Parts of San Rafael, a city north of San Francisco, are sinking at a rate of about half an inch per year. This may not sound like a big impact at first, but it has actually caused communities such as the Canal District, which borders the bay, to sink by about three feet, greatly increasing the risk of flooding from rising sea levels.
It’s not just San Rafael; cities around the world are facing threats from rising sea levels. It is predicted that 300 million people will be at risk of regular flooding by 2050. In the United States alone, the cost of building seawalls to resist seawater intrusion may exceed US$400 billion.
One start-up is proposing an alternative: making cities “elevated.”
Terranova is currently developing a robot that can inject a slurry made from wood waste into the ground. This method will gradually raise the ground level in an attempt to eliminate historical subsidence and hope to prevent flooding in these urban areas.
Laurence Allen, co-founder and CEO of the company, said that the canal zone has long been below sea level. The city of San Rafael has hired flood consulting agencies many times to seek solutions, but the response each time was to build a sea wall costing between $500 million and $900 million. This is an almost impossible task for a small city with a population of about 60,000 and a considerable number of residents living in poverty.
Terranova claims to be able to protect San Rafael and other similar cities at a lower cost. In the case of San Rafael, the company has made a bid to raise the height of 240 acres of land by four feet for only $92 million.
It is reported that Terranova recently completed a round of seed financing led by Congruent Ventures and Outlander, totaling US$7 million, with a valuation of US$25.1 million.
Injecting underground material to raise the ground is nothing new. Terranova's innovation lies in its unique and low-cost material - wood waste is easily available and low-cost, and the company also mixes it with other ingredients to form a slurry, but the recipe is not disclosed to the public. The slurry is then supplied to automated injection robots via 20-foot containers. These crawler-mounted devices move autonomously around the construction site, drilling holes and injecting the wood slurry to a depth of about 40 to 60 feet underground.
As long as the slurry remains moist in the ground, the wood won't rot, and the company can subsidize some of the cost through carbon credits. According to Allen, all work is managed by Terranova’s self-developed software. The system combines public geographic information with core data collected from wells across California to build an underground structure model, and then uses a genetic algorithm to design the optimal injection plan.
City planners, contractors and other interested parties can use a virtual design tool similar to "SimCity" to adjust the terrain. When the plan is determined, the control system will guide the robot to inject the appropriate amount of slurry at the appropriate location. There will still be manual operations on site to ensure safety. It takes approximately two hours to inject the slurry and complete the cure.
The company has been experimenting with the robot and software at a test site for more than a year. Although some experts are concerned that cured wood pulp may intensify earthquake tremors, Allen explained that common alternative methods currently have similar risks, and Terranova believes that this method is more conducive to earthquake response than seawalls and levees.
The company plans to make profits in the future by sharing project proceeds with contractors. In addition to cities, Terranova also hopes to serve other land-lifting projects, such as restoring wetlands that have been lost due to land subsidence or rising sea levels. But given the urgency of rising seawater, urban projects remain the top priority. “I was born in San Rafael and really wanted to make a difference in my hometown,” Allen said.