Hydrodynamic and Sediment Fluxes through the Ria Formosa Inlets André Miguel Duarte Pacheco

Hydrodynamic and Sediment Fluxes through the Ria

Formosa Inlets

André Miguel Duarte Pacheco

Chapter I . IntroductionChapter II. Assessment of Tidal Inlet Evolution and Stability using Sediment Budget Computations and Hydraulic Parameter AnalysisPacheco, A., Vila-Concejo, A., Ferreira, Ó., Dias, J.A., 2008. Marine Geology 247, 104-127

Chapter III. A Statistical Evaluation of Models for Extrapolating Current Velocities from Boat-mounted ADCP ProfilesPacheco, A., Faísca, L., Almeida, L., Ferreira, Ó., Williams, J.J., Dias, A. (under review). Continental Shelf Research

Chapter IV. Hydrodynamics and Equilibrium of a Multiple Inlet SystemPacheco, A., Ferreira, Ó., Williams, J.J., Garel, E., Dias, J.A., 2010. Marine Geology 274, 32-42

Chapter V. Application of Sediment Transport Models to a MultipleInlet SystemPacheco, A., Williams, J.J., Ferreira, Ó., Garel, E., Reynolds, S., (under review). Estuarine and Coastal Shelf Science

Chapter VI. Long-term Morphological Impacts of the Opening of a New Inletin a Multiple Inlet SystemPacheco, A., Ferreira, Ó., Williams, J.J. (under review). Earth Surface Processes and Landforms

Chapter VII. General Conclusions

Hydrodynamics and Sediment Fluxes through Ria Formosa Inlets 2

THESIS OUTLINE


CHAPTER I.Introduction

Scientific interest in the Ria FormosaThe Ria Formosa in the context of International Research on Tidal Inlets• The system has historically responded to disturbances with significant changes in its morphology, always maintaining multiple inlets open;• Several interventions occurred recently (human occupation on the barriers, channel dredging for navigation proposes, inlet openings and stabilisation), which makes Ria Formosa an important test case to evaluate the impacts of human interventions;• On the contrary of single inlet systems, multiple inlets are hydrodynamically connected, where nonlinear processes an important role on their stability, which needs to be better understood;• Data on hydrodynamic variables, tidal prism and sediment fluxes, collected simultaneously on multiple inlet systems is scarce; scientific knowledge of these processes is considered to be the key to understand inlet interactions;

This thesis presents an in-depth study of Ria Formosa Inlets;Results are expected to show how dynamic equilibrium can be achieved, with potential applications for the formulation of ICM’s policies of these systems

CHAPTER II.Assessment of Tidal Inlet Evolution and Stability using Sediment Budget Computations and Hydraulic Parameter AnalysisAPPROACHCouple of sediment budget (best estimates and uncertainty) with inlet hydraulic parameters


The approach developed is applied to Faro-Olhão Inlet

1948 2006

A B

CHAPTER II.Assessment of Tidal Inlet Evolution and Stability using Sediment Budget Computations and Hydraulic Parameter Analysis

A series of digital maps was produced based on multi-year data acquired from charts, surveys and aerial photos;

Sediment volumes and fluxes were determined for 6 coastal cells delineated on the basis of the morphological features of the inlet;

Cell volumes, fluxes and uncertaintieswere calculated for three periods (1929-1962; 1962-1978; 1978-2001);Hydrodynamics and Sediment Fluxes through Ria Formosa Inlets 5

