River restoration in Japan (Keigo Nakamura)

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River restoration in Japan (Keigo Nakamura)

  1. 1. Hokkaido IslandRiver Restoration in Japan:Lessons fromthe Tama River Honshu Island Kyushu Island TSUKUBA (PWRI) Shikoku TOKYO (Tama River) Island Keigo Nakamura, Ph.D Okinawa NILIM, MLIT
  2. 2. Contents Japanese nature and rivers River restoration in Japan River restoration in the Tama River
  3. 3. General Characteristics of Japan Japan’s total area: 377,815 km2 (Ger.357,000km2) Total Population: 127,740,000 (2006) Mountains (Forest) account for about 71% of Japan’s total land area. The islands of Japan lie in the temperate zone and northeast end of the monsoon area. The annual average rainfall is 1,700 mm/year. Earthquakes and Volcanoes
  4. 4. TopographyGeography of Rivers Rhine River Longitudinally steep Joganji River High Sediment yield Abe River Shinano RiverElevation (m) Roire River1,000 Joganji River Abe River Tone River 800 Colorado River Chikugo River 600 Yoshino River Seine River 400 Kitakami River Mekong River 200 0 0 200 400 600 800 1,000 1,200km Distance from river mouth (km)
  5. 5. Precipitation Rainy season Typhoons
  6. 6. Floods and debris flow
  7. 7. 75% of Japanese Assets on theFloodplain FP 10 50 FP 75 FP Area Population Assets
  8. 8. Anthropogenic ImpactsAnthropogenic Impacts onRivers are enormous (Yoshimura. et al) 23.5 % of river banks are artificial 2,675 dams (>15 m) have been constructed http://www.hakkenden.net/hokuriku/a- toyama/anabatoyama.htm
  9. 9. Not only safe, but also nature Number ofNos. of victimes and restoration works 10000 Restoration 1000 victims due to 100 flood has 10 Victims of decreased in the flood 1 last 50 years. 1945 1955 1965 1975 1985 1995 Nos. of victims due to flood, sediment, River restoration and volcanic disaster Nos. of Nature-oriented river works increases since 1990
  10. 10. River Restorationin Japan
  11. 11. History of River Environment ~1960s economic growth and pollution 1970s countermeasure for Pollution :Basic Law for Environmental Pollution Control was enacted after Minamata disease, Yokkaichi asthma, etc. 1980s Dawn for river environment 1990 Nature-oriented river works
  12. 12. River Restoration is rapidly increasing since 1990.Accumulative number of river restoration projects 30000 Over 28,000 projects 20000 (~37,000 in the US) 10000 0 91 92 93 94 95 96 97 98 99 00 01 19 19 19 19 19 19 19 19 19 20 20
  13. 13. Agenda for river restoration Balance flood control and conservation Loss of wetland in watershed (60%) Stable flow regime, loss of dynamics Loss of gravel river bed (sediment yield) Loss of Ecological network (e.g. fishway, reconnection with paddy fields)
  14. 14. Restoration (rehabilitation)projects
  15. 15. Early restoration work in urbanarea (the Itachi River, 1982) Photos: Shinichi Yoshimura
  16. 16. Restoration of Backwater,Restoration of partial floodplainfunction Photo: MLIT, Japan
  17. 17. Design with Nature: Restoration in active riverRestoration using channel narrowing process
  18. 18. Restoration of network betweenpaddy field and stream Paddy field plays important role for aquatic ecosystem in Japan.
  19. 19. Restoration of flow regime by theoperation of dam reservoirs Before After
  20. 20. Lakeshore restoration
  21. 21. July 9, 2002 Restoration of locally extinct aquatic plants by soil seed bank
  22. 22. Academic activities…
  23. 23. Aqua Restoration Research Center Three 800 m experimental rivers
  24. 24. River Ecology Research Group Interdisciplinary association of ecologists, civil engineers, and river managers founded by MLIT (river authority) in 1995 Study at six rivers: Tama, Chikuma, Kizu, Kita, Shibetsu, and Iwaki rivers
  25. 25. The Society of Ecology and Civilengineering Academic society established in 1997 to support applied and practical studies Journal “Ecology and Civil Engineering” Keynote in 2006
  26. 26. Gravel-bed restorationin the Tama River
  27. 27. Location Tokyo10km
  28. 28. Outline of the Tama River Length: 136km Basin area: 1,249 km2 Source: Mt. Kasatori, 1,941 m Population: 4,400,000 Visitors: 22,000,000 per year Over 200 NGO groups
  29. 29. Tama River is a top runner forRiver Environment in Japan NGO for the Tama River environment was founded in 1970. River env. division was established in the Tama River authority in 1975. Tama Riv. Env. Management Plan was published in 1980.
  30. 30. River Ecology Research startedat the Nagata area in 1995. Nagata area Slope: 1/330 Sediment: 35 mm Q=2m3/s MHQ=620 m3/s gravel-bed river on the alluvial fan Photo: Keihin river office
