Landscape Architect & Specifier News

JAN 2018

LASN is a photographically oriented, professional journal featuring topics of concern and state-of-the-art projects designed or influenced by registered Landscape Architects.

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Page 61 of 133

those focused on stormwater management, transportation/ roadways, parks and forestry and urban design/planning. The purpose of the manual was to provide the city guidance in integrating large-scale green infrastructure through best management practices (BMPs) for water quality treatment and stormwater detention. The BMPs are designed to aid engineers, designers, planners, developers and municipalities to implement attractive, maintainable and sustainable stormwater elements that enhance the streetscape and pedestrian environments. The team developed guidelines for BMPs to capture and treat runoff from public roadways and sidewalks, as well as from more typical urban site-generated runoff sources such as rooftops and parking lots. The majority of BMPs include features which collect trash and sediment, provide infiltration, promote biological uptake and support a variety of feasible vegetation alternatives which provide water quality benefits, but also improve aesthetics through natural elements and reduce the heat island effect. The manual provides detailed BMPs for streetside stormwater planters, bumpout stormwater planters, green gutters and alleys and tree trenches. A special focus of the manual was the planning and design of treatment facilities for runoff generated by public streets and roadways. 62 Landscape Architect and Specifier News Above: A green alley handles stormwater by sloping toward a central permeable pavement section, which typically runs within the central third of the alley for its full length. PICPs can greatly increase the attractiveness of alleys. A green alley, however, should not be installed where hazardous materials are loaded, unloaded or stored. If contamination exists an impermeable liner is necessary. In all cases, the outlet from the underdrain (4" PVC pipe with two 45° bends and a threaded cap set 2 inches below the top of the pavement) must be accessible via an inlet or manhole. Right: The upstream end of a block is generally not an effective place to install a tree trench; the middle or downstream end of a block is usually conducive. If serving just the public ROW (street and pedestrian zone), three tree trenches with three trees each can satisfy the water quality requirements for an impervious area measuring 400 feet (a typical city block) by 30 to 34 feet (street crown to ROW) for Denver's local and collector street classifications. Trees are typically located 4-6' from the back of curb. The preferred treatment surrounding the tree is a 4" curb with no tree grate. This allows the soil surrounding the tree to be visible while protecting the soil from compaction. When tree grates are used, a minimum separation of 4 inches between the grate and the tree trunk should be maintained. Grates shall be easily maintainable and need to be inspected on an annual basis. Another option is to use PICPs on top of the tree trench and continuing this to within 6-12" of the tree trunk.

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