Best estimate (BE) values and uncertainties

±4.07 x103±1.35 x104Xbest

±4.88 x103±1.62 x104Xmax

-1.36 x104-4.52 x104BEVd

±3.65 x103±2.73 x104Xbest

±4.38 x103±3.27 x104Xmax

1.46 x1041.09 x105BEVu

±1.43 x104±4.57 x103±1.48 x104Xbest

±1.77 x104±6.06 x103±1.83 x104Xmax

5.72 x1045.08 x1045.91 x104BEVf

±5.50 x103±5.30 x103Xbest

±7.79 x103±7.42 x103Xmax

ODC4.58 x1045.30 x104BEVe

±5.68 x103±7.86 x103Xbest

±6.82 x103±9.43 x103Xmax

-5.68 x104-7.86 x104N/aBEVi

±2.01 x104±1.15 x104Xbest

±2.41 x104±1.38 x104Xmax

-2.01 x105-1.15 x105N/aBEVo

1978-20011962-19781929-1962ValueCell

N/a – not available; ODC – out of data coverage

Inlet Stability Parameters

Configuration of five cross-section profiles along the inlet channel

(P1-5) and 10 equi-spaced cross-section profiles normal to the ebb

and flood flow lines (Acs1 – Acs10)

Average cross-sectional area (Aavg) of inlet channel area (P1-P5) and minimum cross-sectional area (Ac) of

Faro-Olhão inlet measured using the CEM method, 1955-2004

Inlet hydraulic parameters (Ac RH Mdepth) for 13 surveys between 1947-2004

MAIN CONCLUSIONS

from the sediment budget computations1929-1962: capture the LST in order to build both deltas; channel scouring began;1962-1978: both deltas accumulate sediments at the same rate; major changes occurred on the barriers; scouring activity intensifies at inlet channel;1978-2001: stabilisation of both coastlines; drastic intensification of scouring at the inlet gorge

from inlet parameters, generally used to infer equilibriumThe inlet reached equilibrium (1978-1985);

SB revealed that only now the adjacent coast is adjusting to the inlet presence;

Inlet dynamics can be inferred by analysing one budget cell(SAND SHARING SYSTEM)

(Dean, 1988; Elias and van der Speck, 2008)

Evaluate inlet parameters helps; but to infer inlet equilibrium, SB must be considered

Other external controls must be included on Ac/P formulations (e.g. stratigraphy)


CHAPTER II.Assessment of Tidal Inlet Evolution and Stability using Sediment Budget Computations and Hydraulic Parameter Analysis


CHAPTER III.A statistical evaluation of models for extrapolating current velocities from boat-mounted ADCP profiles

SUBJECTPresents a statistical evaluation of two theoretical fitting methods –

logarithmic and power law – commonly used to extrapolate velocities to unmeasured areas of a vertical profile, such as near-bottom velocities

MOTIVATIONIncrease use of boat-mounted ADCPs and the inexistence of any study on

evaluating model performance when using this equipment

To compute cross-sectional discharge, mean velocities and bed-friction velocities, custom ADCP software makes use of theoretical models to reconstruct the

velocity profile in the unmeasured areas, based on models calibrated and tested for fixed current meters

(i.e. using time-average profiles)PROBLEM OF USING BOAT-MOUNTED ADCPs

Instantaneous velocity profiles are incapable of smoothing out fluctuations induced by micro- and macro-turbulence and the potential effects of channel irregularities;

HOWEVER Boat-mounted ADCPs can successfully estimate discharges

WHY? Spatial averaging thought the transect;Measure depth average velocity and cross-section velocities using raw and each model



Statistical analysisR2 between raw Ucs and predictions by the two theoretical models

Two bifactorial ANCOVA tests:1) Model performance was assessed by the correlation (i.e. outcome variable) between

real and model Ucs; tide (2 groups) and inlet (6 groups) as independent variables;

2) Again tide and inlet as independent variables, but now the difference in R2 between PL and LL

as outcome variable.

ANCOVA determines differences between groups while controlling the effect of one or more

continuous predictor variables (COVARIATES). Covariate is controlled allowing the effect of each

independent variables has on the outcome to be analysed.

TWO COVARIATES used separately:

(i) Ucs raw data (expressing the velocity and direction of the water flow);(ii) Ucs raw modulus (expressing the velocity of water flow alone);

Assumption of homogeneity of slopes was checked.



