Floods Trigger Rethink of River Engineering


The desert communities of California, after suffering wild fires and power outages to prevent them, may now have another natural disaster to worry about: flooding.

Federal engineers are warning that the 48-year-old Mojave River Dam, in the high desert about 75 miles northeast of Los Angeles, could potentially flood in the case of severe weather when the region enters the winter rainy season.

“Just a little bit of rain can cause huge flash floods in any area, including the desert,” Lillian Doherty of the US Army Corps of Engineers, said.Opens a new window “We’ve seen events like that happen, and it’s one of the reasons we’re most concerned.”

The Corps is considering strategies to shore up the dam and also counter the impacts of extreme weather shifts due to climate change. “This dam was built in 1971, when climate change was still an unknown phenomenon,” Gary Lee, a chief engineer with the Corps, saidOpens a new window . He added, “Climate change creates more uncertainty.”

Venice floods

Severe storms abound elsewhere. In Europe, the coastal city of Venice was ravaged by floods and the mayor blamed climate change for the calamity. In Spain, Italy, France and Britain, an unusually wet fall has led to severe flooding in many towns and villages.

No doubt climate change is playing a role, but other factors are involved. We’ve been managing our rivers, damming them, shoring up banks to prevent floods in one area so that we can build on the adjacent land, pushing the problem downstream.

As extreme weather events become more commonplace, hemmed-in rivers are bursting in unexpected places.

Monsoon lessons

This week, LiveMintOpens a new window , an India-based financial news organization, opened its pages to summarize a talk on Indian rivers by the geographer Amitangshu Acharya that he gave to the IHE Delft Institute for Water EducationOpens a new window in the Netherlands last month.

India, he said, is a country where monsoons bring sudden powerful blasts of rainfall, leading to gushing rivers that flood lowlands. The country’s normal is already extreme by Western standards. And it has a history of river management that goes back decades, building dams on major rivers, some 900 of them on the Ganges and its tributaries alone.

In all, 21,000 miles of embankments and 4,728 large dams have been constructed. The result has been an increase of flood-affected areas, from 62 million acres in 1952 to 121 million acres in 2011.

Not only have these embankments failed to prevent flooding, Acharya said, but they have worsened the situation.

Where once the fine silts from the Himalayas flooded the plains of north Bihar, making the land fertile, they now clog the river, raising the bed and making flooding “an inevitability, not an accident.”

The rivers are a source of prosperity for the people living beside them, he said, and aren’t something to be organized, corralled and managed without input from the people who know them intimately after a lifetime of observing them from the banks.

Dam removal

He argued that India’s government is still in the grip of colonial thinking, following the British example of building embankments and the Americans of building dams. He noted that the United States has moved away from dams, removing 99 in 2018 alone and restoring the free flow of rivers.

“Our experience of the last 50 years of river engineering projects should convince policymakers to look for new solutions.” he said. “Problems produced by embankments and dams cannot be solved by more of the same.”

There are lessons here for all countries. As extreme weather becomes more frequent, the engineering solutions for river management, already flawed, need to evolve.