By Dr. Robert Thorson

One of President Donald Trump’s primary initiatives is to put workers back to work on public infrastructure. Though transportation is usually the highest priority, I suggest we pay more attention to the tens of thousands of aging dams spread across the country.

As I write, the communities below California’s Oroville Dam – the nation’s highest at 770 feet – remain on high alert. Recently, there’s been so much rain and melting snow that officials had to open the dam’s emergency spillway for the first time in its 50-year history. Then that spillway began to fail by erosion. Officials, worried that the spillway could collapse at any moment, issued an emergency evacuation order affecting nearly 200,000 people. The concern was that a 30-foot wall of turbulent muddy water would roar down the upper part of the Feather River, destroying everything in its path, and that, farther down, the torrent would breach levees to flood residents of three counties.

The best known example of this kind of disaster in the United States was the failure of the South Fork Dam on Pennsylvania’s Little Conemaugh River in 1889. Roaring downstream toward Johnstown was an instantaneous flow comparable to that of the Mississippi River. More than 2,200 people were killed. The cause of the Johnstown flood was comparable to that of the recent almostflood at Oroville: unusually heavy rains, followed by infrastructure erosion.

And while we’re busy fixing aging dam infrastructure here, our diplomats might work to prevent future dam tragedies from happening in Southeast Asia. My biggest concern is for dams along the Mekong River. There, officials and engineers from China, Myanmar, Laos, Thailand and Cambodia are either building or planning to build 11 large mainstream dams and 77 smaller ones before 2030. Their primary goal is electricity generation. This story is nicely told by Richard Stone in the Dec. 2 issue of Science.

Particularly worrying is the Mekong Delta in Vietnam. As with the evacuees at Oroville and the dead at Johnston, the delta’s residents are hostage to whatever takes place upstream. Sixty million people are being threatened with a food security crisis created by upstream dam construction and plans for more dams.

When U.S. soldiers were fighting in the Mekong Delta in the 1960s, it was actively growing, and covered with productive rice paddies. Now it’s shrinking and sinking beneath the sea. So much sediment is being trapped upstream by dams that dropping of the land by compaction cannot be offset by new sediment layers. With rivers no longer flooding naturally, the delivery of nutrients to the farmland will decline precipitously. Climate change is weakening the monsoon, diminishing freshwater flows. This is the result of a reduced temperature contrast between land and sea. Saltwater intrusion is being caused by the combination of reduced freshwater flows and higher sea levels. This is contaminating water supplies and diminishing opportunities for growing rice.

Another critical part of the traditional delta diet is the freshwater fish that migrate up and down its channels. Fishing harvests may decrease by more than half because dams hinder fish passage. Reservoirs will back-flood spawning grounds and stagnate the waters. This will contribute to reduced oxygen, which will release methylated mercury, a known neurotoxin that moves up the food chain.

There are other issues besides food. Human populations will be dislocated. Biodiversity will decline. Many species will be on a path to extinction.

What the upstream nations are doing in Vietnam is something the United States has been doing to Mexico for years. Before dam construction and intensive irrigation, the Colorado River was once a large, lush and fertile wetland environment. Now it’s little more than a salty, shriveled remnant. Bangladesh suffers a similar tragedy. The entire nation lies on the Ganges Delta, whose fate is controlled by what happens in India, Nepal and Tibet.

The residents of Oroville have breathed a sigh of relief. The residents of the Mekong Delta are watching and waiting.