A Flood of Dam Safety Problems

Lori Pottinger
Wednesday, September 8, 2010

The catastrophic flooding in Pakistan provides a terrifying warning of how global warming is changing the hydrological cycle. Almost every month seems to bring unprecedented rainstorms and floods somewhere across the world, and their severity and frequency seems to be rapidly worsening. These floods pose a major threat to the world's dams, and to the many millions of people who live below them. Here we report on a few of the worst examples of dam-induced flooding in recent months.


Northeast Brazil - better known for severe drought - was hit by devastating floods in early July. The floods left 50 people dead and an estimated 150,000 homeless, and damaged towns, farms, bridges and factories. An estimated 80% of the housing in the town of Branquinha was destroyed.

The latest dam burst in northeast Brazil
The latest dam burst in northeast Brazil
Leo Caldas/Revista Veja
In addition to abnormally high rainfall, the unprecedented flood damage was worsened by a series of dam bursts along two rivers. The dam bursts reflect a lack of adequate safety measures on both public and private dams, the latter typically for large sugarcane plantations. In the Northeast region, it is estimated that there are at least 100,000 small and medium dams, most of which were built with little or no regard for environmental impacts and dam safety; at least 200 are reported to be at risk of failure.

The latest dam bursts in the Northeast highlight a recurring problem in Brazil. In the past five years, at least six similar episodes were reported in different parts of the country. Last year, the Algodoes Dam failed in Brazil's northeast, killing at least seven people.

According to Renata Andrade, a specialist in environmental risk and river basin management at the Catholic University of Brasilia, "Populations living downstream from dams are increasingly vulnerable to flooding, due to a lack of dam safeguards and emergency preparedness programs. In the case of the Mundau River, there was no alert system in place to inform local populations of the imminent risks of the dam bursts and the subsequent flooding."

Coming too late to help the victims in the Northeast, the Brazilian Congress in April passed a bill to create the National Dam Safety Program and Policy. The new law calls for the creation of a national commission of dam safety, a risk management system with safety inspections, and emergency plans for dams, including rules of accountability in case of dam bursts. The level of implementation of the new law and its effectiveness remain to be seen.

United States

A dam in eastern Iowa suffered a catastrophic failure in late July, emptying a nine-mile-long reservoir and flooding nearby communities. Thanks to local officials' early warning system and the location of the dam in a low-population rural area, no injuries were reported. The dam failure caused millions of dollars in property damage, and left 900 "lakefront homes" without a lake.

The US has thousands of ageing dams, many privately owned. The American Society of Civil Engineers gave a "D" to the nation's system of 85,000 dams in a report on dam safety last year. More than 4,000 are deemed deficient, including some 1,800 that could potentially cause a loss of life if they failed.

"I think we have found over the last five years that the number of dams that states have identified as being deficient or unsafe is growing at a rapid rate, and that rate is much faster than we are able to do repairs," said Brad Iarossi, a society spokesman and former head of Maryland's state dam safety program.

The 88-year-old Lake Delhi Dam did not have an emergency spillway or additional dam gates to accommodate a record flow of water. The dam was reportedly inspected in 1999, and was not considered high hazard.

According to the Des Moines Register, "Inspectors have said for decades that the Lake Delhi dam could barely handle a historically heavy flood - and one inspector predicted such an event might push water over the top of the dam."


At least one dam failed in late July during the torrential rains in Pakistan. The Tanga Dam in Baluchistan province gave way, inundating seven villages.


The number of close calls on potential dam failures has also been especially high. Here are a few from the recent record.


The huge Three Gorges Dam had some dangerous days during China's recent flood disaster. The dam experienced the biggest surge of water since it began operating four years ago, and its reservoir rose 4m (13ft) in just a day.

In addition, the dam's safety was compromised when the floods washed a thick layer of debris into the reservoir, threatening to jam a key floodgate on the dam. The debris layer was thick enough to support vehicles driving over it.

The flood was the first big one since the dam's completion. "One [flood control official] said the dam's flood-control abilities ‘should not be overestimated,' another reportedly said they were ‘limited,'" according to The Economist.

In recent years, Chinese officials have downgraded the dam's flood-control capacity from "able to withstand the worst flood in 10,000 years" in 2003, to 1,000 years in 2007, and to 100 years in 2008.


Rising water levels threatened to overwhelm one of the country's biggest dams, the Warsak Dam, which threatened one of Pakistan's most populous provinces. Rising water levels at the dam prompted disaster officials to ask residents in the northern outskirts of Peshawar city to leave their homes.

North America

Dams on the Texas-Mexico border were closely watched as two tropical storms brought high runoff to that region in July. Two dams in the region have for years been deemed unsafe by the U.S. International Boundary and Water Commission.

According to a report in The Brownsville Herald, of the four unsafe dams in South Texas, deficiencies at Amistad Dam are "urgent" and at Falcon Dam are "high priority." Sinkholes at Amistad Dam were first identified in 1990. Inspectors noted that Falcon Dam's entire foundation was in need of further evaluation. Both dams also have a hazard-potential classification of "high," meaning that loss of life or significant property damage is expected if the dams fail.

The dams are "multipurpose" projects that are meant to store water and, ironically, provide flood control. A failure of the Amistad Dam could release 4.9 million acre-feet of water, the Herald reports. (An acre-foot is enough to cover one acre in a foot of water.)

And in Kentucky, Wolf Creek Dam, one of the country's largest, was recently designated "high risk" for failure by the US Army Corps of Engineers, requiring "emergency measures" to reduce an "imminent risk of human life" in the Cumberland River valley.

The dam was built on porous limestone. Over time, water has seeped into cracks in the rock, eroding holes and caves. A sinkhole could cause this entire earthen embankment to collapse.
The state has handed out warning radios to all 1,700 residents of Burkesville downstream of the dam.

"If you live downstream from the dam, it doesn't matter whether the dam was attacked by terrorists or whether it failed because of fatigue and age and lack of repair. The people downstream are all impacted the same," said Patrick Natale of the American Society of Civil Engineers.

At this writing, the dam's reservoir levels had been lowered to allow repair crews to work.

The US Army Corps also announced it will begin a US$44 million repair to a dangerous dam near Seatle this fall. The Howard Hanson Dam on the Green River was weakened by heavy rains in January 2009, increasing the dangers of flooding in the heavily developed Green River Valley downstream. The dam's water level is being kept at about half of normal until the repairs can be made.