San Francisco

WHEN the 40-foot-high Kaloko dam collapsed on the Hawaiian island of Kauai last March, its reservoir released a 70-foot-high, 200-foot-wide, 1.6-million-ton wave that carried away 16 cars, hundreds of trees and a cluster of houses, drowning all seven occupants. At least two bodies were swept three-quarters of a mile to the ocean; four were never recovered.

It is tempting to dismiss Kaloko’s collapse as an isolated event, but given the perilous state of the nation’s dams, it is more likely a harbinger. In 2005, the American Society of Civil Engineers gave United States dams a D, a grade that is still justified two years later.

For starters, the nation’s dam stock is rapidly aging. Most dams need major repairs 25 to 50 years after they’re built, and most United States dams are at least 25 years old; some, like the 116-year-old Kaloko, were built more than a century ago.

As dams age, their danger increases. This is a matter of not just advancing decrepitude, but “hazard creep” — the tendency of developers to build directly downstream from dams, in the path of floods that would follow dam failures. The result is that even though Americans now build few dams, more and more dams threaten people’s lives. Chiefly for this reason, the number of dams identified in one estimate as capable of causing death and in need of rehabilitation more than doubled from 1999 to 2006, from around 500 to nearly 1,400. The civil engineers’ 2005 report placed the number of unsafe dams much higher, at more than 3,500.

On top of that, dam safety officials are so overworked that in most states, they don’t come close to carrying out all the inspections required by law. According to the engineers’ society, the average state dam inspector is responsible for 268 dams; in four states the number exceeds 1,200. It is no coincidence that even though Hawaiian law requires dam inspections every five years, Kaloko was never inspected.

We don’t even know how many dams the country possesses. Using one set of criteria, the National Inventory of Dams, maintained by the Army Corps of Engineers, places the number at 79,777, while the sum of dams inventoried by the states is more than 99,000. Even that number is questionable, since it includes suspiciously low counts from several states. In addition, state officials are constantly discovering previously uncounted dams during routine inspection trips. And if the definition of dams is broadened to include the smallest ones, the estimates are as high as several million.

Unlike, say, waterways and sanitation plants, a majority of dams — 56 percent of those inventoried — are privately owned, which is one reason dams are among the country’s most dangerous structures. Many private owners can’t afford to repair aging dams; some owners go so far as to resist paying by tying up official repair demands in court or campaigning to weaken state dam safety laws.

Credit...Josh Cochran

When the Kauai public works department ordered Kaloko’s owner to stop grading a hilltop next to the reservoir in 1997, the local mayor interceded, instructing the responsible county engineer not to interfere; an investigation by a Hawaiian deputy attorney general published on Jan. 8 found that the owner then covered the earthen dam’s emergency spillway with dirt, in the process weakening the dam’s defenses.

Thousands of dams have been abandoned by their owners, and over time, title to them has become obscure — 12 percent of the dams in the Army Corps of Engineers’ inventory have no known owner. As these dams become dilapidated, the states are left with the expensive task of repairing or dismantling them. Privatization advocates, take heed: this is a cautionary tale.

Climate change will also make dams more dangerous by increasing precipitation in many parts of the country, thus undermining the flood assumptions that underlie dam designs. Consider that in October 2005 and last May, two strong but hardly cataclysmic New England rain storms caused the overtopping or breaching of more than 400 dams in three states; a much fiercer storm would compromise far more dams, worsening flooding and potentially endangering thousands of people.

Dams are ranked according to the danger they pose — “high hazard” dams threaten human life if they fail; “significant hazard” dams threaten property; and “low hazard” dams threaten neither. But many dams are inaccurately ranked — the Kaloko dam, for instance, was rated low hazard.

In addition, in most states the rankings do not take into account the potential impact of toxic chemicals from factories, agricultural runoff and mines that gather in sediment behind dams, even though their sudden release can poison humans, wildlife and vegetation far downstream. When a coal tailings dam near Inez, Ky., failed in October 2000, 250 million gallons of coal sludge were sent into the Big Sandy River and its tributaries, killing aquatic life in the streams.

More sobering still, about half the dams in the Corps’ inventory, including many high-hazard ones, do not have emergency plans in case of failure. When these plans are properly executed — by identifying structures likely to be inundated and keeping up-to-date records of residents’ phone numbers — they save lives. But the plans that do exist are often inaccurate, and many of the people they’re intended to protect have no idea of the potential peril they face. California is the only state that even requires property buyers to be informed of potential jeopardy from an upstream dam.

The American Society of Civil Engineers estimated in 2005 that repairing dams threatening human life would cost $10.1 billion, while a 2003 study by the Association of Dam Safety Officials placed the cost of repairing all non-federally owned dams in the national inventory at $36.2 billion. In the last session Congress considered legislation to repair dams at a rate of $25 million a year for five years, but even that feeble gesture didn’t make it out of committee.

Americans are easily persuaded to spend hundred of billions of dollars combating debatable terrorist threats from outside the United States, while failing to notice that inside the country, the infrastructure is crumbling. True, outside forces from time to time topple established regimes, but usually not before their insides have started to rot.

Jacques Leslie

Before the Flood