Geomorphology 320 (2018) 127–141

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Geomorphology

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Assessing the morphodynamic response of human-alteredtidal embayments

Carmen Zarzueloa, b,*, Alejandro López-Ruiza, Andrea D’Alpaosc, Luca Carniellod, Miguel Ortega-SánchezbaDepartamento de Ingeniería Aeroespacial y Mecánica de Fluidos, Universidad de Sevilla, Camino de los Descubrimientos s/n, Seville 41092, SpainbAndalusian Institute for Earth System Research, University of Granada, Avda. del Mediterráneo, s/n, Granada 18006, SpaincDepartment of Geosciences, University of Padova, Via Gradenigo 6, Padova 35131, ItalydDepartment ICEA, University of Padova, Via Loredan 20, Padova 35131, Italy

A R T I C L E I N F O

Article history:Received 31 October 2017Received in revised form 8 August 2018Accepted 8 August 2018Available online 11 August 2018

Keywords:Altered bayMorphodynamicsHydrodynamicsNumerical modelingInterventions

A B S T R A C T

The morphodynamics of coastal embayments and estuarine areas are defined by the flow conditions sincetidal, wind and wave–induced currents are the main drivers of the sediment transport. In turn, gradients inthe resulting sediment transport define sedimentation/erosion patterns and hence the morphodynamic evo-lution of these systems. Any modification on the average flow conditions, such as those generated by humaninterventions (i.e. bridge, port constructions or dredging interventions), can be considered as a potentialdriver inducing morphodynamic changes. This work analyzes the effect of human interventions in estuar-ine areas and coastal embayments and explores the applicability of tidal asymmetries and residual currentsas a proxy for the prediction of the morphodynamic consequences of these interventions. A calibrated andtested numerical model with hydrodynamic and morphodynamic modules is used to compare the varia-tions of tidal asymmetries and residual transport with the bed level evolution in a highly altered bay (CádizBay, Southern Spain). Results show that the future development of the bay will heavily depend on humaninterventions. The agreement between the morphodynamic tendencies obtained after the analysis of thehydrodynamic variations for the altered scenarios, and the results of the morphodynamic simulations con-firms the applicability of the hydrodynamic simulations as a proxy for the morphodynamic evolution. Thisis of special interest for any other similar coastal embayment or estuary where morphodynamic data arescarce or the calibration of morphodynamic models is too complex.

© 2018 Elsevier B.V. All rights reserved.

1. Introduction

Coastal embayments are unique natural environments that arebecoming more important from an environmental and geomorpho-logical point of view due to their strategic locations and ecologicalrelevance (Woodroffe et al., 2006; Syvitski and Saito, 2007). Theselarge bodies of water, frequently dissected by networks of tidalchannels and creeks that crucially contribute to drive their evolu-tion (e.g., D’Alpaos et al., 2005; Hughes et al., 2009), are connectedto the open ocean or sea and are usually formed by two portions(the outer and inner basins), fed by water and sediment fluxescoming from the terrestrial watershed (Syvitski et al., 2005). Thehydrodynamics of these shallow-water systems is mainly domi-nated by tidal asymmetries generated by nonlinear processes thatdrive a net flow of sediment in the direction of such asymmetries

* Corresponding author.E-mail address: czarzuelo@us.es (C. Zarzuelo).

(Galloway, 1975; Aubrey and Speer, 1985; Dalrymple et al., 1992;Orton and Reading, 1993; Aldridge, 1997). Studies based on themorphodynamic response of these embayments show that the tidalasymmetries and the residual flow define the behavior of the resid-ual sediment transport (Boothroyd and Hubbard, 1975; Allen et al.,1980; Van de Kreeke and Robaczewska, 1993; Lanzoni and Seminara,2002; Moore et al., 2009; Nzualo et al., 2018). Thus, variations ofthese hydrodynamic variables can be considered as a proxy forthe geomorphological evolution due to their relation with sedimenttransport patterns (Dronkers, 1986; Aldridge, 1997; Wang et al.,2002; Prandle, 2003; Bolle et al., 2010; Barnard et al., 2013b; Hansenet al., 2013b).

However, understanding and predicting the hydro–morphodynamic behavior of altered embayed systems can bea challenging task due to the high uncertainty around humanactivities (Wang et al., 2014). Among the different anthropogenicinfrastructure modifying the natural landscape of embayments,ports, navigation channels (Wang et al., 2014), bridge constructions(Li et al., 2014; Del Río et al., 2015; Van Maren et al., 2015), urban

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128 C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141

occupation, and marsh reclamation for accommodating new infras-tructure have strong influences on their hydro–morphodynamics(Knowles and Cayan, 2004; Lu et al., 2009; Barnard et al., 2013a;Van Maren et al., 2015). These anthropogenic interventions alsoadd complexity to the understanding of the main physical driversof water circulation (Valle-Levinson and Blanco, 2004; Carnielloet al., 2005; Zhong and Li, 2006; Valle-Levinson, 2008; D’Alpaoset al., 2010) and mixing processes (Waiters et al., 1985; Hetland andGeyer, 2004; Burchard and Hofmeister, 2008; Venier et al., 2014).Despite technical and scientific developments achieved in recentyears, the assessment and prediction of present and future impactsof anthropic interventions on the estuarine geomorphology are stillchallenging tasks for both managers and scientists (Li et al., 2014;Wang et al., 2014).

More specifically, human–induced alterations modify theexchange of tidal fluxes within coastal embayments, disruptingthe pathway of tidal waters entering estuaries, tidal range, and theflushing characteristics of these systems. Consequently, sedimenttransport patterns in many bays and estuaries around the worldhave changed as a consequence of human interventions. Thesepoorly understood effects caused by anthropogenic influences areevident at notable sites, such as the Ems estuary (e.g., Van Marenet al., 2015), China’s Bohai Bay (e.g., Lu et al., 2009), San FranciscoBay (e.g., Knowles and Cayan, 2004; Barnard et al., 2013a) and Venicelagoon (e.g., Marani et al., 2007; Carniello et al., 2009), among others.

