ABSTRACT
ABSTRACT: Different techniques were used to estimate vertical and horizontal flow rates in fractured rock aquifers of the Clare Valley, South Australia. Horizontal flow was estimated from well dilution tests, cubic law and a comparison of unpurged and purged radon concentrations. Vertical flow was estimated by the vertical distribution of environmental tracers to determine groundwater ages combined with a parallel plate model. A flow net analysis indicated that horizontal flow estimated from radon is consistent with recharge rates calculated from vertical groundwater age profiles. Horizontal flow calculated from well dilution tests and the cubic law both on a local and regional scale are not consistent with estimates of recharge. This is attributed to fractures being well connected on a local scale but poorly connected on a regional scale. The geological setting and fracture style in the Clare Valley supports the hypotheses of discontinuous regional horizontal fracturing resulting in a reduction of connectivity with increasing scale. Groundwater flow rates estimated from radon displayed large temporal variability varying by a factor of 3 through out the year. This variability is larger than can be accounted for by seasonal variations in the regional water table. We attribute this to a decrease in fracture connectivity with depth, where the highly weathered fracture zone at the top of the water table becomes disconnected from the regional flow system when the water table declines.
