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Longshore Sediment Transport on the Northern Coast ofthe Yucatan Peninsula

Christian M. Appendini, Paulo Salles, E. Tonatiuh Mendoza, Jose Lopez, andAlec Torres-Freyermuth

Laboratorio de Ingenierıa y Procesos CosterosInstituto de IngenierıaUniversidad Nacional Autonoma de MexicoPuerto de Abrigo s/nSisal, Yucatan 92718, [email protected]

ABSTRACT

Appendini, C.M.; Salles, P.; Mendoza, E.T.; Lopez, J., and Torres-Freyermuth, A., 2012. Longshore sediment transporton the northern coast of the Yucatan Peninsula. Journal of Coastal Research, 28(6), 1404–1417. Coconut Creek (Florida),ISSN 0749-0208.

This paper presents a qualitative assessment of coastal processes along the northern coast of the Yucatan Peninsulabased on a method used to estimate the potential longshore sediment transport. Despite the deep-water low-energy waveconditions (Hs 5 1 m) in the study area, erosion is critical in many locations, including the urbanized stretches of coast.The waves were characterized using a 12 y (1997–2009) deep-water wave hindcast data (WAVEWATCH III) as forcing fora spectral wind-wave numerical model (MIKE 21 SW) used to propagate the waves to the coast. Simulated time series ofsignificant wave height, peak period, and direction are compared against in situ measurements at 10 m water depth.Numerical results are further employed for estimation of the nearshore wave climate along the coast. Wave conditionsare strongly affected by the wide continental shelf in front of the northern Yucatan Peninsula, with an increase in waveenergy at the eastern part of the peninsula where the shelf narrows. The nearshore wave climate is employed for thequalitative assessment of potential longshore sediment transport (LITDRIFT model) in the study area. The sedimenttransport calculations are consistent with both volume impoundment estimations at a groin and dredging estimates at aharbor (235,000 m3/y). A net westward potential longshore sediment transport is found along the entire coast, rangingbetween 220,000 and 280,000 m3/y, except west of Holbox, where longshore transport direction is inverted. Based onsediment transport gradients, potential erosion and deposition areas are identified. Erosion/accretion patterns atnonurbanized areas are consistent with field observations. This dominant westward longshore transport suggests anextremely sensitive shoreline to littoral barriers, as supported by observations in the most urbanized areas. These areasshow no gradients on longshore sediment transport, whereas beach erosion is a common feature enhanced by littoralbarriers. Shore protection should then be oriented toward sediment management strategies.

ADDITIONAL INDEX WORDS: Gulf of Mexico, Yucatan, wave climate, longshore sediment transport, WAVEWATCHIII, MIKE 21 SW, LITDRIFT, beach erosion.

INTRODUCTION

Population increases in coastal areas exceed any other area

in the world, with more than one-third of the population living

within 100 km from the shore (GESAMP, 2001), resulting in an

increased pressure to the fragile coastal systems. Unfortunate-

ly, anthropogenic interventions and poor management have

often produced increased levels of vulnerability and risk. The

Yucatan coast in Mexico is not an exception as an area exposed

to coastal hazards, increased population growth, and lack of

long-term monitoring programs and integrated management.

Indeed, this area has experienced severe coastal erosion in the

last decades (Figure 1a), and hence several actions, such as

hard protection and small-scale sand nourishments, have been

taken to mitigate the problem (Meyer-Arendt, 1991, 1993),

either by the government (Figures 1b–d) or by local inhabi-

tants (Figures 1e–f) ,with limited success. However, one of the

major problems towards the implementation of integrated

programs in this area has been the lack of reliable information

on wave climate and sediment transport patterns.

In order to provide solutions to coastal erosion problems, both

reference conditions on wave climate and sediment transport

patterns are critical starting points. While wave conditions are

relatively easy to determine, either by wave hindcast/reanal-

ysis or long-term measurements, sediment transport is a

complex process involving a vast quantity of parameters.

Mathematical models for determining sediment transport have

been developed to establish sediment transport rates based on

wave and current conditions, sediment properties, beach slope,

and other parameters. Despite the wide use of such models to

determine quantitative values of sediment transport rates,

these have been criticized due to the uncertainties involved in

describing a complex process involving a vast quantity of

variables that are not very well understood (Cooper and Pilkey,

2004a, 2004b; Pilkey and Cooper, 2007; Thieler et al., 2000).

