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  • Santa Cruz River 'in good shape' following record monsoon

    Oct 08, 2021 | Read More News
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     Santa Cruz 1
    After a record monsoon, Pima County staff members and other waterway experts
    deemed that the Santa Cruz River's infrastructure emerged relatively unscathed.
    Summer storms made this year's monsoon one of the wettest on record, with 13 inches of rain — and counting — and, at times, bank-to-bank flows of all the major rivers and washes. 

    After numerous flood events coursed through area waterways, Pima County Regional Flood Control and County staff decided to inspect some areas that saw the heaviest flows. They assessed the conditions of the Cañada del Oro Wash and the Rillito and Santa Cruz rivers; any damage that may have occurred to flood systems; and revisited possible long-term management strategies.

    Joining Flood Control Engineer Evan Canfield on a recent walking tour of three sections of the Santa Cruz River was a representative from the U.S. Fish and Wildlife Service and County contractors from Kimley-Horne and NV5. 

    “The Flood Control District infrastructure has remained in good shape,” said Canfield. 

    The section of the river that County staff and others set out to inspect runs roughly from Silverbell Lake at Christopher Columbus Park north to almost Ina Road. This area includes a section of river known as El Corázon, which has been the site of current and proposed recreation, flood control and environmental restoration projects. The city of Tucson
     santa cruz 2
    This clock was one of the smaller items that was washed down the Santa Cruz River
    by floodwaters. Everything imaginable — from pallets to shopping carts — gets swept
    away by the summer storms.
    and the town of Marana are cooperating with the county in the efforts.

    Canfield said the recent flood events left expected signs of flood scour and sediment deposits in the Santa Cruz, but the overall condition of the river channel and flood structures were good. Even with the countless pallets, shopping carts and other debris swept away in storm runoff that litter the river, flood control infrastructure, such as soil cement embankments, appeared to be in good condition. 

    Trips down the river like the one Canfield and others took in September also can help inform later decisions on where such habitat restoration projects would be most effective. Part of the long-term plan for areas of the Santa Cruz that Canfield and others walked involves habitat restoration for native plants and animal species. 

    Restoration strategies could include removing non-native plants and trees, such as tamarisk trees where feasible, and replacing them with native trees such as desert willow. Such actions would be done strategically and after more study, Canfield said, to ensure the bird and insect species that have adapted to non-native vegetation would not be displaced. 

    Construction of ephemeral pond structures that would fill with rain and stormflows and slowly dry up also could be constructed. While the ponds and smaller pools persist, native species, such as Gila topminnow, can proliferate. 

    Doug Duncan, a fish biologist with the U.S. Fish and Wildlife Service, joined the trek to make an initial assessment of native fish species in the river.
    Many fish were swimming in the shallows of the stream and small pools. When Duncan dropped his net into the water, however, he only pulled out mosquito fish, a non-native species that has proliferated in the Santa Cruz and is the main competition for small native fish like Gila topminnow.

    The topminnow made an appearance in the Tucson areas of the Santa Cruz for the first time in decades beginning in 2017. Their presence has increased since then, and by 2020 the fish was found in two locations downstream of the Agua Nueva Wastewater Reclamation Facility, and last year was also found downstream of the Tres Rios WRF.
    Duncan said the monsoon flooding the region experienced this year will likely result in a reduction of all fish populations in the Santa Cruz. But that was expected given the volume of rain and the nature of flooding that occurs here.

    “I’m slightly concerned, but we have seen topminnow in the Heritage reach,” Duncan said, referring to the downtown sections of the Santa Cruz.

    Duncan also noted that in studies and in field observations, Gila topminnow have shown a resilience to the type of flooding that occurs in the Santa Cruz. Gila topminnow, Duncan explained, are adapted to rapid rises in waterflows brought on by monsoon storms.
    More comprehensive counts, which are planned for later this year, will need to be done to determine the status of topminnow in the river.

    While the purpose of the day’s excursion was not to make final decisions on future river maintenance work, the exercise was productive and gave county staff and partners a better idea of what long-term plans could help to restore as much native, natural habitat to the area as feasible. 

    “We have a great opportunity,” Canfield said. “We hope to improve the habitat and reduce the need for long-term maintenance.”