Middle Blue River Basin Green Solutions Pilot Project

Challenge

In the Middle Blue River watershed, capacity of the existing combined sewer system was regularly exceeded, leading to overflows discharged to the Blue River. The neighborhood-scale green infrastructure initiative was conceived to address this issue. The main design requirement was to use green infrastructure such as rain gardens, bioretention, and pervious pavement in street right-of-ways to intercept stormwater, and reduce the volume entering the combined sewer system. Being limited to the right-of-ways made the design particularly difficult due to the constraints of right-of-way width, slope, soils, utilities, obstructions, and impacts caused by being directly in front of homes and businesses. While residents of the Marlborough Neighborhood were concerned about localized flooding, they also expressed concerns about deficient sidewalks, street surfacing, and speeding vehicles. 

Solution

The green infrastructure feature locations were selected based on predicted runoff volume upstream of the inlet, slope, available right-of-way area, proximity to sewer line or curb inlet, and neighborhood input regarding aesthetics. To capture the most water in the narrow right-of-ways and limit disturbance to the smallest footprint possible, underground pipe storage and storage vaults were used in some locations. Emphasis was placed on designing features that were relatively simple to access and maintain. Kansas City Water Services and other city leaders made the decision to include curbs and sidewalks, street repair, and traffic-calming elements in the project to help address resident requests. These additional elements included standard sidewalk and street improvements, but they also incorporated permeable sidewalk segments, traffic-calming curb extension rain gardens, and traditional landscaping, including tree replacement, to enhance stormwater capture.

• A total of 135 vegetated stormwater best management practices (BMPs) were added throughout the pilot project neighborhood, including rain gardens, curb extension rain gardens, cascade rain gardens, bioretention rain gardens, and, in strategic locations, subsurface water storage systems that are designed to store and infiltrate more than 360,000 gallons of stormwater.
• More than 5,000 sf of permeable pavers and 22,220 sf of porous sidewalk were installed in sections of sidewalk in need of repair. In strategic locations, both types were underlain with either underground water storage pipes or cubes, depending on utility and space conditions.
• 67 standard rain gardens receive overland flow and redirected curb flow to promote water percolation through a mix of topsoil and compost covered with mulch. Predominantly native prairie vegetation lines the bottom of the depression, and native or exotic vegetation is planted along the sides. Rain gardens receiving the largest volumes of water within the project were built with 2-in-diameter underdrains that return excess water back to the street.
• 28 curb extension rain gardens, typically located mid-block or at street intersections, capture runoff and calm traffic in the residential neighborhood. Extended curb locations are marked with reflective bollards. Approximately 71% of the curb extension rain gardens also include underground water storage consisting of 36-in diameter pipes. 
• 2 cascade rain gardens are located along steeper streets (approximately 8% slope) to slow stormwater runoff. These rain gardens are divided into a series of stepped, connected depressions in which pooled water levels are controlled by removable overflow weirs. The highest depressions are bioretention gardens with underdrains, and the lowest depression is a rain garden that releases excess water back to the street. Small pipes poured into the base of the retaining walls ensure that there is no permanent standing water.
• 36 bioretention rain gardens are located throughout the neighborhood. This BMP type is similar to rain gardens for biofiltration, but contains engineered soils (a mix of topsoil, compost, and at least 50% sand) and underground water storage pipes. Excess water is discharged to curb inlets or outlet control structures.
• Stormwater runoff is pretreated through turf grass filter strips and curb-cut forebays that trap sediment.
• As part of this project, a large number of native and introduced plants were installed, including 134 trees, 2,201 shrubs, 6,360 forbs, and 7,290 grasses, sedges, and rushes. The plant species that have proven the most adaptable are palm sedge, blue flag iris, and Morton black chokeberry.
• 6 educational and interpretive signs educate visitors and residents about the sustainable aspects of the project. 
• As part of the pilot project, 5,400 ft of ADA-accessible sidewalks were added or replaced. 
• To ensure maintenance of landscape aesthetics and keep the BMPs performing as intended, an Operations and Maintenance Manual was prepared. It was conceived as a tool for landscape workers as they may be unfamiliar with maintaining various kinds of rain gardens and identifying issues such as plant/weed growth, failure of underdrain systems, soil erosion, and infiltration issues.

A significant financial challenge of the pilot project was dealing with deteriorating infrastructure in an economically disadvantaged neighborhood. Many streets had no curbs and sidewalks, and existing sidewalks were in poor condition. The design required installation of curbs and resurfaced streets to properly direct runoff into the streetside rain gardens and subsurface water storage system. Residents viewed this project as an opportunity for the city to reinvest in their neighborhood and improve its image and quality of life. 

Kansas City Water Services moved forward with the pilot project by balancing the needs of the Overflow Control Program (OCP), building and maintaining goodwill with neighborhood residents, and deciding that it would be more cost effective to remedy deferred curb, street, sidewalk, and sewer maintenance during OCP construction activities. While direct costs might have been higher, offsetting indirect benefits such as elevated housing values, inducing private property improvements, and stabilizing neighborhoods need to be studied and documented. The city continues to consider other green infrastructure options situated, for example, those situated in locations other than directly in front of residences where they could achieve better economies of scale. 