DOI: 10.2112/JCOASTRES-D-11-00162.1 received 30 August 2011;accepted in revision 17 December 2011.Published Pre-print online 15 May 2012.’ Coastal Education & Research Foundation 2012

Journal of Coastal Research 28 6 1404–1417 Coconut Creek, Florida November 2012

In addition, such authors emphasize the advantages of

performing qualitative assessment of longshore sediment

transport using mathematical models, in the sense that

controlling the number of constant and variable parameters

allows the understanding of the general patterns and dominant

mechanisms of coastal processes. Considering that the coast of

Yucatan has been seldom studied, this paper presents a first

approximation to qualitatively estimate gradients in potential

longshore sediment transport (PLST) along the coast. PLST is

defined in this paper as the expected sediment transport

considering an unlimited sediment supply, given the inherent

numerical model and data availability limitations.

Therefore, the aim of this paper is twofold: (i) to qualitatively

estimate the large-scale sediment transport along the northern

Yucatan coast, and (ii) to identify potential erosion and

accretion areas based on the PLST gradients. In this study,

we consider that, while extreme wave events result in beach

erosion with damaging consequences, it is the day to day

chronic erosion that undermines the buffer capacity of beaches

to protect themselves during storms (Appendini and Fischer,

1998; Fischer, 1985). As such, chronic erosion is a result of the

longshore sediment transport patterns, which are driven by the

mean wave climate, determined in the study.

The outline of this paper is the following. First, the available

data for the study area are briefly described. Next, a description

of the wave and sediment transport models employed is given.

The results and discussion section presents the nearshore wave

information here derived for driving the sediment transport

model, followed by the PLST estimates. The model results are

compared with observations, and a discussion of the discrep-

ancies between both is also given, with emphasis on the

qualitative results. Finally, concluding remarks are presented.

STUDY AREA

The study area encompasses the northern coast of the

Yucatan Peninsula (Figure 2) extending from Celestun (Yuca-

tan) to north of Cancun (Quintana Roo). A wide continental

shelf is an important characteristic in the area, with an

approximate width of 245 km and a slope of 1/1000 (Enriquez,

Marino-Tapia, and Herrera-Silveira, 2010). The Yucatan coast

has been characterized as low-lying coastal area, where 57% is

composed by coastal lagoons with barrier islands and 43% is

ocean front, from which 85% is sandy coast (CINVESTAV,

2007). The tidal regime is mixed with a diurnal dominance, and

a tidal range of 0.1 m for neap tides and 0.8 m for spring tides

(Cuevas-Jimenez and Euan-Avila, 2009). Reported grain size

values are only available for the Progreso beach area (see

Figure 2), ranging between 0.2 mm (at ,0.5 m depth) and

0.5 mm (at swash zone) with poorly sorted grains (Uc-Sanchez,

2009). The study area is subject to extreme wave events

throughout the year: high-pressure polar outbreak systems

called Nortes during winter, and tropical storms and hurri-

canes during summer. However, the latter has mainly an

impact at the coast fronting the Caribbean Sea (Quintana Roo),

not covered in this work, with few events affecting the study

area, such as Hurricane Gilbert in 1988. It is also worth

mentioning that on the Yucatan shelf, the dominant current in

the coastal region is from east to west, as is described in

Enriquez, Marino-Tapia, and Herrera-Silveira (2010). This

current has been registered with a magnitude in the order of

20 cm/s (Marino-Tapia, personal communication) using an

Acoustic Wave and Current Profiler (AWAC) moored at 10 m

water depth (Figure 2).

DATA

WavesConsidering the importance of the coastal zones and their

vulnerability, knowledge of the marine conditions is essential for

decision making in coastal zone management. This has motivated

many governments to create monitoring programs for measuring

marine conditions (waves, water levels, temperature, etc.), such

as the National Data Buoy Center (NDBC) from the National

Oceanic and Atmospheric Administration (NOAA) in the United

States, Puertos del Estado in Spain, and the U.K. Met Office in

the U.K., among others. Unfortunately, in Mexico, there is a lack

of such an agency and a formal ocean monitoring network, while

most measurements are short termed and have been done for

specific projects by private companies, research institutes, or

government agencies. This has resulted in sparse data in time

and space and of difficult access, seldom available to third parties.

Therefore, when studying a coastal area in Mexico, a monitoring

program for the specific project is required, or synthetic

information may be used when long-term data are necessary,

such as the present study.

Figure 1. Example of coastal erosion at the Yucatan coast (a); coastal

protection measures taken by the government: geotube (b), groins (c), and

sand replenishment (d); and ‘‘espolones’’ (e, f), a type of groin character-

istically build independently by beachfront homeowners in Yucatan.

