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• Volunteerism is a Two-Way Street

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• Developing a Collaborative Stormwater Management Program

The city of Prescott, AZ, had a big and growing problem: a stormwater detention basin designed on the fly in 2000 was already failing, resulting in severe erosion, siltation, and roadway contaminants in the adjacent Watson Woods Riparian Preserve and Granite Creek. Though required by the Clean Water Act to address the threat to Granite Creek, which flows through the preserve, the city felt it lacked the expertise to tackle the project alone and knew that finding funds for it would involve some very real budget pain.

The solution was an innovative partnership under the leadership of Prescott Creeks, a local nonprofit watershed group, which brought together a range of private, public, and nonprofit players to finish the task—a job none of them could have taken on individually. Prescott Creeks provided project management, wrote grants, and organized tens of thousands of dollars worth of volunteer labor and donated or discounted materials. The city of Prescott provided labor and equipment, as well as vital support at all stages of planning and construction. The Arizona Department of Environmental Quality (ADEQ) was the primary funder, through a 319(h) Water Quality Improvement Grant provided by the USEPA.

Remove any of these pieces, and the project would never have gotten off the ground. But the completed construction demonstrates how an unusual approach to an engineering challenge can succeed where others never even leave the drawing board. This approach should be applicable in other parts of the country where municipalities find themselves stuck between the rock of water-quality requirements and the hard place of strained budgets.

A Broken Basin
Northeast of downtown Prescott, stormwater runoff from the Prescott Lakes Parkway flows from the southeast into a basin adjacent to the Watson Woods Riparian Preserve. When the parkway was originally designed, there was no plan for the stormwater runoff from the new roadway or from the steep, 473-acre watershed it passed through. All of the runoff from this watershed passes through a five-barrel concrete box culvert under the roadway, with an estimated capacity of 1,250 cubic feet per second (cfs).

Near the end of the project, and without much in the way of formal engineering, a basin was designed and constructed to deal with the discharge from the box culvert. The stormwater entered a detention basin with a capacity to store up to 2 acre-feet of water before discharging it through six 24-inch culverts. These culverts had the capacity to discharge approximately 150 cfs (not quite a five-year flood event) when the basin was full.

This original basin was designed only to carry runoff from the Prescott Lakes Parkway and the valley it traverses, and contain it in a rectangular depression that used a major hiking trail as the end stop. It was not designed to control runoff and its associated contaminants before they enter the Watson Woods Riparian Preserve or the waters of Granite Creek and Watson Lake, both of which have been listed as impaired on the state’s 303(d) list.

City of Prescott construction crew foremen

In addition, larger flows caused the basin to fill and could only exit the basin by overtopping a historic railroad grade that served as a berm. This unconsolidated material was highly erosive, and damage to the berm was extensive. Not only was this erosion undercutting the containment of the basin, as well as the nationally recognized Peavine Trail, an extremely popular and scenic recreational rail trail that sees more than 12,000 users a month, but stormwater was also carrying sediment and contaminants into Granite Creek and further downstream to Watson Lake. Beyond the potential damage to the railroad grade berm, the gullies were located in an isolated stand of mature cottonwoods and were threatening to undermine these trees. Left unchecked, the erosion eventually would have continued upstream to the top of the basin and undermined the intersection of the Prescott Lakes Parkway and Sundog Road.

Adding to the challenge, the watershed in question is largely undeveloped but is likely to see substantial construction in the near future. Modeling for the basin redesign indicated that flows of 480 cfs through the basin are currently considered 50-year events, but such flows will become 10-year events with expected future development and increases in impervious surfaces within the immediate watershed.

Basin Design
The finished product (redesigned and vegetated basin, and repaired outflow channels) is meant to capture, slow, and control stormwater flow through the Watson Woods Riparian Preserve and into the adjacent waters. Because the runoff from this area flows directly into Granite Creek, slowing and filtering contaminants before the water reaches the creek is especially important. Prescott Creeks worked with the city of Prescott and Natural Channel Design Inc. to design a new basin that would appropriately handle the flows. The work in preparation for the design included evaluating the watershed and the existing culvert/weir-system contributing flows to the area. In determining the hydrology of the site, Natural Channel Design Inc. used three methods to estimate the hydrology of the drainage as it feeds onto the project site: the Regional Analysis, National Flood Frequency (NFF), and EFM2 programs.

Prescott Creeks considered three alternatives to safely pass the 25-year design flow (425 cfs), while allowing for the passage of higher flows with minimal maintenance. Three possible routes existed for discharging flood waters out of the basin: 1) straight through the existing berm, 2) over the top of the berm and down through the entrance kiosk area of the Watson Woods Riparian Preserve, and 3) down along the existing channel running parallel to the Peavine Trail, passing under the trail at a historic railroad trestle.

Prescott Creeks rejected the second alternative, as it would have directed stormwater through the main entrance and information kiosk area of the Watson Woods Riparian Preserve, cutting across a steep slope of unconsolidated soils.

