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Accueil du site → Doctorat → Australie → 2018 → Influence of urban expansion on groundwater recharge in southeast Melbourne, Australia.

RMIT University (2018)

Influence of urban expansion on groundwater recharge in southeast Melbourne, Australia.

Hall Benjamin

Titre : Influence of urban expansion on groundwater recharge in southeast Melbourne, Australia.

Auteur : Hall Benjamin

Université de soutenance : RMIT University

Grade : Doctor of Philosophy (PhD) 2018

Résumé partiel
This study undertook a detailed investigation of recharge processes of a Cainozoic aquifer system near the city of Melbourne, Australia that is experiencing rapid urbanisation. The aquifer system supports large-scale irrigated horticulture and groundwater dependent ecosystems, and supplies municipal drinking water. Changes to planning zones in 2012 and demand for housing has led to widespread urbanisation and the area now has the fastest growing population in Australia. There is extensive research on the impacts of conversion of land for agricultural production on groundwater recharge ; however, to date there are few if any field-based studies examining impacts of urban expansion on recharge. The aims of this study were to (1) characterise recharge processes and rates and explore their relationships with geology and topography (2) investigate the interaction between new urban water management infrastructure (constructed wetlands) and groundwater recharge, and (3) asses the implications of the current and changing recharge regime for water management and land use planning both in the study area and more broadly in regions experiencing rapid urbanisation.

Through a combination of techniques, including drilling, hydraulic testing, water level, soil moisture and electrical conductivity time-series analysis, and determination of major ions, stable (δ18O & δ2H) and radioactive (3H & 14C) isotopes in groundwater, a new conceptualisation of recharge was developed, including estimation of rates in different areas and description of the major controls on recharge locations and mechanism(s) in the basin. This model challenges the previous conceptualisation of recharge, indicating that opportunities for recharge are limited in much of the urban development area. Sub-cropping basalt was found to be highly weathered to clay with low permeability, resulting in low recharge rates as indicated by chloride mass balance (5-50 mm/yr) and water table fluctuation-based estimates (<5 to 20 mm/yr). Instead, key recharge areas (estimated rates >100 mm/yr) are spatially restricted to a zone along the edge of the basin, where the basalt is absent and Quaternary sand deposits directly overlie the Tertiary sand aquifer. This conceptualisation is further supported by the spatial distribution of tritium in groundwater (ranging from below detection up to 2.40 TU, consistent with modern recharge) as well as vertical hydraulic gradients and soil moisture profiles.

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