River Restoration in Japan

Transcription

1 River Restoration in Japan Keigo Nakamura, Ph.D Water Environment Research Group Public Works Research Institute Contents What is restoration? History of river restoration in Japan Basics for river restoration Case studies 1

2 What is RESTORATION? Restoration is defined as the return of an ecosystem to a close approximation of its condition prior to disturbance. Merely recreating the form without the functions or the functions in an artificial configuration bearing little resemblance to a natural resource, does not constitute restoration. (Berger, 1990) What is RESTORATION? (2) It is axiomatic that no restoration can be ever be perfect; Therefore, all restorations are exercises in approximation and in the reconstruction of naturalistic rather than natural assemblages of plants and animal with their physical environments. (Berger, 1990) 2

3 History of River Restoration in Japan Sukenobu Nishikawa History of River Environment (1) 1957: Contaminated Sediment dredging in the Sumida River (1st aquatic environment project after WW2) 1970:Basic Law for Environmental Pollution Control (Severe pollutions such as Minamata disease, Yokkaichi asthma, etc.) 1974: River Park for urban amenity (The end of rapid economic growth) 3

4 History of River Environment (2) 1990: Naturally-diverse river works, Japanese version river restoration project 1997: Amendment (on River Environment) of River Law and enactment of Environmental Assessment Law River Law for Environment Flood Control Flood Control Water Use Flood Control Water Use Modern river administrat ion system Integrated river system management water-use regulations Environment 4

5 Naturally-diverse river works (Japanese river restoration) Officially started in 1990 by MOC(MLIT) Purpose Ecosystem with high biodiversity Beautiful landscape Planning for river restoration 5

6 Process of Restoration planning Outline survey for targeting Comprehensive target Detailed survey Concrete target, performance index Design, works Monitoring Adaptive management CONSERVATION comes first for good river environment 6

7 What kind of environments should we conserve? (1) River dependent environment What kind of environments should we conserve? (2) Peculiar to this river 7

8 What kind of environments should we conserve? (3) Restoration difficulty > What kind of environments should we conserve? (4) High ecological value 8

9 What kind of environments should we conserve? (5) Rare species Restoration comes second. If a river is not preferable situation, we have to set the target for restoration. But How? 9

10 Comprehensive Restoration target: How to find the reference site? Former river, ex. 1960s Adjacent river with low human impact Upper or lower river with low human impact Recourses for studying Former river situation Old map Old photos Old books and papers Old people 10

11 Study on-site, not on the desk On-site study is the best way to find the reference site. Original lake littoral gradient reclaimed about 300 years ago From Comprehensive to Concrete target Aquatic Creature or community (ex.numbers or dencity of fish and birds) Habitat (ex. Area of Reed bed, gravel bed,pool, backwater) Physical condition ex. Discharge, salinity, water level fluctuation 11

12 Case study 1 Lake Kasumigaura Lake Kasumigaura Restoration of Lake littoral zone 12

13 Outline of Lake Kasumigaura Area 220km 2 Mean Depth 4m Basin area km 2 Fresh water, originally brackish Retention time 200days Eutrophic Decrease of Vegetation Area in Lake Kasumigaura Submerged plants Reed etc. Sakurai,

14 Aquatic Vegetation Emergent Plants Floating leaves Submerged plants 14

15 Why lake vegetation has decreased? Direct damage by lake bank Indirect damage by lake bank Water pollution Artificial water level management Drifting matters, wood, large-size refuses Direct damage by bank construction

16 Indirect damage by Lake Bank Littoral wave energy is higher 10-20% because of high reflection of bank Lateral erosion by indirect wave Speeding up littoral current High reflection rate of Lake bank 16

17 Lateral erosion by indirect wave standoff Erosion of reed front 17

18 Effect of artificial water level fluctuation Natural water fluc. Watere Level New shoots need a bare land in Spring Uprise in fall damages fully grown plants Artificial water Fluc. Spr. Sum. Fall Win. Emergency Countermeasure for vegetation in

19 Countermeasures Committee for conservation of vegetation in Lake Kasumigaura, which members are Scientists, NPO, Governments. Conservation and Restoration of Littoral zone Tentative water level drop in winter Basic concepts for restoration (1) Conservation of Watershed, not only Lake Kasumiguara Conservation and restoration of proper and healthy ecosystem of Lake Kasumigaura Sustainable conservation and restoration 19

20 Basic concepts for restoration (2) Adaptive management Scientific approach Cooperation between government, scientist, and citizens Emergency Countermeasure 11 areas, 200,000m 2 Conservation (breakwater) Restoration (Restoration of mild littoral slope) 20

21 Points 1 for restoration Historical understanding Understanding of former morphology Historical value (natural or reclaimed) Refer the old shoreline Ask old people Point 2: Back to the nature Restore the natural gradient of littoral zone Use sand from Lake Kasumigaura, expect restoration from seed bank Observe nature without prejudice angle of slope 1 : 1-1 : 2 1 : 2-1 : 4 1 : 4-1 : 12 1 : 12-1 : 20 1 : 20-1 : 30 1 : 30-1 : 50 1 : 50-1 : 75 1 : 75-1 : 100 < 1 : 100 Pepple stone ( mm) gravel (6,3-63 mm) gravel (2-20 mm) sand (0,2-2 mm) fine sand (0,02-0,2 mm) clay (< 0,01 mm) substrate / (grain-size) boulders ( cm) boulders ( mm) walls Siessegger 21

22 Schematic cross section of restored bank Submerged and floating plants Grad.1:10 Slope base Dia.=100mm 5kg Emergent plants Grad.1: m 1.1m Beach sand from Lake = mm Pampas grass etc. Original bank Bank cover 50kg Point 3:Adaptive management Maintenance according to the monitored results Optimization by experimental approach 22

23 January 22, 2002 March 19,

24 May 19, 2002 July 9,

25 Conserve Existent vegetation Lessons from this case Seed bank is quite effective way to restore the native plants community Self-design comes first. Install buffer material between solid (concrete) and soft materials (sand) 25

26 Case study 2 Itachi River Restoration at Urban area Itachi river, Before restoration 26

27 After Restoration Lessons from Itachi riv. Minor restoration at Urban river enhances not only the amenity of the life, but the price of land Non-dynamic, or dead, river requires more human assist 27

28 Case study 3: Tama River Restoration of Backwater (Wando) Case 4: The Nuki River Dynamism and self-design 28

29 Active river needs large area Nature is the best designer 29

30 Lessons from Nuki Riv. Freedom to the river More space to the river Self design Case 5: Shojin River Oasis in Urban area 30

31 Before restoration Concrete bank isolates the movement of living things A fence separates river and living space 31

32 After restoration Continuity between river and park 32

33 Recycle of Concrete waste Riffle and pool 33

34 Lessons from Shojin river Remove not only concrete but also a wall between government sectors Recycle of construction wastes Conservation of riparian zone in urban area Case 6 Matsue Horikawa river Restoration of water quality also restored the recreational boat tour around Shimane castle This restoration increased the tourist 300,000 per year. 34

35 Lesson Ecology is economy Boat cruising cookie is a new Omiyage, souvenir Conclusion Concrete target is indispensable for restoration Refer the old map, photos, and old people Do not design too much, follow the principle of self-design After all, Ecology is economy 35