FIRST TESTR2 values are not affected by raw Ucs but by its modulus; Tidal signal (flood/ebb) is negligible;>> Ucs decrease the performance of both models; when this effect is excluded, differences between inlets are highlighted – poorer fit of both models in smaller AcSECOND TESTBetter overall performance of LL method; particular at flood tide;Significance only found for Ucs raw, indicating that both velocity and direction of the flowcontribute to the LL model’s superiority

Fit of both models is negatively correlated with velocity

Better performance of both models at inlets with larger Ac

Both models' performance decrease during ebbNot particular related to velocity but to channel depth

LL model fits the raw Ucs with the greatest statistical significance

MOTIVATIONMultiple inlet systems: existence of residual circulation – direct control on the

net transport of materialUnderstand the interactions between the inlets

How those interactions can contribute to the persistence of multiple inlet systems

CHAPTER IV.Hydrodynamics and equilibrium of multiple-inlet systems


SUBJECTDetailed measurements of hydrodynamic variables over complete

spring andneap tidal cycles in a multiple inlet system (Ria Formosa, Portugal)

BACKGROUND

Multiple inlet systems are unstable (van de Kreeke, 1990)Evidence show that some multiple inlet systems can be stable

Degree of equilibrium depends on the degree of connectivity between basinsvan de Kreeke et al. (2008)

Importance of the connectivity between the inlets on the equilibrium of

multiple inlet systems needs to be better understood



Since the 14th Century to presentSystem maintained 4 to 7 inlets

Opening of Faro-Olhão InletCapture of large P from Armona Inlet

FO reaching equilibriumArmona narrowing

Flood/ebb durations - ST and NTNon-linear tidal distortion varies considerably

Salles (2001) and Salles et al. (2005)

What are the present circulationpatterns?

Can they help to understand themedium to long-term stability

of the system?

(A) tidal prism; (B) mean cross-section velocities; (C) residual discharge; and (D) mean residual velocity

90% of P

ANC 6%FO 62%

ARM 28%



Faro-Olhão and Armona inletsare always interconnected

ST - Faro-Olhão Inlet – although mean ebb velocities are higher and ebb duration shorter, maximum velocities are landward oriented (sediment

import into the system)NT – inlets act more independently; residual circulation is lower; an inner

circulationoperates between the two main channels

As suggested by van de Kreeke, the morphology of the inner channels connecting the inlets exert an important role by controlling the interactions

between inlets

There seems to be a contradiction of the bay to fill or self-maintain through flushing

Strong residual flow and change of PrismTogether with the magnitude and direction of maximum velocity

factors determining the flow and transport dominance

Seems to be the key factor contributing to the short to medium-term stability

(Van de Kreeke and Robaczewska, 1993; Salles et al., 2005)



SUBJECTQuantification of ST in tidal inlets

MOTIVATIONFundamental requirement to support both conceptual and numerical

modelling of tidal inlet function and evolution

High frequency flow measurements of turbulence

Samples of surficial sedimentsWater levels

Vertical current velocity profiles

Time-average shear stress () Drag Coefficient (Cd)

Apparent bed roughness (za)

Empirical relation between Ks and Ka

CHAPTER V.Application of sediment transport models on a multiple inlet systems


30/

)/exp(

aa

a

kz

mcz

sa kk 030zks

]1))(/[(0 exp zCdkzz

/))(( 2DAs UzCd 50)(/ dg sss Estimation of critical

flow conditions (cr)

BED LOAD TRANSPORT (Yalin, 1964; van Rijn 1984a; Madsen 1991; Nielsen, 1992)

5.0]350)1([ dsgbq

h

zaDAs UzCq )(

SUSPENDED TRANSPORT UDA values from ADCP and sediment properties

C(z) was determine by 3 methods (power lar, rouse profile, C-W method)

Ca (Smith and McLean, 1977; van Rijn 1984b;

Zysernan and Fredsoe, 1994)

