Denver is a city in transition. Ranked as one of the best places to live in the country,1 Denver ‘s population is booming. Over the past five years, the city has averaged close to 2.1% annual growth, adding over 14,000 people per year.2 This rapid influx has led to housing demand exceeding supply, resulting in skyrocketing home and land values. As of March 2018, the year over year gain for resale was 8.4% (1.9% higher than that national average of 6.5%).3
Given these market conditions, many residents are deciding to make improvements to their current homes instead of entering the highly competitive housing market to move elsewhere, often leading to larger impervious area footprints on residential lots across the city. In the urban core, the city is seeing increasing densification with some neighborhoods experiencing over 50% growth in just seven years. Industry also recognizes that Denver is attracting a talented and capable workforce and is building and expanding offices across the city. According to the 2018 State of Downtown Denver Report, over $2.3 billion in investments are planned for Denver’s urban core, adding more than 700 hotel rooms, 4,5000 residential units and nearly 3 million square feet of office space.4
This growth makes Denver an exciting place to be but also puts increasing strain on urban infrastructure and services. Roads and public right-of-ways (ROW) are in ever-more demand, needing to serve a greater number of people and accommodate a wide variety of uses, from bike lanes to scooter parking, in addition to serving their traditional roles of vehicle and stormwater conveyance. Infill, increased building footprints, new roads and more sidewalks mean more impervious areas which means more runoff. More runoff means greater stormwater challenges. Denver is currently covered in 49% impervious area and a recent study from University of Colorado/Boulder estimates that impervious cover will increase to 64%-67% coverage by 2040.
Like many cities, these issues are only exacerbated by global trends. In Denver, climate change means increasing temperatures and swings in extreme precipitation from major downpours to long periods of drought conditions. This further complicates stormwater management while making the case for more alternatives to conventional “gray” infrastructure to mitigate higher temperatures and intercept stormwater.
One of the many ways the City and County of Denver is tackling these mounting challenges is through an integrative, data-driven approach to planning, funding and implementing a new green infrastructure (GI) program. Leading the charge on this is the Green Infrastructure Group (GI Group), a division housed within the Public Work’s Executive Director’s Office of Policy, Legislative Affairs and Special Initiatives. The GI Group is responsible for protecting and enhancing Denver’s urban watersheds by designing and implementing a robust, citywide green infrastructure program. The GI Group pursues a multi-pronged approach to growing green infrastructure in Denver that includes a focus on planning, monitoring, guidelines and policies. The GI program also focuses on prioritizing and implementing multi-functional projects that meet the needs of numerous agencies, departments and infrastructure drivers in Denver.
In this context, green infrastructure (GI) specifically refers to natural and engineered systems that mimic natural processes to manage and treat stormwater runoff. The use of green infrastructure also provides a host of other citywide benefits including climate resiliency, urban heat mitigation and increased community livability. While the term green infrastructure can apply to more naturally occurring systems such as forests and floodplains, Denver’s GI Group focuses on implementation of built, structural controls that mimic larger systems and mitigate the impacts of urbanization. These engineered practices can be applied on a large regional-scale or applied using a site-scale approach.
The original driver for establishing Denver’s GI program was to assist in meeting the city’s water quality requirements, as dictated by Denver’s municipal separated storm sewer system (MS4) permit. MS4 refers to Denver’s stormwater conveyance system, which is separated from the sanitary sewer system and discharges to Denver’s local waterbodies. Discharges from this system are regulated through the National Pollution Discharge Elimination System (NPDES), established by the Clean Water Act,5 which establishes pollutant regulations that are administered by the Colorado Department of Public Health and Environment (CDPHE) MS4 permit program.
