Patrick Barnard Patrick Barnard Bruce JaffeBruce JaffeJeff HansenJeff HansenDan HanesDan Hanes

An overview of Delft3D Modeling of An overview of Delft3D Modeling of the the

San Francisco Bay Coastal SystemSan Francisco Bay Coastal System

Edwin Elias and Li EriksonEdwin Elias and Li Erikson

IntroductionIntroduction• USGS interestUSGS interest

• Delft3D Model systemDelft3D Model system

• General introduction into the General introduction into the San Francisco Bay modelSan Francisco Bay model

• Detailed studies:Detailed studies:– Long term ebb-tidal deltaLong term ebb-tidal delta– San Pablo BaySan Pablo Bay– Golden Gate areaGolden Gate area– Ocean BeachOcean Beach– Crissy Marsh InletCrissy Marsh Inlet

IntroductionIntroductionUSGS interest….USGS interest….(1)(1) What are the dominant sediment transport What are the dominant sediment transport pathways?pathways? - San Francisco Bay Coastal System- San Francisco Bay Coastal System - Ocean Beach- Ocean Beach - Dredge disposal sites- Dredge disposal sites - Large sand wave fields- Large sand wave fields - Crissy Marsh Inlet- Crissy Marsh Inlet

(2) Long-term evolution of San Pablo and Suison Bay (2) Long-term evolution of San Pablo and Suison Bay

(3) What is the cause of observed ebb tidal (3) What is the cause of observed ebb tidal delta constriction?delta constriction?

(4) What is the cause of the erosional hot spot (4) What is the cause of the erosional hot spot at Ocean Beach?at Ocean Beach? - Sediment supply?- Sediment supply? - Wave refraction/focusing patterns?- Wave refraction/focusing patterns? - Tidal current patterns?- Tidal current patterns?

Scale Cascade (de Vriend, 1998)

Sand waves Sediment budget ETD

Ocean Beach SF BAY evolution

Modeling Modeling StrategyStrategy

• Use existing tools to do the jobUse existing tools to do the job

• Ability to run this on desktop Ability to run this on desktop computerscomputers

• Selected : Delft3D modeling Selected : Delft3D modeling systemsystem

• Construct a base modelConstruct a base model- Limited in resolution- Limited in resolution- Validated on hydrodynamics- Validated on hydrodynamics- Provides boundary conditions - Provides boundary conditions for detailed studiesfor detailed studies

• Create detailed models Create detailed models for each projectfor each project

• Add complexity where neededAdd complexity where needed

Coastal Morphodynamic Modeling using Delft3D

• Cartesian and spherical co-ordinates

• 2D and 3D (σ or fixed layers in the vertical)

• salinity and temperature

• Online Morphology

• turbulence closure (incl. k-L and k-E) models

• drying and flooding

• sediment and morphology

• Dredging and dumping

• Rain fall and evaporation

• Thermal discharge and heat fluxes

• drogue tracks

• domain decomposition

• Wave – Current interactions

• Particle tracking

• Sediment tracking

Coastal Morphodynamic Modeling using Delft3D

Waves:

• SWAN (40.72)

• XBeach

Processes:

• enhanced bed shear stress

• wave forcing due to breaking

• wave-induced mass flux

• additional turbulence

• wave streaming:

Coastal Morphodynamic Modeling using Delft3D

Multiple sediment fractions

Bed stratigraphy

Transport FormulationsNon Cohesive• Van Rijn

(1984,1993,2004,2010) • Engelund-Hansen (1967) • Meyer-Peter-Muller (1948)

Bijker (1971) • Soulsby/van RijnCohesive• Partheniades & Krone

(default)• Slib3d

Morphological Acceleration:

morphology MOR hydrodynamict f t

FLOW grid

 

Delft3D Base Model Set upDelft3D Base Model Set up

Single domain model application

 

Domain Decomposition andDomain Decomposition andschematized Deltaschematized Delta

Domain Decomposition application (25000 cells)

Run time: 1 month 2dh hydrodynamics

1.5 hours (on a 2.66 Ghz Quad Core machine

 

Domain Decomposition andDomain Decomposition andschematized Deltaschematized Delta

Domain Decomposition application (25000 cells)

Run time: 1 month 2dh hydrodynamics

1.5 hours (on a 2.66 Ghz Quad Core machine

SWAN SetupSWAN Setup

• Four nested grids withFour nested grids with 500 m, 200 m, 100 m, 500 m, 200 m, 100 m, and 25 m resolutionand 25 m resolution

• CDIP buoy #029 data CDIP buoy #029 data used to force model used to force model on 3 open boundarieson 3 open boundaries (2D MEM Spectra)(2D MEM Spectra)

• Current grid generated Current grid generated with Delft3D flow modelwith Delft3D flow model

SF water level

Ocean Beach water level

Dep

th (

m)

MORE validation…..MORE validation…..

cm2/Hz/deg

Velocities at Ocean Beach

Velocities at Crissy Marsh

Swell at Crissy Marsh

IntroductionIntroduction• USGS interestUSGS interest

• Delft3D Model systemDelft3D Model system

• General introduction into the General introduction into the San Francisco Bay modelSan Francisco Bay model

• Detailed studies:Detailed studies:– Long term ebb-tidal deltaLong term ebb-tidal delta– San Pablo BaySan Pablo Bay– Golden Gate areaGolden Gate area– Ocean BeachOcean Beach– Crissy Marsh InletCrissy Marsh Inlet

Long-term morphodynamic predictionsLong-term morphodynamic predictions

Evolution of the San Francisco Ebb Tidal Delta Over the Past Half Century

Observed Depth ChangeObserved Depth Change

WHY has the Ebb Tidal Delta contracted? (and what will happen in the future?)

