the green line Online

Community Parks and Urban Drainageways: Meeting multiple Objectives

by Michelle Leach, Matrix Design Group, Inc.

Fig. 1: Drainageway design for stormwater conveyance.

People desire an active outdoor lifestyle and value natural areas for beauty and appreciation of wildlife and natural habitats. Recent environmental awareness embraced by the communities, public agencies, not-for-profits, and engineering / scientific professionals supports the opportunity to integrate sustainability goals in the restoration of these drainageways. Throughout the Denver metropolitan area many major drainageways exist and transverse through greenways and parks (the Urban Drainage Flood Control District manages over 1600 miles of open channel drainageways occurring through parkland). These two land uses can converge to create connections between people and the natural world. To achieve this beneficial relationship the functional, social, ecological and aesthetic attributes need to be compatible.

Fig. 2: Low Flow Channel at Westerly Creek

Recognizing that adjacent parkland and drainageways mutually support many valuable ecological functions and services, the integration of these landforms at multiple scales within the greater regional system is clearly a desired goal. Both the parkland and the drainageway embody landscape elements that can support multiple objectives necessary to optimize their purpose. The increase in stormwater volumes correlated with impervious surfaces and stormwater management infrastructure may create permanent base flows that can sustain thriving riparian migratory corridors for wildlife and plant species diversity. The adjoining park offers ample space to develop a meander planform for the channel alignment. These inside and outside bends can be stabilized with bio-logs (a bio-degradable coconut coir roll planted with wetland plugs and riparian shrubs). Removing hard controls such as rock edges allows the channel to function naturally. The benefit to vegetating channel edges provides bank stabilization, improves water quality, supports wildlife habitat, fosters appreciation for native plants and offers passive recreation such as wildlife viewing for park visitors.

Since the drainageways are tributaries to a regional system, pedestrian recreation trails can be appropriately located adjacent to drainageways in order to link neighborhoods while simultaneously protecting wildlife movements. By locating the drainageway in the park, more land area is available to create a broad floodplain to dissipate energy and avoid narrow, deeply incised channels. Channel stability and health is increased when the alignment can meander for sinuosity, side bank slopes are graded gently, and a broad channel width is created to reduce flow velocities. Using the earthwork as a design tool, sculptural land forms can contain storm events, delineate planting communities, and provide visual interest.

Fig. 3: Structures, Trails and Riparian Corridor at Westerly Creek

To maintain a shallow channel gradient for stability or accommodate change in grade for utility infrastructure, a grade control or drop structure is integrated into the construction of the channel. To manage the rate and manner in which stormwater flows are received from adjacent land uses before daylighting into the channel, detention facilities, forebays and water quality ponds are required by development criteria to store water, remove sediment, promote infiltration and uptake pollutants. Design of these structures can incorporate stormwater functions, reflect the land use character, and offer a sculptural outdoor amphitheater to view park environs. Throughout the Denver metropolitan region these structures have displayed playful follies such as cascading waterfalls or urban water fountain features.

The expanded activities occurring in these enhanced greenways and parks range from active recreation on athletic fields to passive recreation such as picnicking in green areas. Drainageways often pose significant public safety hazards during flood events, which must be fundamentally considered. Active and passive recreation areas are located outside flood hazard areas but not visually divided from the drainageway. Incorporating public participation with activities adjacent to the drainageway helps to promote environmental stewardship. Greater understanding of this valuable resource can be forged through outdoor environmental education. Many schools and interpretive centers are traditionally located near parkland.

Fig. 4: Outdoor Interpretive Education Station at Westerly Creek

These enhancements for parks and drainageways necessitate the participation from multiple entities to sustain the resource, build community pride and receive economic support. Partnerships and cooperative agreements by private and public parties have accelerated the implementation of these benefits that provide regional amenities to the public and ensure the preservation of ecological and wildlife resources.