Prior to 2013, Denver relied almost exclusively upon a comprehensive maintenance program to reduce pollutant loads and meet the MS4 permit requirements. The city’s existing maintenance program made progress in reducing E. coli levels and loads in dry weather discharges from several of the focus basins; however maintenance alone was not enough to ensure full compliance with the permit. It became clear that Denver needed a more innovative approach to providing water quality treatment at all scales. In 2013, Denver took a step to build a more robust and sustainable stormwater program by hiring a water quality project manager with experience in and focus on green infrastructure. In the following years, a planner and landscape architect were also brought on board. While the program hopes to continue expanding its staff numbers and capacity, the team of three with their diverse backgrounds and skill-sets have begun the complex task of establishing the City and County of Denver’s first ever GI program.
In the absence of a secure funding stream in initial years, the GI program conducted an effort called the Scorecard Analysis (“the Scorecard”) in which a methodology was established to prioritize the 31 major stormwater quality drainage basins that make up the city’s stormwater system. Each basin was scored based on primary and secondary criteria to prioritize basins in need of investment and action. Primary criteria accounted for the majority of the scoring and included water quality criteria such as outfalls of concerns related to the MS4 permit (outfalls where regulated pollutants are an issue), estimated pollutant loads based on land use, existing treatment and amount of impervious area within the ROW. Secondary criteria included urban heat island indicators, poor air quality, lack of tree canopy and socioeconomic factors, all basin attributes that could be improved through GI implementation. One of the outcomes of the Scorecard was a map that indicated six high-priority basins and five medium-high priority basins for GI improvements.
The Scorecard serves as the foundation for Denver’s 2018 Green Infrastructure Implementation Strategy, a data-driven plan that details GI projects in Denver’s priority basins. The projects in the plan include site, sub-regional and regional scale opportunities to implement GI, most of which indicate water quality treatment potential and have a project partner identified. The plan also identifies potential green streets in each high and medium-high priority basin. These are street opportunities where green infrastructure is likely feasible and would be highly beneficial. Green streets were identified using a criteria-based analysis coupled with field surveys. Green streets were further prioritized based on input from other agencies and departments that have complementary efforts on the same streets. Similarly, park opportunities were identified for each basin. The Department of Parks and Recreation created its own methodology for analyzing which parks are potentially compatible with some sort of stormwater facility. Both processes, prioritizing green streets and identifying potential park opportunities, served dual purposes: green infrastructure planning and relationship building across departments and agencies.
Because green infrastructure involves above-ground improvements often in park settings or within the public-right-of-way, it is associated with many other benefits beyond stormwater management. Research studies demonstrate that GI improves water quality, can mitigate peak flows and provide needed detention, reduces the urban heat island effect, lowers cooling costs for nearby buildings, absorbs local carbon emissions, improves air quality and is associated with numerous public health benefits.6 Thoughtfully designed GI can create safer pedestrian and cyclist environments and contribute to placemaking. These, along with the aesthetic value of GI, can combine to increase property values, thus having an important economic benefit as well. Due to the fact that GI meets multiple city goals, the GI program intentionally seeks to align projects with other city efforts including major corridor projects, bike projects, or stormwater pipe projects. Syncing up implementation not only achieves major cost efficiencies but also makes the case for additional sources of funding. Every public GI project in construction or completed in Denver since the GI program began includes at least one other funding partner.
Beyond data-driven planning and cost-savvy approaches to implementing multi-functional projects, Denver’s GI team also provides key tools and resources that make it easier to plan for, design and construct GI. A main aspiration of the program and one that is already beginning to occur, is making GI a standard scope consideration and budget item in plans and projects across the city, regardless of origin. To this end, program staff have developed core messaging that continues to be presented to city planners, engineers, project managers, City Council Members and the public. Evidence that the program’s work is already paying off is the inclusion of GI in plans that make up the Denveright initiative. This multi-faceted planning initiative includes an update to Denver’s Comprehensive Plan, Blueprint Denver (the City’s land use and transportation plan), Denver Moves Transit and Pedestrian and Trails plans, and Gameplan (Denver Parks and Recreations Master Plan). GI has also been identified as a specific task item in the planning department’s new approach to neighborhood plans.
