Did the Canterbury earthquakes harm more than we realise?

The 2010/2011 Christchurch earthquake sequence claimed many lives and damaged and destroyed infrastructure located in the central business district and in the city’s suburbs. As a result, many buildings were deemed structurally unsafe and were subsequently demolished or rebuilt. However, was that really everything the earthquake sequence shattered? What about the local rivers that are so important to New Zealand’s way of life and economy.

Avon River, Christchurch, New Zealand

Avon River, Christchurch, New Zealand by Sarah Pienisch

Water is a predominant part of New Zealand. Kiwis drink it straight out of the tap, use it freely for recreational purposes, and also rely on it for its tourism industry to support their ‘clean and green’ image. Most of the time clean water is taken for granted, especially the access to clean freshwater in urban communities. Domestic contaminated waterways are a problem in most cities; a function of increasing and high density populations, complex and often dated infrastructure, and inefficient use of available water.

The earthquakes had a major impact on the Avon River,which has a length of 14 km and traverses Christchurch City in a west to east direction. The Christchurch sewage treatment plant was majorly damaged during the February 2011 earthquake leading to extreme degradation to water, wastewater and stormwater infrastructure. The damage resulted in large volumes of raw sewage discharging into Christchurch’s rivers. This did not only affect the fish and plants that live in the water but it also adversely impacted on amenity values of the river. It is important to understand that the earthquakes caused more damage than we can imagine in order to rebuild the city in the best way possible.

Devane et al. (2014) conducted research directly after the February 2011 earthquake. They investigated both the impact of the earthquake sequence and the resulting sewage discharges on the water and sediment quality of the Avon River in Christchurch. Choosing three sites along the Avon River (the Antigua Boatshed in the central city, Owles Terrace near the coast, and Kerrs Road midway between them), for water collection, sediment and water quality were measured over a period of 12 months. Factors det ermining water and sediment quality included both microbial analyses, such as the extent of E.coli, bacteria found in intestines, and  other pathogens, during and post raw sewage discharge.

Hilgendorf demolition

Demolished buildings were an obvious result of the quakes. Image from Adrian Paterson.

The results showed that sediment and water quality at all three sites on the Avon River were variously impacted by faecal contamination after the earthquake sequence. The researchers differed between active, implying major continuous sewage discharge from February 2011 until late September of the same year, and post-active discharge, discharge that occurred with on-going aftershocks and a weak sewage system, and contained low volume and irregular discharge from October 2011 until March 2012. The Avon River received up to 38,000 m3 per day of raw sewage during the active phase but this decreased as time passed.

Sewage volume differed between the three sites. Owles Terrace received the highest volume of sewage discharge leading to the greatest variation in water quality. The Boatshed received barely any sewage. However, at two out of three sites water quality levels were so low that the water was deemed harmful for the fish living in it. Pathogen levels varied throughout the different sites and samples but were still concerning. Most inexcusable were E. coli levels. They were high at all three sites and exceeded NZ recreational water guidelines making the Avon River unfit for activities, such as boating and swimming.

Avon statue

The Avon appears clear and serene, but there is a darkness in the depths. Image from Adrian Paterson.

When the research team compared post-quake samples with pre-quake ones, it was found that the water quality of the Avon Rover already occasionally exceeded water quality guideline values prior to the earthquakes, meaning that the river was already in poor condition. This was mainly due to bird and dog faeces. High E. coli levels do not only harm the aquatic ecosystem but are also a threat to human health. With new plans to develop the Avon River Precinct the areas surrounding the Avon River not only need to be aesthetically pleasing but also need to guarantee good water quality in order to avoid health threats to us as well as the aquatic ecosystem.

So what does this tell us about the damage the earthquake sequence caused in Canterbury? The earthquakes were devastating because lives were claimed, a whole city was damaged, and harm was caused to freshwater ecosystems. The Avon River is not as clean as its clarity suggests. While most of the earthquake damage was very visible and obvious, it does not mean that the less obvious causalities were not just as bad.

The author Sarah Pienisch is a postgraduate student in the Master of Natural Resources Management and Ecological Engineering taught jointly at Lincoln University and BOKU, Vienna. She wrote this article as part of her assessment for ECOL 608 Research Methods in Ecology.

For more information regarding the research, you can gain excess to the original report here:

http://www.sciencedirect.com.ezproxy.lincoln.ac.nz/science/article/pii/S004896971400357X

Reference

Devane, M. L., Moriarty, E. M., Wood, D., Webster-Brown, J., & Gilpin, B. J. (2014). The impact of major   earthquakes and subsequent sewage discharges on the microbial quality of water and sediments in an urban river. Science of The Total Environment, 485–486, 666-680. doi: http://dx.doi.org/10.1016/j.scitotenv.2014.03.027

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