Organ Pipe Cactus National Monument’s Ajo Mountain Scenic Drive Reopens After Flooding

Tuesday, October 09 2012 07:05   Scenic Drives
Ajo Mountain Drive at Organ Pipe Cactus National Monument in Arizona has reopened after being closed since Sept, 10, 2012 due to heavy monsoon flooding.

While the 21-mile scenic drive is open again, visitors are cautioned to watch for continuing maintenance work, including large trucks. As always, trailers, buses and RVs over 25 feet are not permitted.

organpipecactus_estescanyonsept11The storms arrived in mid-July bringing much needed rain. But as the monsoon season progressed, the Ajo Mountains experienced a number of typical storms. A few were on the rare side dumping significant amounts of water, moving rocks and debris through the washes in the National Monument.

Maintenance crews had just finished repairing Ajo Mountain Drive from the prior storm when the big storm hit in the evening on Sept. 10.

The rising water level in washes was high enough to close Highway 85 to all traffic. Rain came down in torrents as rain gages recorded the event. At 8 p.m. the gage at Alamo Canyon recorded 2.71 inches and Bull Pasture was almost as impressive at 2.1 inches.

By 10 p.m. over 3.5 inches had fallen at Alamo Canyon and almost 2.5 inches at Bull Pasture. The water had no time to seep into the ground and produced flooding in the washes and over the roads.

The average rainfall in September is less than one inch. Since Jan. 1, 2012 Alamo Canyon has received over 18 inches of rain and Bull Pasture over 17 inches of rain. Yearly rainfall average is 8.8 inches.

The enormous amount of debris came down Alamo Wash during the night with a significant amount of water and debris coming from the North Fork. The larger contribution to the flood may have been Tillotson Wash, which drains Arch and Boulder Canyons and the east-facing slopes of the Diablo Mountains.

That night, a portion of the flood flow turned south through the Diablo Mountains and crossed the highway at mile 66.5. During major flood events such as this, rubble can plug up the old channel and can force water to flow in new directions.

This aggradation happened at a number of points along the channel in Alamo Wash. The flooding created some new channels and deepened older ones.

Kuakatch Wash also changed its channel on Sept. 10, with 520 feet of the barbed wire fence on the east boundary removed by the flood and all riparian trees are gone. The channel is changing where it crosses the highway, but it is changing more elsewhere upstream and downstream.

Organ Pipe Cactus National Monument is located in southern Arizona, south of Ajo, west of Tucson, and east of Yuma. For more information, visit the park's Website at .


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