Safety Be Dammed: High-Risk Dams on the Rise

by Benjamin Preston | September 9, 2011

In the still hours just before midnight on March 12, 1928, thousands of people slumbered in the handful of agricultural communities nestled along the Santa Clara River in Ventura County, California. Tony Harnischfeger and his family slept quietly in a small house at the foot of the St. Francis Dam, a 195-foot high concrete gravity arch dam built on one of the Santa Clara’s tributaries to store water for Los Angeles. The stillness did not last. Harnischfeger, the dam’s keeper, had noticed a muddy leak at the base of the dam the previous day, but William Mulholland, chief engineer of the Los Angeles Bureau of Water Works and Supply (now the L.A. Department of Water and Power) inspected the leak personally and said the mud was most likely from a freshly graded access road near the dam. Several days later, authorities were still unsure of how many people perished when the dam suddenly collapsed in the middle of the night. Bodies and bits of houses washed out into the Pacific Ocean by the 12 billion gallon deluge floated ashore as far afield as the Mexican border. To this day, no one knows the exact death toll, but more than 400 were found, some decades later.

The St. Francis Dam catastrophe wasn’t the first big dam failure in modern history nor was it the last, but its proximity to a population corridor made it one of the worst. More than 2,000 people died in the Johnstown, Pennsylvania flood of 1889, when the South Fork Dam collapsed, and nearly 200,000 perished in 1975 when China’s Banqiao Dam failed. Today, there are more than 84,000 dams in the U.S. alone. Almost 30,000 of America’s dams were built before 1960, but many of the largest ones, built more recently, are aging and in need of repair. Most dams are privately-owned and stand less than 50 feet high, but nearly 1,700 U.S. dams are more than 100 feet high. Although dam safety legislation has ramped up since a string of catastrophic dam failures in the 1970s, the number of high risk dams needing repairs has actually increased over the last decade as dams age and government budgets dwindle. Dams once situated in desolate places far from populated areas now have communities parked within their potential impact zones, but because of the sheer number of them, maintenance has been difficult to keep up with.

Whether you are for or against dams, it’s difficult not to be impressed by the sheer scale of the larger ones. They can hold back billions of gallons of a river’s water, supplying cities and vast agricultural regions with the essence of their survival and success. If a better way exists to provide a huge and burgeoning global population with drinking and irrigation water, it hasn’t become mainstream enough to replace dams as a method of water storage. Despite the immediate practicality of using huge reservoirs as the key component in widespread water distribution systems, numerous biological problems have been caused by disrupting the flow of rivers. Pelagic fish are cut off from their spawning streams hundreds of miles inland. Spikes in mosquito populations, along with attendant disease outbreaks, accompanies slow-moving reservoir water. NASA geophysicist Dr. Benjamin Fong Chao said that redistribution of the world’s water weight, caused by dams, has actually speeded up the Earth’s rotation by 0.2 millionths of a second per day over the past four decades. Some scientists and engineers dedicate their lives to solving these problems, and as Water Matters’ Renee Cho noted in her post last week, removing poorly-sited or inefficient dams has become a popular way to undo the errors of the past and reduce the number of problems needing solving. But if a threat to human life can be viewed as a biological problem, slipping dam safety fits the profile.

It’s difficult to imagine a colossal structure like the Hoover Dam failing, and the likelihood that it would ever happen in fairly low. But Hoover Dam is maintained by the federal government, which still has a reasonably robust program in place to account for maintenance costs. Smaller dams managed by state and regional agencies don’t always have the same funding available for maintenance. According to the U.S. Army Corps of Engineers National Inventory of Dams, more than 57,000 U.S. dams are privately owned. Out of 14,000 high hazard dams–a few of which are federally owned–half lack an emergency action plan in case of a catastrophic failure.

Luckily, America’s newer dams were constructed using improved technology and advanced geologic site study techniques. The St. Francis Dam would not have been built in San Francisquito Canyon had data from modern geology been available. Plus, while the American Society of Civil Engineers and the Association of State Dam Safety Officials push for more emergency action plans to be instituted, a FEMA-administered National Dam Safety Program provides incentive grants to states for training and research.

But that’s just in the U.S. Viewed in a historical context, dam construction is a sign that an industrializing nation has made it. In China, South America, and other parts of the world, the number of dams is exploding as developing infrastructure becomes more robust. Hopefully, governments in those places will take an active and interested role in ensuring that dams are well-sited and designed from the beginning. Americans are likely to see more poorly-sited and silted-in dams removed over the coming decades, but federal, state, and local officials have their work cut out for them if we’re going to continue using and maintaining the essential ones left behind.

With so many people now dependent upon dams for drinking water supply and food production, maintaining them should be one of our top priorities. But perhaps it’s time for a fundamental shift in the way we think about dam construction, development and maintenance. A dam costs a lot of money throughout its service life, so picking a good site the first time is essential. At the same time, keeping development away from dams is important, too. Regardless of economic pressure from the real estate market, it doesn’t make much sense to build in areas where a dam failure could cause a terrible catastrophe. Nothing built by man or nature is immune to the forces of chance. No matter how well designed or ideally sited, any dam could suddenly spill its contents violently onto a sleepy, unsuspecting landscape.

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