Achieving SSc Rainwater Management in LEED v4.1
Green Building Team on July 28, 2020
To earn the LEED v4.1 BD+C SSc Rainwater Management credit, project teams must design the site to retain the runoff from the developed site for at least the 80th percentile of rainfall events. The strategies used must replicate natural site hydrology, using low-impact development (LID) and green infrastructure (GI) practices.
Green infrastructure (GI) management approaches and technologies infiltrate, evapotranspire, capture and reuse rainwater to maintain or restore natural site hydrology. Low impact development (LID) emphasizes on-site natural features to protect water quality, by replicating the established natural land cover of existing watersheds and addressing runoff close to its source.
So, what strategies qualify as LID and GI?
- Rain gardens
- Vegetated roofs
- Permeable paving
- Vegetated swales
- Permanent infiltration or collection features (vegetated swales, rain gardens or cisterns) that can retain 100% of the runoff from at least the 80th percentile rainfall events
Conventional rainwater management strategies include grey infrastructure, such as retention or detention ponds, pipes and vaults. These types of strategies employ a centralized approach to managing runoff, which does not effectively replicate the natural site hydrology and does not address the runoff close to the source. Conventional grey infrastructure strategies can only be accepted if they are integrated within a combination of LID and GI techniques.
Typically, stormwater (retention or detention) ponds designed to meet municipal requirements will not meet credit requirements, regardless if they are sized to control the minimum 80th percentile rainfall events. This is because a retention or detention pond is not typically designed to infiltrate and are most often used for flood control.
As such, it would not be acceptable for a detention pond alone to manage the required runoff volume. However, a pond can contribute to the site’s rainwater management strategy as long as it is used as the structural means to capture the water and slow down the runoff before distributing to a LID or GI strategy, such as bioswales, where infiltration is designed to take place.