Problems including overgrown stream beds, erosion, seepage, damaged spillways and vegetation growing on embankments could leave at least half of the dams and reservoirs on O'ahu vulnerable to flooding, according to state reports released yesterday.

Investigators found that half of the 16 reservoirs surveyed on O'ahu had at least one feature in poor condition, raising the possibility of flooding in downstream areas, some of which are located in heavily populated urban and suburban residential neighborhoods.

A poor rating means that the specific feature of the reservoir might not be able to fulfill its intended function and that maintenance or repairs are necessary.

While the 16 individual survey reports paint a picture of dams and reservoirs in generally fair or acceptable condition, most have lacked basic monitoring and maintenance programs for many years. None of the dams is in imminent danger of failure, inspectors noted.

However, many of the reports cited one or more specific features of the reservoirs that need attention. In many cases, the reservoirs themselves were free of problems, but upstream and downstream slope areas were cluttered with heavy vegetation that could be uprooted during heavy rains or high winds and cause damage to the dam embankments.

Several landowners yesterday said they had begun to address the problems noted in the report.

"We've already budgeted more than half a million dollars for the next fiscal year to remove vegetation at the (Nu'uanu) dam," said Board of Water Supply spokeswoman Su Shin. "We were planning to do that and other fixes even before this report was made available." The board also has installed wireless data collectors that allow it to gauge water levels at the reservoir remotely, she said.

"It's good to have these reports to help us identify potential problems, but one important thing to remember is that the water in the reservoir has never risen above 43 feet and we have a crest of the dam at 66 feet," she said.

A Schofield Barracks spokesman said the Army was studying the report on the Ku Tree Reservoir, but noted that the reservoir had been mostly empty over the past 20 years.

"The most important thing in dam management is maintaining a relatively low level of water," Shin added.

The reports are based on emergency visual inspections conducted in May by the state and U.S. Army Corps of Engineers following flooding that left seven people dead March 14 when a dam was breached on Kaua'i.

An earlier survey found that all of the 54 dams and reservoirs on Kaua'i had at least some problems similar to those found on O'ahu. The O'ahu results also found that almost all the dams and reservoirs lacked regular inspections and maintenance in recent years.

State Civil Defense officials declined comment on the surveys, saying they had not had time to review all the details before they were released and posted yesterday on a Web site of the state Department of Land and Natural Resources.

State officials plan to conduct similar inspections of dams and reservoirs on Maui and the Big Island in coming months.

Responsibility for fixing the problems will be left up to individual owners, which include Kamehameha Schools, the U.S. Army, and the Honolulu Board of Water Supply, state officials said.

"The DLNR intends to pro-vide copies of the individual inspection sheets to each dam owner for their information and action," said spokeswoman Deborah Ward. The department also has provided each owner with a proposed time line to remedy problems at the dams, she said.

Reach Mike Leidemann at mleidemann@honoluluadvertiser.com.