Table 2.1 Summary of Existing Drainage Conditions in Mui Wo

Locations	Drainage Conditions
Pak Ngan Heung River	(a) In some parts of the river, the flood protection level is less than 1-in-2 years and the river will not be able to contain flood flow within its banks during heavy rainstorms. (b) The previous flood records have revealed that floodwater overtopped an existing bridge near Mui Wo Rural Committee Road and flooded houses immediately downstream of the river. (c) For the upstream area of Pak Ngan Heung River, the flooding problems are caused by very fast super-critical flow around bends. The super-critical flow has a great inertia and prefers to flow straight ahead rather than around bends and hence causing overtopping. In addition, cross-waves and bow-waves are created. A box culvert has been proposed to convey the flow directly to downstream without passing through sharp bend during heavy rainstorm. (d) Around the main confluence at downstream of Pak Ngan Heung River, the problem is mainly due to low bank levels. The area is at risk of flooding caused by both high sea water level and extreme rainfall.
Ling Tsui Tau	(a) Ling Tsui Tau is a flooding black spot. (b) Due to the inadequate drainage system, surface runoff from Butterfly Hill cannot be effectively discharge to Pak Ngan Heung River during heavy rainstorm.
Luk Tei Tong (2) River	(a) The Luk Tei Tong (2) River is a tributary of Luk Tei Tong River. It flows through an existing floodplain in the north of Luk Tei Tong Village. (b) Most parts of the Luk Tei Tong (2) River has a flood protection level of less than 1-in-2 years and it is far too small (1m – 1.5m wide) for conveying flow during extreme storm events. This is the main cause of widespread flooding in northern edge of Luk Tei Tong Village which cuts off the footpaths and isolates houses in floodplain.
Luk Tei Tong River	(a) Luk Tei Tong River is the continuation of a newly engineered channel that crosses the Mui Wo Marsh. The upstream section of the river was constructed by the Home Affairs Department under the Rural Planning and Improvement Strategy (RPIS) Project from in 1998. (b) The Luk Tei Tong River stretches from the confluence with the Luk Tei Tong (2) River to the confluence with the Silver River. (c) Most parts of downstream of Luk Tei Tong River remain natural and have flood protection of less than 2 years.
Tai Tei Tong River	(a) The downstream of Tai Tei Tong River has a flood protection level of less than 1-in-10 year. (b) During heavy rainstorm, floodwater will overflow from existing rivers and inundate adjacent houses.