Li Tsun Sang 52621940Ng Tsz Wa 52622020Chow Lai Yin 52621822Tam Chun Man 52379840Lam Kwok Tung 52610985

• surface water > carrying capacity of the channel

• exceed bankfull stage

• inundation occurs at flat ground (flood-plain) alongside the river banks

Blackspot Scales:

Small - affecting area >0.25 hectares agricultural damage , isolated property damage/ traffic disruption

Medium - affecting area > 10 hectares significant property damage/ serious traffic disruption

Major - affecting area > 100 hectares

serious socio- economic disruption

Source: DSD

Source : DSD

1. Causes of flooding

2. Measures taken by government to tackle flooding

3. Evaluation of gov.’ s effort and suggestion

Natural factors

Weather

Catchment features

Human influence

• Hong Kong has no large rivers. • The larger rivers are mainly in the

northwest, including: Shan Pui River, Shenzhen River, Kam Tin River, Sheung Yue River, and Ng Tung River.

• Mountain• Low lying

Private land developer and government continue change the use of land in north

Land area use to dredge water greatly reduces due to the reconstruction of land.

In order to continence the work of drain flooded, government connect the drains directly from Sheung Shui, Fanling Town Centre to Ng tung river

Rivers in Hong Kong are generally short and small, without a distinctive middle course.

Upper course - steep, many narrow, V-shaped valleys are formed by the prevailing downward erosion

Lower course - flat terrain, it is easy cause flooding

From the distribution of tributary(river), three kind of shape are list below :

Dendritic Drainage Pattern

Rectangular Drainage Pattern

Radial Drainage Pattern

Dendritic Drainage Pattern the most common drainage pattern

in Hong Kong

e.g. Lam Tsuen River

Rectangular Drainage Pattern Appear at regions of the western New Territories

e.g. the upper course of Tuen Mun River

Radial Drainage Pattern found on roughly conical mountains

e.g. Sunset Peak

Longest river in Hong Kong

Dendritic Drainage Pattern

Between New territories and Shenzhen

Early 90s, lots rainfall lead to flooding

Total four Regulation work of Shenzhen River

Main source of flooding in Hong Kong

Bend, meandering taking place

Poor drainage of water

Depth of water increase from 3m to 7m

Straight lower course flow

has upgrade Thread of

flooding Eliminate

The problem of flooding reduce.

Amount of silt bring the problem of flooding again

Poor maintenance

• Located at northern hemisphere• Close to Equator• Humid subtropical climate condition

Equator

Hong Kong

• Humid subtropical climate• Average temperature: 22.7 °C• Annual rainfall: 3066.2mm (at 2008)

• Summer is a rainy season• some region in northern N.T. and

low-lying area cause serious flooding• the drainage system is overloaded.

• The rainfall is mainly came from typhoon, trough, precipitation

• During summer, trough came across southern Chinaand bring heavy rainfall produce

• Precipitation also produce rainfall

• Global warming• El nino• La nina

Increase annual rainfall by El nino and La nina

Year of El nino

Year of La nina

Normal Year

.rainfall (mm)

• Industrial activities• Deforestation• Excessive greenhouse gases (especially

CO2)• Increase in temperature

• Flooding Warning System

• The government policies can not show the effect in a short period

• It is no evidence to support there are any significant improvement

• Cooperate with other countries

• Set up the rules to limit the emission of carbon dioxide

• Educate the concept of protect the city to citizens

• Cooperate with other countries

• Set up the rules to limit the emission of carbon dioxide

• Educate the concept of protect the city to citizens

Humaninfluence

Construction

Many constructions of rivers and channel operating in North New Territories

Some constructions need many years to finish

Construction

Kind of waste or barrier at riverbed Industrial waste Sand , stone and mud

Construction

The roads are paved with sand and stones

Dug from the riverbed Not be held tightly Wash away easily Clog up the river and channel Decrease the velocity of water flowing

Sha Po Tsai Village accident

Serious accident causing death in 2010 The river constructions near found many industrial barriers and big

stones after flooding maybe caused by the construction

Deforestation or removal vegetation

Removal of trees near the river Solid is washed away easily River bank collapses

Sha Po Tsai Village accident

One of the branches in the village is blocked by the construction

The rainstorm water cannot be drained out

Ownership of the place

Rural village Some private places cannot be built

with channel No right to clean up and repair Not enough regulation of use of rural

place incomplete drainage system

Ownership of the place

City planning and developing

Many natural rivers in New Territories Need to develop and construct channel Channel need to be changed or

designed into narrow or bend Avoid the buildings or facilities Lower the strength of draining out

water

City planning and developing

Surface is made with concrete Increase water flowing on the surface Water cannot be held Stored in the farm, pond, underground

or other

City planning and developing Yeun Long

Result

Rivers are destroyed and cut down Channels are not able to handle the

rainfall Drainage system cannot drain the

rainfall effectively

Drainage Channels

Flood Pumping

Flood Storage

Shenzhen River

Ng Tung River

Sheung Yue River

Ma Wat River

Before the improvement

Flooding was always appearing in NNT when a rainstorm came

Flooding was risked who living in low-lying area

After the improvement

The repaired Shenzhen River section required a drainage capacity that can resist a 50-year return flooding

The flooding problems in Sha Tin, Fanling, Sheung Shui and Ta Kwu Ling area can be resolved.

• Collect rainwater within the village • Pump out the water collected in the pond • Convey the water to a floodwater from storage pond

Flooding situation in the NNT has been alleviated because of the 4 main channel were rehabilitated and the flood pumping has been completed

Around 30,000 people who live in low-lying are being protected

Flooding problem have not totally complete

Increasing the flood pumping station

Installing additional drainage pipes

Installing additional grilles that can reduce the possibility of blockage

“In 2008, drainage improvement works along Ma Wat River in NNT was substantially completed. The level of protection against flooding at Kau Lung Hang has been raised.” adapted from DSD 07-08 annual report

Then, in 2011…

“Recognising the aspirations of the public for greening to enhance quality of life and to help protect the environment, the DSD places great emphasis on the greening of drainage channel…”

“One of these examples is the 'Drainage Improvement for Ma Wat River at Kau Lung Hang' where large-scale greening work has started.”

DSD Newsletter (09/04/2011)

Criticism: channel project carried out without comprehensive planning (e.g. lack of beautification work)

extra cost incurred in redundant greening work

Government should consider all aspects before implementation of the project

Consultation on experts from different fields (e.g. engineers, environmentalists)

Consultation on public (esp. local residents)