Slow Water: how to combat floods and droughts

Treating water management as an engineering problem ignores the complex systems in which it operates, a US author says.

Just as floods and droughts are the first obvious sign of climate change, we are making things much worse by the way we manage or mismanage water, award-winning independent journalist and author Erica Gies says.

In her book Water Always Wins: Thriving in an Age of Drought and Deluge, she travels the world, examining ‘slow water’ systems where wetlands, floodplains, high altitude grasslands and forests soften flood peaks, store water for droughts, and keep natural systems healthy.

“Water has relationships with soil and rock and microbes, and beavers and plants and humans even.

“And so, if you're just focused on one thing, then you're causing a lot of unintended consequences.”

As cities have expanded, and we pave over more land, we have also been draining wetlands, the natural sponges which regulate water, she says.

“Humans have actually filled or drained as much as 87 percent of the world's wetlands.

“We've intervened with dams and diversions on two thirds of the world's big rivers. And just since 1992 the land area covered by cities has doubled.”

These interventions prevent water from behaving in the way it wants, she says.

“We're blocking water from those slow phases on the land where it can absorb floods, filter underground to supply water in the dry season, store carbon dioxide three to five times as much as forests and provide really important habitat for all kinds of plants and animals that also help to sustain these systems.”

Just as hard engineering has worsened urban flooding, it is possible to restore water systems she says. In California, they are making use of ancient, hidden underground waterways to manage high water flows.

“A lot of places have ancient rivers and streams that are buried underground. These ones in California are special, because they were made by the last ice age.”

They are like the ancestors of today’s rivers, she says

A hydrogeologist in California named Graham Fogg had the idea to find these underground rivers and to direct water into the valley during flood.

“The water can then go underground very quickly, and then it will seep into the surrounding clays, which are less permeable over a longer period of time and raise the groundwater table for quite a large area.

“In California, we've done a lot of over-pumping of groundwater, we've tended to use that as extra water when surface water runs low. But in fact, that's not the case at all, surface water and groundwater are connected, they're effectively the same water.”

A creek in Seattle has been brought back to life by restoring its hyporheic zone. The hyporheic zone is between the aquifer and the surface water, she says.

“It's basically part of the stream or the river that is also moving downstream, but much, much more slowly, because it's moving through rock and soil.

“And there are many critical things that happen here in terms of nitrogen, phosphorus and carbon cycling - so that's cleaning pollutants. It's serving as the base of the food web, and it's a highly oxygenated area so fish like salmon lay their eggs there.”

If the stream doesn't have a healthy hyporheic zone, then it's also going to be a sick system, she says.

“It’s not going to be able to support diverse life and spread its sediment in a way that helps reduce flooding and provide water through the dry season.”

Thornton Creek in Seattle had been engineered to death, she says; straightened, built over and diverted into pipes.

“A biologist working for the city named realised that ok, we can put back some S curves, we can put back some trees and logs and rocks and kind of make it look habitaty.

“But, you know, if we don't pay attention to the hyporheic zone, then it's going to be a sick system. And we're going to have to continue trying to prop it up and keep it working, which is very expensive.”

And so they rebuilt the hyporheic zone that had been scoured away fast urban water and repopulated it with river life.

"The area has not flooded since they did this project. And then they did various scientific studies to show that the water was moving underground, and through the hyporheic zone 89 times more than before they did the project.

“They studied the life to see if the critters they introduced had survived and a lot of them had, there was seven times more species diversity.”

The stream was also processing run-off pollutant much more efficiently, she says.

“And then in 2018, a couple of years after they finished the project, Chinook salmon actually came back and spawned in the hyporheic that they had created.”

Similar restoration projects are happening all over the world, from creating sponge cities in China to mapping and restoring the wetlands of Chennai, she says.

“Chennai is a really water-rich area. It has three rivers, all different kinds of wetlands, including backwaters, because it's right there on the Bay of Bengal.

“And historically, water would move very slowly through these complex systems ultimately out to the ocean.”

This was aided by a 2000 year-old Tamil tradition of gently diverting water into depressions and slowly releasing it when needed.

“And so in this way, they really inserted themselves into the hydrological cycle.”

Rapid urbanisation has largely destroyed that hydrological system, and the city now regularly floods or is without water, she says.

Now these ancient wetlands are being mapped, restored and protected by law, she says.