HR: 15:10h
AN: H42H-07    [PDF]
TI: Impacts of Vegetation Change on the Water Balance of Superficial, Coastal Aquifers: a Comparative Study of Pre-clearing and Post-clearing Recharge Under Native Vegetation, and Pine Plantations
AU: * Bekele, E B
EM: Elise.Bekele@csiro.au
AF: Commonwealth Scientific and Industrial Research Organization, Division of Land and Water, Private Bag No. 5, Wembley, WA 6913 Australia
AU: Salama, R B
EM: Ramsis.Salama@csiro.au
AF: Commonwealth Scientific and Industrial Research Organization, Division of Land and Water, Private Bag No. 5, Wembley, WA 6913 Australia
AB: Replacing native vegetation with pasture across the northern Perth Basin in Western Australia has profoundly altered the water balance and led to dramatic increases in recharge and groundwater levels from about the mid-1960's, whereas replacing native vegetation with pine plantations and market gardens further south in the Gnangara groundwater Mound together with declining rainfall has caused continuous declines in recharge and water levels. Long-term monitoring of water levels in the Parmelia Formation, a superficial, semi-confined aquifer of predominantly weathered sand in the northern Perth Basin, indicates maximum rates of water level rise on the order of 40 to 55 cm/yr within the past decade. In the Gnangara Mound, water levels are falling by 10 to 20 cm/yr in the unconfined aquifer. Quantifying groundwater capture due to the removal of native vegetation is crucial for predicting the extent of groundwater development in the northern Perth Basin, whereas in the Gnangara Mound, it is necessary to limit the total water use to the declining resource to arrest the trend in falling water levels. Estimates of groundwater recharge before the removal of native vegetation in the northern Perth Basin determined from chloride tracer measurements in the soil water beneath native bushland and from groundwater samples ranged from 12 to 16 mm/yr, while estimates from soil water flux at the water table are approximately 5 mm/yr. In contrast, recharge estimates under cleared conditions since 1970 are between 24 and 50 mm/yr, based on hydrograph analyses of different bores. CFC and chloride analyses of water sampled from piezometers screened at the water table gave recharge estimates of 20 to 30 mm/yr and less than 10 mm/yr, respectively. In the Gnangara Mound recharge varies between 70 to 200 mm/year; the lowest recharge values were under the pines and the highest in the urban areas. Due to increasing demand on the groundwater resources and the declining water levels, additional resources can be provided only by removing the pine plantations, proper management of the Banksia woodland areas and capture of fresh groundwater discharging to the sea.
DE: 1829 Groundwater hydrology
DE: 1836 Hydrologic budget (1655)
SC: Hydrology [H]
MN: 2003 Fall Meeting