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
Poor maintenance lack of regular checking
Processing slowly lack of stringent supervision Incomplete drainage sys. objection from private land owners
More pumping stations should be set up to pump massive water from channels and discharge water.Also, installing additional drainage pipes helps to collect or drain out more water.Then, installing additional grilles which is to screen out the slit, stone or industrial waste prevents channels clogging up.
The government should also speed up the flooding prevention constructions in order to deal with the heavy rainfall in summer.To manage the industrial waste is also important in the constructionsIn order to build a complete drainage system in rural villages, the government should have more co-operation with them, the villager.
Before build channels and flooding prevention, the government should consider all aspects such as the greening on the case of Ma Wat RiverMoreover, the consultation on experts from different fields like environmentalists is also important.And, the government should listen to public opinions especially residents .
TO conclude, the reasons of serious flooding in northern N.T. are heavy rainfall, variation of drainage basin and problems of constructions.Although the government had achieved improvements of flooding in northern N.T. , it still need more to reduce the occurrence of floodingThere.This is the reference and it is the end of our presentation! Thank You!
Final verson ppt
UNDERSTAND THE OCCURRENCE OFFLOODING IN THE NORTH NEWTERRITORIES Li Tsun Sang 52621940 Ng Tsz Wa 52622020 Chow Lai Yin 52621822 Tam Chun Man 52379840 Lam 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 HKBlackspot Scales: Major - affecting area > 100 Medium - affecting hectares area > 10 hectares Small - affecting serious significant area >0.25 hectares agricultural property socio- Minor - affecting area damage , damage/ economic < 50x50m isolated serious (0.25 hectare) property traffic disruption minor damage/ public traffic disruption nuisance and disruption inconvenience Source: DSD
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 INNORTHERN DISTRICT Private land developer and government continue to change the use of land 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 HONGKONG 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 to cause flooding
SHAPE OF RIVER BASIN IN HONGKONG From the distribution of tributary(river), three kind of shape are listed 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 CASE OF SHENZHEN RIVER Longest river in Hong Kong Dendritic Drainage Pattern Between New territories and Shenzhen Early 90s, much 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
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 river flow
Deforestation or removal of vegetation Removal of trees near the river Solid is washed away easily River bank collapses water comes out
Urban planning and development 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
Urban planning and development Surface is made of concrete Increase surface run-off Water cannot be held or stored in the farm, pond, underground or others
Urban planning and development A map of Yuen Long and the shape of the channel
Ownership of land Rural village Channelization cannot be carried out in some private lands No right to clean up and repair Clog up the river flow
Ownership of landA private land in rural village
THE IDEAS 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 Residents who living in low-lying area were at risk
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 alleviated.
THE FUNCTION OF THE FLOOD PUMPINGSTATION AND FLOODWATER STORAGEPOND Collect rainwater within the village Pump out the water collected in the pond Transfer the water to a floodwater from storage pond
IMPROVEMENT Flooding situation in the NNT has been alleviated because of the 4 main channels were rehabilitated and the flood pumping has been completed Around 30,000 people who live in low-lying areas are being protected
BEFORE THE CONSTRUCTION OFSHENZHEN RIVER Bend, meandering taking place Poor drainage of water
AFTER THE CONSTRUCTION OFSHENZHEN RIVER Depth of water increase from 3m to 7m Straightened Lower course flow has upgraded Threat of flooding eliminated
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 carried out at too slow a pace Not enough regulation on rural villages incomplete drainage projects
LACK OF PLANNING “In 2008, drainage improvement works along Ma Wat River in NNTwas substantially completed. The level of protection against flooding atKau Lung Hang has been raised.” adapted from DSD 07-08 annualreport 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) channel project carriedCriticism: comprehensive out without planning (e.g. lack of beautification work) extra cost incurred in redundant greening
SUGGESTION Set up more pumping stations Install additional drainage pipes Install additional grills 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 on the case of Ma Wat River) Consultation on experts from different fields (e.g. engineers, environmentalists) Consultation on public (esp. local residents)
CONCLUSION Serious flooding in northern N.T. caused by1. Heavy rainfall2. Variation in drainage basin3. Problems of construction The government had achieved improvements of flooding in northern N.T. Still need to reduce the occurrence of flooding