Although many previous pioneering studies aiming to under-stand the effects of human interventions were based on in situmeasurements or historical data (i.e. Gartner, 1986; Blott et al.,2006; Anthony et al., 2015; Garel et al., 2016; Luan et al., 2017),the prediction of the behavior of such complex systems requires theuse of numerical models and field surveys to simulate the physi-cal processes. During the recent decades, the increase in computingcapabilities combined with hi-tech sensors for field measurementsand the use of remote sensing (e.g. Ouillon et al., 2004; Carnielloet al., 2014) have led to the development of advanced 2D and 3Dnumerical models in combination with precise field data for cali-bration and testing; these models can be applied not only to gain abetter understanding of the physical processes but also to improveour prediction capabilities at different spatial and temporal scales.The best known examples of these models are Delft3D (Lesser et al.,2004), COHERENS (Shi et al., 2010) HEM-3D (Hong and Shen, 2012),MIKE (Schoen et al., 2014) and MOHID (Liu et al., 2004; Vaz et al.,2009), although several authors have developed their own models(Umgiesser and Bergamasco, 1993; Walstra et al., 2001; Zhong andLi, 2006; Hong and Shen, 2012; Carniello et al., 2012). However, themain limitation of these numerical models when applied in complexcoastal settings is the difficulty of their morphodynamic calibrationand testing due to: (1) the complexity of the modeled processes;and (2) the lack of bathymetric data with the necessary spatial andtemporal resolutions (French and Clifford, 2000; Hibma et al., 2003).

The main goal of this study is to analyze the applicability of tidalasymmetries and residual currents to predict the sediment trans-port and sedimentation patterns, and morphodynamic evolutionof altered embayments and/or estuaries. A hydro–morphodynamicmodel is used to check the validity of the hydrodynamic predictionsas a proxy of the geomorphological variations induced by humaninterventions. The model is applied to the Cádiz Bay (SW Spain),which is a heavily altered bay with historical records indicatingthat the first human settlements took place more than 3000 yearsago. Recently, the bay has experienced rapid and significant changesas a result of human activities: a new bridge was completed in2015 and a new container terminal is under construction at thePort of Cádiz since 2012; furthermore, the navigation channel thatcrosses the entire bay will soon be deepened (Zarzuelo et al., 2015).Although there have been a number of previous studies on thecomplex dynamics of the site, they were focused on other aspects

such as the seasonal variability of the tidal constituents, the long-term(centuries) influence of tidal circulation on pollutant transportand marine sediment evolution (Álvarez et al., 1999; Álvarez et al.,2003; Periáñez et al., 2013), the variability in storm climate alongthe Gulf of Cádiz (Plomaritis et al., 2015; Garel et al., 2016), the tidalbehavior in Sancti-Petri creeks (Vidal, 2002), the wave-tide inter-actions (Kagan et al., 2005, 2001), the feedback between flow andsuspended sediment (Álvarez et al., 1999; Periáñez et al., 2013) andthe potential of tidal energy as a renewable energy source at the bay(Zarzuelo et al., 2018).

The complexity of the Cádiz Bay is increased due to the creeksand tidal flats in the inner part of the bay. The geometric char-acteristics of this area, which complicated the analysis performedin previous works (Zarzuelo et al., 2015), are here treated using aspecific morphodynamic model developed by Carniello et al. (2011,2012). Moreover, data collected during a field survey carried outprior to human interventions were used to calibrate and test thehydrodynamic module of the model (Carniello et al., 2005).

The paper is organized as follows. Section 2 describes the studysite, the field survey and the model. The calibration and testing ofthe numerical model and the four scenarios defined on the basis ofthe planned interventions are presented in Section 3. Section 4 ana-lyzes the main results, in particular, the impacts of the constructionson the residual currents, tidal asymmetries and morphodynamics.Model results describe significant changes in the hydrodynamic andmorphodynamic behavior between before and after the interven-tions. Section 5 discusses the main findings of the work; in particularthe relation between the changes in the hydrodynamics and themorphodynamic evolution, which allows us to predict future mor-phological evolution in the presence of anthropogenic interventions.Finally, Section 6 summarizes the main conclusions of this work.

2. Materials and methods

2.1. Field site

The Cádiz Bay is a semi-diurnal, meso– to macro–tidal, and low-inflow estuary located in the SW of the Iberian Peninsula, facingthe Gulf of Cádiz (Atlantic Ocean). Three areas configure the bay,with a total extension of 140 km2: a deeper outer area connected tothe open sea (A-Fig. 1a); a shallower inner area (C-Fig. 1a); and theconnection between A and C, the Puntales Channel (hereinafter PC)(B-Fig. 1a), characterized by irregular boundaries due to urban settle-ments and port infrastructure. The current morphology is the resultof the interaction between the natural evolution induced by past geo-logical events, climatic agents, biological factors, and the impact ofhuman activities.

Like many other semi-enclosed coastal water bodies, the mainforcings driving the hydrodynamics of the bay are tides, wind, wavesand river inputs. The tide in the Gulf of Cádiz is semi-diurnal andmesotidal. The main tidal constituent is the M2 (semi–diurnal period,12.42 h). The tidal range in the adjacent coastal waters varies from ∼1 m during neap tides to ∼ 4 m during spring tides. The tidal charac-ter inside the bay is co-oscillating, induced by the Kelvin-type wavewhich propagates northward along the North Atlantic easter mar-gin (Zarzuelo et al., 2017). Tides penetrate into the lagoon mainlyfrom the outer area (A) towards the inner bay (C) through the Pun-tales channel (B). The inner bay is also connected intermittently tothe open sea through the Carracas and Sancti–Petri creeks (Fig. 1a),although the water exchange is significantly smaller through theseconnections and the creeks dry out at approximately mid-tide stageduring spring tides (Zarzuelo et al., 2017).

Since 2012 the morphology of the Cádiz Bay has been changing asa result of three simultaneous human interventions (see Fig. 1b–e).First, “La Constitución de 1812" Bridge was completed in Septem-ber, 2015. Second, a new container terminal (which increased the

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Fig. 1. A-Location of the Cádiz Bay and the boundaries of the computational domain (dashed red line). The outer, central, and inner areas of the Bay are denoted as A, B, and C,respectively. The insets show the four scenarios. B-Sc1: initial case, C-Sc2: the new bridge, D-Sc3: the deepening channel and new port, and E-Sc4: all interventions. Labels P2.1(P2.2) and P3.1 (P3.2) correspond to the terminal (new terminal) and the navigation channel (new navigation channel), respectively.

port surface by 22.5%) is under construction at the Port of Cádiz.Finally, as a part of the new port terminal, large-scale dredging willbe undertaken at the outer bay to shift and deepen the current navi-gation channel. Assessing the morphological changes of the completebay due to these interventions, through the tidal asymmetry and theresidual current, is the main goal of this work.

