For many years the Heathcote-Avon estuary was the dumping ground for Christchurch's sewage. Then, in 2010, the wastewater was diverted well out to sea, via a long pipe. David Schiel from the University of Canterbury and John Zeldis from NIWA were investigating the effects of this diversion on the health of estuary when the 2011 Christchurch earthquakes happened, re-engineering both the estuary and their experiments.
The 2011 Christchurch earthquakes and the sewage outfall diversion have had profound impacts on the Heathcote-Avon Estuary
A digitally manipulated image of two chairs sitting among rubble. The photographer comments, "There is a strip of land that has been declared as the red zone. This means that the houses facing towards the tidal estuary must be abandoned as they are on land that has been declared uneconomic to repair after the Christchurch earthquakes. These chairs are at the front of one of these properties that will be bulldozed. These seem to be saying come hell or high water we will not be moved".
A 'sand volcano' of liquefaction silt. The photograph has been rotated 180 degrees. The photographer comments, "This could be just a horrible hole caused by liquefaction pouring out of a hole after the Christchurch earthquake in January, but turn it upside down and it becomes an outcrop on the floor of an unseen tidal estuary".
The Avon and Heathcote Rivers, located in the city of Christchurch, New Zealand, are lowland spring-fed rivers linked with the Christchurch Groundwater System. At present, the flow paths and recharge sources to the Christchurch Groundwater System are not fully understood. Study of both the Avon and Heathcote Rivers can provide greater insight into this system. In addition, during the period 2010-2012, Christchurch has experienced large amounts of seismic activity, including a devastating Mw 6.2 aftershock on February 22nd, 2011, which caused widespread damage and loss of life. Associated with these earthquakes was the release of large amounts of water through liquefaction and temporary springs throughout the city. This provided a unique opportunity to study groundwater surface water interactions following a large scale seismic event. Presented herein is the first major geochemical study on the Avon and Heathcote Rivers and the hydrological impact of the February 22, 2011 Christchurch Earthquake. The Avon, Heathcote, and Waimakariri Rivers were sampled in quarterly periods starting in July 2011 and analyzed for stable Isotopes δ¹⁸O, δD, and δ¹³C and major anion composition. In addition, post -earthquake samples were collected over the days immediately following the February 22, 2011 earthquake and analyzed for stable isotopes δ¹⁸O and δD and major anion composition. A variety of analytical methods were used identify the source of the waters in the Avon-Heathcote System and evaluate the effectiveness of stable isotopes as geochemical tracers in the Christchurch Groundwater System. The results of this thesis found that the waters from the Avon and Heathcote Rivers are geochemically the same, originating from groundwater, and exhibit a strong tidal influence within 5km of the Avon-Heathcote Estuary. The surface waters released following the February 22nd, 2011 earthquake were indistinguishable from quarterly samples taken from the Avon and Heathcote Rivers when comparing stable isotopic composition. The anion data suggests the waters released following the February 22nd, 2011 Christchurch Earthquake were sourced primarily from shallow groundwater, and also suggests a presence of urban sewage at some sites. Attempts to estimate recharge sources for the Avon-Heathcote Rivers using published models for the Christchurch Groundwater System yielded results that were not consistent between models. In evaluating the use of geochemical constituents as tracers in the Christchurch Groundwater System, no one isotope could provide a clear resolution, but when used in conjunction, δ¹⁸O, δ¹³C, and DIC, seem to be the most effective tracers. Sample sizes for δ¹³C were too small for a robust evaluation. Variability on the Waimakariri River appears to be greater than previously estimated, which could have significant impacts on geochemical models for the Christchurch Groundwater System. This research demonstrates the value of using multiple geochemical constituents to enrich our understanding of the groundwater surfaces-water interactions and the Christchurch Groundwater System as a whole.