surface screened intake implementation considerations€¦ · erosion events), o) reduced hydraulic...
TRANSCRIPT
Surface Screened Intake Implementation Considerations
Zita Yu, PhD, PETechnical Planning Supervisor
CalDesal Conference 2019February 7, 2019
www.westbasin.org/desal1
Mission
Provide a safe and reliable supply of high-quality water to the communities we serve.
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West Basin Board of Directors
Division I Harold C. WilliamsTreasurer
Division IIGloria D. GrayVice President
Division IIICarol W. KwanSecretary
Division IVScott HoustonPresident
Division VDonald L. DearImmediate Past President
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Service Area
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100%
Groundwater
55%
19%
9%
>1% 16%
Imported WaterPotableMetropolitan & West Basin
GroundwaterPotableCities & Retailers
Recycled WaterNon-Potable and Potable ReuseWest Basin
Brackish GroundwaterDesalinationPotableRetailerConservationWest Basin & Retailers
Water Supply Diversification Over the Years
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Now
Pre-
1947
80%
20%
Imported Water
Groundwater
1990
Sources
Future Water Reliability Through Supply Diversification
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39%
18%
13%
11%
19%Imported WaterPotableMetropolitan & West Basin
GroundwaterPotableCities & Retailers
Recycled WaterNon-Potable and Potable ReuseWest Basin
Ocean Water Desalination (Potential)PotableWest Basin
ConservationWest Basin & Retailers
Projected
2030
Sources
Ocean Water Desalination Program Step-wise Approach Development
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Pilot Study (2000 – 2008)
Demonstration Study
(2008-2017)
EIR Preparation
(2015 –Present)
EIR Certification and a Board
Decision (Summer / Fall
2019)
Permitting (if approved by Board, TBD)
Ocean Plan Surface Screened Intakes
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• Screen opening size: 1 mm (0.04 in.)
• Through-screen velocity: <0.5 feet per second
Wedge Wire Screens
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CA Fish Screening Criteria (Freshwater)
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California Fish & Game Commissions• Criteria
• Structure placement• Approach Velocity • Sweeping Velocity • Screen Openings• Screen Construction
Screening Mechanism• A size-selective mechanical barrier that prevents
objects (marine life, sediments, or rubbish) greater than the opening size from passing through it.
• Two main driving forces for objects to pass through:
• Sizes • Approach velocity vs sweeping velocity• Motility
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Ocean Plan: Mortality Reduction by Screens
“The regional water board may apply a one percent reduction to the APF acreage calculated in the Marine Life Mortality Report to account for the reduction in entrainment of all forms of marine life* when using a 1.0 mm slot size screen.”
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Size
• :
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Approach Velocity vs Sweeping Velocity
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Approach velocity
Through-screen velocity
Sweeping velocity
Approach Vs Sweeping Velocities in Reservoir (2-inch from Screen)
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Sweeping velocity Approach velocity
Through-screen velocity: 0.66 ft/s
Screen Orientation
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Prevailing current flow
Operations: Corrosion and Biofouling Management
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• Material selection• Passive screens
• Slot openings: • Hydroburst backwash screen intake system
(passive screens)• Main structure
• Macro-biofoulant is manually removed by divers
• Active screens, rotating screens• Regular diver inspection • (Mechanical failure)
Material Selection and Biofouling
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Stainless Steel with Antifouling Coating Cu-Ni Alloy
Closing
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• Ocean water desalination can be an important climate change adaptation strategy to increase water reliability and drought resiliency in freshwater resources limited regions
• Subsurface intakes may not always work• Intake entrainment and impingement impacts are reduced
effectively by the use of screens, especially with low through-screen velocity
• Mortality reduction credit of 1% should be based on what can physically enter the screens
• Mitigation measures prescribed in the Ocean Plan could provide California an important resource to restore coastal resources to benefit the ecosystem as well as our communities
Thank you!
Zita Yu, PhD, PETechnical Planning Supervisor
Tel: 310-660-6213
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Proposed Project Location
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Nourished Beaches
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Ballona Creek
Coastline with sand nourishment
Coastline without sand nourishment
Littoral transport
Subsurface Intake Technologies
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• Vertical wells• Slant wells• Radial (Ranney) collector wells• Horizontal directional-drilled (HDD) wells (sometimes
called drains)• Seabed infiltration gallery• Beach (surf zone) infiltration gallery• Deep infiltration gallery (water tunnel)
• Key findings presented in the 2018 CalDesal Conference https://bit.ly/2REsNsW
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Coastal Margin in El Segundo
Constraints of Using HDD Wells
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Construction• Clay layer (20 feet) below the ocean floor limited hydraulic connection
• Overburden < drilling mud pressure drilling mud leakage
• The presence of gravel and cobbles 1) deflect an HDD boring, 2) obstruct the reaming pull-back of the intake pipe, 3) drilling mud leakage
• Existing subsurface infrastructure (oil pipelines and submarine cables) damage C) from drilling activities O) from leakage from oil pipelines
Operations• Closure depth of 50ft @ 6,500ft from coastline O) expose the drains (major
erosion events), O) reduced hydraulic connection (major deposition events)
• Fine-grained deposition carried by the prevailing southward littoral transport clogging
• Lack of precedence of intake systems operating in similar settings.
Conveyance System
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