2.2. Field survey

A comprehensive field survey was carried out with a total of6 instruments deployed at 6 stations from December 22, 2011 toApril 18, 2012 (Fig. 2). These instruments were 4 current profiles(crosses in Fig. 2; hereinafter ADCP) and 2 tidal gauges located at thetwo main creeks (triangles in Fig. 2). Their positions were selected

considering the location of the new bridge “La Pepa”(36.52◦N;6.27◦W) and the new port terminal (36.54◦N; 6.27◦W), and theirpossible impacts on the water exchange between the inner and theouter bay. Measurements of sea level, currents, water quality, andwind were used to evaluate water circulation and sediment transportwithin the bay and, in particular, the water exchange between theinner and outer basins on intratidal and subtidal–morphodynamictimescales (see Zarzuelo et al. (2015) for further details). The datawere filtered using the standard harmonic analysis (Pawlowicz et al.,2002) to reconstruct the signal when there were gaps or failedmeasurements, and analyzed to study the hydrodynamic behav-ior of the bay, employed a proxy for patterns in sedimentation.Measurements revealed that the estuary is short tidally-driven,and elevations and currents are in quadrature. At the semi–diurnal

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Fig. 2. Mesh of the Cádiz Bay with the all interventions (pink: new terminal and newNC, red line: new bridge). I1-I4 (crosses) ADCP stations. T1-T2 (triangles) tide stations.Orange dashed lines correspond to the six sections to analyze the water exchangebetween ocean to outer basin (O-O), between outer basin to Guadalete river (O-G), SanPedro creek (O-SP) and PC (O-PC), between PC to inner basin (PC-I) and between innerbasin to Carraca Creek (I-C).

timescale, the inner (hypersaline) and outer (thermal) parts operatealmost independently.

2.3. The morphodynamic model

The model is made up of two modules: i) a hydrodynamic modulecoupled with a wind-wave tidal module (hereinafter WWTM), devel-oped by Carniello et al. (2011, 2005) and calibrated and tested for theCádiz Bay study site using the field data described above; and ii) asediment transport and bed evolution module (hereinafter STABEM)developed by Carniello et al. (2012). The model was adopted dueto its capability to deal with wetting and drying in very irregulardomains, as is the case of the Cádiz Bay. It has been widely tested bycomparing model results to hydrodynamic, wind-wave and turbiditydata collected in Venice lagoon (Defina et al., 2007; Carniello et al.,2011) and in the lagoons of the Virginia Coast Reserve, USA (Mariottiet al., 2010). The two modules of the model are briefly described inthe following.

The hydrodynamic module solves the two-dimensional shallowwater equations and includes a refined sub-grid modeling of thebathymetry to deal with wetting and drying processes in very irreg-ular domains. The two-dimensional shallow water equations aresolved using a semi-implicit staggered finite element method basedon Galerkin’s approach (the reader is referred to Defina (2000)and D’Alpaos and Defina (2007) for further details). The hydrody-namic module yields tidal levels which are used by the wind-wavemodel to assess parameters (e.g. wave group celerity, time-varyingwater depth) influencing wind-wave generation and propagation(Carniello et al., 2011).

The wind-wave module uses the approximation of the waveaction conservation equation (Hasselmann, 1973) parameterized

using the zero-order moment of the wave action spectrum in the fre-quency domain (Holthuijsen et al., 1989). The spatial and temporalvariations of the wave period are estimated with an empirical cor-relation function, which relates the mean peak wave period to thelocal wind speed and water depth following the approach suggestedby Young and Verhagen (1996). WWTM further considers the spatialheterogeneity of the wind field implementing the interpolation tech-nique of the available wind data proposed by Brocchini et al. (1995)(see Carniello et al. (2011) for further details). Hence, WWTM is ableto model wind waves generated locally at the computational domainby a prescribed wind field. However, it does not consider the swellwaves propagated from outside the domain, although in the case ofthe Cádiz Bay these swell waves are significantly attenuated as theypropagate across the outer bay, being only important in the outerbasin close to the Valdelagrana beach (see Fig. 1) which is out of theinfluence of the ongoing human interventions (Zarzuelo et al., 2017).

The sediment transport and bed evolution module (STABEM) con-siders mixtures of sand and mud (sum of clay and silt, Carnielloet al., 2012) and distinguishes between both types of sediments usingthem to characterize the bed composition and behavior(cohesive ornot cohesive). The transition between cohesive and non–cohesivesediments is mainly determined by the mud content which variesin space and time, updated by the model on the basis of the localentrainment and deposition.

STABEM solves the advection diffusion equation and the Exnerequation for each class of sediment (sand and mud) coupled withWWTM. The combination between hydrodynamic and morphody-namic processes is carried out “in line”, i.e. bed elevation and com-position are updated each time step but the option of introducinga morphological factor to speed up the morphological evolution isavailable in the code (Cao et al., 2002). Furthermore, the compari-son with suspended sediment retrievals derived from the analysis ofsatellite images enabled us to assess the ability of STABEM to repro-duce observed spatial patterns of suspended sediment concentrationduring storm events (Carniello et al., 2014) and to statistically char-acterize the spatial and temporal dynamics of resuspension events(D’Alpaos et al., 2013; Carniello et al., 2016). We refer the readerto Carniello et al. (2012) for a detailed description of the numericalmodel.

3. Application of the model to the Cádiz Bay

3.1. Model implementation and calibration

The model was calibrated and tested for the study site during theperiod between February 22nd, 2012 and March 14th, 2012, charac-terized by different meteorological and tidal forcings. The numericalsimulations presented herein were carried out within a compu-tational domain which was suitably set up to predict the tidallyinduced circulation in shallow basins such as the Cádiz Bay. Theshape of the computational mesh (Fig. 2) was set according to theavailable bathymetry data, optimizing the adaptation of the triangu-lar elements. The grid consists of 31,367 nodes and 62,105 triangularelements of different size (smallest size about 10 m, larger elementsize about 80 m). The time step for the computation was set equal to2 s. The bathymetric data were provided by the Instituto Hidrográficode la Marina (Spanish Ministry of Defense) and the Port Authorityof Cádiz. In areas where multiple data sets overlapped, preferencewas given to the higher resolution multi-beam data (Hansen et al.,2013a).

Table 1Distribution of the parameter Ks along the bay.

Nav. channel Outer bay Inner bay Central section Tidal creeks Marshes

Ks 10 30 20 30 25 35

C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141 131

Table 2Root mean square errors (RMSE), correlation coefficients (R) and skill coefficients (S), for the calibration period of the elevations and velocities at I1 and I2.

