Grand Canyon Flood Kills 1 After 1.24 Inches Fall, Fueled by El Niño and Iselle

Q: With over 20 people unaccounted for, what hidden dangers are complicating the ongoing inner-canyon rescue efforts?

The rescue effort is being complicated less by the number of missing people than by a cascade of hidden hazards inside the canyon: unstable terrain, destroyed crossings, and dangerous debris in fast-changing water. Park officials say nearly all footbridges over Bright Angel Creek were wiped out, and the Black Bridge and Silver Bridge over the Colorado River were also washed out. That has cut off normal foot access, isolated sections of the inner canyon, and forced rescuers to rely heavily on helicopters rather than ground teams. The flood also swept a metal building and other debris into the Colorado River, prompting a shutdown of river traffic. That means rescuers cannot easily use the river as an alternate route, and debris in the water creates collision and entanglement risks for boats and anyone near the banks. Just as serious is the terrain itself. Officials warned that additional thunderstorms could trigger more flash flooding, debris flows and rockfall. In the Grand Canyon, even roughly 1 to 1.75 inches of rain can funnel rapidly through steep side canyons; in this event, river gauges rose as much as 9 feet. That makes conditions highly unstable even after the rain appears to stop, with trails turning impassable and runoff surging suddenly through narrow areas such as “the Box.” The result is a rescue environment where access routes are broken, water and debris remain hazardous, and weather could quickly worsen, slowing efforts to locate those still unaccounted for.

3 articles · Updated · The Washington Post · Aug 31

At least one person died after 1.24 inches of rain fell near the Grand Canyon in three hours Saturday, including 0.84 inches in a single hour.
Record-breaking El Niño, a Pacific marine heat wave and moisture from Tropical Storm Iselle’s remnants raised atmospheric moisture 5% to 15% above average, helping drive the extreme downpour.
Steep, rocky and drought-affected terrain limited absorption, sending runoff rapidly into canyons and creeks as thunderstorms squeezed out the moisture.
Flood watches remained in effect Monday from Arizona to Utah and western Colorado, with the National Weather Service warning of dangerous currents in creeks, washes and slot canyons.
Forecasters are also tracking another possible tropical system near California in about a week; even without a direct hit, its moisture could intensify rain across the Intermountain West.