Along Urban Waterways: Cities Try New Strategies for Clean Waters and Shaded Streets
by Lucero Radonic, Graduate Outreach Assistant and Susanna Eden, WRRC
In the City of Prescott, the Watson Woods Riparian Preserve, along Granite Creek, is an oasis for wildlife and humans surrounded by development. The city’s wastewater treatment plant and transfer station are located a block to the east, a lumber company and a concrete block manufacturer are located to the south, Highway 89 and some dense subdivisions are to the west. Over the last century, this riparian area has been a sand and gravel mine, a dumpsite, a 4-wheel playground, and a shooting range. In 1995, the City of Prescott established the Watson Woods Riparian Preserve and transferred its management to Prescott Creeks, a grassroots organization working to improve the health of the local Granite Creek Watershed. With the labor of community volunteers, Prescott Creeks realigned four sections of the degraded creek channel giving them a more natural course and revegetated the floodplain to restore riparian habitat and improve water quality. In an area where non-point source pollution is a serious water quality issue, these changes help slow stormwater runoff and filter E-coli bacteria and other contaminants.
In 2012, the Arizona Department of Environmental Quality (ADEQ) awarded the Prescott Creeks group funds to create green infrastructure demonstration sites across the city. Green infrastructure refers to constructed landscape features that rely on natural systems to provide services such as capturing, cleaning and infiltrating stormwater; creating wildlife habitat; and shading and cooling streets. Examples of green infrastructure include rainwater harvesting basins along restored streams and vegetated drainageways in parking lots and along streets. The funds granted by ADEQ to Prescott Creeks are being used to create microbasins–small depressions lined with rocks and native vegetation that catch stormwater. They allow pollutants to be absorbed and broken down through microbiological processes while creating green shaded pockets in the city.
In 2013 the Environmental Protection Agency (EPA) launched the Urban Waters Initiative to advance the restoration of urban waters and promote public access to urban waterways. The initiative supports community groups like Prescott Creeks working towards the restoration of urban waterways through improved stormwater management. Granite Creek restoration work was featured in the series of Urban Water Voices videos the agency has posted to highlight local efforts and strategies.
Other communities across Arizona have also begun to address the challenges presented by deteriorated urban waterways. One of the earliest examples of stream restoration at the heart of an urban metropolis is the Rio Salado Environmental Restoration Project, which restored a 5-mile section of the Salt River that runs through central Phoenix. With upstream dams and diversions, the riverbed was dry except after storm events. In 2001, Phoenix residents approved a $16 million bond issue to fund riverbed cleanup and habitat restoration.
The project converted the river from an industrial dumpsite into an oasis of native wetlands and riparian habitats. More than 1,000 tons of trash were removed from the area during cleanup. Then the City worked with the Flood Control District of Maricopa County and the U.S. Army Corps of Engineers to construct a low-flow channel, plant thousands of native trees, and create a 20–mile network of trails. In addition to five non-potable groundwater wells, the site is irrigated by 22 stormwater drains that discharge into it at multiple locations. Today, this oasis offers passive recreational and educational opportunities like bird walks, bike rides and interpretative hikes, while also providing stormwater management to reduce flood damage in the urbanized floodplain. In addition, 60 percent of the water delivered to the project is expected to infiltrate into the aquifer.
In Yuma, the wetlands and riparian areas along the lower Colorado River are experiencing a similar transformation aimed at habitat restoration and riverfront redevelopment. The Yuma East Wetlands is a 1400–acre restoration project supported by a public-private partnership between the City of Yuma, the Arizona Game and Fish Department, the Yuma Crossing National Heritage Area, the Quechan Tribe and private landowners. Over the 20th century, this area became disconnected from the Colorado River, dried up and turned into a landfill dominated by non-native vegetation like salt-cedars and tamarisks.
Starting in 2004, non-native vegetation was cleared and a backwater channel was excavated and reconnected to the Colorado River through water-control structures at the inlet and outlet of the new channel. Volunteers planted native vegetation, including 5,000 bare-pole willow and cottonwood cuttings, along 40 acres of the channel’s shoreline and wetlands. With the return of the water, the native cattail/bulrush habitat naturally rebounded, and during the breeding season the bird population doubled. The initial 350–acre area was restored with $2.5 million in funding from the Arizona Water Protection Fund to support wildlife habitat as well as year-round recreation and educational opportunities, complete with trails and picnic areas.
