Mining braided rivers

Context

Braided rivers are some of the most biologically productive and rare ecosystems on Earth. In Canterbury, they formed during the Quaternary Period when glaciers bulldozed through the Southern Alps, their ephemeral waterways carving out wide alpine valleys and carrying large amounts of gravel from glacial moraines to the shallow ocean at the coast. Over 2.5 million years, the sediments and gravels fanned out across braidplains, coalescing into mega alluvial fans that today we call the Canterbury and Amuri Plains. Dynamic ecosystems evolved, adapting to this extraordinary and ever-changing environment. We know this because of the widespread geomorphological evidence[1].

We also know that these braidplains provided numerous irreplaceable life-supporting ecosystem services, otherwise known as critical natural infrastructure. The sediment they delivered to coastal lands counteracted the erosive forces of wind-driven waves and storm surges. Permanent wetlands acted as kidneys, cleaning waterways and drawing carbon dioxide from the atmosphere and storing it in their peaty soils. Ephemeral wetlands played a role too, acting as sponges, absorbing floodwaters and calming their destructive tendencies. In the diverse braidplain ecosystems that formed, and with the assistance of microbial, fungal, and invertebrate communities, water was filtered and nutrients cycled, enabling and supporting unique and endemic aquatic and terrestrial biodiversity. For the early human inhabitants of Aotearoa New Zealand, braided rivers provided plentiful and safe drinking water and mahinga kai; natural infrastructure that enabled them to thrive.

Without natural infrastructure and the ecosystem services and resources that braided rivers provide, there can be no built infrastructure. The reverse is not the case. Thus, natural infrastructure is a first order human necessity over built infrastructure, and—unlike built infrastructure—natural infrastructure is provided free of charge.

Ironically, failing to recognise braidplains as critical natural infrastructure has now put critical built infrastructure[2]—along with farms, businesses, and indeed entire towns—at huge risk. One prominent risk, flooding, was identified in 2019 in NIWA’s extraordinarily well-ignored report, which concluded than the level of exposure of built elements at risk within Canterbury’s flood hazard area to be $40 billion (based on 2016 valuations)[3]. The rivers’ waters are polluted, costing ratepayers to clean it to standards that fall below the World Health Organisation’s recommendations[4]. What mahinga kai remains—a mere fraction of historical levels—is tainted. Some endemic bird and fish species integral to maintaining healthy ecosystem services are near extinction. Coastal ecosystems that could have acted as buffers to rising sea levels and storm surges are now starved of the sediments the rivers once delivered along coastal margins. This is in part due to water harvesting for irrigation:

“The conventional wisdom is that you harvest flood water in the winter and store it until it’s needed (for agriculture) in the summer. However, floods are required to carry gravels to the coastal zone and if there’s not enough gravel, the waves get hungry and start eroding the land.” – Dr Scott Lanard, NIWA[5]

And in part because the once wide braidplains have been forced into ever-narrowing spaces. During high water flows, the constricted fast-flowing rivers shoot lighter sediments and gravels out into ocean waters too deep for beach-building waves to return to the shore[6].

Importantly, these are not the ‘opinions of a few’, but rather, grounded in peer-reviewed science[7], on research and investigations that Environment Canterbury (ECan) has commissioned[8], and on facts supported by empirical evidence^1-9.

We applaud the efforts of those at ECan who have presented unequivocal evidence that braidplains and their rare, life-supporting ecosystems continue to be destroyed. And we support their hard mahi as they endeavour to navigate outdated and often conflicting legislation and equally conflicting values in a rapidly changing climate.

When it comes to gravel extraction, rivercare groups, most notably the Ashley Rakahuri Rivercare Group (ARRG) have supplied robust data and evidence[9] that gravel extraction consenting processes in their current form do not consistently adhere to ECan’s stated goals in the Canterbury Water Management Strategy (CWMS): to ‘protect and restore the natural character of braided rivers’. Further, that by 2025—a mere three years from now—‘Five priority braided rivers are under active management to increase habitat area usable by all species of indigenous braided river birds.’[10] Birds are not simply nice to have; they are bioindicators of the health of critical natural infrastructure.

The Ashley Rakahuri River is one of these stated ‘active management areas’. Over the last two years, ARRG’s concern about riverbed management and gravel extraction has been expressed to ECan on a number of occasions, but significant changes in operational management have yet to see the light of day. Meanwhile, consents for gravel extraction have been issued with little regard for natural character, biodiversity, and mahinga kai values, and without due consideration of climate-related risks, including the risk of maladaptation:

“There is increased evidence of maladaptation across many sectors and regions since the AR5. Maladaptive responses to climate change can create lock-ins of vulnerability, exposure and risks that are difficult and expensive to change and exacerbate existing inequalities.” – IPCC AR6 WGII [11]

The points above are critically important and need inclusion in the pending review of ECan’s Gravel Management Strategy.