Tidal level (m) East velocity (m/s) North velocity (m/s)

RMSE R S RMSE R S RMSE R S

I1 0.070 0.99 0.99 0.083 0.94 0.83 0.059 0.96 0.91I2 0.075 0.99 0.99 0.062 0.95 0.91 0.062 0.95 0.91

The WWTM module was calibrated and tested using the fielddata described in Section 2.2. A four–step approach (Zarzuelo et al.,2015) was followed to ensure that the simulations reproduce asaccurately as possible the field data. First, boundary conditions con-sisting of tidal levels imposed at the seaward boundary and spatiallyuniform winds were applied. The tidal levels were defined with theamplitudes and phases of the twelve dominant components pro-vided by the Oregon State Tidal Prediction Software (OTPS) (Egbertand Erofeeca, 2002), using the tools developed by Pawlowicz et al.(2002). The uniform wind was obtained from Buoy 2342 (the upperleft panel-Fig. 1), for which data were provided by Puertos del Estado(Spanish Ministry of Public Works). Second, the model was runand calibrated at stations I1 and I3 (Fig. 2), modifying the Stricklerbed roughness coefficients through an iterative process. Finally, themodel performance was checked by comparing the model resultswith the observations at I1-I4 and T1-T2 (Fig. 2).

3.1.1. Calibration and testingThe period from January 17 to January 26, 2012, was selected

to calibrate the model (not shown for the sake of brevity). For thisperiod of time, the influence of wind and waves on tidal circula-tion was negligible (wind speed always lower than 4 m/s). Similarto other studies (Lesser et al., 2004; Iglesias and Carballo, 2009;Elias and Hansen, 2012), the flow model was very sensitive tothe Strickler coefficient (Ks), describing bed roughness, which wastherefore considered as the primary calibration parameter. Ten dif-ferent values for Ks were selected and calibrated to describe thebed roughness of different portions of the bay. Table 1 showsthe spatial distribution of Ks, ranging from 10 to 35 m1/2 s−1,within the computational domain. Using these parameters, excellentagreement between the observed and simulated tidal levels wasachieved (correlation coefficient R = 0.99) considering the selectedno-wind conditions. The regression coefficient and skill values

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Fig. 3. Tested (circles) for stations I1, I2, I3, I4, T1, T2 and T3. Dots (line) correspond to the observed (modeled) data. The tidal level is shown in the left panels; the East and Northvelocities are shown in the right panels.

132 C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141

Table 3Root mean square errors (RMSE), correlation coefficients (R) and skill coefficients (S), for the testing period of the elevations and velocities at I1, I2, I3, I4, T1 and T2. T1 and T2 onlymeasured tidal level, thus there are no measurements of velocity.

Tidal level (m) East velocity (m/s) North velocity (m/s)

RMSE R S RMSE R S RMSE R S

I1 0.080 0.99 0.99 0.099 0.90 0.83 0.110 0.80 0.81I2 0.070 0.99 0.99 0.087 0.91 0.91 0.160 0.94 0.93I3 0.100 0.99 0.99 0.260 0.79 0.77 0.330 0.77 0.51I4 0.120 0.99 0.99 0.090 0.79 0.71 0.100 0.93 0.85T1 0.820 0.82 0.67 − − − − − −T2 0.560 0.87 0.80 − − − − − −

(Wilmott, 1981; Olabarrieta et al., 2011) for the tidal currents arelower, but the agreement is still very good (R = 0.94, S = 0.9)(Table 2). The formulations used are described in Appendix A.

Once calibrated, the model was tested (Fig. 3) considering thedata collected in the period from February 22 to March 14, 2012. Dur-ing this period, wind velocities reached 10 m/s, which correspond toa 98.8% percentile of the wind velocity distribution, thus assuring thevalidity of the model even for extreme conditions. The high valuesof the skill parameter (Table 3), lower for the eastern currents, indi-cated that the model is generally able to accurately reproduce thetidal dynamics of the Cádiz Bay. Furthermore, the correlation coeffi-cients only exhibited a slight decrease with respect to the calibrationperiod for I1 and I2 (the instruments compared in both periods). Themajor discrepancies were found for T1 and T2, although the agree-ment is still very good (R ∼ 0.85). These tidal gauges are located inproximity of the tidal creeks; therefore the differences are attributedto the lower resolution of the available bed elevation data in theseareas.

Although the capability of reproducing the residual currents(Fig. 4-upper panel) is a quite demanding task, a good agreement,according to the classification proposed by Van Rijn et al. (2003), wasalso obtained with values of R ∼ 0.8 (Table 4). Residual currents,defined as the tidal-cycle average of tidal currents, were obtainedapplying a low pass filter to the time series, removing the fluctuationat semi-diurnal and higher frequencies (Jonge, 1992). Furthermore,the tidal prism, which was calculated following the approach sug-gested by Jonge (1992) (for more details see Zarzuelo et al. (2015)),was also calibrated (Fig. 4-middle panel) with a good agreement(R ∼ 0.73, Table 4).

Finally, the suspended sediment concentration (Fig. 4-lowerpanel) was analyzed at station I3. We initially prescribed sand sed-iment at the bottom of the outer bay, transition between sand andmud in the navigation channel and inner bay, and mud in the creeksand marshes. According to the classification defined by Wilmott(1981), the agreement between the computed and the measureddata (R ∼ 0.65, Table 4) is good and similar to the one obtained insimilar studies (Di Toro and Fitzpatrick, 1993; Chao et al., 2007; Liuand Huang, 2009) although the calibration of sediment transport ismuch more demanding than for the hydrodynamics.

3.2. Definition of model scenarios

To analyze the influence of the recent human interventions in thesediment dynamics of the estuary, different scenarios were defined:

Scenario 1 (Sc1): configuration of the Bay in 2012, beforeinterventions. This first scenario corresponds to the con-figuration of the Cádiz Bay prior to the beginning of theinterventions (upper left panel in Fig. 1b).

Scenario 2 (Sc2): Sc1 + new bridge. The nine piers of the newbridge across the Puntales Channel were added to Sc1.These piers have dimensions ranging between 3×33 m2and 8×33 m2 (length per width) (Fig. 1c). The new bridge

is one of the longest (5 km) and the highest (69 m abovemean sea level) bridges in Europe, and crosses the Pun-tales Channel connecting the city of Cádiz with the IberianPeninsula. The piles of a bridge modify the average hydro-dynamics due to the constriction of the section and also thelocal hydrodynamics around the piles, which will changethe morphological evolution of the bay.

Scenario 3 (Sc3): Sc1 + new port terminal + navigation chan-nel. These interventions were expected to be finishedat the end of 2017, but they have not yet been com-pleted. The emerged land at zone A will be expanded witha new 590 m long container terminal that will form anarea of 380,000 m2. Additionally, the operational schemefor the new terminal includes a significant dredging of∼3.86 • 106m3 of sediment from the navigation channel toachieve a maximum depth of 20 m (P2.2 and P3.2, respec-tively, in Fig. 1d). The deepening of channels due to dredg-ing interventions will modify the velocity gradients, thuschanging the sedimentary dynamics.

