Baseflow in Lockyer Creek

Abstract

The basic question which this thesis seeks to answer is: 'Was the baseflow which flowed continuously in Lockyer Creek prior to 1980 outflow from adjacent alluvial aquifers or was it outflow from basalt aquifers on the Main Range?' This question was not obvious at the start of the project when information from 'official' sources suggested that Lockyer Creek was ephemeral, and there was no baseflow.To answer this question, it was necessary to define baseflow (as outflow from aquifers) and to devise a means of separating it from overland flow, because the existing methods separate 'quick flow' from 'prolonged flow': not overland flow from baseflow. The existence of baseflow presumes the existence of aquifers in the catchment, so geology of the catchment was examined to identify its aquifers.Streamflow records at four sites: three upstream and one downstream, were analysed to establish that baseflow was a significant component (25%) of streamflow over the period 1910-2000, and that average baseflow over this period was close to the estimated long-term safe yield of the Lockyer alluvium. The process of aquifer recharge was analysed and it was concluded that the alluvial aquifers are recharged by infiltration of water mainly through the bed of creeks and saturated flow in the aquifer below the water table, followed by unsaturated flow across a saturated/unsaturated boundary at the wetting front. Saturated flow is driven by the hydraulic gradient on the water table (which was shown in 1949 to slope away from creeks) while unsaturated flow is driven by the matric potential across the wet and dry sides of the front. Unsaturated flow is orders of magnitude slower than saturated flow but takes place over a much greater area than saturated flow. Because it is such a slow process, long duration flows are required to achieve significant aquifer recharge. Chemical analyses of water from basalt aquifers, baseflow and alluvial aquifers confirmed that the 'ionic signature' of the three waters was similar, which would be expected if baseflow was outflow from basalt aquifers, which in turn recharged alluvial aquifers. The ionic signature of water in the adjacent sandstones is quite different from that of these three waters. Ions present in water in the alluvium, including the sodium vii Glossary Adsorbed water: The water held in soil by surface-attractive forces: the attraction between unlike charges, such as the positive charges on hydrogen ions and the negative charges on oxygen ions. Generally, the more surface (the more clay and organic matter) a soil has, the greater is the amount of adsorbed water.Aquifer: A saturated permeable geological unit that can transmit significant quantities of water under ordinary hydraulic gradients (Freeze and Cherry 1979); a geological unit which contains water and transmits it from one point to another in quantities sufficient to permit economic development (Linsley et al. (1982). It is suggested that, for a lithologic unit to be considered to be an aquifer, it should have a hydraulic conductivit...

Further closing the integrated total water cycle in the Lockyer Valley: a catchment scale integrated water resource management conceptual model

“…For decades the area has been exposed to the pressures of population growth, climate variability, agricultural intensification, overused groundwater, stream flow loss, water intensive lifestyles and urbanisation, reactive and inconsistent water policies and environmental demands on available water supplies (Sarker et al 2009;Galletly 2007;Cox & Wilson 2005;DNRM 2005a). Despite nearly two decades of research studies and consultancies, the Lockyer Valley lacked an IWRM approach to further close the water cycle and effectively manage water as a common pool resource.…”

“…Variables include surrounding soils, possible discharge paths (groundwater or baseflow) and recharge paths (rainfall infiltration, infiltration from overflow flooding, streamflow and or baseflow) and the lifetime of an aquifer (whether recharge water replaces extracted water) (Galletly 2007;Cox & Wilson 2005;DNRM 2005a;Fetter 1994). …”

“…The soils of the Lockyer Valley are renowned for their exceptional crop growing properties (Powell et al 2002;James et al 1974). Although most of the high quality arable land in the Lockyer Valley is covered by heavy black cracking clays that retain water, the underlying brown calcareous loams are highly permeable, rapidly draining water away (Galletly 2007). …”

“…Regarding the complex issue of investment in water infrastructure, the WCRWP scheme may have been approached differently if an understanding of aquifer and creek recharge was widely known (Galletly 2007). Following major deluges in 2010-11 the short term need for recycled water in the Lockyer Valley for irrigation was seen by some as redundant, and WTP for it negligible (Interviewees 1 to 8,2011).…”