When we build impervious surfaces like roads and parking lots, we are reducing the area available for absorbing stormwater, which disturbs the natural hydrology of an area. This stormwater is then channeled away to a storm drain, carrying with it contaminants and sediments that become concentrated elsewhere. The practice of low-impact-development (LID) is intended to reduce or mitigate the negative environmental impacts created by development, particularly its effects on water systems and hydrology. Many tactics and strategies exist for LID; however, many of these practices in an urbanized or developed setting remain a challenge, given the needs for durability, accessibility, and functionality. One technology, permeable paving or paver systems, seems most appropriate when it comes to LID in urban areas.
The Los Lunas Transportation Center in Los Lunas, NM. is in the process of expanding the use of the center from a municipal office building and commuter train stop to a community center and transit hub with the addition of several plazas and a courtyard in which to hold community events and facilitate interaction. Given the need for substantial durable walking surfaces across the site, the amount of unpaved surface area was limited and budget limitations could not support the use of permeable paver treatments throughout, so our efforts were focused on developing a site-specific LID strategy that fit into the aesthetics and would meet the budget. Though there are several LID interventions on this project, this article will examine the intervention in the North Plaza.
The North Plaza is intended for hosting community events such as music, farmer’s markets and other gatherings. The plaza is primarily concrete, but the aesthetics and layout draw from the Spanish-style grid of trees visually connected by bands of pavers that accentuate the pattern. The need for accommodating a large number of people and minimizing the potential for tripping hazards required that tree wells be reduced to only 36 SQ FT, not a friendly environment for any tree species.
To address both the increased stormwater runoff generated by the impervious surfaces of the plaza and the constraints on the trees, we implemented LID strategies in the form of a permeable paver system in the gridded bands on the plaza surface and provided structural soils (a blend of gravel and organic materials that promote robust and healthy root systems) around each tree to provide healthier growing conditions.
The concept is that the plaza will drain from the southwestern corner to the northeastern corner and that the surface runoff will be intercepted as it crosses the band of permeable pavers. As it is intercepted, it will percolate into the subsurface and structural soils surrounding the tree wells, therefore providing supplemental water to the tree roots, which will encourage a denser tree canopy providing more shade for users in this space.
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