Scenario 4 (Sc4): Sc1+Sc2+Sc3. This scenario represents the com-bination of all the interventions, and corresponds to thefuture final configuration of the Cádiz Bay (Fig. 1e) by theend of 2018.

4. Results

The numerical model described in Section 2.3 was forced for thefour different scenarios considering the external forcings (wind, tidallevels) during the period from February 22nd, 2012 to March 14th,2012 as boundary conditions. During the selected period all the sta-tions were simultaneously deployed (Zarzuelo et al., 2017). The pres-ence of different wind speeds (ranging between 2 and 10 m/s), anddurations allowed us to carry out a comparative analysis betweenspring and neap tides (Fig. 5).

We analyzed in detail four different variables that are closelyrelated with the morphodynamic behavior of estuaries: tidal levelsand flows to analyze tidal asymmetry, residual transport and sed-iment concentrations. Variations of tidal asymmetries characterizehow the human interventions modify the bay hydrodynamics, whichin turn determines its morphodynamic evolution (French, 2002;Wright and Thom, 1977) that alters the tidal flow regime in a com-plex feedback (Perillo, 1995). Furthermore, according to Elias andvan der Spek (2006), the residual transport represents a proxy of thetidal asymmetry which is one of the mechanisms responsible for theunbalance of morphodynamic equilibrium in estuaries (Zhou et al.,2017). Finally, sediment concentration is also a key variable to deter-mine the morphodynamic evolution of the bay, since its variationsprovide a clear diagnostic of morphodynamic changes.

4.1. Tidal asymmetry

In this section, the analysis of tidal levels and flows is used todescribe how tidal asymmetry is modified across the estuary due

C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141 133

Table 4Root mean square errors (RMSE), correlation coefficients (R) and skill coefficients (S), for the calibration period of the residual currents, the water exchange and the suspendedsediment concentration at I3.

Residual current (m/s) Water exchange (m3) SSC (mg/l)

RMSE R S RMSE R S RMSE R S

I3 0.04 0.79 0.8 1.01 0.74 0.73 24.1 0.66 0.65

to the human interventions. The study of the tidal asymmetry andthe residual circulation improves not only the knowledge of thedynamics of the embayment systems, but allows the qualitative esti-mation of morphological evolution because an increase (decrease) ofboth variables indicates sedimentation (erosion) area (Jonge, 1992;Hoitink et al., 2003; Lopes and Dias, 2007).

4.1.1. Tidal levelAmong the tidal components in the Cádiz Bay, M2 and M4 are

the most important for the semi–diurnal and quarter-diurnal species,respectively (Zarzuelo et al., 2015). Fig. 6a; b shows the variabilityof the amplitude and phase for the M2 and M4 components overthe bay, whereas Fig. 6c to f depicts these variables along a tran-sect that crosses the study area from the outer bay (point A, Fig. 6a)to Carracas Creeks (point B, Fig. 6b) through the Puntales Channel(hereinafter PC). This transect corresponds to the main navigationchannel (hereinafter NC) across the bay.

As a general trend for all the scenarios, the amplitude and phaseof both the M2 and M4 components increase as the tidal wave prop-agates from the outer to the inner bay due to the presence of thePC constriction (Zarzuelo et al., 2015). The increase of the ampli-tude and phase of the M2 and M4 components within PC is moreabrupt due to strong water depth gradients along the constriction.Values of the amplitude of the M2 component for Sc2 (Fig. 6c) areslightly higher than those obtained for Sc1 along the complete tran-sect A-B. However, in the case of Sc3, the amplitude of the M2component is reduced (increased) when compared to that charac-terizing Sc1 seaward (landward) of the bay. For Sc4 the results donot show significant differences when compared to those obtainedfor Sc3, indicating that the influence of the dredging is significantlylarger than the influence of the new bridge. As for the M4 compo-nent, its amplitude for Sc2, Sc3 and Sc4 is higher (lower) for the outer(PC and inner) part of the transect, and the effect of the dredgingis again more important than the effect of the new bridge. For thephases of the M2 (Fig. 6e) and M4 (Fig. 6e) components, no signifi-cant changes are obtained for the outer part of the transect, althoughthe values of the phase grow faster for Sc2, Sc3, and Sc4 in the innerbay along the transect. This implies that the interventions tend to

speed up the propagation of these components from the PC towardsthe inner bay along the transect due to the increase in the depth ofthe new NC, implying a strong mobilization of the sediment whichwill be deposited landward where there is a delay.

The non-linear distortion factor is defined by aM4/aM2 (Friedrichsand Aubrey, 1988). The increase of the M2 component is around0.005, although the increase of M4 is higher (0.1). Thus, the increaseof the M4 determines that the distortion factor increases at PC andinner bay. For Sc2, Sc3 and Sc4 the modification of both amplitudes issimilar and follows the same pattern in the three scenarios. The dis-tortion factor increases along the transect with more abrupt changesin the PC and inner bay, although it decreases slightly landward.These changes are related with the geomorphological evolution ofthe bay, as analyzed in Section 5.

4.1.2. Tidal flowWe analyzed the variations in tidal fluxes induced by the differ-

ent scenarios throughout the simulated period, specifically for themaximum flood and ebb and during high and low tides (Fig. 7). Thesevariations are related to the tidal asymmetry and, therefore, with thesediment dynamics. For all scenarios, the maximum tidal flows areconcentrated within NC that connects the outer bay with CarracasCreeks through the PC, where the maximum depths are found. Forinstance, the results for Sc1 (Fig. 7, 1st row) show that tidal flowsare greater at the inner and outer part of NC, while they decreaseat the central part of the PC due to variations in the bathymetry.Moreover, in these areas, tidal fluxes are parallel to NC and off-shore (onshore) directed for ebb and low tides (flood and high tides),respectively. These trends are similar for the four instants of timeanalyzed, although maximum flows are higher for the maximum ebband flood (values up to 11 m2/s), being two times lower for maxi-mum high and low tides. The maximum values of flood and ebb havesimilar values and are obtained in the same area, although they arehigher for ebb tides at the outer bay close to the shallower area.

The comparison between the four scenarios suggests that signif-icant differences emerged in particular at the sides of NC. For Sc2(Fig. 7, 2nd row), changes are important at the northern side of theinner part of NC, where the flow increases up to 80% with respect to

Fig. 4. Comparison of measured (black line) and computed (blue lines) for station I3. The residual current magnitude is shown in the upper panel; the tidal prisms are shown inthe middle panel; the suspended sediment concentration is shown in the lower panel.