Use of ADV data

sDAs dUq ,50

1.21E+030.0010.0020.001Standard deviation

-1.44E+04-0.011-0.0180.007Mean

-1.54E+04-0.012-0.0190.007C-W (Soulsby, 1997)

-1.33E+04-0.010-0.0170.006C-Power (Soulsby, 1997)

-1.33E+04-0.010-0.0170.006C-Rouse (Soulsby, 1997)

m3year-1*Net (kgm-1s-1)Ebb (kgm-1s-1)Flood (kgm-1s-1)SUSPENDED TRANSPORT

6.39E+040.0270.0380.012Standard deviation

-1.94E+05-0.084-0.1420.058Mean

-1.81E+05-0.078-0.1440.066Nielsen (1992)

-1.51E+05-0.065-0.1150.050Madsen (1991)

-2.88E+05-0.124-0.1950.071Van Rijn (1984)

-1.57E+05-0.068-0.1140.046Yalin (1964)

m3year-1*Net (kgm-1s-1)Ebb (kgm-1s-1)Flood (kgm-1s-1)BED LOAD TRANSPORT

Estimates of mass (kgm-1s-1) and volumetric (m3year-1) transport rates using different models for bedload and suspended transport for a ADCP tidal cycle performed at Ancão tidal inlet

For bedload, porosity (ε =0.4) is considered, i.e., volume of settled-bed material The cross-sectional width is w=110 m, integrated transect value derived from the ADCP measurements



Bedload transport methods derive by a maximum factor of 2van Rijn method produces the higher estimates

Mean value of bedload is 3 times higher at ebb than at flood

The suspended sediment estimates are all very similar

Sediment transport mainly occurs as bedload

Despite the presence of waves, the bulk of suspended sediments is accomplish by turbulent diffusion processes related to the strong tidal

currents

Changes on hydraulic bed roughness between flood and ebb tides due to the increase of current speed, enhanced sediment transport offshore



ESTABLISHMENT OF A USEFUL CONCEPTUAL ST MODELApproach accurately reproduce the magnitude and direction of ST

Ancão Inlet net annual seaward sediment flux is estimated to be 100,000m3/year~ to the annual LST rate measured at the updrift margin during fair-weather conditions

Faro-Olhão Inlet is a net importer of sediment to the system(1/3 of the annual sediment entry in the system by comparing pre and pos dredging

surveys)

The other inlets seem capable of flushing sediments during fair weather conditions

(EVIDENCE OF MULTIPLE INLET PERSISTENCY)

Armona ST balance 0Armona exports sand during ST and imports during NT

IMPORTANCE ON PROPERLY QUANTIFY EBB TIDAL VOLUMES FROMPREVIOUS HYDRAULIC CONFIGURATIONS

METHODOLOGY PROVED TO BE AN USEFUL TOOL TO COMPUTE MEDIUM TO LONG-TERM SB’s

IF coupled with long term quantification of ebb/flood deltas volumes

SUBJECTEvaluate the morphological response of the coastline to the opening

and stabilisation of an inlet on a multiple inlet system

MOTIVATIONRelate those changes to the inlet Ac and P redistributions until a new

equilibrium is reached

Understand the importance of the ebb tidal deltas on SB’s as “valves” for the coastal sedimentary supply

FOCUSFO inlet became the main inlet of the system, ARM lost efficiency

EVALUATE SYSTEM EQUILIBRIUM AND PREDICT IT FUTURE EVOLUTION

METHODSUse of a range of morphological and hydrodynamic indicators

(evolution of Ac and P, length and area of barrier islands)

CHAPTER VI.Long-term morphological impacts of the opening of a new inlet on a multiple inlet system


