Stormwater retrofitting is the practice of updating existing developed sites with modern stormwater management features and practices to improve water quality and reduce flooding. A retrofit project may include a construction or renovation project to incorporate green infrastructure practices on an existing residential, commercial or industrial site. The specific features chosen for a site may vary depending upon available space and land use, but native landscaping or some form of bioretention are typically the easiest to implement and provide increased aesthetic value.
When evaluating an existing developed site for stormwater retrofit, there are several key areas that must be considered:
- Check whether the site has an existing permit/license for stormwater management with either the local municipality, the local drainage district, the Broward County Development and Environmental Regulation Division or the South Florida Water Management District. If a permit/license exists, check with the regulatory authority to ensure the proposed retrofit is consistent with the existing design. If a permit/license does not exist for the development, check with each regulatory authority to determine the permitting/licensing requirements for the proposed retrofit.
- Observe the topographic features of the site, including building placement, downspout locations, slopes, pipe inverts and ground elevations to establish the direction of flow and, thus, the best placement for features.
- Avoid planting trees or other landscape features where their mature trunks or root structure will impede or block flow along the low point of a drainage feature.
- Avoid placing mulch in or immediately adjacent to the drainage ways. Mulch often floats and can easily be washed into stormwater inlets and potentially impede the flow of stormwater runoff, clog the drainage system, or similarly impact downstream elements of the drainage system.
- Use root barriers to protect underground infrastructure that may be damaged by root systems.
- Plant trees so that the estimated mature root zone is at least 5 ft. horizontally from exfiltration trenches (French drains) and from earthen berms, which are designed to impound water.
- Avoid planting trees on an earthen embankment berm, which acts like a dam. The tree roots may penetrate the earthen embankment and create paths for water to erode the embankment should the roots die and decay. Erosion and failure of the embankment may lead to a release of a significant volume of water onto the adjoining lands.
- Ensure the placement of landscaping and trees affords sufficient light penetration to avoid killing the ground cover or otherwise destabilizing the ground surface.
- Develop and implement a maintenance plan to:
- Routinely remove live and fallen branches and leaves so they do not impede the flow of stormwater runoff or clog the drainage system;
- Control the detritus created by deteriorating leaves, branches and other plant matter; and
- Control the reproduction of the trees and understory so the required water storage volume is provided and so the bioretention area may be effectively maintained.
Native landscaping adds more area for water to be absorbed into the ground. Courtesy of SWFWMD