0012.02..1 Managing River Sediment in Extreme Conditions: Lessons for California Hsiao-Wen Wang Professor, Department of Hydraulic and Ocean Engineering National Cheng Kung University, Taiwan Fulbright Visiting Scholar at University of California Berkeley California Taiwan Taiwan and US Comparison https://www.wrap.gov.tw/en/paper7.aspx 3 Taiwan California Facts Hydrology variable, Hydrology variable, Geologically active, Geologically active, EarthQuake, Changing EarthQuake, Changing climate… climate… Annual rainfall (mm/yr) 2509 54.5 Mean length of river (km) 124 584 Population density 639 93 (people/km2) Per capita distribution of 3860 588 rainfall (m3/person/yr) No. of Reservoirs 61 major 3190 Owners Mostly public Public and private Total Capacity of Reservoir 2.2 billion m3 52.5 billion m3 Reservoir Sedimentation 30% lost for 61 major 7% lost for 43 reservoirs by reservoirs by 2011 2008 4 California Taiwan 423,970 km2 36,000 km2 ~ 39 million people ~ 23 million people • Ratio in SIZE = 12 • Ratio in POPULATION: 1.7 Chishan River Before and After Typhoon Morakot in 2009 Bedrock exposed Chishan River Before and After Typhoon Morakot in 2009 15m deposition HWM in Tainan Characteristics of Taiwan • Northeast monsoon • Mean annual precipitation of 2.5 m/year • Annual average of 3~4 typhoons; Frequent earthquakes • The rainfall ratio of wet to dry season is 1.5 in northern and 9 in south region • Water demand more in the west • Denudation rates of 3~6 mm/year • Sediment yield are high 9 10 Taiwan supplies the oceans with 384 M tonnes of suspended sediment per year, about 1.9% of the world’s total, from its 36,000 km2 (only 0.024% of the world’s land area). Mean annual coastal SSL Bedrock erosion rate Denudation Elevation (Dadson et al., 2003) 11 (Minear and Kondolf 2009) California Ø The median denudation rate is 0.18 mm/yr (Heimann et al. 2011) Ø The highest is 0.52 mm/yr in the Mississippi River Transverse Ranges (T) Ø The highest is 0.74 mm/yr in the lower Ø The lowest is 0.09 mm/yr in the Central Missouri tributaries Valley (CV) Taiwan Ø Denudation rate (Wang et al., 2018) • Shihmen reservoir: 2.5 mm/yr • Wujie reservoir: 0.5 mm/yr • Zengwen reservoir: 13.7 mm/yr (Dadson et al., 2003) Reservoirs are filling more rapidly! By 2011, 30 % of the initial capacities of the major reservoirs lost to sedimentation (WRA, 2011) Wujie Reservoir Wushe Reservoir 61 major reservoirs in Taiwan impound a total of 2.2 billion m3 for municipal, industrial, and agricultural water supply 13 Emerging Worldwide Issues 14 Emerging Worldwide Issues 15 Sediment Management Alternatives (Morris, 2015) 16 Shihmen Reservoir • 1964~ • 133 m high • Initial total capacity: 309 Mm3 • Mean annual runoff: 1,468 Mm3 • Mean annual sediment inflow: 3.42 M m3 • Flood control, hydropower generation irrigation and municipal supply, recreation 17 Mechanically dredging 18 123 check dams upstream of Shihmen Reservoir 2002 (Wang and Kondolf, 2014; Wang et al., 2015) 19 The three largest check dams Yixing Dam (1966) Ronghua Dam (1984) Barlin Dam (1977) 12 Anuual deposition 33% 10 Initial capacity of check dams 8 Cumulative deposition (Shihmen Reservoir) Cumulative capacity of check dam 6 4 2 0 Reservoir Sedimentation (m3 x 107) 1958 1967 1976 1985 1994 2004 2012 (Wang and Kondolf, 2014; Wang et al., 2015) year 20 3 4 Mm3 7.5 Mm Barlin dam failure 3 • 1977~2007 3.5 Mm • 38-m-high • 10.47 Mm3 2007 2002/10 2005/9 2005 2006/8 (Wang and Kondolf, 2014) 21 Dam structure condition in 2007 Dam Initial Apparent Integrity Filled (stream) Capacity of Dam (from with (103 m3) visual inspection) Sediment? (year built) Barlin 10,470 Failed Yes (prior (Dahan) (1977) to failure) Ronghua 12,400 Main dam condition Yes (Dahan) (1984) good (after repairs) Yixing 5,800 Defense dam failed, Yes (Dahan) (1966) dam undercutting possible Ronghua Dam (Wang and Kondolf, 2014) 22 Typhoon Aere (2004) Ø 18 days water supply interruption Ø Debris clogging intakes Ø Sedimentation of approximately 27.9 Mm3 Shihmen Reservoir during Typhoon Aere in 2004 23 Deposited Muds in Penstocks in Shihmen 24 Floating Debris after Typhoon Aere at Shihmen From Water Resources Agency (WRA) 25 Modifications to Shihmen Reservoir to Manage Sediment 26 New sediment concentration monitoring techniQue - Time Domain Reflectometry, TDR (Chung and Lin, 2011) S7 S15 S20L Typhoon Soulik in 2013 27 New hydraulic facility Amuping desilting tunnel (~2021) Dawanping desilting tunnel (planning) Ø 3.7-km long; multi-purposes Ø O.9-km long; turbidity currents Ø $133M USD Ø $160M USD Ø 0.64 Mm3 Ø 0.71 Mm3 RESERVOIR hydraulically Low water dredged Coarse grains Fines RESERVOIR Typhoon Without tunnel flushed RESERVOIR Very low trucked With tunnel 28 Sediment Sluicing at Shihmen in 2013 2.9 M m3 sluiced (FROM WRA 29 4.3 Unit: Mm3 Mechanical dredging (2002-2015) 6.7 8.5 - Power plant penstock (2005-2015) Hydraulic Dredging/ Sediment