Sediment Transport in Yucatan 1405

Journal of Coastal Research, Vol. 28, No. 6, 2012

While there are different sources of hindcast wave data in the

Gulf of Mexico, the only documented source in the public

domain, to the best of the authors’ knowledge, is from NOAA’s

WAVEWATCH III model (Tolman, 2009). The calibration and

validation of the model can be found at http://polar.ncep.noaa.

gov/waves/validation.html. WAVEWATCH III (WW3) is a

third-generation wave model developed by the NOAA/National

Centers for Environmental Prediction (NCEP) based in the

WAM model (Komen et al., 1994). The numerical model solves

the random-phase spectral action density balance equation for

wave number–direction spectra. The model has been applied on

a global scale for wave prediction as well as in hindcast mode.

The model employs a 15 min grid resolution in the Gulf of

Mexico, including the Yucatan Peninsula area, with a finer grid

covering the U.S. coastal area (in 2007, the operational WW3

model increased grid resolution to a 10 min grid for the Gulf of

Mexico and 4 min grid covering the U.S. coastal area). Due to

the low grid resolution at the Yucatan coast, it is not adequate

to characterize the nearshore wave conditions based on these

model results. However, the model results can be employed as

the offshore wave boundary condition in wave propagation

models in order to estimate the nearshore wave conditions.

The available WW3 data used in this study encompass 12 y of

wave information, from February 1, 1997, through February

28, 2009. The locations of the data selected for creating

boundary conditions to the coastal wave model are listed in

Table 1 and shown in Figure 2.

The corresponding wave roses for the 12 y of data at each

location are presented in Figure 3. The wave roses show that

the dominant waves are from the northeastern sector, with

increased importance of the eastern and southeastern sectors

as the Caribbean Sea is approached. The highest waves are

from the northern sector, but again the eastern and southeast-

ern waves become important as the Caribbean Sea is

approached. From the WW3 data, a frequency of approximately

Figure 2. Northern coast of the Yucatan Peninsula showing locations and data sites mentioned in the text.

Table 1. Location of WAVEWATCH III data used as boundary conditions.

Name Longitude (uW) Latitude (uN)

WW3-01 91.25 21.00

WW3-02 90.00 22.00

WW3-03 88.75 22.00

WW3-04 87.5 22.00

WW3-05 86.25 21.00

1406 Appendini et al.


18 storms per year, with a mean significant wave height (HS) of

2.5 m, was determined, from which less than 1 storm per year

corresponds to hurricane waves. A storm was defined as an

event with a significant wave height (Hs) exceeding 2 m

(approximately the long-term value plus two standard devia-

tions) during a minimum period of 12 h.

Besides the long-term hindcast wave data, there are short-

term wave measurements in shallow waters (10 m) close to

Telchac, Yucatan (location marked as AWAC in Figure 2). The

data were gathered by the Group of Coastal Processes and

Management (GCPM) from the Marine Resources Department

(CINVESTAV IPN, Merida Unit), covering the period from

April 2008 through February 2009, with a gap of data between

July and October 2008. The wave rose from the measurements

is shown in Figure 4. Consistent with the deep-water wave

data, the wave rose indicates that the most frequent waves are

Figure 3. Wave roses from 12 y of WAVEWATCH III results, going from west (WW3-01) to east (WW3-05) as shown in Figure 2.



from the north-east sector, while the highest waves are from

the north.

BathymetryThe bathymetry data used for wave propagation correspond

to NOAA’s 1 arc-minute global relief model of Earth’s surface

ETOPO1 (Amante and Eakins, 2009), which was considered to

be the best source available for the area of interest based on an

analysis of different data sets, such as GEBCO (2009) and

Smith and Sandwell (1997). On the other hand, the nearshore

bathymetry used for sediment transport calculations was

obtained from the Program for Beach Profile Monitoring

database, from the GCPM. These data provided information

on the subaerial coastal profiles, so that the selected profile

(PROG06) was extended beyond the surf zone to a depth of 10 m

using a detailed bathymetry surveyed by the GCPM at

Progreso, Yucatan (Figure 5). The location of the beach profile

PROG06 and the area covered by the bathymetry used to

extend the profile are shown in Figure 2. While it could be

difficult to define this beach profile as representative for the

entire study area, this is the only available information. Also,

Figure 6b shows that the bathymetry contours are very

uniform along the coast, with the exception of some areas

where the slope from the shore to a 10 m depth is milder in

comparison to the location of the PROG06 profile (shown in

Figure 2). Thus, using the same beach profile to characterize

the longshore sediment transport in the entire study area will

provide a qualitative description of the dynamics in the study

area, which is considered more adequate in the sense that

reducing the number of variables allows for a better interpre-

tation of the coastal processes under study (Cooper and Pilkey,

2004b).

