Climate change threat to sewers
NZ wastewater and stormwater systems need upgrading
Much of New Zealand’s more than $20 billion of wastewater and stormwater systems aren’t designed to withstand the potentially extreme impacts of climate change, researchers say.
The latest study from the Deep South National Science Challenge — a research collaboration with a focus on climate change — has looked at the threat extreme weather events and rising seas could pose to our sewer networks. In the recent Edgecumbe floods, for example, raw sewage floated through the streets, making the clean-up extremely challenging.
Six months later, 500 houses are uninhabitable and flood-proofing the town remains a distant goal.
“The way climate change is predicted to affect our stormwater and wastewater will have a considerable impact on many aspects of New Zealand life, including health, disaster resilience, drinking water, ecology, and transport, not to mention how flooding or infrastructure failure will impact on communities,” said the report’s co-author, Professor Iain White of Waikato University.
New Zealand’s infrastructure includes 24,000km of public wastewater networks with more than 3000 pump stations, and more 17,000km of stormwater networks.
Much of it, however, was not designed for the challenges climate change will bring, from sea-level rise to the predicted changes in precipi- tation frequency and intensity.
“For example, in many local water systems, roads are designed to be used as a secondary stormwater routes in extreme flooding.
“This is fine in most situations, but in extreme inundation events wastewater containing sewage may mix with the stormwater overflows, which of course brings problems such as we saw in Edgecumbe.”
The increase in extreme rainfall events would also add stress to the system by overwhelming the networks, restricting opportunities for maintenance, and increasing the occurrence of infiltration of wastewater into stormwater.
“We already know that sea-level rise will affect all coastal infrastructure, and as many of our water networks use gravity to discharge to water bodies, the most costly areas of the network are often located in low-lying areas or on the coast,” White said. “From this, increasing sewage overflows, pipes corroded by salt water, and exposure to liquefaction are all more likely.”
An increase in the number and frequency of coastal storms would hit coastal infrastructure in particular, causing increasing inundation, physical damage, and electrical failure at treatment plants.
“It’s not just too much water, though,” White said. “Drought brings its own problems, disrupting gravity systems by slowing flow and leading to blocked pipes. Particularly lengthy droughts can also affect wastewater treatment processes, creating functional and safety concerns.”
The report suggested areas for further research — with the priority being to quantify the precise risks to these systems.
“Once we have this knowledge, we need to consider the most appropriate adaptation response.”