In Tucson, the city and county are also working to restore degraded riparian environments of the major regional drainage systems, according to recommendations made in the Sonoran Desert Conservation Plan (SDCP). The SDCP integrates natural resource protection and land use planning activities into one single plan for Pima County. One of their recommendations was to restore the Rillito River arguing that this would bring ecological and social benefits to the urban area. The Rillito is part of a network of intermittent and ephemeral streams that crisscross Tucson and serve as water drains during storms. Although the Rio Antigo stretch of the Rillito once supported a forest of mesquite, cottonwood and willow, by the turn of the 21st century, it was a dry, bank-stabilized wash that flowed only during storm events.
As part of the Rio Antiguo Restoration Project, approximately 36 acres of riparian habitat along the south bank of the Rillito River were restored. Some minor land recontouring was done, bank slopes were flattened and native vegetation planted. In some areas the cement lining the existing drainage channel was removed and more sinuous channels were shaped to slow water movement. Small earthen catchment basins and drainage channels enhanced passive water harvesting. Reclaimed water was used to supplement rainwater harvesting during the early phase to ensure the establishment of the vegetation.
Tucson is also addressing urban waterways restoration through promotion of green infrastructure practices that control stormwater pollution onsite before it reaches the city’s streams and washes. The city’s commercial water harvesting ordinance, adopted in 2008, requires commercial developments to meet 50 percent of their landscape water demand using harvested rainwater, prepare a water harvesting site plan and water budget, meter outdoor water use, and use irrigation controls that respond to site-specific soil moisture conditions. More recently, Tucson’s Green Street Policy requires that green infrastructure features, such as vegetated street-side basins, be integrated into all publicly funded roadway development and re-development projects. The policy also requires that projects provide 25 percent tree canopy and 25 percent shrub and grass cover.
The EPA is now encouraging municipalities and community groups to integrate green infrastructure features like those installed in Tucson and Prescott into their stormwater management practices. Originally developed and implemented in temperate states, green infrastructure is providing a growing number of communities across Arizona a strategy to convert stormwater runoff from an urban waste to a resource. The use of green infrastructure constitutes a major change from former techniques that straightened stream channels to improve their ability to convey urban runoff while armoring their banks to reduce erosion. These techniques often resulted in dry riverbeds with overturned shopping carts, piles of debris and overgrown invasive shrubs. Whereas single-purpose stormwater infrastructure directed urban stormwater away from the built environment, green infrastructure captures and treats rainwater where it falls and directs the resource to creating environmental, social, and economic benefits for urban communities.
As explained by the EPA, green infrastructure is a cost-effective tool for stormwater management, water conservation and flood mitigation. In the arid and semi-arid Southwest, it can also help alleviate the heat island effect by providing water for irrigating urban landscapes.
The fast growing cities of the Southwest experience the urban heat island effect as an issue of growing concern. The general measure of urban heat island effect is an increase in the overnight low temperature, meaning that urban desert nights do not cool down as they used to and they stay significantly warmer than surrounding non-urbanized areas. Land developments with vast expanses of concrete and asphalt absorb heat during the day and emit it during the night. For example, Tucson’s urban temperatures are approximately 5.5 degrees Fahrenheit warmer than they were last century, with more than 3.5 degrees of the warming occurring in the last 30 years. More notoriously, from 1948 to 2000 the average daily temperature in central Phoenix increased by approximately 5.5 degrees Fahrenheit and the nighttime minimum temperature by approximately 9 degrees Fahrenheit.
Green spaces help mitigate heat, but vegetation requires water. Green infrastructure features capture stormwater to irrigate shade trees and vegetative cover and can reduce or eliminate the need for supplemental water. In Tucson some neighborhoods are retrofitting their streets to divert stormwater to green infrastructure features. Guided by the Watershed Management Group, a local nonprofit organization, residents plant native vegetation and build bioretention basins to hold stormwater for onsite irrigation. Bioretention basins are simple landscaped depressions that slow and treat on-site stormwater runoff via a number of physical, chemical and biological processes. They capture, clean and infiltrate storm water from nearby roads and driveways reducing flooding along city streets while providing passive irrigation to native vegetation that provide much needed shade and green space.
Three out of four Arizonans now live in urban areas. Buildings and pavement dominate their landscape. Urban waterway management in the 21st century is working to restore and enhance a greener landscape, while maintaining public safety. Although not without challenges and controversy, projects like those undertaken in Prescott, Phoenix, Tucson, and Yuma point towards acknowledgement of the values of healthy urban stream ecosystems and roadside green spaces.