Linear roadway and street corridors are often constrained in approaches to providing traditional stormwater management (SWM) measures. Yet these corridors can make up about 40 per cent of the urban area of a large city and contribute most of the dry weather pollutants that impact our lakes and rivers. Corridor widths are often standardized by municipal requirements and determined by the required number of traffic lanes and standards for boulevard design, not by SWM requirements. The demands of the trafficked area are such that integrated runoff management systems inside the road corridor that would best approach a source control definition are discouraged or very short lived. The items best suited to addressing runoff management, such as large trees, are often viewed as obstacles or impediments to traffic design and flow management or they conflict with utility requirements.
绿色基础设施的方法的一个步骤right direction, but right-of-way dimensions and the required roadway functions can limit their effectiveness. In addition, most green infrastructure design approaches to existing roadways are retrofitted, with all of the built-in limitations that retrofits bring. An alternate approach that incorporates street character, corridor setting, and vehicle and active transportation functions is required to ensure runoff impacts from these urban areas is addressed in a manner that doesn’t impact the vehicle and active transport needs of the street users.
The Green Streets design approach that has been developed for the City of Toronto moves away from the concept of collecting roadway runoff with a storm sewer system and moving it to a central location, such as a SWM pond, as the only method to address precipitation impacts. It also removes the idea that certain classifications of roadway should receive similar approaches based on a potentially limiting set of previously approved measures or standards. A newer method that systematically determines which approaches to use based on street “reaches” (from intersection to intersection), its setting, its character, the population it serves, and the functions it provides, presents an opportunity to “dial in” performance while passively supporting corridor vegetation that is often otherwise neglected.
The selection process begins with an inventory of surface and subsurface corridor features compared with municipally-prepared mapping of its natural features, including soil type and identified flooding hazard zones. It then follows a long-list approach to available runoff reduction and treatment options that mesh with and complement the street’s characteristics, resulting in a customized approach that integrates green infrastructure functionality into the street fabric. This process then leads directly into the conceptual design process followed by preliminary and detailed design and subsequent construction.
这种方法应用于多伦多的温内特和谢尔大街，这是两个具有不同街道特征的住宅街道地区。温内特大街（Winnett Avenue）是一条密集开发的单向街道，几乎没有林荫大道区域和不断的南部坡度。街上的房屋有小的前院，有许多树木，这些树木将受益于街道上的道路径流的被动灌溉。Schell Avenue是一条双向住宅街道，密度相对较小，但交通量较大。树木较少但更大，在较大的前码中，草皮区域较大。该过程有助于了解如何在不同的街道类型中实施绿色街道的过程，并扩展到主要的通道，动脉道路，目的地景点或“著名”街道。
At the north edge of Winnett Avenue, near a school block, where the boulevard area widened sufficiently, a bioswale treatment is planned for water balance and water quality treatment. It will be installed as a future project extension. Downgrade, where the street boulevard narrows and houses are present close to the street, a strip of permeable paving for parallel parking areas is being installed prior to oil/grit separator units for infiltration and water quality treatment. On Schell Avenue, the available boulevard area is elevated so a bioswale treatment for roadway runoff isn’t feasible and another strip of permeable pavement for parallel parking was installed. Oil/grit separators will perform backup water quality treatment prior to discharge to storm sewers.
The results of the installation include a significant reduction of annual runoff volume—a 91 per cent reduction for Winnett Avenue, and a 60 per cent reduction for Schell Avenue. The results also include retrofitted water quality treatment—78 per cent and 88 per cent TSS removal on an average, annual basis for Winnett and Schell Avenues. One-hundred-year event peak flow rate reductions of 16 per cent and 17 per cent in Winnett and Schell Avenues, respectively, from pre-project rates due to pavement net impervious area reductions were also realized.
However, municipalities will require high quality background and characterization of their roadway assets to allow for a systematic evaluation of how to apply these measures.
标题图片来源：史蒂文·范·哈伦（Steven Van Haren）。