  31. 31. Research Group stimulated therestoration project. Research group started meeting with citizens since 1997. People realized the necessity of restoring gravel-bed river though the meeting. Gravel-bed river restoration also fitted the needs of river authorities for flood control. Discussion has started for the restoration in 1999.
  32. 32. Problems in the Tama River?
  33. 33. River incision Gravel mining (stopped in 1967) Dams and weirs
  34. 34. Encroachment of invasivevegetation (Robinia pseudoacacia )19741997
  35. 35. Gravel-Gravel-bed species decline Aster Kantoensis Phragmites Japonica Eusphingonotus japonicus Floodplain grasshopper Copyright Prof. Oohori Robinia pseudo-acacia
  36. 36. Restoration measures Channel widening (Aufweitungen) Removal of Forest of Robinia pseudoacacia (invasive) Sediment augmentation (sediment from upstream weir)
  37. 37. Studies onrestoration projects
  38. 38. Irreversible impact of gravel mining at the incised reach 160 Sediment fills Time interval between lines: 96 years Riverbed elevation in 1923 only upstream ofAverage bed elevation (m) 150 624 years 140 Ozaku weir 48 years Nagata area Hamura weir Kabe district No recovery with 130 Nagata district Narrow section the incised channel 120 Groundsill (Hattori et al. 2003) 110 50 52 54 56 58 60 62 Longitudinal distance (km) → Channel widening is necessary for restoration to reduce the tractive force.
  39. 39. Sediment supply to restore the fluvial system (Hattori et al. 2003) Shields number at the Top bar Bar Shields Number at the Topofof Bar Shields Number atthe top ofBar 116 0.14 0.14 116 116 Water Level atat AverageAnnual Water Level atAverage Annual 0.14 Riverbed Slope Changes Shields Number atat thetop ofofbar Water Level Average Annual Maximum Discharge Maximum Discharge Maximum Discharge 0.12 1/350→1/250 Shields number the Top 115 115 0.12 115 Before Before 0.12 Critical Value of Critical Value ofof Just After Just After Critical Value Excavation Excavation Common Reed Destruction Common Reed Destruction Excavation Excavation 0.1 Common Reed Destruction 0.1Elevation (m) 114Elevation (m) 114 114 0.1 Excavation + 113 113 113 Increase of 0.08 0.08 0.08 Riverbed Excavated Area Excavated Area Channel Widening 112 112 112 Slope Bar Bar Bar 0.06 0.06 0.06 Before Excavation Before Excavation Before Excavation Just After Excavation 111 111 111 Riverbed Slope Changes 0.04 0.04 0.04 ExcavationExcavation of Just After + Incarease 1/350→1/250 Riverbed Slope 110 110 110 0.02 0.02 00 0 50 50 50 100 100 100 150 150 150 0.022 4 6 8 10 Transversal distance Left Levee(m) Transversal Point on (m) Levee(m) Distance From the Starting distance (m) Levee(m) Distance From the Starting Point on Left Distance From the Starting Point on Left 22 44 66 88 10 10 Transversal distance (m) Occurrence period (year) (year) Return Probability Occurrence period (year) Return Occurrence Probability (year) Probability (year) Sediment supply is necessary to sustain gravel bed
  40. 40. Sediment augmentation volumeSediment volumewas estimated5,500 m3/year tomaintain gravelbed by calculationand large scaleexperiment.
  41. 41. Outline of the restoration A工区 B工区 C工区 D工区 E工区 400mSediment supply River widening1.7 km upstream Vegetation removal (~21,000 m2)
  42. 42. Enlarged gravel river bed Photos: Fukushima M, PWRI2001 Sep 20 2002 Jul 5 2003 Aug 252004 Aug 4 2005 Jul 22 2006 Jul 28
  43. 43. Results: Gravel-bed restoration Gravel- Increased the number of plover (Charadrius placidus), floodplain grasshopper, gravel-bed plants (e.g. Aster Kantoensis), benthic fishes. Mitigation of river incision
  44. 44. Decision-Decision-making processes Interdisciplinary Elicitation 1995- research group meeting, seminar Demand Citizen 1997- Tama River Decision Authority Committee for Strategy 1999- restoration consultation Tama River Implementations 2001- Authority
  45. 45. Lessons fromthe Tama River
  46. 46. Interdisciplinary research groupincluding river authorities are ofgreat importance for riverrestoration.Researchers Practitioners
  47. 47. Scientist should explain theirresearch results to local people. Scientific and accurate information gives great effect for decision making process. Importance of sharing information and enlightenment
  48. 48. Scientist should give quantitativeestimation as much as possible. Gravel augmentation and that volume was decided by large scale experiment. River widening was decided based on the calculation.
  49. 49. Scientist should publish theresults to multiple readers. Books for citizens Reports for specialists
  50. 50. Thank you for your attention ! Nishizawa Valley in Yamanashi Pref.

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