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
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
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
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
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
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
37.
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
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
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
Private land developer and government continue change the use of land in north district, agricultural land was converted into car park, high-rise buildings and Container yard etc.Land area use to dredge water greatly reduces due to the reconstruction of land. Natural land has been paved by hard surface. Lead to rainfalls flow into the river directly. In order to continence the work of drain flooded, government connect the drains directly from Sheung Shui, Fanling Town Centre to Ng tung river, however do not widen the river channels or open another channels, it leads to problem of flooding
Rivers in Hong Kong are generally short and small, without a distinctive middle course. Typically, the upper course is steeper, the middle one gentle while the lower course is nearly flatThe upper course includes the headwaters of a river, As the upper course is steep, many narrow, V-shaped valleys are formed by the prevailing downward erosion, With proper geological conditions, waterfalls form along the upper course. Ng Tung Chai waterfalls, Bride's Pool waterfalls and Man Cheung Po are all tourist hotspots with waterfalls in Hong KongThe lower course is the section with most abundant water flow, it is a flat terrain, Sediments from the river are carried to the river mouth, where they may form an delta, is easy cause flooding, During floods, the rivers overflow their banks, carrying sediments that are deposited to form the floodplain. In Hong Kong, the largest floodplains are at Yuen Long, Kam Tin and Sheung Shui.
Based on the distribution of tributaries, local rivers can be mostly classified into three drainage patterns: dendritic, rectangular and radial.
Tributaries from the upper course merge with the main stream at fairly regular intervals. The angle between the major channel and its tributaries is less than 90 degrees, similar to that between a tree trunk and its branchesthe major channel and its tributaries are connected at angles close to 90 degree. This can occur if faults and joints in the bedrock are arranged at right angles, so rivers and streams flow and erode along these lines of weaknessRadial drainage patterns comprise several streams that diverge from the same point. Streams and rivers often radiate in all directions from the peaks of mountains.
淹浸農田、房屋，居民在屋頂等待救援Sham Chun serves as the natural border between Hong Kong and Mainland China, together with the Sha Tau Kok River.
隨著深圳河治理第一期、第二期和第三期工程分別於1997年年中、2000年年中和2006年底完成後，新界北部沿深圳河與平原河匯合處的低窪地帶的水浸情況已大大得到改善渠務署終落實在二○一三年，在深圳河上游近香園圍一段，展開最後一期治理工程，預計二○一七年完工With the Shenzhen River’s Regulation work stage 1, 2 and 3 finish on mid 1997, 2000 and 2006. the confluence of New Territories and shenzhen’ low-lying areas the situation has greatly improved
