1. UNDERSTAND THE OCCURRENCE OF
FLOODING IN THE NORTH NEW
TERRITORIES
Li Tsun Sang 52621940
Ng Tsz Wa 52622020
Chow Lai Yin 52621822
Tam Chun Man 52379840
Lam Kwok Tung 52610985

2. WHAT IS FLOODING ?
• surface water > carrying capacity of the channel
• exceed bankfull stage
•inundation occurs at flat ground (flood-plain)
alongside the river banks

3. MAGNITUDE OF FLOODING IN HK
Blackspot Scales: Major - affecting
area > 100
Medium - affecting hectares
area > 10 hectares
Small - affecting
 serious
 significant
Minor -
area >0.25 hectares
 agricultural property socio-
affecting
area <
damage , damage/ economic
isolated serious
50x50m
(0.25 property traffic disruption
hectare)  damage/
traffic
disruption
minor public
nuisance and disruption
inconvenienc Source:
e DSD

4. FLOODING BLACKSPOTS IN H.K.
Source :
DSD

5. WHY IN NORTHERN NEW TERRITORIES?

6. COMING UP NEXT …
Rainfall
Natural
factors Catchment
1. Causes of flooding features
Human
influence
2. Measures taken by government to tackle
flooding
3. Evaluation of gov.’ s effort and suggestion

7. RAINFALL

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

9. 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.

10. OTHER FACTORS OF HEAVY
RAINFALL
•Global warming
 El nino
 La nina

11. OTHER FACTORS OF HEAVY
RAINFALL
.
rainfall (mm)
Year of El nino Year of La nina Normal Year
Increase annual rainfall by El nino and La nina

12. OTHER FACTORS OF HEAVY RAINFALL
 Rainfalls intense
 More easily to cause flooding especially in
northern N.T

13. RAINFALL + CATCHMENT FACTOR
=
FLOODING

14. CATCHMENT FACTOR

15. 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

16. 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

17. 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

18. 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

19.  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

20. 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

21. RAINFALL + CATCHMENT FACTOR +
HUMAN INFLUENCE
=
HEAVY FLOODING

22. Human
influence

23. Construction
 Many constructions of rivers and channel
operating in North New Territories
 Some constructions need many years to
finish

24. 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

25. Sha Po Tsai Village accident
 One of the branches in the village is blocked
by the construction
 The rainstorm water cannot be drained out

26. Construction
 Kind of waste or barrier at riverbed
 Industrial waste
 Sand , stone and mud

27. 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

28. Deforestation or removal vegetation
 Removal of trees near the river
 Solid is washed away easily
 River bank collapses
 water comes up

29. 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

30. 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

31. City planning and developing
A map of Yuen Long and the shape of the channel

32. 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

33. Ownership of the place

34. FLOODING
PREVENTION

35. THE IDEA OF FLOOD PREVENTION
 Drainage Channels
 Pumping station
 Flooding Storage

36. THE MAJOR DRAINAGE CHANNELS IN NNT
 Shenzhen River
 Ng Tung River
 Sheung Yue River
 Ma Wat River

38. Before the improvement
 Flooding was always appearing in NNT
when a rainstorm came
 Flooding was risked who living in
low-lying area

39. 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.

40. 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

41. THE EFFICIENCY OF THE FOOD
PREVENTION

42. EVALUATION

43. 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…

44. “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

45. EVALUATION
 Rivers are destroyed and cut down
 Drainage system cannot handle the rainfall
effectively
 Poor maintenance of channels

46. EVALUATION
 Amount of silt bring the problem of flooding
again
 Flooding constructions are processing slowly
 Not enough regulation with rural villages
 incomplete drainage system

47. 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

48. BEFORE THE CONSTRUCTION OF
SHENZHEN RIVER
 Bend, meandering
taking place
 Poor drainage of
water

49. AFTER THE CONSTRUCTION OF
SHENZHEN RIVER
 Depth of water
increase from 3m
to 7m
 Straight
 lower course flow
has upgrade
 Thread of flooding
Eliminate

50. SUGGESTION

51. SUGGESTION
 Set up more pumping stations
 Install additional drainage pipes
 Install additional grilles that can reduce the
possibility of blockage

52. 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

53. 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)

54. 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

55. END OF PRESENTATION