NUMERICAL MODELS

Wave ModelingThe wave model used for wave propagation was the MIKE 21

SW (DHI, 2011c) developed by DHI Water & Environment.

This is a third-generation spectral wave model that simulates

the growth, decay, and transformation of wind-generated

waves and swells in coastal and offshore regions. MIKE 21

SW simulates wind waves by means of the wave action density

spectrum N(s,h), formulated in terms of wave direction, h, and

relative angular frequency, s, where the action density is

related to the energy density by:

N(s,h) ~E(s,h)

s

The model is applied using the directional decoupled paramet-

ric formulation, which is based on a parameterization of the

Figure 4. Wave rose from the wave measurements at Telchac.

Figure 5. Extended beach profile (PROG06) corresponding to the Progreso area as used in sediment transport modeling. (Note: Profile specification in

LITPACK requires offshore being located at x 5 0, as opposed to the usual beach profile presentation with the coast at the initial x position.)



wave action conservation equation (Komen et al., 1994; Young,

1999), made in the frequency domain by introducing the zeroth

and first moment of the wave action spectrum. The wave action

conservation equation is written in Cartesian coordinates as:

LN

Ltz+:(�nnN) ~

SinzSnlzSdszSbotzSsurf

s

where the action density is defined by N(x,s,h,t), where x

represents the Cartesian coordinates (x,y), t is time, and

ı(cx,cy,cs,ch) is the propagation velocity of a wave group in the

four-dimensional phase space x, s, and h. The wind input

source term, Sin, is based on the quasi-linear theory of wind-

wave generation presented by Janssen (1989, 1991) and

Janssen, Lionello, and Zambresky (1989) as implemented in

WAM Cycle 4 (Komen et al., 1994). Snl represents the nonlinear

wave-energy transfer, as defined by Hasselmann and Hassel-

mann (1985) and Hasselmann et al. (1985) for quadruplet-wave

interactions and by Eldeberky and Battjes (1995, 1996) for

triad wave interaction. Sds represents the dissipation due to

whitecapping based on Komen and Hasselmann (1984), as

modified by Komen et al. (1994) based on the wind input

description by Janssen, Lionello, and Zambresky (1989). Sbot is

the energy dissipation due to bottom friction as described by

Johnson and Kofoed-Hansen (2000). Finally, Ssurf is the energy

dissipation due to depth-induced wave breaking as derived by

Battjes and Janssen (1978) and written by Eldeberky and

Battjes (1996).

The model domain was set up to cover the northern coast

of the Yucatan Peninsula with an unstructured mesh with a

resolution of approximately 3 km (see Figure 6a for the mesh

definition and Figure 6b for the final bathymetry showing

the locations of the boundary conditions from Figure 3). The

offshore limit is defined by the position of the WW3 data

used as offshore forcing boundary conditions for the model.

An interpolation of the wave conditions was done between

the five WW3 data points defining the boundary conditions

shown in Figure 6a. The directional discretization was done

in 10u bins. Varying water levels (tides) were not considered

due to the small tidal range and in order to avoid additional

complexity in the interpretation of the longshore sediment

transport calculations.

Longshore Sediment Transport ModelingThe annual sediment drift was calculated using the sediment

transport model LITDRIFT, which is a combination of a one-

dimensional surf-zone hydrodynamic and wave model with the

intrawave-period sediment transport model STP; STP is based

on the model for turbulent wave- current boundary layers

described by Fredsoe (1984). LITDRIFT has been applied in

many different areas of the world; some of the most recent

research studies using LITDRIFT are found in Elsayed and

Mahmoud (2007), Elsayed et al. (2005), Pandian et al. (2004),

Rao et al. (2009), and Troels (2011). Complete descriptions of

Figure 6. Unstructured mesh showing location of boundary conditions used for wave modeling (a) and bathymetry used in wave modeling showing location

of extraction points and wave measurements from CINVESTAV (b).



LITDRIFT and STP are found in DHI (2011a) and DHI (2011b),

respectively, while the basic equations are provided herein.

The total sediment transport (qt) is calculated as the sum of

bed-load sediment transport (qb) and suspended sediment

transport (qs). Bed-load transport is calculated as function of

the instantaneous dimensionless bed shear stress (Shields

parameter) as described by Engelund and Fredsoe (1976):

h0~u02f

(s{1)gd

qb ~1

T

ðT

0

f (h)dt

where h9 is the Shields’ parameter related to skin friction, u9f is

the friction velocity, s is the relative density of bed material, g

the acceleration of gravity, d is the median grain size, T is the

wave period, and t is time.

