3D Hydrograph Analysis for Constraining the Construction of Hydrogeological Models.

Groundwater is an important resource for irrigation agriculture. To monitor the irrigation extractions various NSW state government departments installed monitoring boreholes and the measurements are available on the ‘Historic data CD “PINNEENA”for groundwater works’ (http://waterinfo.nsw.gov.au/pinneena/gw.shtml).Borehole hydrograph data from this CD were analysed to provide insights into the 3D geometry and connectivity of the aquifers throughout the Namoi Catchment. This could be done for all catchments throughout the Murray-Darling Basin. Borehole hydrograph analysis provides an independent methodology to map recharge zones, access aquifer connectivity, and delineate areas of groundwater mining or recovery. The impact of historical groundwater extractions and current water sharing plans can then be analysed in the context of the mapped aquifer connectivity. The major goals of the 3D hydrograph analysis are to: •map hydraulic connectivity throughout the alluvial sequence,•develop a 3D conceptual site model,•examine the long-term impact of irrigation extractions,•compare zones of declining groundwater head to the connectivity interpretation, and•examine the changes in groundwater head since the introduction of the water sharing plan. This 3D borehole hydrograph spatial and temporal analysis shows that the largest zones of decline in the Namoi Catchment correspond to semi-confined aquifers with low connectivity to the unconfined aquifer and thus recharge from streams, floods, diffuse rainfall or irrigation deep drainage.3D hydrograph analysis of pumping induced groundwater head fluctuation maps unconfined and semi-confined aquifers. It also delineates palaeochannels.An implication of the 3D aquifer connectivity analysis is that managed aquifer recharge will be required to replenish some portions of the Namoi Catchment. 3D borehole hydrograph analysis is another tool to enhance the conceptualisation of aquifers.It complements other methods including gridding lithologicallogs, palynologystudies, water chemistry investigations and geophysical surveys. These conceptual site models will guide the future construction of water balance models and provide an important visual representation of the catchment for communicating changes to a non-scientific audience.