Hydrodynamics and equilibrium of a multiple

inlet system

SFRH/BD/28257/2006Grant holder: André Pacheco Supervision: Óscar Ferreira (UALG) and Jonathan Williams (UOP)

“Hydrodynamic Evolution and Sediment Fluxes of Ria Formosa

Inlets”

Seminário Doutorandos Dez.2009

Hydrodynamic and equilibrium of a multiple inlet system

The PhD Program

APPLICATION

(i) Support the decision making process by giving an overview on the hydrodynamic evolution of the system;

(ii) Quantify the relations of interdependency on a multi-inlet system relatingtidal prism with sediment fluxes;

[iii] Infer system equilibrium which can be applied to understand similar systems Worldwide

PROPOSE. In-depth study of the hydrodynamic and sediment fluxes (historic/present) of Ria Formosa Inlets

GOALS

1. Establish empirical relationships between the cross-sectional area (Ac) and the tidal prism (Tp);

2. Determine the sediment fluxes through the inlets, migration patterns and recent historical evolution in relation to anthrophic influence.

Hydrodynamic and equilibrium of a multiple inlet system

The PhD ThesisChapter I. Hydrodynamic evolution and sediment fluxes at Ria Formosa Inlets Objectives and Outline

Chapter II. State of the art International Research on Multiple Inlet Systems

Chapter III. The Ria Formosa System Recent evolution of the inlets

Chapter IV. Historical sediment budgets at tidal inletsPACHECO, A., VILA-CONCEJO, A., FERREIRA, Ó., DIAS, J.A. (2008). Assessment of Tidal Inlet Evolution and Stability Using Sediment Budget Computations and Hydraulic Parameter Analysis. Marine Geology 247, 104-127.

Chapter V. Measuring water velocity profiles using ADCP’sPACHECO, A., FAÍSCA, L., ALMEIDA, L., FERREIRA, Ó., WILLIAMS, J.J., DIAS, J.A. (accepted). Statistical approach to the best fit model to extrapolate velocities from free stream current profiles collected with boat-mounted ADCPs. Continental Shelf Research.

Chapter VI. Estimating shear stresses from high frequency dataPACHECO, A., WILLIAMS, J.J., FERREIRA, Ó., DIAS, J.A. (2009). Evaluation of shear stress computation at a tidal inlet using different methods. Journal of Coastal Research 56, Proceedings of the 10th International Coastal Symposium, 1385-1389.

Chapter VII. Hydrodynamics and Equilibrium of a Multiple Inlet SystemPACHECO, A., FERREIRA, Ó., WILLIAMS, J.J., GAREL, E., VILA-CONCEJO, A., DIAS, J.A. (under review). Hydrodynamics and Equilibrium of a Multiple Inlet System. Marine Geology.

Chapter VIII. Sediment transport at a multiple inlet systemPACHECO, A., FERREIRA, Ó., WILLIAMS, J.J., GAREL, E. (in preparation). Estimates on sediment transport for a multiple Inlet system.

Chapter IX. Conclusions

Hydrodynamic and equilibrium of a multiple inlet system

Fieldwork. Planning and execution

BENCHMARKING/SITE VISITTransect definition

1

Sontek/YSI 1500kHz ADP

Boat Mounting

2

RTK/DGPS and ADP syncronisedfor navigation and data collectionthrough Hypack®Max 4.3ª Gold

and Current Surveyor v4.3

3

Topo-Bathymetric survey aDcp Surveys (12.5h Tidal Cycle)

4

Sediment sampling

Hydrodynamic and equilibrium of a multiple inlet system

aDcp characteristics (SONTEK/YSI ADP)

Sensor type/frequency: 1500kHzBeam geometry: 3 Beams

Slant angle: 25ºBottom tracking

Compass/tilt sensor: yesTemperature sensor: yes

Pressure sensor: yes

Hydrodynamic and equilibrium of a multiple inlet system

HOW it WORKS?

3-dimensional hydrodynamic data (obtained during the transect) is used to compute a velocity vector cross product at each depth in a vertical profile;

Cross-productis first integrated over the water depth measured by the aDcp and them integrated by time,

over the width of the cross section;

How subtract the boat velocity?aDcp measures the Doppler shift of reflected acoustic energy (from the bottom of the channel)

to infer boat speed – bottom tracking;

And the measured cross-section?aDcp also reports an averaged depth in real-time, which can be used to determined the

measured cross-section.

Hydrodynamic and equilibrium of a multiple inlet system

Hydrodynamic and equilibrium of a multiple inlet system

RESULTS Spring-tides

TWO Hydrodynamic sub-system

90% Tidal PrismAncão 8%,

Faro-Olhão 61%Armona 23%

RESIDUAL FLOWStrong

interconnection

Hydrodynamic and equilibrium of a multiple inlet system

Neap-tidesRESULTS

Inlets work more independently

Reduced residual flow

Inlets expand through a vast areaChannels to shallow to promote important hydraulic connections

Flood through Olhão and ebb through Faro

Faro-Olhão and Armona45% and 40% Tidal Prism

Hydrodynamic sub-system

Area of the bay that contains most of PDetermines the overall ebb/flood dominance

SYSTEM EQUIBRIUM (Pendleton and FitzGerald, 2005)

Question: Is the system in equilibrium?

Hydrodynamic and equilibrium of a multiple inlet system

1927

1955On going work

1948

107 Cross-section14 surveys (1948-2006)Ac,RH,CL,Tw,Dmax

1948

Hydrodynamic and equilibrium of a multiple inlet system

Escoffier (1940,1977)Combines hydraulic and sedimentary stability criteria

Conservation of mass

Equation of motion (Bernoulli equation)

dt

dA

dt

hAdhUQ b

bbbbbo

ib

)]([]

2

)([

02

)4

()(

g

UU

R

flkk

t

U

g

l

Hexenob

Keulegan (1967) – repletion coeffecient K

Hexen

o

bo

c

Rflkk

ga

Aa

AK

4/

2

ocbmm aAAUU )/('

1. Ratio ab/ao

2. Tidal phase lag (ε)3. U’m

cEc TAPUPeA /489.7 86.04

sedimentary stability criteria

Jarret 1976 for dual jettied inlets at the Atlantic Coast

stableclosure

unstable

Minimum Ac 2006

Hydrodynamic and equilibrium of a multiple inlet system

)../().( 20062006 RcmcRm TAUAMTU

)/)(()( mcs UtUarcsent

))(sin()( tUtUU m

Imput parametersMean Ac

Ucs(t)TR and MTR

For any given TR

cAtUUtQQ ).()(

Thank You!