Sustainable Reservoir Strategy and Flood Management in Taiwan

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1 Sustainable Reservoir Strategy and Flood Management in Taiwan NCTU-DPWE Enhancing Life Security Prof Jinn-Chuang Yang National Chiao Tung University Disaster Prevention and Water Environment Research Center

2 Outlines Natural Environment in Taiwan Landform, geology, & hydrology Water related disasters Short summary Sustainable Reservoir Strategy Flood management Collaboration with Deltares

3 Natural environments in Taiwan Landform and geology Total area Mountainous area Population Population density 36,000 km 2 66% 23 M 639 per km 2 (10 th highest over the world) TW Tachia Tamshui Chaoshui River slopes Elevation (m) JP Shinanogawa Tonegawa US Colorado River Europe Rhine Elevation distribution Slope distribution Distance from the river mouth (km) From: WRA

4 Natural environments in Taiwan Hydrology Annual average: 2,500 mm Rainfall concentrates in May-Oct 63% 76% Wet season - Rainfall induced landslide in watershed Reservoir sediment deposition Storage capacity loss Turbid water Clean water shortage Dry season - Water demand Reservoir water supply meet 30% of water demand Groundwater abstraction meet 20%-40% of water demand Landsubsidence 89% 76%

5 Rainfall induced disasters Landslide and Debris Flow Deposition and Water Quality Watershed 圖片來源 : 農委會林務局 (2006) 圖片來源 : 水保局網頁 Reservoir Degraded ecological environment Overflowing 圖片來源 : 網頁新聞畫面 圖片來源 :FISRWG (1998) River instream Urban Area Inundation Damage of instream structure Land Subsidence 圖片來源 : 洪夣祺 圖片來源 : 網頁新聞畫面 圖片來源 : 地層下陷防治服務團 圖片來源 : 網頁新聞畫面

6 Landslide disasters Mountain village 2009 Typhoon Morakot doomed Xiaolin Village Xiaolin Landslide volume > 20 M m 3 Casualty > 600 Debris dam

7 Flood disasters 2009 Typhoon Morakot Rapid river evolution in southeast Taiwan Before After 7

8 Disasters in subsidence area Legend Location Accumulated subsidence in 20 yrs(m) Annual subsidence (cm/yr) Inundation Sea water intrusion 圖片來源 : 地層下陷防治服務團

9 Storage reduction in reservoirs Reservoir Completion Total storage capacity (M m 3 ) Capacity loss (M m 3 ) Storage capacity loss Feitsui % Shihmen % 70% of all reservoirs storage Wuseh % Baiho % Tsengwen % Nanhua % Averaged 36% of storage capacity loss 17% storage capacity loss in 2009 TP Morakot Wushanto % Agondian % Mutan % 12 M m 3 sediment dredging during

10 Short summary Young Geology & steep hillslope Extreme hydrology Landslide River erosion Rapid river evolution Inundation Reservoir capacity loss Clean water supply risk Economic loss Life loss Sustainable Reservoir Strategy Hsimen reservoir rehabilitation project one billion dollar Flood management Improvement project for subsidence prone area, 4 billion dollars

11 Sustainable reservoir strategy -ShihmenReservoir

12 Brief info on ShihmenReservoir watershed Watershed: km 2 Full water level: 245 m Dam Height:133 m Total storage: 309 M m 3 Design effective storage: 251 M m 3 Effective storage: 209 M m 3 (in 2011) Lost 11% storage in 2004 Typhoon Aere Post-Aere Landslide sites

13 Facilities Tunnel spillways EL 220m Dia 7.0m 2400 cms Spillways EL 235m 8600 cms PRO EL 169.5m Dia 1.37m 31 cms Power plant Penstock EL 173m Dia4.57 m 65/300 cms Stratified water intake shaft From WRA website

14 Damages by 2004 Typhoon Aere Floating debris Power plant valve Turbid water >> 3000 ntu Turbine 967 mm rainfall in area average 8600 cms of peak discharge 665 million m3 of inflow vol. (3 times the effective capacity) Landslide area: 673 hectares Sediment deposition 27 M m3 (11% of design capacity) Water supply stopped for 18 days Trash racks

15 Sustainable reservoir strategy and key technologies Goal Sustainability: Storage preservation and water supply stability Strategy Soil conservation Prevent sediment deposition Reduce water supply risk Objective Reduce sediment inflow Reduce sediment deposition Reduce raw water turbidity Key issue Sediment yield control Sediment discharge through reservoir facilities Water supply improvement under high turbidity Technology developed Landslide volume estimation TDR extensometer piezometer FBG inclinometer piezometer TDRSSC monitoring system Sediment transport & density current models Sediment sluice tunnels & penstock renovation Water supply risk evaluation Stratified water intake shaft

16 Landslide and reservoir sediment deposition Shihmen Reservoir Decrease in capacity Typhoon Landslide area Decreased capacity Storage capacity history of Shihmen reservoir Annual decreased capacity in million m Percentage of design capacity 2004 Aere 673 ha m 3 11% GLORIA 1,375 mm ELSIE 493 mm BETTY 607 mm Annual decreased capacity Total capacity Year NELSON 538 mm AERE 967 mm HERB 715 mm KROSA 666 mm Total capacity in million m 3 高程 (m) 累距 (m) 原始底床 1964( 葛樂禮颱風 ) 2004( 艾利颱風 ) 2007( 科羅莎颱風 ) 2009( 莫拉克颱風 )

