A percolation trench, also called an infiltration trench, is a type of best management practice (BMP) that is used to manage stormwater runoff, prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. It is a shallow excavated trench filled with gravel or crushed stone that is designed to infiltrate stormwater though permeable soils into the groundwater aquifer.
A percolation trench is similar to a dry well, which is typically an excavated hole filled with gravel. Another similar drainage structure is a French drain, which directs water away from a building foundation, but is usually not designed to protect water quality.