In [[bioretention]] systems a choker layer of ≥ 100 mm depth is the recommended method to prevent migration of finer [[filter media]] into the underlying [[Reservoir gravel|storage reservoir aggregate]]. | In [[bioretention]] systems a choker layer of ≥ 100 mm depth is the recommended method to prevent migration of finer [[filter media]] into the underlying [[Reservoir gravel|storage reservoir aggregate]]. |