Floodgates of terror. (Terrorism And Dams).

In the wake of the tragic attacks of September 11, emergency security measures were put in place at major dams in the Colorado River system, but the federal government's initial security plans were flawed.

The Bureau of Reclamation's (BuRec) security measures are weakest at two of the system's most vulnerable structures, Glen Canyon and Flaming Gorge Dams. The failure of either could set the stage for a series of catastrophic events with massive human and economic impacts extending from Utah to Mexico.

While federal resources are currently focused on protecting the 726-foot Hoover Dana near Las Vegas from terrorist attack, comparatively little is being done to safeguard Glen Canyon Dam upstream on the Colorado River or Flaming Gorge Dam upstream on the Green River. After Hoover, these two dams represent the second- and third-largest dams, respectively, in the Colorado River Basin.

Dam failure would cause catastrophic damage to the reservoir and immediate downstream areas. A possible "domino effect" could cause major damage to the water supply systems of more than 25 million people in the lower Colorado River Basin, triggering economic disruptions throughout Nevada, Arizona, California and northwestern Mexico.

While around-the-clock patrols at Hoover prevented boaters from approaching the dam within a mile upstream and a half-mile downstream, no such controls were in place at either Glen Canyon or Flaming Gorge.

While trucks and trailers were prohibited from crossing Hoover Dam and passenger vehicles were subject to search by state highway patrol officers at checkpoints on either side, truck traffic still moved freely over the crest of Flaming Gorge Dam and across the Glen Canyon Dam Bridge. No security checkpoints were erected at either site.

Hoover is by far the best-constructed component of the Colorado River plumbing system. Anchored into massive granite canyon walls and designed with enough mass for gravity to hold its reservoir -- the nation's largest -- in check, a major attack is unlikely to cause structural failure. The real problems are further upriver.

The 710-foot Glen Canyon Dam sits tucked into porous Navajo sandstone that constantly leaks water around the structure. Large pieces of canyon wall adjacent to the dam routinely break away. BuRec must install increasingly longer "rock bolts" in an attempt to ensure stability of the dam's abutment and to protect the dam's powerplant from falling rock.

In 1983, high water caused portions of the dam's sandstone spillway tunnels to crumble, posing a threat to the abutment.

Any rupture of the dam's crumbling abutments would release two years' annual flow of the Colorado River to blast its way around the dam, scouring the Grand Canyon before surging across Lake Mead on its way to Hoover Dam. In the best-case scenario, this water would flow over the top of Hoover, creating a downstream flood similar to a Hoover Dam collapse. At worst, the collapse of Glen Canyon could damage Hoover Dam, sending four years' annual flow of the Colorado River heading toward Mexico all at once.

Glen Canyon Dam is an accident waiting to happen. Serious plans must be put in place for the dam's controlled decommissioning, as the dam very likely could fail on its own.

A failure at Flaming Gorge Dam, with a full pool of 3.7 million acre-feet of water, would threaten Glen Canyon Dam downstream.

Below Hoover Dam, where the smaller Davis, Parker and Imperial dams constitute critical elements of the Colorado River plumbing system. Damage to the Central Arizona Project Canal, California Aqueduct and All-American Canal -- the region's major water delivery systems -- would jeopardize municipal water supplies from Las Vegas to San Diego.

Riverside communities in Nevada, California and Arizona as well as the reservations of the Fort Mojave, Colorado River Indian Tribes, Chemehuevi, Cocopah and Quechan nations are all at risk in the event of a major lower-basin flood. Three interstate highways and numerous oil and gas pipelines cross the river below Laughlin, Nevada.

David Orr is on the staff of Living Rivers [PO Box 466, Moab, Utah 84532, [phone] and PO Box 1589, Scottsdale, Arizona 85252, [phone], fax -2662, www.livingrivers.net].