Coastal hilly forests can slow tsunami flow speeds: Study

Rows of hilly forests strategically arranged along coastlines can help put the brakes on tsunami flow speeds in nearby villages and towns, according to a Stanford University research.

The research was published in the journal Proceedings of the National Academy of Sciences on May 4.

Plant-covered hills can offer a sustainable substitute to towering seawalls, which do not preserve ocean views and access to the shore. Seawalls are also expensive to build and environmentally destructive.

Following tsunami waves crashing through and flattening coastal communities throughout its eastern part in March 2011, Japan has built hundreds of miles of concrete walls that are taller than 40 feet in some places. The walls cost Japan over $12 billion.

Senior study author Jenny Suckale, an assistant professor of geophysics in the School of Earth, Energy & Environmental Sciences (Stanford Earth), said, “If the wall collapses, the consequences are life shattering.”

She explained that not only can seawalls develop a safety illusion that can discourage quick evacuations, they can also end up breaking apart into rubble blocks that tsunami waves then toss throughout a town, village or city.

Suckale’s collaborators include scientists from the New Jersey Institute of Technology, the Naval Postgraduate School, Indonesia’s Ministry of Marine Affairs and Fisheries and MIT.

Vegetated hills and other nature-based coastal risk management solutions are increasingly becoming important, write the scientists. Still, decades are required for trees to grow strong enough to offer any meaningful protection against tsunamis.

The study says that although trees don’t have enough effect on the energy of an incoming wave, they may have a significant part in combating erosion, and thus assist in maintaining the spacing, height and shape of hills that make them effective.

In tsunami-prone countries, an alternative solution that seeks to combine seawall and coastal hilly forest is cropping up.

The design of green hills matters.

Shaping the hills according to the coastline’s shape, and more site-specific factors can assist in reflecting back more energy, said Suckale.

Homes and infrastructure will have to be set back behind a broad buffer zone, as hills can accelerate flows and thus cause more damage to the area close to the hill. The scientists said that to avoid this unintended result, designs with several staggered rows of hills that are larger toward the shore and smaller inland should be considered.