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Performance-Based plant selection for Bioretention

In LA 403, we have the option of doing river-restoration or designing a residential landscape; I decided to do a residential landscape. Our residential site is essentially flat, with a slope of .5% throughout the site. Drainage is the primary issue within the site. Creating a Bioretention swale and a rain garden to catch the sidewalk and roads water is a necessity. In the article, “Performance-Based plant selection for Bioretention”, they emphasized that there are two main goals for bioretention projects; pollution reduction and flow control.

The article depicts the importance of water flow and how this affects the way vegetation properly grows. A big factor that plays into the successful function of a bioretention plant is its ability to tolerate sediment loading. For example, herbaceous shrubs have a specific form that allows for it to be maintained well. Alongside, it’s important to take in the site’s context into consideration, as always. Our site is located in a residential community, therefore, the planting needs to be meticulously chosen to avoid hindering the pedestrian and car visibility along the street. California native plants may be beneficial to the site, but only when they are checked with the hardiness zones of the vicinity. Despite this, it is best to pick plants that can withstand hydroperiods and flow characteristics.

Plants serve multiple functions within bioretention swales. Minimizing erosion and enhancing infiltration are some of the most important functions. Plants allow for the soil to be held into place so that when storm surges occur, or when pollutants are in the swale, they can be easily redirected. Plant root systems allow for water to penetrate the soil. Alongside, the presence of plants improve the drainage of the soil as the plant matures and establishes.

Plants within a bioretention swale should have the following characteristics: Year round foliage, upright habitat, and a dense rooting system. A lush, full set of foliage prevents erosion to occur throughout the year. The plants must be able to fill up space within the swale. The verticality of the plant is important in order to combat the flow of incoming water.

Our studio is currently in the process of drawing out a grading plan. Our site has two contours to work with, so we are creating a series of bioretention swales and rain gardens to deal with the drainage issue present. Bioretention swales are an LID necessity and should be properly researched in order to reach maximum functionality and success.

Source: https://thefield.asla.org/2020/01/09/performance-based-plant-selection-for-bioretention/