The final design combined alternatives one and three. Because the intakes for these culverts are 12 inches over the grade of the catchment, most storms will pool in the basin and filter into the local water table, an important consideration in arid Arizona. Large storms will discharge through four 42-inch-diameter corrugated steel culverts designed to reduce the energy of stormwater flows over the 16-foot drop in elevation from the basin to the Granite Creek floodplain. Very large storms (more than 480 cfs) will exit the basin through an overflow channel that diverts the water along the Peavine Trail. Passage under the trail at a historic railroad trestle has been contoured and strengthened to avoid damage to the trail.

Building Bridges
While the need to rebuild the basin became more evident with every heavy winter storm and summer monsoon, the city did not have the direct expertise to tackle the redesign. Furthermore, finding the money for the project was not an enticing prospect for a city government facing a host of other pressing needs. The solution to these obstacles was to build a partnership that brought to bear the strengths of a variety of public, private, and nonprofit players under the leadership of a nonprofit watershed group, Prescott Creeks.

Prescott Creeks and the city have forged a strong partnership over the years, so both felt comfortable entering into this project. Most notably, the city contracted with Prescott Creeks to act as preserve manager when it created the 126-acre Watson Woods Riparian Preserve in 1995, signing a 25-year, renewable lease with the nonprofit on the property.

Both worked closely together on the design of the Prescott Lakes Parkway where it crossed Granite Creek and the preserve. At Prescott Creeks’ urging, the city did not use its original design for a bridge across Granite Creek, a 125-foot span that would have severely restricted the creek and wildlife that use the riparian corridor. Instead, the city agreed to a 625-foot span that gave the creek full access to its natural floodplain, and put Prescott Creeks in charge of managing construction where the parkway crossed the preserve.

“The city didn’t have the expertise for this basin rebuild in-house, and would have had to bring in consultants,” notes Prescott Mayor Jack Wilson. “Having access to Prescott Creeks and leveraging their expertise has been a unique and efficient way to get this done.”

Even more important than technical experience, Prescott Creeks was able to find key funding for the project, while also furnishing hundreds of hours of volunteer labor and sourcing reduced-cost materials to make the finances for the basin come together. The basin rebuild was funded by a grant from the ADEQ, which furnished more than $109,000 for the basin reconstruction from a 319(h) Water Quality Improvement Grant provided by the USEPA. Because the proposal was outside the normal range of projects for these grants, it was crucial for the ADEQ grant review staff to look at the program in creative ways, while making sure that the final result met federal and state standards. The result of this close cooperation was a project that can be mirrored elsewhere in the state and outside Arizona.

“This project was a statewide model for how 319 funds should be used,” says Steve Owens, director of ADEQ. “It will help to abate silt flowing into Granite Creek and Watson Lake, and it will also improve the impaired water quality of both.”

Volunteers and Vegetation
Financially, the basin rebuild still would not have added up without a substantial input of donated labor and donated or reduced-cost construction materials. Much of that volunteer time focused on revegetation of the site following construction, beginning with the harvesting and storage of native cottonwood poles and cuttings from trees to be removed during construction.

Cottonwoods (here Populus frémontii, P. augustifolia, and P. ×hinckleyana) have several unique characteristics that lend themselves well to this sort of revegetation work. Most important, planting stock can be harvested from trees onsite, which means it is already well-adapted to the area where it will be replanted. Cottonwoods, like aspen, also reproduce clonally, which means that plantings will spread and fill in the site over time, reducing erosion.

Harvesting relatively straight poles of 8 feet or longer can be done without significant harm to mature trees during dormant seasons, or even for a short time from still-viable trees that have been removed during construction, as occurred on this site. Soaked upright in water for approximately two weeks to induce rooting, the poles are then planted with their cut ends in a hole or trench that reaches to the local water table—cottonwoods are “riparian obligate” species that cannot thrive without rooting in water—and pruned of all but two or three budding branches so that most of the plant’s energy goes to root development. This technique has been used successfully elsewhere in Watson Woods.

Stored in water in a large dumpster onsite while the machinery was pushing dirt, the cuttings were planted in late March 2008 by a team of volunteers. Because the water table is generally deeper than these poles could reach, drip irrigation of the plantings will continue for at least two years while they become established; the irrigation system was also installed by volunteers. Along with the planting of native grass seed timed to occur before the summer monsoons, these cottonwood plantings will propagate trees that were not only much less expensive than nursery stock but are already well-acclimated to that specific site.

Donated materials by local suppliers were also important, including the donation and installation of Filtrexx Filtersoxx by Windswept Organix of Phoenix during the construction phase. Arizona Pipe and Culvert also was helpful as a supplier, understanding quickly that a tiny, nonprofit watershed group would need more customer care and explanation than its normal clients—typically large construction companies or municipalities.

Watson Woods
Prescott Creeks’ primary interest in the project is protection of the Watson Woods Riparian Preserve directly downstream of the detention basin. Although significantly degraded, this riparian ecosystem represents the best remaining riparian habitat along Granite Creek. Mayor Wilson calls the preserve a “jewel” and notes that the city’s projected growth means that Watson Woods will soon be a natural area largely surrounded by development.

“Watson Woods is a unique feature in the city, and a lot of people don’t even know it’s there,” says Wilson. “Our number one priority in this project was the protection of Watson Lake, which was a major purchase for the city back in 1998.”

