Hidden on a hillside in the eastern part of the island of São Miguel, in the Azores, is the largest natural wall in the Iberian Peninsula. It is ‘hidden’ not only because it is in a remote corner of an island in the middle of the Atlantic, but because it is so well embedded in the landscape that it goes unnoticed.
And that’s not by chance.
The wall is an example of natural engineering, an approach that applies natural processes to construction. Instead of relying only on concrete and heavy infrastructure, this approach uses materials such as logs, stones, and native vegetation to create structures that work with ecosystems rather than against them.
SPEA, our Partner in Portugal, has pioneered this approach since 2012. It all started as a response to a very practical challenge. The organisation was working to restore the Azores’ native Laurissilva forest, but faced difficult conditions: unstable volcanic slopes, landslides, invasive plants, and streams damaged by intense rainfall. Traditionally, the solution would have been concrete. But concrete structures are not always suited for these dynamic landscapes.
So, SPEA began experimenting with another way.
At Mata dos Bispos, the team created a living laboratory to test natural engineering techniques. On a slope dropping more than 200 metres, where torrential rain was washing away soil and flooding the road below, they combined drainage systems with timber terraces. The logs slow the flow of water, trap sediment, and help prevent flash floods. On unstable slopes, larger structures are sometimes needed. One example is the largest natural retaining wall in the Iberian Peninsula, more than nine metres high and 30 metres long, with a retention capacity of over 270 tonnes. Unlike a concrete wall, which would require deep foundations on unstable volcanic soil, the structure uses logs and vegetation. The roots help stabilise the ground while allowing water to drain naturally.
“In living walls, water seeps through and drains away, rather than accumulating as it does in concrete. And even if an earthquake breaks the roots, they regenerate on their own.” – Rui Botelho, coordinator of SPEA Azores.
It is no coincidence that these techniques have been in use for 40 years in countries such as Switzerland, to prevent landslides and avalanches, or on Mount Etna in Italy. They have also been applied to river restoration. Thanks to the LIFE IP Azores Natura project, more than 3 km of streams in the archipelago have already been restored, with their banks stabilised and renaturalised using natural engineering techniques.
SPEA’s experience and success with this approach are already recognised and the team in the Azores has been commissioned to restore the two main springs supplying Vila Franca do Campo’s public water supply, and to restore access to Lagoa do Congro.
Natural engineering is also helping tackle the effects of tourism. On popular trails, especially in areas with peat or clay soils, poor drainage creates muddy sections. Visitors often step off the path to avoid puddles, damaging fragile vegetation. The solution is to improve drainage so that staying on the trail becomes more appealing than leaving it. Sometimes this means a raised walkway or using natural engineering to channel the flow of water.
“Humans were already creating nature-based solutions long before they started building with concrete.” – Tarso Costa, Senior Conservation Officer at SPEA Azores.
Many of these practices have ancient roots. The difference lies in combining ancestral knowledge with the data and calculations of modern science and engineering. Natural engineering is not suitable for every situation. It cannot replace large infrastructure such as dams, and it requires collaboration between engineers, biologists, and agronomists.
From restoring streams and peatlands to building almost invisible walls, SPEA’s work shows that natural engineering can provide practical, resilient solutions inspired by nature. Like the ecosystems it supports, its greatest strength lies in something concrete cannot offer: the ability to grow stronger with time.
Article by Sonia Neves, pictures by SPEA.
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