Perched on the Pali above Nu'uanu Valley and downtown Honolulu, Nu'uanu Dam is among nearly two dozen in the state with structural or functional deficiencies.

It isn't the worst-maintained dam in Hawai'i, but it has been deemed "high hazard" because of its precarious location. If the dam were to fail, it could send floodwaters cascading toward the ocean — through some of the most highly populated areas in the state, according to engineers.

Dams above Waialua and Hale'iwa also are potential threats.

"We've been very fortunate we haven't had a major dam failure here," said Edwin Matsuda, state dam safety engineer responsible for monitoring the safety programs of more than 130 dams throughout Hawai'i.

At least 22 dams have deficiencies that raise safety concerns, according to the ASCE, and 20 of those are among 77 state dams classified as "high hazard," a category that includes dams whose failures would cause loss of life and significant property damage.

Nu'uanu residents don't like thinking about a potential dam break.

"I just hope to God nothing like that happens," said Paula Kurashige, a longtime Nu'uanu resident who works to help her neighbors cope with routine levels of flooding in that area.

For years the American Society of Civil Engineers, or ASCE, has been warning that state-regulated dams and levees throughout the nation are in dire need of repair.

Nearly all of Hawai'i's dams are earthen structures erected early in the past century, Matsuda said, before federal standards existed and long before Hawai'i created a state office for assessing dam and levee safety. Many of them, including some of the largest in the state, need work.

The situation is a recipe for disaster repeated across the country, said Peter Nicholson, a University of Hawai'i professor and civil engineer who recently returned from leading a team of experts into New Orleans to examine the levee failures there.

Nicholson is the chairman of the ASCE's committee on embankments, dams and slopes.

In March, the ASCE issued a report on the state of the nation's infrastructure and, as it did in 2001, gave state-regulated dams a D on a traditional A-through-F grading scale.

Nicholson sees New Orleans as a wake-up call for the nation to take note of the ASCE findings.

"A 'D'," Nicholson said. "If my kid brought home a report card with a D, I'd be a little upset. If my kid brought home a D in dams, and there was information that progress was declining, I'd be in someone's office."

The Association of State Dam Safety Officials has called for national legislation to pay for repairs needed on dams across the country.

NU'UANU: 'LIKE A SIEVE'

Hawai'i's dam safety program consists of Matsuda, one quarter-time clerical assistant, a vacant half-time position and a state budget of $164,000 that covers little more than salaries.

Matsuda won't say how much it would cost to make all the dams in the state safe. Owners of the dams, he said, are responsible for maintenance and repairs.

The owner of Nu'uanu Dam is the city's Board of Water Supply.

Constructed in 1910, Nu'uanu Dam is an earthen dam built for hydroelectric power and drinking water, but used only briefly for those purposes, said Su Shin, a spokeswoman for the water board. The reservoir is now stocked with catfish.

Shin said the water supply agency controls water levels in the dam, monitors seepage and keeps appropriate agencies apprised.

There is plenty of seepage to monitor, Nicholson said.

"That thing leaks like a sieve, and has since it was built," he said.

Nicholson, who was among the inspectors contracted to examine Nu'uanu in 1993, said seepage at dams is not uncommon, but Nu'uanu's persistent leaks could indicate erosion within the dam itself.

"All dams leak," he said. "This dam is leaking badly, and has been for nearly 100 years."

Civil engineers from across the country are examining whether seepage, similar to that seen at Nu'uanu Dam, might have affected the failure of some of the New Orleans levees, Nicholson said.

Shin said water supply crews watch carefully to see that seepage from Nu'uanu isn't clouded or muddy, indicating that the interior is eroding.

Nicholson said a thorough examination is difficult if not impossible because of dense vegetation. In addition to preventing proper inspection, the roots of the plants, including a row of Norfolk Pine planted along the dam's crest, are reaching deep into the embankment, making erosion of the interior even more likely, he said.

The Army Corps of Engineers, in the Nu'uanu Dam's first formal inspection report in 1978, directed the owners to remove the vegetation.

"Until the downstream area is clear ... the seepage or leakage deficiency will remain a real safety concern," civil engineer Robert J. Yunker wrote in April of that year.

But the dam was even more overgrown when Nicholson inspected it in 1993. In 1999, another inspector estimated it would cost about $400,000 to clear the crest and upstream and downstream slopes.

At this point, Matsuda said, removing the deeply embedded vegetation would necessitate substantial reconstruction of the dam.

Shin said city landscaping crews now trim the trees and vegetation on their regular rounds.

The dam was designed to hold between 80 million and 1.2 billion gallons of water in the reservoir, but the Board of Water Supply makes up for the dam's deficiencies by keeping its gates open and the water level low.

"Right now the water is at 28 feet and that is very, very low," Shin said. "The upper flood gate is 47 feet. This helps to reduce the stress on the dam, but it is a balance; we have to keep from killing the fish."

That technique seems to be working, said John Cummings, a spokesman for O'ahu Civil Defense, the organization that would evacuate areas beneath the dam if something were to go wrong. Nu'uanu Dam has held.

'OPAE'ULA: OLD, ERODING

According to dam safety office inspection records, a series of agricultural dams on property once farmed by Waialua Sugar Company and now owned by Kamehameha Schools are in particularly bad shape.

Formal investigations of two of the 'Opae'ula Dams revealed seepage, erosion, slides and other irregularities, according to a contractor's report from December 1996.

Because of their alignment down the side of a mountain, Matsuda worries that if one of the dams were to collapse, it might take out the next dam, domino style, sending a surge of water into Hale'iwa.

Kekoa Paulsen, spokesman for Kamehameha Schools, said the 'Opae'ula Dams — including a third dam that stands in the center of a large field — are monitored daily.

Although the dams are old, he said, they remain the only source of irrigation for 2,000 acres of land still used for agriculture.

WAHIAWA: MAY OVERTOP

Dole Food Co. still uses Wahiawa Dam on Lake Wilson for irrigation, as it has since 1906, said Dan Nellis, the company's operations director.

Keeping water levels down is a strategy used by Dole Food Co. to mitigate downstream flooding, he said.

And, Nellis said, "we continue to monitor, conduct routine maintenance and contract third-party inspections as required."

Cummings, the O'ahu Civil Defense spokesman, said the dam still floods downstream.

Nearby Otake Camp has been evacuated for flooding three times in the past eight years, most recently in early October, Cummings said. Parts of Waialua town were evacuated about 15 years ago.

Nicholson said in a worst-case scenario, a failure at Wahiawa could take out Waialua town —and Wahiawa Dam's flaws make such a scenario possible, he said.

"Wahiawa Dam is susceptible to overtopping," Nicholson said. "And that would not be good. Overtopping is what happened in New Orleans."

The storm surge from Hurricane Katrina swept over the top of many of New Orleans' levees. The soil began to erode beneath moving water, "and the earth embankments simply disappeared," he said.

Nellis said some dam operation issues are out of the control of Dole or any other dam owners.

"No one can prevent a complete major dam failure in the event of an act of God or extreme act of nature," he said.

Reach Karen Blakeman at kblakeman@honoluluadvertiser.com.