Which material is added to the sides of a bioretention installation to enhance drainage?

In the context of bioretention installations, enhancing drainage is crucial for managing stormwater effectively. Geotextiles serve as a permeable fabric that helps in allowing water to pass through while filtering out sediments. This use of geotextiles promotes better drainage by preventing soil erosion and maintaining the stability of the bioretention system. It facilitates appropriate water movement and prevents clogging of the media in bioretention areas.

Geotextiles also act as a separation layer that prevents fine materials from migrating into the drainage layer, which is vital for maintaining the porosity of the drainage medium beneath. By using geotextiles, designers enhance the effectiveness of the bioretention system in managing runoff and improving water quality.

While other materials like stone aggregates can contribute to drainage as well, they primarily serve as structural support and provide space for water movement rather than offering filtration benefits. Using concrete would not support drainage as it is impervious, and clay soil is known for its poor drainage capabilities, making it unsuitable for these types of installations.