Arizona Officials: Improved Flood Alert System Could Help Tribe

Recent flooding on an American Indian reservation in the Grand Canyon has renewed talks of an alert system in Arizona that could help tourists and residents evacuate more quickly during floods.

Without many river or rain gauges upstream from the village of Supai, forecasters can have a tough time determining when flood waters might reach the remote community — home to the Havasupai Tribe and an area popular with hikers because of the towering blue-green waterfalls nearby.

Forecasters rely on a radar system to estimate the rainfall, but Supai is well to the northwest of the radar, and while the estimates are good at times “they’re not perfect,” said George Howard, warning coordination meteorologist for the National Weather Service in Flagstaff, Arizona.

“The idea is, let’s take some of the uncertainty out of this with the prospect of locating a gauge in a strategic position so we can time things more precisely,” Howard said.

Thunderstorms late last month sent a rush of water down Havasu Creek and led to the evacuation of hundreds of people who had to be airlifted from the canyon. Some trails and footbridges were washed out and trees uprooted. Authorities said Supai appeared to have sustained only minor damage from the storms.

It was flooding in the early 90s that first prompted talks of an alert system that would allow the National Weather Service to access real-time data from stream and rain gauges to plot estimates of stream flows. Based on that information, the weather bureau could issue a flood warning and better determine when the village might be affected.

The canyon is accessibly only by foot, helicopter or mule, making it crucial to have as much of a heads-up as possible when floods are approaching so that people can seek higher ground.

Former Bureau of Indian Affairs superintendent Bob McNichols said a system had been designed in response to floods on the reservation in the early 1990s, but it never was installed. “I don’t know exactly why it wasn’t,” he said. “There is a real need for it.”

Havasupai officials have declined to comment, saying they are focused on recovery.

Heavy runoff in 1993 caused the collapse of several livestock tanks and small earthen dams in Cataract Canyon — which changes name downstream to Havasu Canyon. The riparian vegetation that survived a flood the year before was damaged again in an area downstream from Mooney Falls — one of several waterfalls that cascade into blue-green waters.

Only a few young trees and grasses remained adjacent to the creek following the 1993 flood, according to a report by the USGS on historical flooding in Havasu Creek.

Cassandra Anderson, Arizona flood warning coordinator, said the state has plans to reach out to tribes to help link them to a statewide flood warning network, but she wasn’t sure of the timeframe.

The statewide network was set up in 2001 in response to heavy rain in 1993 that caused extensive flooding and millions of dollars in damage around Arizona. The state, working with the U.S. Army Corps of Engineers, increased the number of precipitation gauges, improved real-time data from established gauges and set up a communication network with base stations to better inform people of potential flooding.

The system is more efficient than pre-1993, but Anderson said “there is still room for improvement.”

A rainfall station at Supai was discontinued in 1987, and the nearest river gauges are downstream from the village and upstream at the head of Cataract Creek — about 35 miles upstream from Supai. The weather service said it was able to get only one reading from the downstream gauge during the latest flooding before it stopped working.

“Certainly having a gauge upstream from that town would add value to forecasting the flows through that canyon,” said Mark Stubblefield, a meteorologist with the National Weather Service in Flagstaff.

During the flooding that began Aug. 16, the radar had estimated up to three inches of rain, prompting flash flood warnings that afternoon, Howard said. The weather service notified the tribe and law enforcement agencies of a potential flood, and most tourists were able to get to Supai before catching a helicopter ride to the rim.

“It took the flood waters many, many hours to get downstream and have an effect on Supai,” Howard said. “We were fortunate in this case because it did take a long time.”