134 C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141

0

-2

qI1

(m2 /

s)

03/03 03/0902/27I1

(m)

6

2

5

10

03/03 03/0902/27I1

(m)

2

qI1

(m2 /

s)

003/10

06:0004:00 09:00 18:00

03/11

a) b)

d)

-2

c)

0

7

0

Fig. 5. Tidal levels (A and C) and module of the discharges per unit width (B and D) at the reference point I1. Vertical dashed lines in panels c and d indicate middle flood (04:00),high water (06:00), middle ebb (09:00) and low water (18:00) times during spring tide. Comparisons at these times are discussed in the main text.

Sc1 for all the instants analyzed except for maximum low tides, andalso in the southwestern part of the stretch of the NC that crosses PC.This is the area where the harbor infrastructure of the city of Cádiz isplaced; our results show that flows are generally greater for Sc2 com-pared to Sc1. Furthermore, the areas where the maximum variationsare obtained correspond to those characterized by low tidal flows,and even when large variations are observed, the magnitudes of tidalflows are small. Regarding the direction of the flows, no significantchanges are found between Sc1 and Sc2.

In the case of Sc3 (Fig. 7, 3rd row), changes are also concentratedat the sides of NC. However, in this case flows are significantly higherin the outer part of the new port terminal, whereas the opposite isobserved at its inner part and the southwestern side of the PC. Thesevariations (up to 80%) are obtained for the four instants analyzed.Furthermore, flows are also higher at the sides of the inner part of theNC compared to Sc2, the new port terminal and the related dredg-ing works have higher influence on tidal flows because in this case,important variations are obtained at the areas with strong tidal flows.In fact, the maximum flow rates at the outer part of PC increase up to14 m2/s (40%). Regarding the direction of the flow, for Sc3 the mostsignificant changes are obtained at the outer boundary of the PC,where flows clearly rotate clockwise for flows entering and exitingthe bay. As for tidal levels, the results for Sc4 (Fig. 7, 4th row) showthat the influence for the new terminal and the dredging is moreimportant than the one of the new bridge, the variations of the flowfor Sc4 being very similar to those of Sc3. Only at the southwesternside of PC, is the reduction in flow rates less pronounced than for Sc3.The increase in tidal currents in the inner basin is located at the sameplaces where the tidal levels decrease, highlighting the role of bedfriction.

The flood/ebb dominance plays an important role in tidal asym-metry and therefore in the sediment dynamics (Blanton et al., 2002;Ghinassi et al., 2018). The maximum tidal currents are found bothat the northern boundary of the navigation channel and in the innerbay, transporting these sediments to other areas of the bay such asthe south of the PC, where the tidal flows are weaker and the relationaM4/aM2 is increased abruptly. This effect is discussed in Section 5.

4.2. Residual transport

The residual current is commonly defined as the tidal-cycleaverage of tidal current. Residual transports are caused by multi-ple factors, ranging from non-linearities in the bed stress to non-linear interactions of tidal flow with variable bathymetry (Balzano,1995; Lopes and Dias, 2007). Although residual transports are muchsmaller in magnitude than tidal flows, they play a key role in thelong-term mass transport and in the long–term morphodynamicevolution of the bay (Carter and Orford, 1993; de Vriend et al., 1993;Lanzoni and Seminara, 2002). We also use the results obtained hereto analyze the variations in sediment dynamics derived from thehuman interventions, which can be contrasted with the morphody-namic results of the numerical model.

Fig. 8a shows the residual transport obtained after the timeintegration over the semidiurnal period for the time span of thesimulations for Sc1, whereas Fig. 8b–d depicts the changes in thesame residual transport for Sc2, Sc3 and Sc4, respectively. The trendsare very similar to those for tidal flows (Section 4.2). Results forSc1 (Fig. 8a) show higher values concentrated within the NC with areduction at the middle part of the PC. In this case, residual trans-port reaches values up to 20 m2/s. However, contrary to tidal flows,the changes between scenarios are higher within the NC rather thanon its sides. At the inner bay, the magnitudes of the changes are verysimilar for Sc2, Sc3 and Sc4, with a decrease of approximately 10% atthe NC. For the PC, significant differences between Sc2 and Sc3 arise:whereas for the first there is an increase in the residual transport(�15 %) in the NC and the southwestern side of the constriction, theopposite effect is obtained for the latter, with reductions of up to 20%.For the outer bay differences are also observed with no importantchanges for Sc1 and a rise of 15–20 % at the NC for Sc3.

The directions of the residual transport are also modified by theinterventions. For Sc2, the transport rotates anti-clockwise at thearea of the inner bay closer to Carracas Creeks and the southwesternside of the PC. In the case of Sc3, the same effect is obtained for thearea close to Carracas Creeks, although a clockwise rotation is alsoobtained at the central part of the inner bay. As for the other portions

C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141 135

Fig. 6. A and B show the change of tide amplitude (line) and phase (dashed line) fields of the tidal elevation obtained from the model for the M2 and M4 constituents, respectively,from February 22nd to March 14th. The lower panels correspond to the comparison of the amplitudes C and D, and phases E and F of the section defined in black line in panels Aand B. Black, red, blue and green color correspond to Sc1, Sc2, Sc3 and Sc4, respectively.

of the NC, rotations without a clear pattern are obtained, implyinga very complex behavior of the residual transport and, hence, of themorphodynamics during the simulated period.

Summarizing, for Sc1 the residual current increase at the north ofPC and the connection of inner bay with the NC; these areas coincidewith the maximum flood/ebb currents, and the increase of the phaseof the tidal constituents M2 and M4. However, the residual currentsstrongly decrease at the south of PC and inner bay and in the outerarea, where the highest distortion factors and the minimum tidalflow and tidal current are found. For Sc2, Sc3 and Sc4, the residualcurrents increase (decrease) around the NC at outer and inner basins(around the NC at PC and in the NC at inner basin), where there isa decrease (increase) of the distortion factor and increase (decrease)of the tidal flows. Thus, accretion (erosion) areas will potentially be

found at NC in the outer and inner basins (around the NC at PC andinner basin).