The distribution of suspended sediment concentration is

described by the vertical diffusion equation:

Lc

Lt~ ws

Lc

Lzz

LLz

(esLc

Lz)

where c is the instantaneous concentration by volume, ws is the

fall velocity of suspended sediment, z is the vertical coordinate,

and es is the instantaneous turbulent exchange factor for

suspended sediment. The suspended sediment transport, qs, is

then calculated as the product of the instantaneous flow

velocities and the instantaneous sediment concentration:

qs ~1

T

ðT

0

ðD

0

(cU)dzdt

where T is the mean wave period, D is water depth, and U is the

instantaneous velocity of combined wave-current motion.

The hydrodynamic and wave model in LITDRIFT includes a

description of the wave transformation (i.e., shoaling and

breaking), including the calculation of radiation stresses,

which are used to calculate the longshore current:

{L(Sxy)

Lx~ tb{

LLx

(rEDLV

Lx)

where Sxy is the shear component of the radiation stress tensor,

tb is the bed shear stress from the current, x is the coordinate

perpendicular to the coast, r is the seawater density, E is the

momentum exchange coefficient, and V is the current velocity.

The calculations were performed over a coastal profile on

every point from its toe to the shoreline, and results were used

as input to the LITDRIFT model in order to calculate the

sediment transport potential at each point according with the

prescribed sediment characteristics. The calculations of the

sediment transport were performed for each event in a wave

climate, obtaining the individual event sediment transport

rate, which was weighted with the wave-event occurrence in

order to calculate the transport contribution. Therefore, the

annual littoral transport for a determined beach profile and

wave climate is obtained from the summation of all the

sediment transport contributions for all the wave events. This

method allows the characterization of the littoral drift under a

mean wave climate based on the local conditions (nonuniform

bathymetric and sediment profile), giving a deterministic

description of the longshore sediment transport. For further

details, interested readers are referred to Deigaard, Fredsoe,

and Hedegaard (1986a, 1986b) and Fredsoe, Andersen, and

Silberg (1985), where a detailed description of the fundamen-

tals of the sediment transport model is presented.

Considering the scarce data available in the area and the

qualitative aim of this study to determine sediment transport

rates, the model was simplified by varying the forcing agent

(hydrodynamics) and maintaining constant the receptor (beach

profile and sediment properties).

The latter allows for a better interpretation of PLST

gradients toward an assessment of potential erosion-deposition

areas, without the uncertainties introduced by varying param-

eters and their inherent uncertainties (e.g., grain size, sorting,

and profile geometry). The assessment of sediment transport

was only based on wave-generated currents, so that the varying

forcing agent was the wave conditions obtained from the MIKE

21 SW model results at 10 m depth. A Battjes-Janssen spectral

wave description was used for the boundary waves, with a

spreading factor of 0.35 representing a complex directional sea.

The receptor was then considered constant and characterized

by beach profile PROG06, with a 5 m spatial resolution, and a

sediment size (d50) of 0.35 mm, with a geometrical spreading of

1.2. Sediment characteristics were selected based on Uc-

Sanchez, (2009), who reported values between 0.2 mm to

0.5 mm from the beginning of the surf zone and the swash zone,

respectively. This value was confirmed by local samples taken

at the area of Progreso, which provided a mean diameter d50 of

0.35 mm for samples at different locations. For the sediment

calculation parameters, the Stokes first-order theory was used,

convective terms were included, and bed concentration was

determined by a deterministic approach. In summary, the

varying parameters are wave conditions (Hs, Tp, and mean

wave direction) and orientation of the coast, while the constant

parameters are bathymetry (beach profile), sediment size and

sorting, and water level. This allows us to evaluate longshore

sediment transport along the Yucatan coast in response to

varying wave conditions and shoreline orientation. Cross-shore

sediment transport is not part of this study, since our analysis

is oriented to understand longshore sediment transport and

potential erosion/deposition areas based on PLST gradients

only as a result of the mean wave climate.

RESULTS AND DISCUSSION

Wave ModelingThe wave model was calibrated employing in situ wave

measurements from the buoy at Telchac during the two

measurement periods. Several tests were performed to calibrate

the model using the wave data. During the calibration phase, it

was found that the local winds and breeze system play an

important role over the wave pattern, so that winds from the

WW3 data were also included in the simulation. An assessment

of the accuracy of the simulations shows a bias of 0.18, a root

mean square of 0.32, and a correlation coefficient of 0.80. An

example of the measured and simulated wave parameters for an

interval of time in the simulation period is shown in Figure 7.

