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University of Western Australia (2011)

A hydrogeochemical investigation of the surface water and groundwater interactions of a semi-arid wetland system, Western Australia

Bourke, Lindsay

Titre : A hydrogeochemical investigation of the surface water and groundwater interactions of a semi-arid wetland system, Western Australia

Auteur : Bourke, Lindsay

Université de soutenance : University of Western Australia

Grade : Master of Science M.Sc.(Hydrogeol.) 2011

Résumé partiel
A 932 ha subcatchment and its associated wetland suite, located in the semi-arid wheatbelt region Western Australia, was investigated in this study. The lower part of the subcatchment exhibits environmental degradation due to altered hydrology resulting from clearing of deep-rooted perennial vegetation. Two main potential threats exist ; firstly, upgradient migration of hypersaline groundwater from a regional primary saline valley floor ; secondly, increased water and solute loads due to enhanced recharge within the local subcatchment. The hydrological function of the subcatchment and individual wetlands, and uncertainties relating to spatial scales of influence was investigated through combing physical hydrological and hydrochemical methods. A long-term trend of rising groundwater levels within the study area is evident since the clearing of vegetation, and levels have continued to rise since 2006 at about +0.06 m/yr. A ten-fold increase in the TDS at a hyposaline wetland since 1970 indicates active discharge of both stored and replenished water and solutes to the lower catchment. These trends are occurring in spite of a declining regional rainfall trend since the mid 1970’s. The aquifers in the lower discharge area appear to be near full capacity although the subcatchment is yet to reach a post-clearing hydrological equilibrium. Significant groundwater TDS and density gradients occur across the study area, increasing rapidly down gradient in both the unconfined and semi-confined aquifers. The ionic compositions of groundwater, surface water and rainfall are dominated by Cl- and Na-, with overall composition being largely proportional to seawater

Mots clés : Groundwater/surface-water relations ; Stable isotopes ; Australia ; Local meteoric water line ; Hydrochemistry ; Salinisation ; Wetland

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Page publiée le 18 juin 2013, mise à jour le 4 mai 2018