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IN-DELTA STORAGE PROGRAM STAKEHOLDERS COMMITTEE MEETING. URS Corporation January 22, 2003. Engineering Investigations  Embankment Heights and Design. Two Embankment Concepts Were Evaluated Rock toe berm on slough side Bench on slough side (variable width). Rock Toe Berm Option.

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IN-DELTA STORAGE PROGRAM STAKEHOLDERS COMMITTEE MEETING

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In delta storage program stakeholders committee meeting l.jpg

IN-DELTA STORAGE PROGRAMSTAKEHOLDERS COMMITTEE MEETING

URS Corporation

January 22, 2003


Engineering investigations embankment heights and design l.jpg

Engineering Investigations Embankment Heights and Design

Two Embankment Concepts Were Evaluated

  • Rock toe berm on slough side

  • Bench on slough side (variable width)


Rock toe berm option l.jpg

Rock Toe Berm Option


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Bench Option


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Freeboard Studies

  • Freeboard Criterion Greater of:

    • 3’ + 100-yr. flood stage, or

    • Wind wave runup + setup + 100-yr. flood stage

  • Embankment Crest:

    • Webb Tract: Crest El. 10.0 to El 10.1

    • Bacon Island: Crest El. 10.1 to El. 10.3

  • Crest elevation lower than for 2001 study


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Stability Analysis

  • Stability analyses performed for various conditions

    • Rock toe berm and bench options

    • Various water levels in slough and reservoir

    • Min/max elevations of base of peat layer

    • Load conditions

  • Foundation conditions for analysis from reports

    • Department of Water Resources

    • Bureau of Reclamation

    • Army Corps of Engineers

    • Consultants


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LOAD CONDITION

W.S. SLOUGH/RES.

EMBANKMENT SIDE

ROCK TOE BERM

BENCH

LONG-TERM

-1.0 / 4.0

SLOUGH

1.6 - 1.8

1.5 - 1.6

LONG-TERM

7.0 / empty

RESERVOIR

1.7 - 1.9

1.5 - 1.6

SUDDEN DRAWDOWN

6.0 / 4.0 to empty

RESERVOIR

1.5 - 1.6

1.3 - 1.4

POST-SEISMIC

-1.0 / 4.0

SLOUGH

1.4 - 1.6

1.1 - 1.2

POST-SEISMIC

3.5 / empty

RESERVOIR

1.3 - 1.4

1.1 - 1.2

Summary of Calculated Factors of Safety*

  • * Lowest F.S. shown for peat at El. –40 and –20, for rock toe berm and bench.

  • Factors of safety for rock toe berm are greater, and seismic deformations lower, than for bench option.

  • Risk and cost to be considered to recommend rock toe berm or bench option


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Borrow Area Investigations

  • Field investigation conducted in December 2002

    • 10 borings drilled (15’-19’ deep) totaling 165 ft on each island

    • Laboratory tests performed to characterize materials

  • Borrow areas delineated

    •  Sandy soils within 15 feet of ground surface

    •  Volumes being estimated

  • Results to be used for construction cost estimation


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Seepage Studies

  • Seepage control alternatives considered (mostly on Webb Tract & Bacon Island)

    • Interceptor wells

    • Slurry walls

    • Reservoir floor clay blankets

    • Collector trenches

  • Capital cost, constructibility, and operation & maintenance considerations


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Seepage Studies (cont’d)

  • Estimated pumping rates to control seepage & exit gradients

    •  Reservoir water surface @ el. +4.0

    •  Well spacing @ 160 feet

    •  6 gpm to 8 gpm per well

    •  Exit gradients less than 0.3 (criterion)

  • Seepage control can be on Webb Tract and Bacon Island

  • Seepage quantities are less than for 2001 study


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