The total constructed cost of the 100-acre pilot project was $10.41 million, and the “green infrastructure” portion cost $6.02 million for 360,320 gallons of storage equating to $16.71 per stored gallon. A 3-million-gallon storage tank alternative first proposed in 2008 was used for comparison, which included storage tanks, screening facilities, and an outflow pumping station at a total cost of $50.6 million, a constructed storage cost of $16.87 per gallon. The cost difference between the approaches is less than 1%.

Total green infrastructure costs were around $6.02 million, but the extra street improvements and sewer rehabilitation increased the total project cost to $10.41 million. The project is sized for a Design Storm D (1.4-in) event with a peak intensity of 0.6 in per hour and duration of 16.75 hours, and the constructed storage volume within the pilot project area is 360,320 gallons. This equates to $16.72 per gallon relative to green infrastructure costs, or $28.92 per gallon relative to total project costs. Ongoing maintenance costs must also be taken into account, the challenge being equitably evaluating green infrastructure costs relative to deferred infrastructure maintenance needs which elevate overall costs.

• Pretreatment devices have been one of the most enduring challenges of this project. Some of the forebays and curb inlets with sumps for sediment ended up ponding water for longer than 48 hours. Holes on the sides of the sumps were not sufficient to drain water from the sumps. Concrete forebays with impervious sumps also held water for too long, causing odor and the risk of creating mosquito breeding areas. More holes were drilled in bottom of the concrete forebays in the rain gardens, but in retrospect, it would have been better to ensure that the pretreatment devices properly drained within the targeted timeframe before acceptance of the project.
• For the pilot project, the 5-ft radius used for the curb extensions was too small and the street sweeper could not reach the entire curb line. Future curb extensions will use a minimum inner radius of 10 ft.
• The reflective bollards were relatively effective in marking curb extensions, with only a few bollard strike instances. The bollards warn cars to slow down and warn snowplows of curb extension locations, but since they have a significant impact on the look of the project, more resident input regarding the markers will be sought in future implementations. Over time, it should be expected that the curb markers will be hit by cars and they will need to be repaired or replaced. Off-the-shelf products are recommended for ease of replacement and potential for lower replacement cost.
• The rain garden plants grew more quickly than expected. It is recommended that 2 pruning and trimming visits (rather than 1) be specified to provide the opportunity to reduce plant sizes in rainy years. Pruning and trimming larger plants in early summer can help achieve a more compact appearance and is generally not harmful to plants. This would help prevent complaints that plants are too big and blocking visibility later in the summer. It is especially important to keep plants under 18 in to preserve visibility at intersections.
• Since the pilot project involved an entire neighborhood and inconvenienced many residents during construction, public outreach was an important component. The extensive public outreach campaign included pancake breakfasts, flyers, door hangers, regularly scheduled neighborhood meetings, and coordination through block captains. While the initial outreach was appreciated, residents felt they could have been better informed if the formal outreach efforts had continued through the construction phase and beyond. Since the neighborhood is interspersed with rental homes and has frequent newcomers, it would also be good to periodically reintroduce the project through a mailed flyer which could include a direct phone number for questions.

Native and Ornamental Plants: Bohn’s Nursery; Taylor Creek Nursery
Trees: Stonegait Farm & Nursery
Planting Soil Mix: Missouri Organic Recycling
Custom Steel Bollards with Drop Cutouts/Reflectors: URS/Taliaferro & Brown (designers); Zahner (fabricator)
Water Inlet Grates: Zahner (fabricator)
Water Inlet Filters: Inlet & Pipe Protection, FleXstorm
Water Storage Cubes: Atlantis Corporation
Biofiltration Underdrain: Smart Drain L.L.C., Smart Drain
Pervious Concrete Pavement: Mega Industries Corporation
Permeable Concrete Pavers: Belgard, Aqua Roc

Project Team

Client: Kansas City Water Services
Prime Design Consultant: URS Corporation
Engineering Subconsultants: Barr Engineering Co.; Taliaferro & Browne, Inc.; Delich Roth & Goodwille
Landscape Architect: Vireo (formerly Patti Banks Associates); Taliaferro & Browne, Inc.
Public Outreach: Shockey Consulting Services
Branding: Phillips West Public Relations
General Contractor: Mega Industries Corporation
Porous Pavement Contractor: Mega Industries Corporation
Landscape Contractor: Stonegait Farm & Nursery

Rain Garden Performance Monitoring (2013): Facilitators from United States EPA, Tetra Tech, University of Alabama, and University of Missouri-Kansas City

Role of the Landscape Architect

The landscape architects were responsible for supporting the engineering team with planning, general layout, and detailing of the green infrastructure features, including: street tree coordination with the city forestry division, partial hardscape details, landscape details, planting design, construction oversight of planting, punch lists, and development of the maintenance manual.