At 7:30 Sunday morning, April 21, 2013, people began to gather on a barren lot in downtown Phoenix, Arizona. The temperature was already climbing into the 80s and the lot’s bare dirt reflected both heat and light, making lingering uncomfortable. By 8:00 AM, more than 30 neighborhood volunteers, Youth Hostel guests, Green Living Co-op members, PDC and university students were on-site, eager to start the day’s activities. They were here to celebrate Earth Day by installing a green infrastructure retrofit project in the Garfield Historic District; an eclectic neighborhood that is part of the larger Arts District.
The event was hosted by Watershed Management Group, who designed the project and provided funding through a Community Challenge Grant from the Arizona State Forestry Division.
The project took place at two locations along 9th Street; a side street in the Arts District. The first location was in front of the aforementioned vacant lot on the NW corner of Roosevelt and 9th Street – a bleak corner that desperately needed some greening.
By contrast, the second location a few houses up the street in front of the Phoenix Hostel and Cultural Center, is surrounded by trees, shrubs and other plants making it cool and inviting.
In both locations, the idea was to use curb cores to convey storm water from the street into bioretention basins in the right-of-ways. The harvested water would be used by native vegetation that would filter pollutants while shading and beautifying the streetscape.
So what is “Green Infrastructure”?
Green infrastructure (GI) refers to constructed features that use living, natural systems to provide environmental services, such as capturing, cleaning and infiltrating stormwater; creating wildlife habitat; shading and cooling streets and buildings; and calming traffic. GI is a strategy that a growing number of communities are using to manage stormwater more sustainably, while using that water to grow vegetation that provides myriad benefits.” — Watershed Management Group
The Garfield Project Timeline
Six months before event: Watershed Management Group announces mini-grant opportunities for GI projects, solicits applicants and assesses the feasibility of proffered sites. Grant recipients are notified and begin the process of arranging for volunteers for the day of the installation.
Because this is a Community Challenge grant, the community must match the funding amount of the grant either with their own funds or with volunteered time. Most recipients use the volunteer match option.
Two months before event: Plans are drawn and submitted to the City of Phoenix for approval. During this process, the City informs Watershed Management Group that the more efficient curb cuts in the original design would not be permitted due to the fact that the high curbs in the Garfield neighborhood were historic and their profile could not be modified. However, curb cores were acceptable. Permits are acquired and the project timeline determined. Initial contacts with contractors are made.
Two weeks before event: Utilities are contacted to mark lines and pipes in the vicinity of the area to be dug (critical). Most states have one contact number to call that will coordinate all the utilities in your area. Materials are ordered and a delivery date set.
Oh no! Gas lines (yellow markings) and power lines (red markings) are discovered in the right-of-way, which will impact the coring of the curb. For the basins in front of the Hostel, the utilities were close enough to the curb to be able to core and not have to dig the retention basin too deep. The planned basins in front of the empty lot had utilities that came off the curb almost 4 feet. Because codes state you cannot dig any closer than 2 feet from a utility line, the uncertainty of how deep the lines ran, and the 6 feet that the water must travel to reach the basins, it was decided that the coring of these basins would not be advantageous.
Week of event: Materials are delivered. Mulch and rip rap (coarse, blocky rock) are placed near each project site. Plants are stored in the backyard of the Hostel until the day of the event. Traffic barricades are delivered and set up.
Two days before event: Basins are pre-dug by a backhoe, extra soil was removed (almost 2 dump truck’s worth) and the curb cores cut. Note that the cores are cut at an angle into the curb. The mouth of the core faces upstream, into the flow of water — in this case north — at a slight angle, allowing the water to flow more readily into the basin. If you cored straight on, the water would essentially have to make a 90° turn to flow into the basin. The core was also cut just slightly below grade which creates a tiny depression in front of the core and a tiny lip downstream which helps guide more water into the core hole.
Day of event: A signup sheet records volunteer hours for the grant. The neighborhood provides snacks and water for the event and Watershed Management Group provides tools and safety equipment as well as project oversight.
Step 1: Rip rap is separated into different sizes. Larger pieces will be used to support terraces within the basins. Flatter pieces will be used for spillways. Small, flat pieces will be used to make the lips of the sediment traps.
Step 2: Large rocks that will form the terrace walls are lined up along the edge of the basins, ready for use. Another oddity that was discovered when the site was marked for utilities was a large cement pipe that ran close to the sidewalk (you can see it at the back of the basins below). The pipe was not part of any modern utility and appears to be an artifact from when the Garfield neighborhood was first established in the 1930s.
Step 3: Let the terracing begin! Large rip rap forms the walls for a terrace within the basin which will be planted with smaller plants. The rocks also help reinforce the integrity of the structure of the basin itself. On the opposite side near the curb, a spillway is being installed with smaller, flat rocks. Rock work is time-consuming and must be done carefully. The bulk of the project is spent on constructing the terracing and spillways, tamping them to make sure they are solidly constructed.
Step 4: The height of the rocks that form the lip of the sediment catchment is carefully measured. The sediment trap will be cleaned out by the neighborhood from time to time as debris builds up behind this lip.
Looking good! The planting terraces and spillway with sediment lip are complete.
Step 5: Dig holes for larger plants like trees and shrubs. We were fortunate to have access to a jackshovel which made digging a deep hole in our heavily compacted clay soils a breeze. The guys all wanted to try this tool, and a line soon formed.
Step 6: James DeRoussel, WMG project manager explains the planting process. The plants are positioned in and around the bioretention basin, ready for planting. For a complete list of the native and desert adapted plants used, click here.
Step 7: Because this project is being installed during the hot, dry months before our summer monsoon rains, extra precautions were taken to ensure plant establishment. A product called DriWater, a time-release water in gel form, is added to each planting hole. Larger trees got 3-4 full containers while smaller plants got half a container. The containers are installed at an angle with the tops just breaking the surface of the planting basin so that they will be easy to remove and replace if rains are late.
Step 8: The test run! This is the moment everyone’s been waiting for! A hose is brought out and the gutter flooded to imitate stormwater runoff. You can see the eddies as the water enters the slight depression to the core and comes up against the tiny ridge. Inside the basin, the water seeps in and sediment is captured.
Step 9: Mulch the basins and plants and water thoroughly. Celebrate a job well done!
Step 10: Ongoing maintenance is provided by neighborhood residents. Maintenance tasks include: watering the basins until the plants are established, cleaning out the sediment trap and maintaining the vegetation.