UNDERSTAND THE OCCURRENCE OF FLOODING IN THE NORTH NEW TERRITORIES

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

WHAT IS FLOODING ?

• surface water > carrying capacity of the channel

• exceed bankfull stage

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

MAGNITUDE OF FLOODING IN HK

Blackspot Scales:

Minor - affecting area < 50x50m (0.25 hectare) minor public nuisance and inconvenience

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

FLOODING BLACKSPOTS IN H.K.

Source : DSD

WHY IN NORTHERN NEW TERRITORIES?

COMING UP NEXT …

1. Causes of flooding

2. Measures taken by government to tackle flooding

3. Evaluation of gov.’ s effort and suggestion

Natural factors

Rainfall

Catchment features

Human influence

RAINFALL

BACKGROUND

• Humid subtropical climate condition Located at northern hemisphere Close to equator• Many typhoons and rain band Heavy and more rainfall

SEASON OF RAINFALL

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

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

• Global warming El nino La nina

OTHER FACTORS OF HEAVY RAINFALL

Increase annual rainfall by El nino and La nina

OTHER FACTORS OF HEAVY RAINFALL

Year of El nino

Year of La nina

Normal Year

. rainfall

(mm)

OTHER FACTORS OF HEAVY RAINFALL

Rainfalls intense More easily to cause flooding especially in

northern N.T

RAINFALL + CATCHMENT FACTOR

=FLOODING

CATCHMENT FACTOR

CATCHMENT FACTOR OF NORTH DISTRICT

• 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

THE REASON OF FLOODING IN NORTH DISTRICT 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

THE STRUCTURE OF RIVER IN HONG KONG

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

SHAPE OF RIVER BASIN IN HONG KONG

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

THE OCCURRENCE OF SHENZHEN RIVER

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

RAINFALL + CATCHMENT FACTOR + HUMAN INFLUENCE

=HEAVY FLOODING

Humaninfluence

Construction

Many constructions of rivers and channel operating in North New Territories

Some constructions need many years to finish

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

Sha Po Tsai Village accident

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

The rainstorm water cannot be drained out

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

Deforestation or removal vegetation

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

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 or stored in the

farm, pond, underground or others

City planning and developing

A map of Yuen Long and the shape of the channel

Ownership of the place

Rural village Some private places cannot be built

with channel No right to clean up and repair Clog up the water to flow out

Ownership of the place

FLOODING PREVENTION

THE IDEA OF FLOOD PREVENTION

Drainage Channels

Pumping station

Flooding Storage

THE MAJOR DRAINAGE CHANNELS IN NNT

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.

THE FUNCTION OF THE FLOOD PUMPING STATION AND FLOODWATER STORAGE POND• Collect rainwater within the village • Pump out the water collected in the pond • Convey the water to a floodwater from storage pond

THE EFFICIENCY OF THE FOOD PREVENTION

EVALUATION

LACK OF PLANNING

“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

EVALUATION

Rivers are destroyed and cut down Drainage system cannot handle the

rainfall effectively Poor maintenance of channels

EVALUATION

Amount of silt bring the problem of flooding again

Flooding constructions are processing slowly

Not enough regulation with rural villages

incomplete drainage system

IMPROVEMENT

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

BEFORE THE CONSTRUCTION OF SHENZHEN RIVER Bend,

meandering taking place

Poor drainage of water

AFTER THE CONSTRUCTION OF SHENZHEN RIVER Depth of water

increase from 3m to 7m

Straight lower course flow

has upgrade Thread of

flooding Eliminate

SUGGESTION

SUGGESTION

Set up more pumping stations

Install additional drainage pipes

Install additional grilles that can reduce the possibility of blockage

SUGGESTION

Speed up the flooding prevention constructions

Manage the industrial waste carefully

More co-operation with the rural villages so as to build a complete drainage system

SUGGESTION

Government should consider all aspects before implementation of the project(e.g. Greening)

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

Consultation on public (esp. local residents)

CONCLUSION

Serious flooding in northern N.T. caused by

1. heavy rainfall

2. special river pattern

3. Low lying area

4. Problems of construction The government have done improvements of

flooding in northern N.T. Still need to reduce the occurrence of

flooding

END OF PRESENTATION