Once the model was calibrated with the wave measurements at



Telchac, the wave information at the 10 m isobath was extracted

at selected locations (P01–P18 in Figure 6b) for its further

application on driving the sediment transport model. Figure 8

shows the significant wave height (maximum, minimum, and

mean values), peak wave period (Tp), and mean wave direction

for each selected point. Notice that the mean wave conditions

remain low (HS ,1 m) along most of the Yucatan coast as a

consequence of the wide continental shelf. The highest HS are

found from P15 to P18 (HS .3 m), where the continental shelf

becomes narrower and the coast becomes exposed to the

influence of the swell waves approaching from the Caribbean

Sea. The latter is suggested by both the higher values of Tp and

the mean wave direction (MWD).

Potential Longshore Sediment Transport CharacterizationWhile the wave results presented for points P01 through P18

provide an overall picture of the wave climate on the northern

part of the Yucatan Peninsula, only points P01 through P15

were used for the assessment of sediment transport. This was

done given that the aim of the study is to characterize

transport patterns in the northern coast of Yucatan, whereas

P16–P18 are located in a region where much steeper profiles

are expected. The results from the sediment transport model

provided estimates of net and gross PLST. For instance,

Figure 9a, corresponding to the area of Progreso, shows the

accumulated net and gross PLST along PROG06 considering

an orthogonal shoreline orientation of 350u from north and the

wave conditions from P04. Westward and eastward PLST

values of 52,850 m3/y and 17,150 m3/y were established,

respectively. This yields a net PLST of approximately

35,700 m3/y moving westward and a gross PLST of approxi-

mately 70,000 m3/y for Progreso. To support the net PLST

calculation, an evaluation of sediment impoundment was

conducted using an aerial orthophotograph of the Chuburna

Figure 7. Measured and simulated significant wave height (upper panel), peak wave period (middle panel), and wave direction (lower panel).



harbor, located 20 km west of Progreso. The jetties were

completed in 1988, and the aerial orthophotograph corre-

sponds to 1995. While the sediment impoundment calculation

corresponds to a yearly rate of approximately 20,000 m3/y, this

value is considered to underestimate the PLST, since it is

known that this area has been used for sand extraction.

Moreover, the governmental agency that operates sand

extraction in this area (Secretarıa de Comunicaciones y

Transportes), based on their yearly dredging programs,

estimates a longshore sediment transport rate of approximate-

ly 30,000 m3/y (Rubio-Cerna, personal communication). There-

fore, the results of this study are in good agreement with both

estimates for longshore transport in the area. It should be

noted that the quantitative estimates of PLST rates might be

under- or overestimating real values owing to the uncertain-

ties involved in sediment transport modeling assumptions and

available data. Therefore, the qualitative results obtained from

the modeling are emphasized, allowing for the interpretation

of potential erosion/deposition/stable areas. Figure 9b shows

the PLST distribution along the beach profile from a depth

of 4 m to the shore, suggesting that most of the sediment

transport occurs within the shoreline and a depth of 3 m (first

250 m from the shoreline), although there is still a significant

contribution up to a depth of 6 m (as shown in Figure 9a).

Furthermore, the PLST rates for different shoreline orienta-

tions and wave conditions along the coast were calculated and Q-

alpha curves were constructed for each area (points P01 through

P15). Q-alpha curves show the variation of the net PLST rates for

a given wave climate and beach profile as a function of shoreline

orientation. This provides information on the equilibrium

orientation (net PLST equals to zero) and the sensitivity of the

PLST to shoreline orientation. It has been established by Q-alpha

curves that a zero net PLST is obtained when the resulting wave

energy approaches normal to shore, and it is increased until a

peak in net PLST with waves approaching at an approximate

angle of 50u and then decreases until zero net PLST with waves

approaching with an angle of 90u or more (Mangor, 2004).

As an example, Figure 10 shows the net PLST rates as a

function of shoreline orientation (Q-alpha curve) for Progreso

(negative values represent westward transport and positive

values represent eastward transport). The figure shows that a

small variation in the shoreline orientation results in a steep

change in the PLST rate, indicating a very sensitive shoreline. At

the Progreso area, shoreline orientation is approximately 350ufrom north, while the estimated equilibrium orientation is

approximately 1u from north, resulting in a strong and dominant

net PLST toward the west. Considering that Progreso is far from

an equilibrium orientation, the stability of the shoreline is

strongly dependent on a constant supply of sediment to feed the

sediment transport capacity. Figure 9b (showing the extent of

the PLST across the beach profile) and Figure 10 (showing the

net PLST for varying shoreline orientation) indicate that any

structure along the coast located between land and 3 m depth will

significantly interfere with the PLST path and create erosion

areas downdrift. This is supported with the existing evidence of

downdrift erosion created by structures in the area.