Sediment removal 14.5 (1977-2015) pass-through (2005-2015) 1.2 - Modified Power plant penstock (2013-2015) Hydraulic 0.9 - Permanent River Outlet (2012-2015) - Spillway (2008-2015) Dredging 1.9 (1985-2015) 1.8 - Diversion way (2008-2015) 0.2 - Tunnel spillway (2008-2015) 8.1 Strategy Years Cumulative volume of sediment removed Cost Unit cost Hydraulic dredging 31 8.1 Mm3 $160 M USD $20 USD/m3 Sediment pass-through 10 12.6 Mm3 $67 M USD $5 USD/m3 While the sediment removal innovations have a high initial capital cost, they are more cost effective over the long term than traditional dredging 30 Sustainable sediment management plan at Shihmen 31 (Wang et al. 2018) Sediment management at other reservoirs From Chung and Lin (From WRANB) (From WRASB) (From TaiSugar) (From WRASB) 32 Converted to tourism, stopped sluicing Sluicing in 1955 Sluicing resumed in 2013 33 Conflict with tourism, Flushing not empty Renovation 1998-2005 34 Sediment Management Alternatives (Morris, 2015) 35 (modified from Sumi et al. 2015) 36 Pros and Cons of Sediment Management Strategies For example: • Dredging- low initial capital capacity, high long-term operational cost, low effectiveness • Sediment Bypass Tunnel- high initial capital capacity, high effectiveness Available at Riverlab website http://riverlab.berkeley.edu/ 37 Shih- Rong- Wu- Jen- A-gong- Zeng- men hua jie san-pei dian wen Reduce sediment yield Reduce sediment production ● ● ● ● ● ● from upstream Sediment trapping above reservoir ● ● ● x ● ● Sediment bypass ● x x ● Route sediments Sediment pass-through ● x x ● ● Mechanical excavation ● x x ● ● ● Remove or redistribute Modify operating rule ● ● ● ● ● ● sediment deposits Hydraulic scour x ● ● ● ● x Reallocate storage x x x x x ● x x ● ● alternatives been Modify facility to handle sediment Adaptive strategies Raise dam to increase volume x x x ● x ● considered/implemented? Water loss control and conservation ● x x x x x Have the sediment management management sediment the Have Decommission infrastructure x x x x x x Has a sustainable sediment management plan been developed to identify the management- strategiesA real-time that may sediment be used over monitoring time to combat system and sediment● x -guidedx x x ● sedimentation? operation is needed, but has only been incorporated into the Have or Will measures be implemented to enhance sustainability with ● x x x x implementation schedule?projects of the two principal reservoirs. Are the dam, intakes, and other hydraulic structures designed to facilitate ● x ● ● ● implementation- ofThere future sedimentis not a control viable measures? end-of-project scenario. Has the need for a real-time sediment monitoring system and sediment- guided operation been evaluated, and if needed has it been incorporated ● x x x x ● into the project? Is there a viable end-of-project scenario? x x x x x x Has a reservoir monitoring program been developed that includes a standardized bathymetric protocol starting with the first bathymetric survey ● x x x ● ● soon after initial filling? Has a monitoring program for impacts downstream of the dam been ● x x x ● designed? (Wang et al. 2018) : Considered and implemented; :Only considered; x: Not considered 38 There in no ‘end-of –project’ scenario… These costs are substantial, as has been demonstrated at over 1200 dam removals Year Cost Name Height (m) Comments removed (millions of USD) Privately owned irrigation diversion, removed ChiloQuin (Oregon, US) 7 2008 18 due to aging structure and fish passage; replaced by new pumping station Privately owned irrigation diversion, removed Savage Rapids (Oregon, US) 12 2009 39 due to aging structure and fish passage; replaced by new pumping station Privately owned hydropower (22 MW) dam, Marmot (Oregon, US) 15 2008 17 removed due to cost of fish passage and upkeep 2 dams; both publicly owned; water supply and Elwha and Glines Canyon 32, 64 2012 325 hydropower (15 MW) dams, alternate water (Washington, US) supply constructed Privately owned hydropower dam (1.4 MW), Largest Superfund site in US, 6 million tons of Milltown (Montana, US) 7 2008 120 contaminated (arsenic, lead, zinc, copper, and other metals from mining and smelting) sediments removed 4 Klamath River Dams (Copco I & II, Iron Gate, and 41, 10, 58, 21 2020 Est. 291 4 privately owned hydropower (163 MW) dams JC Boyle) (Oregon, US) (Wang et al. 2018) 39 Chijiawan dam removal • 13-m high, 1972~2011 • 200,000 m3 • Coarse bed sediment • Safety concern and Habitat restoration Formosan Landlocked Salmon 40 • 2013/7/12~7/15 41 1800 1790 1780 1770 20102010/4/11411 (m) 1760 20112011/6/969 20112011/6/30630 1750 20122012/2/13213 1740 20122012/7/22722 Elevation 201299 1730 2012/9/9 20132013/9/13913 1720 20142014/10/301030 20151124 1710 2015/11/24 20162016/11/141114 1700 -1600 -1200 -800 -400 0 400 800 1200 1600 Distance from the dam (m) (Wang and Kuo, 2016) 42 Dam removal V.S.