surface screened intake implementation considerations€¦ · erosion events), o) reduced hydraulic...

Surface Screened Intake Implementation Considerations

Zita Yu, PhD, PETechnical Planning Supervisor

CalDesal Conference 2019February 7, 2019

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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

ZitaY@WestBasin.org

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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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