The spatial variation of equilibrium orientation is a valuable

parameter for the assessment of the potential erosion/accretion

along the coast. Applying the Q-alpha curves to the study area

and selecting the PLST rates according to the general shoreline

orientation in the different coast segments, the PLST gradients

were established, allowing the identification of areas of

expected erosion/deposition, as shown in Figure 11b. The

PLST shows a clear dominant westward direction ranging

between 220,000 and 280,000 m3/y, with a single nodal point,

location where sediment transport is inverted, east of Holbox.

We acknowledge that the complex two-dimensional circula-

tions expected in areas such as Holbox and tidal inlets are not

incorporated with this analysis, although they certainly play

an important role in the local shore dynamics.

Sedimentary ProcessesBased on the PLST results, a first regional-scale description

of the sedimentary process in the area can be provided. At the

most western part of the Yucatan coast, near Celestun, the

equilibrium orientation departs from the coast orientation,

which has an orthogonal orientation that ranges from NW

toward the W (moving N to S along the shore). At this area, the

waves approach the shore at more than 50u with respect to the

shoreline, so that the PLST gradient is reduced toward the

Figure 8. Variation of wave conditions along the northern coast of

Yucatan based on 12 y of simulated data.



south, maintaining the accreting longshore spit at the Celestun

lagoon (Figure 12). From Celestun to Sisal, the area of El

Palmar is identified as a potential erosion area from the

resulting PLST gradients due to a change in shoreline

orientation (Figure 11). The area of El Palmar is a nonurba-

nized area where an erosion berm has been observed.

To the east, from Sisal to San Felipe, the shoreline

orientation varies from 30u to 10u west from the equilibrium

orientation (orthogonal shoreline orientation approximately

340u to 350u from N), resulting in high PLST rates, which

require a constant supply of sediment to maintain a stable

coastline. The area between Sisal and Chuburna shows an

important sediment transport gradient, resulting in a potential

erosion area (Figure 11b). The western part of this area is a

pristine area where dune erosion is a common feature, whereas

the east part is an urbanized area with severe erosion

problems.

The area starting east of Chuburna and west of Progreso

towards Telchac (Figure 11b) deserves special attention: here,

the PLST remains constant (thus no longshore gradient).

Based on the PLST gradients, this area is expected to be stable

as long as the sediment supply is enough to constantly fulfill

the sediment transport load. Nevertheless, this area is known

to be the most eroded coast in Yucatan (based on in situ

evidences, mainly damaged beach property as shown in

Figure 1a and water-line position relative to the construction

line—houses—as shown in Figure 13). The reason for the

erosion in this area is that the potential stability of the coast is

Figure 9. Accumulated wave-generated potential longshore sediment transport rates along beach profile PROG06 (a) and potential longshore sediment

transport rates at surf zone of beach profile PROG06 (b). Positive (negative) values represent eastward (westward) transport.



Figure 10. Q-alpha curve for Progreso, Yucatan.

Figure 11. Shoreline equilibrium orientation along the northern coast of the Yucatan Peninsula (a) and potential longshore sediment transport (in m3/y 3

1000) based on shoreline orientation for the northern coast of the Yucatan Peninsula (b). Hatched line in (a) represent the shoreline orientation for

equilibrium. Potential erosion, deposition, and stable areas are identified in (b).

Figure 12. Longshore spit at Celestun, Yucatan. (Photo: Aerozoom).



only achieved given a constant supply of sediment, with no

interference from any coastal barriers. On the contrary, this

stretch of coast is the most urbanized and thus has several

human interventions, such as harbors and houses. Meyer-

Arendt (1993) provides a thorough description of settlement in

the area, where armoring of the coast typically followed the

construction of harbors, establishing erosion rates of 0.9 m/y,

for the period 1948–1978, downdrift of the Yucalpeten harbor

located immediately west of Progreso (Figure 11b). Based on

the established PLST rates, the construction of harbor

structures (groins and jetties) interrupted the sediment supply

into the area, thus leading to erosion and a response by

landowners of armoring the coast and building groins. The

increased blockage of sediment supply has exacerbated erosion

problems, leading to an armoring-erosion chain of events. This

has been reported by Meyer-Arendt (2001) based on an historic

review and observations, stating that the erosion-deposition

fluctuations are common in this area, but the inability to cope

with such phases has led to the chain of events mentioned

previously. This stretch of coast is an interesting example of a

coast with high PLST rates but no PLST gradients, so that

equilibrium would be achieved given a constant supply of sand

(e.g., natural conditions and sand bypassing).

