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  • Under the Dome: Balancing protecting nature with protecting lives and property

    Under the Dome
    By Chuck Huckelberry
    Pima County Administrator

    huckelberryOne of the primary responsibilities of County government is to protect the health and welfare of our citizens. In the late 1970s, after a series of devastating floods statewide claimed lives and destroyed property, the state required counties to create flood control districts to raise the funds needed for the mitigation of flood risk in populated areas.

    In the decades since, Pima County’s Regional Flood Control District has spent hundreds of millions of dollars building flood protection infrastructure throughout the county. The benefits of these assorted public works are incalculable. Thousands of homes and businesses worth hundreds of millions of dollars are now protected from flooding and their owners are no longer required to purchase costly flood insurance. The bank protection along the metropolitan rivers and washes has become a beloved and heavily used recreational amenity called The Loop. And large and occasionally historic storms have pounded the Tucson valley over the past 30 years with no widespread harm done to property or resulted in significant flooding.

    Having constructed this system of flood protection, it is essential we maintain it. A big part of that maintenance need is the removal of sediment that builds up over time in the rivers. Our summer and winter rainy seasons wash thousands of tons of sediment into the rivers and over several years this sediment raises the level of the riverbed in some places, reducing the carrying capacity of the channel.

    sediment Sometimes the sediment just needs to be spread out into low spots and doesn’t need to be removed. Other areas require the sediment to be hauled out of the river. We do this annually around the region. Recent sediment mitigation has been done in the Rillito River and Alamo Wash.

    This month, the county will begin reducing sediment buildup in the Santa Cruz between Speedway Boulevard and Grant Road. It’s the first of an intended three-phase project to reduce the sediment in the Santa Cruz between 29th Street and Grant. There are parts of that river near downtown where the sediment has made the river “bottom” eight feet or more higher than it was when the bank protection was built in 1970s. Where that section of the river once ably handled flows of 37,000 cubic feet per second of water before reaching the bottom of the Congress Street bridge, there is now a risk of water impacting the bridge with flows of only 13,000 cfs.

    Sediment is not the only thing that has grown in the rivers over the years. Our rivers also have trees, bushes and grasses. This vegetation provides food and homes to a variety of critters – snakes, lizards, rodents, birds and the occasional bobcat and coyote.

    Our community loves these urban riparian areas and the wildlife in them and the County is committed to doing all we can preserve or rehabilitate as much of the vegetation and wildlife as possible. Our Flood Control District is working with the city of Tucson and several community stakeholders to minimize the impact on the river’s residents and restore and rehabilitate these areas after we’ve reduced the sedimentation.

     But that preservation effort needs to be balanced with the need and requirement to protect lives and property.

     There’s also one more thing to consider, it’s not just sediment that washes into the rivers. There are tons of trash and scrap metal buried among the sediment. Our sediment maintenance also removes all that gunk, which makes the river healthier for everyone, including the wildlife.

     To learn more about the three-phase plan for the Santa Cruz, read this whitepaper prepared by the Regional Flood Control District.

    Photo Caption: Sediment buildup in the Santa Cruz near downtown. 

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