What type of drainage system utilizes gravity to remove fluid?

The gravity flow system is a type of drainage system that relies on the natural downward slope of pipes or channels to facilitate the movement of fluids. This method utilizes the force of gravity to direct water or other liquids from higher elevations to lower ones, effectively allowing for a passive and energy-efficient way to manage drainage.

Gravity flow systems are commonly used in various applications such as sewerage systems, stormwater management, and agricultural drainage, where the elevation difference is optimal. By harnessing gravity, these systems eliminate the need for mechanical pumps or pressurization, which not only simplifies the design but also reduces operational costs and maintenance concerns.

In contrast, the other options involve active mechanisms or technologies that move fluids without relying solely on gravity, making them unsuitable for this particular definition of drainage systems.