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Final verson ppt


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Final verson ppt

  1. 1. 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
  2. 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. 3. 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
  6. 6. COMING UP NEXT … Rainfall Natural factors Catchment1. Causes of flooding features Human influence2. Measures taken by government to tackle flooding3. Evaluation of gov.’ s effort and suggestion
  7. 7. RAINFALL
  8. 8. BACKGROUND• Humid subtropical climate condition Located at northern hemisphere Close to equator• Many typhoons and rain band Heavy rainfall
  9. 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. 10. OTHER FACTORS OF HEAVYRAINFALL•Global warming El Nino La Nina
  11. 11. OTHER FACTORS OF HEAVYRAINFALL . (mm) rainfall Year of El Nino Year of La Nina Normal Year Increase annual rainfall by El nino and La nina
  12. 12. OTHER FACTORS OF HEAVY RAINFALL Intense rainfall More easily to cause flooding especially in northern N.T.
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18.  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
  19. 19. 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
  21. 21. Humaninfluence
  22. 22. Construction Many constructions of rivers and channel operating in North New Territories Some constructions need many years to finish
  23. 23. 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
  24. 24. Sha Po Tsai Village accident One of the branches in the village is blocked by the construction The rainstorm water cannot be drained out
  25. 25. Construction Kind of waste or barrier at riverbed Industrial waste Sand , stone and mud
  26. 26. 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
  27. 27. Deforestation or removal of vegetation Removal of trees near the river Solid is washed away easily River bank collapses water comes out
  28. 28. 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
  29. 29. 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
  30. 30. Urban planning and development A map of Yuen Long and the shape of the channel
  31. 31. 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
  32. 32. Ownership of landA private land in rural village
  34. 34. THE IDEAS OF FLOOD PREVENTION Drainage Channels Pumping station Flooding Storage
  35. 35. THE MAJOR DRAINAGE CHANNELS IN NNT Shenzhen River Ng Tung River Sheung Yue River Ma Wat River
  36. 36. Before the improvement Flooding was always appearing in NNT when a rainstorm came Residents who living in low-lying area were at risk
  37. 37. 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.
  38. 38. 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
  40. 40. EVALUATION
  41. 41. 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
  42. 42. BEFORE THE CONSTRUCTION OFSHENZHEN RIVER Bend, meandering taking place Poor drainage of water
  43. 43. AFTER THE CONSTRUCTION OFSHENZHEN RIVER Depth of water increase from 3m to 7m Straightened Lower course flow has upgraded Threat of flooding eliminated
  44. 44. EVALUATION Rivers are destroyed and cut down Drainage system cannot handle the rainfall effectively Poor maintenance of channels
  45. 45. 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
  46. 46. 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…
  47. 47. “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
  48. 48. SUGGESTION
  49. 49. SUGGESTION Set up more pumping stations Install additional drainage pipes Install additional grills that can reduce the possibility of blockage
  50. 50. 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
  51. 51. 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)
  52. 52. 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
  53. 53. REFERENCE AND SOURCE lications/Press_Releases/news148.html ers.asp
  54. 54. END OF PRESENTATION Thank you !!!