Drainage layers are materials used in construction and landscaping to manage water flow and prevent flooding. They are typically made of gravel, sand, or other permeable materials that allow water to pass through while filtering out larger particles. These layers help direct excess water away from structures, ensuring stability and longevity. In landscaping, drainage layers are often placed beneath soil or grass to improve drainage in gardens and lawns. They can also be found in building foundations to protect against water damage. Proper installation of drainage layers is essential for effective water management in various environments.