4.3. Morphodynamics

The numerical model also reproduces the morphological evolu-tion of the domain (Fig. 9). In the case of Sc1, two different areasalong NC are observed: (1) at PC, model results suggest a slighterosion at the west boundary and close to the NC with impor-tant accretion on the rest of PC; and (2) in the inner bay accre-tion is observed along the NC axis, whereas a smooth erosion isobtained on its lateral boundaries. In the transition between thesetwo areas, there is an important accretion in the same place wherethe abrupt changes in the bed level are present. The most active

136 C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141

Fig. 7. Influence of the interventions on across-flow rate per unit width (qx (m2/s))in the Cádiz Bay at maximum flood, ebb, high tide and low tide (panels a–d, respectively) (seeFig 5). Panels 1–4 correspond to Sc1, Sc2 ∗ 100/Sc1 − 100, Sc3 ∗ 100/Sc1 − 100 and Sc4 ∗ 100/Sc1 − 100, respectively (blue=decrease and red=increase).

area is the nearshore of Valdelagrana beach (Figs. 1, 9a) with a sig-nificant erosion. This erosion is not realistic for two main reasons.First, the bathymetry (and topography) data for this area have alower resolution than those for PC and inner bay. After the bedlevel interpolation over the numerical mesh, the obtained beachprofiles were inaccurate and far from their equilibrium shape result-ing in unrealistic morphodynamic changes. Second, the numericalmodel does not consider the propagation of swell waves gener-ated far from the domain. However, as demonstrated through-out the previous sections, the influence of the interventions atthis area is negligible, and this important bathymetry changes atValdelagrana beach are identically obtained for all the scenarios(Fig. 9b–d).

The differences between the final bed levels obtained for thevarious modified scenarios and Sc1 are depicted in Fig. 9b–d. ForSc2, no significant changes are observed at the outer basin, whereasaccretion (erosion) is observed at the inner bay part of the NC (inproximity of NC). Areas of significant erosion are also observed closeto the bridge piers. For Sc3 there are significant variations in the outerbay, where the NC experiences accretion and its margins are eroded.This behavior tends to smooth the bathymetry with a loss of theoperational capacity of NC. A similar effect is observed for PC, wherean important erosion in the area with abrupt changes in water depthis found. A significant erosion at the main channel of Carracas Creeksis also observed. Results for Sc4 are very similar to those obtained forSc3, although the sedimentation along the axis of NC is reduced at

C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141 137

Fig. 8. A-D represent the residual transport at Sc1, Sc2, Sc3 and Sc4, respectively, at flood tide (see Fig. 5). Black arrows correspond to the Sc1 and cyan arrows correspond to eachscenario after the interventions. The colormap in the background in panels b-d represents the variation in the magnitudes (Sci ∗ 100/Sc1 − 100, where i=2,3,4).

the inner bay and bed level changes were not observed at CarracasCreeks.

Variations of the bathymetry for each scenario with respect to Sc1are shown in panels b–d in Fig. 9. For Sc2, the sedimentation of theseareas is more pronounced, although the most important changeswere obtained for Sc3. The sediment transport pattern deduced ispronounced deposition at the NC, over all of the PC and in the innerbay, and close to the new terminal. However, erosion is observedclose to the NC. This behavior agrees with the hydrodynamic pro-cesses (Sections 4.1.2 and 4.2). The maximum decrease (increase)of currents correspond to the areas where deposition (erosion) isobserved. Accordingly to the results obtained for the rest of thevariables analyzed, results for Sc4 are very similar to those of Sc3,implying the dominance of the effect of the new port terminal andthe dredging along the PC.

5. Discussion

The results of the harmonic analyses were used to quantify thetidal asymmetry and relate the hydrodynamic changes identified atthe bay and its morphodynamic evolution. Usually, tidal asymme-try refers to the distortion of the predominant semi-diurnal tide as

a result of overtides, and according to Aubrey and Speer (1985),Friedrichs and Aubrey (1988) this non-linear distortion implies anincrease of the parameter aM4/aM2. The results for this parameteralong the transect A-B (Fig. 6) are depicted in Fig. 10a. This figureshows the variation of the ratio aM4/aM2 for Sc1 and Sc4; theirvariations with respect to Sc2 and Sc3 are negligible. The resultsalso show that the ratio aM4/aM2 increases along PC from 0.07 (A)to 0.14 (B), due to a higher growth of aM4 than aM2 along PC.These significant non-linear effects are also present in tidal cur-rents, as discussed below. Results also suggest that the ratio aM4/aM2increases up to 0.01 along the PC for Sc4 thus showing that tidalasymmetry is affected by human interventions, although this differ-ence is maintained along the inner bay. The section where maximumdifferences in aM4/aM2 between scenarios are observed coincideswith the section where the major morphodynamic changes are found(Fig. 10d). Thus, the interventions increase the role of non-lineardistortion and bed friction on the bay hydro–morphodynamics.

The tidal asymmetry obtained from tidal currents is assessedthrough the relative phase 20M2 − 0M4 (Aubrey and Speer, 1985)and (Friedrichs and Aubrey, 1988). When this relative phase is below(over) 180◦, flood (ebb) tides dominate. According to Zarzuelo et al.(2015), the Cádiz Bay is flood-dominant in NC and the shallower

138 C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141

Fig. 9. Bottom elevation (mm) in the Cádiz Bay at the end of the simulation. Panels 1-4 correspond to Sc1, Sc2 ∗ 100/Sc1 − 100, Sc3 ∗ 100/Sc1 − 100 and Sc4 ∗ 100/Sc1 − 100,respectively (blue=accretion; red=erosion).

areas of the inner basins, whereas it is ebb-dominant in the sur-roundings of NC. The results along the transect A-B (Fig. 10b) showthat the flood dominance increases with the interventions. Thechanges in tidal flows and asymmetry are related to the sedimenttransport within the bay (Chen et al., 2012; Zarzuelo et al., 2015), andmorphodynamic changes are expected in areas with alternate domi-nance of flood and ebb. These changes are confirmed by the bed levelvariations along the transect A-B (Fig. 10d).

The residual currents along the transect A-B (Fig. 10c) are alsoclosely related with the morphodynamics. The areas where thesecurrents are weak coincide with the areas where no significantbathymetry changes are observed. The majority of these changesare concentrated along PC and the external boundary of the innerbay, where consecutive peaks of residual currents are correlatedwith local maxima of bed level variations. Furthermore, results forSc4 show an attenuation of the maximum absolute values and thedirection of residual currents at PC with respect to Sc1. The bedlevel differences show that these variations promote a change fromaccretional to an erosional trend in this area.

Hence, the results shown in Fig. 10 illustrate that the morpho-dynamic evolution along the transect A-B is closely related to thehydrodynamic processes, as described by Mehta et al. (1989). Thesediment transport patterns are related to the increase and decreaseof the currents, discussed in Sections 4.2 and 4.1.2. This importantconclusion applies not only to the transect A-B, but also to the wholearea where the interventions modify the hydrodynamics. As shownin Section 4.1.2, they increase the magnitude of tidal flows aroundNC and close to the new terminal. These variations cause signifi-cant changes in the seabed topography due to the occurrence oferosion processes, since the decrease (increase) in the magnitude oftidal flows will decrease (increase) the ability of the bay to trans-port sand, accelerating (decelerating) the accumulation of sedimentduring flood and ebb tides in the future.

