Rivers and washes stay dry most of the year in the Sonoran Desert, but when monsoon hits, we get to see them in action.

The Chuck Huckelberry Loop stretches more than 130 miles along the Tucson areas major watercourses, including those washes and rivers. Its one of the most-frequented paths for walking and biking, but it also serves a greater purpose.

In 1983, the Tucson area saw one of its most severe floods in history. It caused damages of over $100 million according to Camille Hall with Pima County Flood Control District. The county decided to invest in preventing severe flooding, which paid off several years later.

History of monsoon in Tucson: Santa Cruz River record flood of 1983 History of monsoon in Tucson: Santa Cruz River record flood of 1983

We saw another flood event in 1993, where we saw record volumes of flow going through the washes, but we only saw $17 million in property damage, which is still a huge amount. But of course, going from $100 million in damages to $17 million is great. It’s our job to continue to reduce those damages year after year, explained Hall.

She went on to describe the environment of the Sonoran Desert that causes major flooding. In areas with a lot of vegetation, that type of flooding is mitigated through the area’s natural environment.

We are a very desertous, sandy state compared to some place maybe in the Midwest or the Northeast where you have a lot of that dense vegetation. Thats holding a lot of that soil in place. So when the rains come, it seeps into that ground and is soaked up by those plants. In the desert, we dont have a bunch of that, so theres a lot more runoff, she said.

The washes in the Tucson area play a huge role in flood mitigation, but in more ways than serving as a place for water to fill. The structures are engineered through bank protection to keep water flowing, and not flooding.

So something youll see on the side of the bank is the soil cement structures. We build those structures as a wall to limit the erosion of the banks. Washes naturally meander, theyll move, theyll erode, but that bank protection is built to keep those washes in place, said Hall.

The washes are monitored by Pima County Flood Control to prevent overgrowth of trees, plants, and other vegetation. This manages how quickly a wash or river will fill. Its like filling two cups with the same amount of water, but one has a rock in it. The one with the rock will overflow.

So part of what we do is remove the excess sediment and vegetation to keep the channels at their maximum capacity, she said. But when we do this, its really important that we do this and get surveys of the local animals. Making sure that we are moving lizards, doing nest surveys, so were disturbing as little of the natural environment as possible.

This is monitored through LIDAR (Light Detection and Ranging), which is a special type of technology that measures the topography of areas. This gives Pima County Flood Control District an idea of whats needed to prevent flooding when monsoon rolls around.

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