BASEFLOW IN LOCKYER CREEK By James Craig Galletly M Agr Sc, University of Queensland A thesis submitted for the degree of Doctor of Philosophy School of Land, Crop and Food Sciences and School of Natural and Rural Systems Management University of Queensland Gatton, Australia 2007 Declaration of Originality This thesis reports the original work of the author, except as otherwise stated. It has not been submitted previously for any degree at any University. __________________________________ (James Craig Galletly) ii 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 iii ions, are therefore consistent with the idea of basalt water being concentrated by evaporation and/or evapotranspiration. It was concluded that water use by phreatophytes (historically) and irrigation (recently) was largely responsible for the slope on the water table in aquifers (towards aquifer margins). Since the commencement of irrigation, flow duration in Lockyer Creek has progressively decreased, and the depth of water in alluvial aquifers has also declined, indicating that, in many years since 1937, the rate of water use for irrigation has exceeded the rate at which water was supplied by the catchment. The water in alluvial aquifers is derived from baseflow which, in the Lockyer Valley is outflow from basalt aquifers on the Main Range, not from adjacent alluvial aquifers. The water is not infiltration from rainfall, bank flow or cross-formational flow from adjacent sandstones as is often reported in the literature. This new understanding should be useful in devising a strategy for managing irrigation water use in the Valley as part of an integrated catchment management strategy. iv Acknowledgments I wish to acknowledge gratefully the many people who have contributed to the development of this thesis and especially Dr Eugene Moll who encouraged me to undertake the task and contributed to early discussions, and to my main academic advisors, Dr Jeff Tullberg and Dr Iean Russell who have been generous with their time and expertise and encouragement in guiding me through the maze of problems this thesis generated. I am also particularly appreciative of the encouragement given by the late Mr Cliff Thompson (of CSIRO) to publish my ideas on aquifer recharge prior to the commencement of this project, and also to Mr. Barry Fitzhenry who assisted with an early submission to the Gatton shire Council relating to the Lockyer water supply. Special thanks are due to all members of the UQ Gatton Campus Library Staff who assisted in many ways but especially with inter-library loans and references and also to the Printery Staff for assistance with the final layout of the thesis. The project was made possible by Mr Paul Martin of the Queensland Department of Natural Resources, Mines and Water who kindly supplied me with Lockyer streamflow data, and officers of the Bureau of Meteorology in Brisbane kindly supplied rainfall data for the area. I am also indebted to Dr Roger Shaw, Mr Bob Talbot, Ms Katherine Raymont and Dr Bernie Wills for commenting on an early draft of material on baseflow and salinity and to Dr Bernie Powell for helpful discussions on Lockyer Valley soils. Thanks are due to Mr. Chilla Johnson for providing access to past editions of ‘The Gatton Star’ giving Lockyer groundwater level and to Mr David Schofield who kindly provided photographs of stormflow in Lockyer Creek. Also, I wish to acknowledge the many helpful casual discussions, with Dr Len Bahnisch, Dr Geoff Bahnisch, Dr Badri Basnett, Dr Madan Gupta, Dr. Doug George, Mr. Bruce Alchin, Mr. Ross Murray, Mr. Alan Lisle, Mr. Bob Hampson, and Mr Brett Jahnke who also helped in making equipment to demonstrate flow in porous materials. Also, the contributions by Ms Alice Schwarz Brunold and Ms Elana Stokes greatly improved the clarity of four diagrams. Mr David McClymont assisted in the development of a computer program to separate baseflow and a brief discussion with Professor Tom McMahon was especially valuable in assessing the importance of interflow. v I should also like to acknowledge the many discussions with local farmers, especially Messrs Allan and Russell Qualischefski who were helpful in providing local knowledge, and also to Messrs Neil Robinson, Des Dallinger, Peter Schimke and John Dolley for their contributions regarding local geology and aquifers. The valuable contribution by the examiners of this thesis is also gratefully acknowledged, recognizing the significant improvement their comments and suggestions made to the final result. Not least I wish to thank my wife Lenor for her forbearance in tolerating my frequent absences to pursue this work and also my family for their support and encouragement throughout the project. I also wish to express my thanks to University of Queensland for granting me an Australian Postgraduate Award to provide financial assistance without which the work would not have been done and to the University staff and students who attended and contributed to seminars during the course of the work. vi 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 conductivity of at least 0.0864 m/day. Aquifer mining: The process, deliberate or inadvertent, of extracting groundwater from a source at a rate so that the ground water level declines persistently, threatening actual exhaustion of the supply (ASCE 1987). Aquiclude: A saturated geological unit that is incapable of transmitting significant quantities of water under ordinary hydraulic gradients (Freeze and Cherry 1979). Aquitard: A less-permeable bed in a stratigraphic sequence, with sufficient permeability to transmit water in quantities that are significant in the study of regional groundwater flow, but not sufficient to allow the completion of production wells within it (Freeze and Cherry 1979). Baseflow: Natural, prolonged, clear, surface outflow of meteoric water from groundwater aquifers in specific geological strata adjacent to or upstream from an observation point. (For the purposes of this definition, it is suggested that ‘prolonged’ means ‘more than 28 days’.) Bedrock interflow: Surface streamflow water which initially infiltrated the soil surface and percolated to a perched water table, occupying the space mainly between the original depth of tree roots (or bedrock) and the current depth of plant roots, causing a water table to form, rise and the water to move laterally, enabling exfiltration and surface flow in streams. Bedrock flow: Prolonged, lateral subsurface flow of groundwater in soil. Capillary water: The water held in the ‘capillary’ or small pores of a soil, usually with attraction forces exceeding the pull of a 60-cm column of water. Connate water: Water trapped in sediments at the time of their deposition. Deep percolation: The downward movement of water below the soil or below the depth of plant roots in soil (see percolation). vii Effluent reach: A section of a stream which receives groundwater from adjacent aquifers. Effluent stream: A stream which receives groundwater discharge from adjacent or upstream aquifers. Flood flow: Water which overflows stream banks and moves over a floodplain away from streams rather than towards them.