What three purposes do under-drains serve?

Under-drains serve several essential functions in managing water flow and maintaining structural integrity in various applications, most notably in construction and environmental engineering. The correct choice highlights that they support the filter media, which is crucial in filtration systems, such as in stormwater management or wastewater treatment systems.

Under-drains help to collect and direct excess water away from the filter media. This function is vital because it prevents the filtration system from becoming overloaded with water, which could reduce its efficiency and effectiveness. By supporting the filter media, under-drains ensure that the media can perform its function effectively, maintaining the desired water quality and flow rates.

While stabilizing the ground is an important consideration in construction, under-drains don't primarily serve that purpose; they mainly focus on water management. Enhancing water pressure is not a function associated with under-drains, as their role is to relieve pressure rather than increase it. Preventing soil erosion is more about surface water management and stabilization techniques rather than the specific role of under-drains in ground water management.