of every hydrograph within the Macquarie catchment is presented in the Appendix.
Through the implementation of water sharing plans there have been changes to groundwater allocations. At some locations there has been a reduction in the water allocated per share, with the aim of improving the long term viability of the groundwater resource for all users and the environment. The groundwater hydrographs provide a record of baseline conditions and can be used to assess the impact of variations in allocation and guide future management decisions.
Almost 40 years of groundwater hydrograph records enable long term groundwater level trends to be analysed throughout the alluvial regions of the catchment. Groundwater head change over long and short periods of time are analysed using traditional hydrograph plots and 3D plots to show the yearly and interdecadal impacts of groundwater extractions. The groundwater hydrograph data are interpreted in the context of existing geological knowledge, streamflow, rainfall and groundwater usage data.
Within the Macquarie Catchment a unique balanced needs to be achieved in the way water is managed if urban centres and farms dependent on the water are to prosper, while maintaining important wetlands at the end of the catchment. The Macquarie River flows northwest from the head waters on the western side of the Great Dividing Range just south of Bathurst, to join the Barwon River west of Brewarrina. The southern portion of the Macquarie River is highly regulated by Burrendong and Windamere Dams and by a series of weirs, bypass canals and irrigation channels that assist the diversion and abstraction of water for irrigation, industrial and domestic purposes. The major irrigation district is north of Narromine and south of the Macquarie Marshes on the fertile soils of the floodplain. This flood plain overlies up to 150 m of valley-fill sediments which lie within the Macquarie River palaeovalley. It is the fresh groundwater within these sediments that is used for irrigation. The Macquarie Marshes just north of the irrigation district are a large and diverse system of semi-permanent freshwater wetlands created by irregular flooding of the flat lands adjacent to the river and are an important ecological habitat.
This study identifies zones along the river where aquifers within the sediments that fill the deep palaeovalley are locally hydraulically connected to the river, and zones where the deep aquifers are disconnected from the shallow aquifers and do not receive direct river recharge. The largest zone of aquifer depletion is west of Narromine. This zone requires further extensive hydrogeological and water chemistry investigations to better understand the recharge pathways. If the management goal is to reduce the decline in the groundwater head, then this region may require managed aquifer recharge.
North and west of Narromine there are zones of local rising watertable in the upper unconfined aquifer due to irrigation recharge (deep drainage). Further research is required to determine if this will result in future soil and water quality problems.
Based on these findings it is suggested that a detailed 3D lithofacies model needs to be constructed for the Lower Macquarie Catchment. This 3D model could then guide the construction of a coupled surface and sub-surface flow model. Also required is an extensive groundwater chemical investigation (with a focus on dating the ages of the groundwater zones) and coupled river and aquifer flow modelling, linked to the water chemistry investigations. The results of these investigations should help to better inform water management decisions
