Wind waves and sediments

Calm

Stephen MonismithJeremy Bricker, Satoshi Inagaki, and Nicole Jones

Stanford University

Windy

Supported by UPS Foundation and CALFED ERP

Sediment model (ca. 1999)

• TRIM3D - Casulli code as modifed by Ed Gross - calibrated for Winter/Spring 1995

• Sediment model = 3D transport + standard cohesive sediment model (Inagaki and Bricker)

• Use Krone’s (1962) values for sediment model parameters (Erodability etc.)

• (for seds) Increase bed stress to min. drag coeff. value

• (for seds) Include wave friction factor in bed stress calculation

• Waves modeled using USACE Shore Protection Manual

(kg/m3)

Tide Only

Waves:H=0.6m T=2.8s

Effects of waves on computed concentrations (1 m below

MLLW)

Wave Estimation

Shore Protection Manual (US Army Corps of Engineers, 1984)

(s) period wave:

(m)height wave:

T

H

(m) depth :

(m) fetch :

(m/s) speed wind:

d

F

U A

Wave Estimation

Fetch

SF PORTS winds Wind from W

Winds

+

N

Comparison: Measurement vs Prediction at Coyote Point

(using SFO wind)

Modeled sediment concentrations with and without winds

Effect of more realistic waves

(kg/m3)

From 4/19/1993, 6 days

Suspended sediment concetration at 1m below MLLW

hindcast with tides, winds, and waves

Two wave models

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Shore Protection SWAN (Bricker)

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Wind waves over shallow estuarine shoals

Steady bottomboundary layer

Steady surface boundary layer

Whitecapping-affected layer

Wind stress

z

U(z)

-dP/dx(tides)

Oscillatory bottom boundary layer

Coyote Pt. observations

Tidal stage and sea state at Coyote Point, June-July 2002

Conditions at Coyote Point, June-July 2002

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currents dominate

waves dominate

Wind waves dramatically enhance bottom stress(Bricker et al J. Hyd. Eng. 2005)

C

D

u*2

U1002

10-2

10-1

10-3

Mean velocity/orbital velocity

No waves

Effect on drag coefficient

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15 x 10-3

10 x 10-3

5 x 10-3

“canonical”

Wind waves in Suisun Bay

Jones and Monismith JPO 2008

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Wind

Breaking

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Turbulence due to breaking

Bre

akin

g

Bott

om

BL

Langmuir cells

(Franks Tract)

Wind wave evolution

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Day

Summary

• Waves important to sediment dynamics on shoals

• Waves modify bottom drag and thus flows and transport on shoals

• Waves modify vertical turbulent mixing of sediments on shoals

Needs

• Validated wave model for SF Bay (SWAN?)

• Wave data for whole bay• Spatially variable parameters for

sediment model (Sedflume?)• Parametrization of effects of wave

damping by soft muds

• Compare sediment model (with waves) to both short and long term data sets

The bottom (Elkhorn Slough)