A statistical analysis of hydrograph data for estimating recharge in the Lower Namoi Valley, N.S.W., Australia

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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Statistical analyses of borehole hydrographs reveal a new understanding of the spatial distribution of hydrogeological properties throughout the multi-layered alluvial aquifer system of the Lower Namoi Valley, NSW, Australia. Principal component analysis and k-mean clustering divided the Narrabri Formation hydrographs into 6 clusters, and the Gunnedah Formation hydrographs into 7 clusters. The clusters relate to variations in- recharge and extraction throughout the Lower Naomi Valley. A comparison of rainfall residual mass curves with the water level trends displayed in the borehole hydrographs shows that there is a strong correlation between the water level fluctuations and the rainfall history. The analysis also indicates that the irrigation extractions are in balance with recharge near the southern, northern and western boundaries, but in the southeast comer and throughout much of the central region of the Lower Namoi Valley there are numerous areas where extractions exceed recharge. A comparison of the results from the statistical analyses with two previous studies, a MODFLOW model of the aquifers and a chemical investigation of the aquifer chemistry, highlights where there is agreement on recharge and groundwater movement, but it also shows that there are regions where the various approaches provide a different or unique understanding of aquifer processes.
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