Drainage Services Department

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Background

Review of Flooding Problem in Northern Hong Kong Island

The following photos were taken in 2005, 2006 and 2008, featuring the flooding problem in Northern Hong Kong Island.


Flooding at Hillier Street (2005)	Flooding at Leighton Road (2006)	Connaught Road Central during the black rainstorm (2008)

Major Causes of Flooding in Northern Hong Kong Island

In the past, during rainy seasons, flooding occured in various areas of Northern Hong Kong Island. The main causes of flooding are as follows:

Geographical Location - Located in the sub-tropical region, Hong Kong has a oceanic climate and therefore is vulnerable to heavy downpour and tropical cyclones in summer.
High Rainfall - Hong Kong has an annual average rainfall of about 2,200 millimetres, one of the highest among cities in the Pacific Rim.
Urban Development - Over the years, intensive development associated with urban development has taken place in Northern Hong Kong Island. The district is one of the most densely-built areas in Hong Kong. Continuous development and expansion of the community at the upper catchment have increased the quantity of surface runoff considerably, thus reducing the flood carrying capacity of the drainage system in urban area, aggravating the flooding problem during rainstorms.
Low-lying Topography and Effects of Tides - Sheung Wan, Central, Admiralty, Wan Chai, Causeway Bay and Happy Valley are located in low-lying areas. When the tidal level is high, the seawater will affect the discharging capacity of the existing drainage system and therefore these areas are susceptible to accumulation of stormwater.
Aged Drainage System - The drainage systems in the area built decades ago are no longer sufficient to satisfy and meet the current flood preventions standard. The discharge capacity of the aged drainage system has also been reduced.

Impacts on Flooding

Affect Economic Activities - Areas like Sheung Wan, Central, Admiralty, Wan Chai and Causeway Bay are the key financial and business areas of Hong Kong. Flooding occurring in those areas would disrupt economic activities and business operation and hence lead to huge economic losses.
Disturbance to the Public - Flooding disturbs the daily lives of the public, causing inconvenience to pedestrians on their way to work or study. Schools are sometimes suspended.
Traffic Congestion - During heavy downpours, areas in Northern Hong Kong Island such as Sheung Wan, Central, Admiralty and Wan Chai are prone to flooding. Flooding causes serious disruption and congestion to traffic.

Stormwater Drainage Master Plan Study in Northern Hong Kong Island

To minimize the impacts of flooding to daily lives of the public, as well as the economy, the Drainage Services Department commissioned a “Drainage Master Plan Studies” from 1996. The “Stormwater Drainage Master Plan Study in Northern Hong Kong Island” is part of the study.

The western areas covers under the “Stormwater Drainage Master Plan Study in Northern Hong Kong Island” includes Kennedy Town, Shek Tong Tsui, Sai Ying Pun, Sheung Wan, Central and Wan Chai. The objectives of the study are to comprehensively examine the conditions of the existing stormwater drainage systems and to devise long-term stormwater drainage improvement measures to meet current flood prevention standards and future needs.

The following drainage improvement options were considered in the study:

Upgrading and improvement of existing systems;
Flood storage;
Drainage Interception tunnel; and
Water pumping scheme


Upgrading and improvement of existing systems	Flood storage	Water pumping scheme

Various options were assessed by the Drainage Services Department based upon the characteristics of individual catchment area as well as the following criteria:

Existing drainage system configuration
Land requirements
Environmental considerations
Traffic considerations
Utilities and other underground structures

With detailed planning, analysis and public consultation, the Drainage Services Department finally adopted the stormwater interception option. The Project involves building of a drainage tunnel in the western part of Hong Kong Island to intercept stormwater from the upper catchment at the Mid-Levels and discharge it to the sea directly, thus reducing rainwater flowing to the low-lying areas downstream. With the tunnel commissioning, the overall flooding problem on Northern Hong Kong Island will be alleviated. The Project commenced in November 2007 and completed in August 2012.

Drainage Tunnel Scheme