17 Sediment yield & reservoir deposition estimation Landslide volume estimation modeling Potential landslide area Landslide occurrence probability Probability (%) Potential landslide volume Total landslide volume ( 10 4 m 3 ) Variable 200 mm 400 mm 600 mm 800 mm 1,000 mm 1,200 mm 2000 Landslide volume estimation conditional on rainfall amounts 2250 Probability (%) Sediment yield & reservoir deposition Sediment yield Increase sediment discharge efficiency to 40% After treatment of high potential landslide slopes 600 Annual decreased storage ( 10 4 m 3 ) Probability distribution of annual deposition

18 TDR SSC monitoring system TDR advantages: 1. Transmission Line (like TV cable, cheap) mechanism based 2. Waveguides without any electronics 3. Easy installation and maintenance 4. Multi-function and multi-channel 5. (Semi-) profile scan in one cable SSC measurement: Accuracy ~ ±1000 ppm Range from 1000 ppm to >300,000 ppm Particle size independent Error <15%

19 SSC monitoring during 2013 Typhoon Soulik Peak Inflow 5458cms Peak rainfall 94.2mm/hr Q>300 cmsover 47 hrs 19

20 Delta deposition Sediment transport behaviors Density current 2008 Typhoon Fungwong Density current Density current submerge section Floating debris circulation Typhoon Fungwong Sinlaku Morakot Peak discharge (cms) Surface Clear/turbid water interface Outlet 2,040 3,446 1,838 Elevation 高程 (m) SSC profile wrttime at section SSC,mg/L 月 28 上午 3:00 7 月 28 上午 8:00 7 月 28 下午 12:00 7 月 28 下午 5:00 7 月 29 上午 12: Inflow volume (M m 3 ) Density current velocity (m/s) Thickness (m) N/A 215

21 Sediment transport modelingsediment sluice tunnel planning PRO Sluice tunnel Plan D (at Amuping) Under planning 4.2 km 1600 cms For coarse sediment Penstock renovation Completed in 2013 For silt and clay 300 cms Sluice tunnel Plan C (at Dawanping) Under planning 1 km 1200 cms For silt & clay 2D/3D models verified with the TDR SSC monitoring data

22 Sediment discharge and water intake shaft Penstock renovation Stratified water intake shaft EL236 m Water supply failure probability SSC lasts less than 1 day EL 228 m EL 220 m

23 Sediment discharge through penstock 2013 Typhoon Soulik

24 Sediment sluicing and dredging for Shihmen Reservoir Average annual sediment Inflow (10 6 m 3 ) 3.42 PRO sluice way 0.15 (4%) Expected average annual sediment outflow Power plant penstock renovation 1.02 (30%) Dawanping siltsluice tunnel 0.71 (21%) Amuping sediment sluice tunnel 0.64 (19%) Dedging near dam 0.50 (15%) Dredging u/s from reservoir Unit: 10 6 m 3 Sum 0.40 (12%) % 19% 26% 100% Gated sediment sluice tunnels FEWS may help optimal gate operation

25 Flood management

26 Impervious area increasing - Land use in Taipei Basin From: Tsing-Chang Chen et al

27 Flood disasters 171 typhoons occurred during 1958~ ,456 injured, including 2455 dead, 1098 missing 342,378 houses failed Dike failure in 2004 TP Mindull Turbid water by floods Taipei inundation in 2001 TP Nari Bank retreat in 2009 TP Morakot Kalmaegi Dike failure in 2008 TP Kalmaegi TP Morakotafter math Coastal erosion Kaohsiung inundation in 2006 TP Tanmi Kaohsiung inundation in 2006 thunderstorm Landslide killed

28 4 Channel erosion 2008 Typhoon Sinlaku damaged 5 bridges Tuming Bridge Hofong Bridge Niouming Bridge Wuhuliao Bridge Chiashiang Bridge 圖片來源 : 網頁新聞畫面 reintallation 圖片來源 : 蔡長泰教授 5 3

29 Flood management New Low impact development Land use management Disaster prevention and mitigation Conventional practices Watershed management Environment and biology Water resources management

30 Ideal flood defense system Structural measures Non-structural measures Household rainfall dten Soil conservation Early warning & evacuation Detention pond Ring dike Land restoration Plantation Retention basin lood diversion Retention in parks Flood plain management Channel desilting Detention pond River dike Early warning & dodge Flood insurance Channel remediation Basement detention pond V-storage between buildings

31 Flood detention ponds 台北大湖楊梅高山頂 雲林南公館 嘉義白水湖 A1 嘉義四股 嘉義內田考試潭 台南立德南科 D 池台南三舎 台南都會公園

32 Detention ponds for protecting high value fish farms 新塭北側滯洪池 新塭南側滯洪池

33 Collaboration with Deltares

34 FEWS_Taiwan River basins 26 rivers ready Models SOBEK HEC-RAS WRF Ensemble Real-time water level correction System FEWS_Taiwan Live System Collaboration groups Deltares, WRA, NCTU Model integration into FEWS Landslide model Reservoir operation model River bank retreat model

35 Look forward to future collaboration Education Professional training for government employees NCTU-DPWE Enhancing Life Security R&D Technology integration & development Increase project spectrum and technology integrity New problems to be solved Think Tank Consultancy

36 Thanks for your patience Comments? Visit NCTU-DPWE at

37 Enhance joint security by joining force with Deltares Real-time monitoring and modeling in Sediment transport River dike safety Landslide forecasting River structure safety Long term planning Landsubsidence modeling and monitoring Inundation mapping Groundwater resources management Safe drinking water Clean water supply & life expectancy of reservoir Life security near river bank Life security near/on slopes Life security near hydro-infrastructure Levee design and inundation prevention Clean water supply subsidence prevention planning Ind. & agr. development