Another key function the GI team plays in moving Denver towards more widespread implementation of GI is providing design guidance and resources. In 2015, the GI team began development of the Ultra-Urban Green Infrastructure Guidelines (UUGIG)7 with the goal of helping developers and other city agencies implement a range of urban green infrastructure strategies that are suitable for tight urban spaces found throughout Denver. Prior to this document, there were limited resources Denver practitioners could turn to for design guidance on GI in urban areas. As a result, projects that sought to implement green infrastructure had a challenging time engaging local professionals that had the experience and skill-set to design these best management practices (BMPs) in a way that could be reviewed and approved by local agencies. Recognizing this as a challenge shared by both the private design community and the approving agencies, the City of Denver partnered with the EPA and the Urban Drainage and Flood Control District (UDFCD)(the regional flood control district) to develop the UUGIG, intended for use by both the public and private sector. Chosen for their suitability in Denver’s ultra-urban environment including the ROW (source of some of the most polluted stormwater runoff), the guidelines include planning and engineering criteria for site-scale GI and recommendations on siting/urban design, aesthetics, planting/vegetation and maintenance.
Since the adoption of the UUGIG in 2017, there have been several private and public projects that utilized the guidelines for the development of site-scale water quality treatment. There are more than 100 streetside stormwater planters completed or under construction in local transportation and wastewater projects. The guidelines established a baseline for consistent evaluation and feedback from reviewing agencies for private developers and public capital projects. A handful of potential revisions have already been identified based on contractor and designer feedback and plan to continue updating the UUGIG in the future to adapt to changing needs. Importantly, the city’s adoption of these guidelines sent a clear signal to the engineering and design community that green infrastructure is a practice that will be expected on more and more projects throughout the city. The GI team not only intends to improve upon the UUGIG as lessons are learned but use it as a model for the development of more guidance documents moving forward.
In terms of policy, the GI program relies heavily on research and best practices from across the country to inform any GI or water quality related policy. The GI team is currently finalizing a project with the Community Engagement, Design and Research Center (CeDAR) program at the University of Colorado/Boulder to develop an impervious forecasting model. This model looks at the anticipated impervious area growth based on four different development scenarios and the impact each scenario will have on water quality. The study makes the important link between types of land uses and their contribution to impervious area. This work is already informing policy discussions related to water quality thresholds and other mechanisms for limiting impervious area growth.
Clearly there is much left for Denver’s Green Infrastructure program to tackle. Densification, climate change, limited resources and complex urban challenges all make a strong case for Denver to continue expanding its green infrastructure program. The plans, projects and policies discussed are just the beginning of what Denver hopes will be an effective program. For Denver to truly be successful in building a more sustainable and resilient city, all Denver stakeholders will need to involved in understanding and working towards a comprehensive green infrastructure solution.
1. U.S. News and World Report. U.S. News Unveils the 2018 Best Places to Live [online] (2018). https://www.usnews.com/info/blogs/press-room/articles/2018-04-10/us-news...
2. Colorado Department of Local Affairs: County Data Lookup [online]. https://demography.dola.colorado.gov/population/data/profile-county/
3. McClung, Kelcey. Home-resale price growth still rising in metro Denver, report says. Denver Business Journal [online] (2018). https://www.bizjournals.com/denver/news/2018/04/24/home-resale-price-gro...
4. State of Downtown Denver Report. (Downtown Denver Partnership, Denver, CO, 2018). [online] https://www.downtowndenver.com/wp-content/uploads/StateofDowntownDenver_...
5. Environmental Protection Agency: Clean Water Act (CWA) Compliance Monitoring. [online]. https://www.epa.gov/compliance/clean-water-act-cwa-compliance-monitoring
6. Green Infrastructure Implementation Strategy, 9-13. (City and County of Denver Public Works, Denver, CO 2018).
7. Ultra-Urban Green Infrastructure [online]. https://www.denvergov.org/content/denvergov/en/wastewater-management/sto...
The author would like to thank Sarah Anderson and Brian Wethington for their contributions to the article and all they have done to make Denver’s growing green infrastructure program successful.