1) FO Ac versus ARM W R2 =0.76

2) CUL A versus ARM W R2 =0.91

Exponential behaviour from mid-1980’s to present

Coincident with increase scouring

in the submarine gorge of FO

ARM lost flow dominance to FOBetween 1970’s-1990’s

Ratio between Faro-Olhão inlet Ac / Armona Inlet W and between

Culatra island A / Armona Inlet W

Year FO ARM

1970 32x106 m3 46x106 m3

1980 35x106 m3 58x106 m3

1990 53x106 m3 49x106 m3

1996 70 x106 m3 49x106 m3

2001 59x106 m3 46x106 m3

2006 64x106 m3 24x106 m3

ARM P ~ c.25% of original volumeAc FO on 1948 ~ c.25% of Ac in 2006



Opening of FO greatly reduced the flow through ARM (~ 75%)Ebb-tidal current loss over the ebb shoal

Pushed the shoal landward (EBB DELTA COLAPSE)

SUPPLY of SEDIMENT TO THE GROWTH OF CUL & ARM NARROWINGProcess peaked up between 1980s and 2000Coincident with the intensify scouring at FO

FO AND ARM INLET EVOLUTION SHOW A CLEAR MORPHOLOGICAL RELATIONP EXCHANGE AND DOMINANCE

FO Ac stabilised; ARM W is constant; CUL dimensions stabilisedFO retains LST; CUL processes are cross-shore (net change 0)

NO CONTRIBUTION TO ARM EBB TIDAL DELTAARM BYPASSES SAND DOWNDRIFT AND IS EBB DOMINATED

FURTHER RESEARCH IS NEEDED TO QUANTIFY EBB DELTAS STORAGE AND HOW THAT SEDIMENT IS MOBILISED DURING INCREASE WAVE

ACTIVITYHydrodynamics and Sediment Fluxes through Ria Formosa Inlets 18


Develop inlet history based on SBs and link it with inlet parameters(1) interpret sediment pathways;(2) revealed accretion/erosion tendencies of different coastal cells;(3) uncertainty computations avoided over-interpretation and highlights how the SBs can be better constrained in the future

Evaluating the impacts of opening of tidal inlets on multiple inlet systems

(1) understand P readjustments and it importance on shaping the adjacent coastlines;

(2) understand the role that ebb-tidal delta have as “valves” of sediment supply;

Methods to determine P and ST were presented(1) infer the stability of the system;(2) understand the circulation patterns and evaluate their influence on ST

patterns;(3) highlight inlet interconnections and hypothesise it role on multiple inlet

stability;(4) both conceptual and numerical modelling of tidal inlet function and

evolution;(5) planning of coastal actions;

Evaluate the performance of theoretical methods on U extrapolations(1) define the best method to estimate bed-friction velocities used on ST formulae;(2) improve the use of boat-mounted ADCPs on P and ST estimates;

CHAPTER VII.General conclusions


FARO-OLHÃO OPENINGProvides an important informative case on multiple inlet dynamics

Coast is reaching dynamic equilibrium;FO and ARM are always interconnected, an interconnection that is

variablethrough the lunar cycle and seems to contribute to inlet stability;Brouwer, 2006; Brouwer et al., 2008; van de Kreeke et al., 2008

RECCOMENDATIONS FOR FURTHER WORK

Formulae used to evaluate inlet equilibrium must be reviewed

Annual variations of LST should be enclosed on various models of coastal morphology

The role of residual circulation in enhancing stability must be better understood

Evaluate the importance of the long-term equilibrium of sediment storage in the ebb tidal delta have on the equilibrium of multiple inlet systems

Causes and conditions that determine equilibrium (van de Kreeke et al., 2008), mainly length and friction of inlet channels, are not clear and must be

better studied

Supervised byÓscar Ferreira (Universidade do Algarve, Portugal)Jon Williams (University of Plymouth, UK)

Financial support for the fieldwork given by the project IDEM-Inlet Dynamics Evolution and Management at the Ria Formosa (POCI/MAR/56533/2004)

Historical data provided by Parque Natural da Ria Formosa and Instituto Portuário dos Transportes Marítimos

THANK YOU

Documents

Hydrodynamic and Sediment Fluxes through the Ria Formosa Inlets André Miguel Duarte Pacheco