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Abstract
The catchment of Avon River springs, Christchurch City, New Zealand, is proposed that includes: the Waimakariri River, three geomorphic areas in the Christchurch City groundwater recharge area (Harewood Floodway, Airport Floodway and part of Springston Formation 3) and the Fendalton gravel lobe. Potential aquifers are identified in the Christchurch City groundwater recharge area from pseudo-logs of geomorphic areas, from geological logs of groundwater wells and from groundwater levels in wells. The Fendalton gravel lobe is identified with a geological model of Holocene gravel and marine sediments under Christchurch City in the geographic area that includes the locations of most Avon River springs. The Waimakariri River probably deposited the Fendalton gravel lobe after flowing through the area of the Harewood Floodway and the Airport Floodway. Avon River spring flow is supported by recharge from the Waimakariri River and by recharge from rainfall. Recharge from the Waimakariri River is probably the most significant component of Avon River spring discharge because: (i) estimated rainfall recharge in the land between Christchurch City and the Waimakariri River within the proposed Avon River springs catchment only accounts for about 325 L/s of estimated 1697 L/s Avon River base flow; and (ii) the Waimakariri River loses an estimated 6–7 m3/s of flow to groundwater in the recharge area. Flow in the Waimakariri River may influence Avon River spring flows by pressure transmission in the confined aquifers located between the Waimakariri River and the Avon River.
Acknowledgements
My thanks to John Weeber (Environment Canterbury), David Scott (Environment Canterbury) and Gil Zemansky (GNS Science) for reviews of a draft of this paper. Thanks also to Mike Scarsbrook (National Institute of Water and Atmospheric Research) under the Groundwater Ecosystems research project (Foundation for Research, Science and Technology contract CO1X0503), and to Environment Canterbury, for providing partial funding for this work.