The maximum erosion (Figs. 7 1st row and 8 1st column) isobserved in the NC, where the maximum currents are found. Themaximum deposition is reached in two areas: (1) the surroundingsof the NC which are characterized by shallower areas and an impor-tant tidal asymmetry (Section 4.1.1); and (2) the abrupt bathymetric

C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141 139

0.05

0.1

0.15

aM

4/a

M2

-200

0

2002

M2-

M4 [

]

-20

0

20

qre

s [m

2/s

]

0 3 6 9 12

-10

0

10

ben

d-b

in [m

m]

7.43 7.47 7.51

X-UTM [105 m]

4.051

4.049

4.047

4.045

Y-U

TM

[106

m] ! P1!

P2!

P3!

P4!

P1 P2 P3 P4!

A B!

A!

B!

Distance [km] !

a) !

b) !

c) !

d) !

Fig. 10. Hydrodynamic and morphodynamic variables along the navigation channel: A-aM4/aM2, B-20M2 − 0M4, C-residual transport, and D-bed level differences for Sc1 (solidline) and Sc4 (dashed line). Right panel: transect A-B (dashed line) and location of point P1 to P4.

change in the south of PC, where there is an important reduction ofthe currents.

6. Conclusions

In this work, a morphodynamic numerical model was used tosimulate the effects of different scenarios corresponding to the futureinterventions planned at the Cádiz Bay (southern Spain). Morpho-dynamic results (namely suspended sediment concentrations anddeposition/erosion rates) were compared with hydrodynamic modi-fications induced by human interventions in order to highlight causeand effect relationships. Based on accurate modeling of the flow field,the main characteristics of hydrodynamics, sediment transport andmorphological evolution in the Cádiz Bay have been reproduced.Hydro- and morphodynamic simulations were performed for differ-ent real scenarios analyzing the changes in tidal levels, tidal flows,residual transport and sediment concentration.

The hydrodynamic and morphodynamic analyses presentedherein are potentially of interest for altered embayment systems.Nonetheless, the adopted approach provides insights into the effectsof human interventions that are of general interest since the linksbetween the hydrodynamic variations induced by human interven-tions and the morphodynamic evolution of the bay are discussed.After the analysis of the results, the following main conclusions weredrawn:

1. The comparison between model results and field data demon-strated the capability of the WWTM+STABEM morphody-namic model to accurately reproduce the hydrodynamic andmorphodynamic processes at the areas of the Cádiz Bay wherethe human interventions lead to important changes, includ-ing tidal creeks. The use of an unstructured mesh allowedus to reproduce in detail the interventions within the bay(bridge, navigation channel, new terminal) without increasingthe computational effort.

2. The agreement between the morphodynamic tendenciesobtained after the analysis of the hydrodynamic variations forthe altered scenarios and the results of the morphodynamicsimulations confirms the applicability of the hydrodynamicsimulations as a proxy for the morphodynamic evolution. Theimpact of the hydrodynamic variations on the morphodynamicevolution can be described in terms of variations of tidal asym-metry and residual currents. Variations of tidal levels and flowsinduced by the interventions alter the tidal symmetry of the

bay and strengthen the morphodynamic changes, specially inthe PC. Moreover, the residual transport is also affected by theinterventions, which reduce its maximum values and alter itsdirection along the PC, thus possibly changing the future evo-lution from accretion to erosion in this area. Results show thatan increase (decrease) of the tidal asymmetry and a decrease(increase) of the residual transport cause sedimentation (ero-sion) over the bay.

3. The hydrodynamic changes and their effects on sediment ero-sion, deposition and transport may cause geomorphologicalchanges away from the dredge location, including the potentialerosion of intertidal areas. Our results show that the dredgingwill increase deposition (∼50%) in the shallower areas closeto the new channel, thus subsequently promoting a reduc-tion in the amount of sediment input into the basins. Themain changes in the erosion/deposition patterns are foundin the area with strong bottom frictions and tidal asymme-tries. Dredging increased sedimentation in the shallower areasclose to the new channel, which subsequently reduced theamount of sediment input into the basins, thus leading toincreased dredging actions to maintain the depths of the chan-nels for navigation purposes, that is likely to increase dredgingactivities for maintenance.

4. The future development of the bay will heavily depend on thefuture constructions. The interventions have a relatively largeimpact on the bay dynamics, which is most obvious for thetidal flow and the residual current. However, our results indi-cate that the ability of the bay to transport sediment betweenthe inner and outer bays will deteriorate, thus impacting theecological dynamics of the Cádiz Bay. For example, the changescould promote sedimentation in the inner bay because of thelower current velocities.

Acknowledgments

This work was funded by the Cádiz Bay Port Authority, theDepartment of Innovation, Science and Business of the AndalusianRegional Government (projects P09-TEP-4630 and P10-RNM-6352)and project BIA2015-65598-P (MINECO/FEDER). The work of the firstauthor was partially funded by the Andalusian Regional Government,research grant RNM-6352. Three anonymous reviewers and the edi-tor are also acknowledged for their comments and suggestions whichsignificantly improved the manuscript.

140 C. Zarzuelo et al. / Geomorphology 320 (2018) 127–141

Appendix A

The agreement between the modeled and observed data wasassessed using the root-mean-square error (RMSE), the correlationcoefficient (R) and the skill coefficient (S). Considering that Mn and Onare the modeled and observed data, respectively, at N discrete points,the RMSE is defined by:

RMSE =

[1N

N∑n=1

(On − Mn)2]1/2

(.1)

The correlation coefficient (R) between Mn and On is given by:

R =1N

∑Nn=1

(Mn − M̄n

) (On − Ōn

)sMsO

(.2)

where sM and sO are the standard deviations of the modeled andobserved data, respectively. The overbar represents the mean value.The correlation ranges from 0 (no correlation) to 1 (complete corre-lation).

The Skill coefficient (S) (Wilmott, 1981) is defined as

S = 1 −∑N

n=1 |Mn − On|2∑Nn=1

(|Mn − Ōn|2 + |On − Ōn|2

) (.3)

The Skill coefficient ranges from 0 (bad skill) to 1 (good skill).

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Assessing the morphodynamic response of human-altered tidal embayments1. Introduction2. Materials and methods2.1. Field site2.2. Field survey2.3. The morphodynamic model

3. Application of the model to the Cádiz Bay3.1. Model implementation and calibration3.1.1. Calibration and testing

3.2. Definition of model scenarios

4. Results4.1. Tidal asymmetry4.1.1. Tidal level4.1.2. Tidal flow

4.2. Residual transport4.3. Morphodynamics

5. Discussion6. ConclusionsAcknowledgmentsReferences