Présentations Colloques

Oral Presentation
7.02
Session 7.02: Urban Hydrogeology
Hall Ben
Changing recharge dynamics from urbanisation in southeast Melbourne, Victoria/Impact on groundwate from urbanisation in southeast Melbourne TITRE?!
Melbourne’s urban growth boundary was extended in June 2012 by 6,000 ha which will push residential development into a Water Supply Protection Area. This area has been used for irrigated horticulture for the past century, and is considered to be a regionally important recharge area. Changes in land use associated with urbanisation have the potential to significantly alter the hydrological cycle and recharge in particular. **In this study, a combination of nested groundwater monitoring bores, spatial groundwater sampling data (including natural and radioactive isotopes), surface water monitoring and time series monitoring data provide evidence of a changing regime of groundwater recharge due to urbanisation. **Drilling and installation of nested monitoring bores has shown that the water table aquifer locally consists of a basalt aquifer which overlies a sandy confined aquifer. Groundwater head measurements indicate an upward vertical gradient. Groundwater sampling results show that shallow groundwater contains 2,300 mg L total dissolved solids, minor amounts of tritium (0.023 Tritium units), and a radiocarbon age of 2,255 years before present (76 percent Modern Carbon). Deeper groundwater, on the other hand, is fresher (660 mg L TDS), contains no detectable tritium and has a radio carbon age of 9,840 years BP (29 pMC). This data suggest that over the longer-term that groundwater system is locally confined with limited opportunity rainfall recharge with recharge to the deeper sand aquifer likely to be coming from further upstream in the catchment. **However times series data shows a strong correlation between water levels, groundwater salinity and rainfall events. This suggests that rainfall recharge is currently locally active at the water table. The two most likely explanations for the apparent change in recharge regime in this area are- (1) leakage from the constructed wetland adjacent to the monitoring site and or (2) increased permeability of soils due to mechanical disturbance during site earthworks. This has implications for the future development of land in this region and management of water resources.**
Australia