The 126-acre preserve is the remaining portion of what was once a 1,000-acre riparian gallery forest near Prescott. Following trends around the Southwest, the riparian habitat at Watson Woods has been lost or severely degraded due to human activities and general neglect. Its watershed has been subjected to urbanization, channelization, stock grazing, water diversions, and pollution (from nonpoint-source pollution and two EPA Superfund sites). Within its borders, illegal dumping, sand and gravel mining, hunting, woodcutting, and four-wheel-drive road “carving” have occurred.

Rapid growth in the Prescott region, and on the neighboring slopes, continues to put pressures on the health and function of the Granite Creek floodplain within the Watson Woods Riparian Preserve. The growing population of the area also means that the preserve and adjacent lake are becoming increasingly precious as close-in open space and natural recreation.

To protect this incredible community asset, Prescott Creeks established Watson Woods Riparian Preserve in 1995 to protect and restore the cottonwood/willow riparian gallery forest found there. A 25-year renewable lease with the city of Prescott (owner of the property) ensures long-term protection and authorizes Prescott Creeks to manage Watson Woods as a nature preserve.

“Watson Woods demonstrates that if you really want to protect a riparian area, you’ve got to keep looking upstream,” says Michael Byrd, executive director of Prescott Creeks and preserve manager. “Our long-term restoration plans for Granite Creek and Watson Lake would have a gaping and possibly fatal hole if we hadn’t first addressed this failing basin.”

Prescott Creeks will be managing a larger restoration of the preserve starting in the fall of 2008. The project will substantially restore hydrologic function and proper stream geomorphology, improve floodplain function, and (re)create wetland/backwater areas associated with Granite Creek. Byrd says that providing community members with direct, meaningful interactions with the land will foster a sense of stewardship and will help individuals understand why this and other restored riparian ecosystems and their dependent wildlife are important.

Lessons Learned
During this first major engineering project that Prescott Creeks has undertaken, a number of important lessons emerged through the process of planning, constructing, and revegetating this stormwater basin.

Build Right the First Time. The clearest lesson of this project is that it would have been simpler and far less costly to have planned for the expected flows from the parkway during the engineering phase of the road itself. By dealing with the runoff from the highway and the changed runoff patterns and volume from the entire watershed as an afterthought, Prescott added to the already serious burden it faced in dealing with stormwater pollution in the watershed. By choosing an inadequate solution in 2000, the city found itself facing additional expenses in very short orders and added to the pollutant burden in the impaired waters of Granite Creek and Watson Lake.

Think Outside the Box. This project could not have happened without a willingness on the part of ADEQ and the city of Prescott to approach the problem in a decidedly nontraditional way. Grant review staff at ADEQ did an excellent job of finding a new and innovative approach to completing this job, matching the clear water-quality gains to be derived from the project with sources of funding and technical support. Instead of hiring outside consultants to manage the project, the city of Prescott was willing to entrust management duties to a small, local watershed group that had tremendous knowledge of the riparian area most threatened by the failing basin and connections to other groups and firms that could lend technical and engineering expertise.

Unusual Partnerships Help With Unfunded Mandates. Local governments across the country face federal requirements to design and implement stormwater management plans with no clear source of funding for compliance. As a small city subject to the National Pollutant Discharge Elimination System (NPDES) Phase II program, Prescott has very limited resources to deal with some substantial stormwater issues. Its partnership with Prescott Creeks not only brought in needed expertise, but also enabled the city to tap into sources of funding that might not otherwise have been available in order to supplement its own share. While the city’s contribution of labor, equipment, and materials to the project was substantial and essential, construction would have been highly unlikely without additional funding.

Always Build in a Public Outreach Component. Because the basin is located next to a heavily used recreational rail-trail, there was a tremendous amount of public interest at all phases of construction. The project offered an unparalleled opportunity to educate the community about this basin in particular and issues regarding stormwater in general through local media, public presentations, volunteer education, and onsite signage.

Volunteers Are a Tremendous Budget Multiplier. Do not underestimate the level of interest local people have in getting directly involved with a major stormwater project like this one (see sidebar). From site preparation, inventory, site cleanup, and monitoring to revegetation and irrigation, volunteer labor was essential to the success of this endeavor. That involvement will pay dividends for years to come; not only did volunteer labor allow every budget dollar in the project to stretch further, it also helped Prescott Creeks educate a cadre of dedicated volunteers in skills that will be essential to the larger restoration of Watson Woods later this year. However, it is important to budget for volunteers; they cannot be regarded as simply “free labor.” A successful volunteer program requires money for recruitment, management, and stewardship; throwing in a free lunch and a T-shirt can’t hurt.

Conclusion
Cities all across the country are facing up to the responsibilities of managing stormwater, meeting federal requirements, and simply treating their rivers and creeks as tremendous community assets. But doing these projects well is often beyond the budgets or in-house expertise that these local governments can access. By looking outside of government, and particularly by sharing some of that responsibility with a local nonprofit organization that has access to knowledge and resources that the city might not, cities might find a new tool to deal with some of their thorniest stormwater problems.