The proposed Tsuen Wan Drainage Tunnel aims to improve the flood protection level in Tsuen Wan and Kwai Chung by intercepting excess stormwater from the upland catchments, for discharge into the sea. It saves the need to implement extensive pipe upgrading works in busy streets and will raise the flood protection standards, in the Tsuen Wan and Kwai Chung districts, to withstand rainstorms with a return period ⁽¹⁾ of 1 in 50 years.

(1) “Return period” is a statistical means to describe the severity of rainfall. The higher the severity of the rainfall, the less likely will be its recurrence. The rainfall return period is defined as the average period of time expected to elapse between occurrences of rainstorm events at the particular location with the described severity or higher.