Several potential causes:

(1) Change in sediment supply2) Rising sea level3) Tidal Prism change in SF Bay4) Increase in Pacific Ocean Waves

Prerequisite: can the model approximately reproduce the observed delta?

Model: Tides only, 50 yrModel: Tides and Waves, 50 yr

Measured 2004/2005

Model-reality consistencies:- Overall shape and orientation Asymmetry- Secondary Flood Channels

Model: T0

Long-term morphodynamic predictionsLong-term morphodynamic predictions

Evolution of the San Francisco Ebb Tidal Delta Over the Past Half Century

Observed Depth ChangeObserved Depth Change

Model: Tides only, 50 yr

Measured 2004/2005

Long-term morphodynamic predictionsLong-term morphodynamic predictions

Evolution of the San Francisco Ebb Tidal Delta Over the Past Half Century

Observed Depth ChangeObserved Depth Change

Model: Tides only, 50 yrModel: Tides and Waves, 50 yr

Measured 2004/2005

Long-term morphodynamic predictionsLong-term morphodynamic predictions

Evolution of the San Francisco Ebb Tidal Delta Over the Past Half Century

Observed Depth ChangeObserved Depth Change

WHY has the Ebb Tidal Delta contracted? (and what will happen in the future?)

Several potential causes:

(1) Change in sediment supply2) Rising sea level3) Tidal Prism change in SF Bay4) Increase in Pacific Ocean Waves

Prerequisite: can the model approximately reproduce the observed delta?

Higher Sea Level > ETD Contraction

Shallower Bay > ETD Contraction

Deeper Bay > ETD Expansion

100 year long simulations with tide only

Hindcasting bathymetric change in San Pablo BayMick van der Weegen (IHE) & Bruce Jaffe (USGS)

Measured: 1877 1856 - 1877

Modeled: 1877 1856 - 1877

Measured: 1856 Measured - Modeled:Residual sediment transport:

Wet period Dry period

Predicted sediment transport - ‘hydrodynamic tidePredicted sediment transport - ‘hydrodynamic tide ’’

Ocean – Bay interactionOcean – Bay interactionUnderstand the processes of flow and sediment Understand the processes of flow and sediment transport in and around the San Francico Bay transport in and around the San Francico Bay

entranceentrance

Predicted mean flow – 1-month periodPredicted mean flow – 1-month period

Predicted flow over the Predicted flow over the sandwave areasandwave area

Hot-spot erosion at Ocean BeachHot-spot erosion at Ocean BeachJeff Hansen (USGS, Santa Cruz)

Fy

S

x

S

yhg

y

vv

x

vu

t

vh by

yyyx

)()(

The Alongshore Momentum Balance

LHS = Advective terms

A= Pressure gradient, g= gravity

B= Radiation stresses

C=Bed shear stress

D=Turbulent momentum flux (Reynolds stresses)

LHS A B C D

LISST

January 2008: collected synoptic sediment samples and CTD-LISST profiles and nearly continuous ADCP current measurements over a spring and neap tide along two transects across the Gate

Flux through the Golden GateFlux through the Golden Gate

Inne

r tr

anse

ct n

eap

tide

Sediments at Crissy Marsh inlet

Net bedload transport over morphodynamic tide

Tide-induced transportTide-induced transport

Wave componentWave component

Forcing: 2.0 m / direction sector

Forcing: 5 m / direction sector

N

S

C

EW

1

5

6

2

3

42

Swell penetration through the Swell penetration through the Golden GateGolden Gate

0o

180o

270o 90o

Boundary forcing Wave focusing past the GG

Swell penetration through the Swell penetration through the Golden GateGolden Gate

SummarySummaryo Models are available that can address sediment transports in SF Bay

on a variety of spatial and temporal scales.

o Ocean-bay interaction is critical for understanding sediment transport within San Francisco Bay ; You need to model bay – ocean – and probably the delta to get it right….

o Currently, sediment transport is inferred from fairly well validated hydrodynamics; for true calibration and validation of models, there is an urgent need for sediment transport and morphologic change measurements

o However….it is not that simple…..

o Changes in morphology are usually small; hence you need a look over a long-time frame to get a “realistic” estimate.

o Modeling over these long-time frames is difficult especially if forcing processes and physical setting are complex.

o Short term modeling can be more accurate, but instantaneous sediment measurements are costly, usually limited to a few locations, and inaccurate.

Future DirectionsFuture Directions

• (better) Quantify (better) Quantify sediment flux through sediment flux through the Golden Gatethe Golden Gate

• 3D Modeling3D Modeling

• San Francisco Bay San Francisco Bay Coastal System Coastal System sediment budgetsediment budget

http://walrus.wr.usgs.gov/coastal_processes/http://walrus.wr.usgs.gov/coastal_processes/

Future DirectionsFuture Directions

http://walrus.wr.usgs.gov/coastal_processes/http://walrus.wr.usgs.gov/coastal_processes/

• Calibrate and validate a Calibrate and validate a coupled ocean-bay-delta coupled ocean-bay-delta model (unstructured)model (unstructured)

• Operational (real-time/now Operational (real-time/now cast) modelcast) model

• Use beyond sediment…..Use beyond sediment…..– Search and RescueSearch and Rescue– Track and Trace (e.g. oil spills)Track and Trace (e.g. oil spills)– Rapid assessment model for Rapid assessment model for

disasters disasters – Flood predictionFlood prediction