From Telchac to Chabihau, beach erosion is expected due to

the increase in PLST gradients, whereas in the area towards

Dzilam de Bravo, deposition is expected (Figure 11b). It is

important to point out that despite the long stretches of coast

that are expected to be stable, this area is also affected by

harbor entrance structures, and thus exacerbated erosion

problems as mentioned by Meyer-Arendt (2001), in particular

from Sisal to Dzilam de Bravo.

From Dzilam de Bravo toward Cabo Catoche, the coast shows

quite different coastal orientations, some of which are close to

equilibrium orientation (east of Las Coloradas and east of

Holbox) and some others which show positive or negative PLST

gradients resulting in erosion or deposition. The areas of

expected erosion are west of Chisahcab, west and east of San

Felipe, east of Las Coloradas, from Holbox to the west, and east

of Cabo Catoche. The areas of expected deposition are east of El

Isolte San Felipe, El Cuyo, and east of Holbox; the last two

locations represent large stretches of depositional coasts

(Figure 11b). It is known that Holbox has experienced erosion

problems as well as the salt flats at Las Coloradas.

Finally, as we approach the Caribbean Sea, there is more

influence from southeastern swells, so that the equilibrium

orientation varies greatly from the rest of the study area. This

area has a shoreline closer to equilibrium, and thus it is

expected to have fewer erosion problems, such as south of Cabo

Catoche, where a stable area is expected (Figure 11b).

The previous description is a qualitative characterization of

expected erosion/deposition areas based on PLST calculations

under the assumptions of a coastline characterized by a

constant sediment supply and a constant beach geometry and

composition. The Q-alpha curves could be used to analyze more

detailed areas, for instance, the areas of San Felipe, Holbox, or

Dzilam de Bravo, in order to identify erosion hotspots as a

result of PLST gradients given by shoreline orientation.

However, for a full interpretation of the coastal processes

involved, more detailed analyses considering the two- and

three-dimensional effects of the local features such as struc-

tures, harbors, coastal lagoon inlets, etc., have to be taken into

account.

Although the sediment transport description in this paper

is based on wave-driven transport, a sensitivity test was

performed to assess the effect of the coastal current registered

by Marino-Tapia over the PLST. The test was performed for the

Progreso area applying the LITDRIFT model using the

PROG06 profile described before, but adding a 20 cm/s

current at a depth of 10 m. The PLST was largely increased

at depths below 3 m, with no effect over the PLST at the surf

zone (where the PLST is given by wave-generated currents).

The effect of the current shows that although the wave

conditions in the study area generate PLST between 0 and

6 m depth, they do generate enough bottom shear in deeper

areas to enable the suspended sediment to be transported by

the coastal current. This should have special attention in

further investigations of coastal processes in the area since

it implies important processes not included in this study,

which may provide insight to the formation of submerged

sandbars and sand waves, which are visible in aerial photos

and satellite images (e.g., see Google Earth at lat 21.5952uN, long 88.3067u W), and at depths deeper than the surf

zone and more than 5 km from the shore.

CONCLUSIONS

The results presented here are a first effort to characterize

wave conditions and PLST in the study area for coastal

management purposes. Wave climate was determined from

12 y of wave hindcast data propagated to the nearshore along

the northern coast of the Yucatan Peninsula. Based on the

nearshore wave information, a qualitative estimate of coastal

processes was performed employing a methodology to calculate

the PLST based on varying conditions for the forcing agent

(hydrodynamics) and maintaining the receptor variables

constant (bathymetry and sediments). This study then pro-

vides a qualitative overview of the coastal processes in an area

with limited data. Based on the numerical results, the main

conclusions are:

Figure 13. Beach erosion in Chelem, Yucatan. (Photo: Aerozoom).



(1) The northern coast of the Yucatan Peninsula is subject to

a low-energy wave climate with predominant waves from

the NE sector. However, the eastern and western parts of

the northern coast of the Yucatan Peninsula still present

different wave climates: In the eastern end of the

northern peninsula, a more energetic SE component

becomes relevant due to the swell generated in the

Caribbean Sea, whereas the energy decreases toward the

west owing to the widening of the continental shelf and

the sheltering from Caribbean swell.

(2) The net PLST is from east to west as a result of wave

conditions and shoreline orientation, with a single nodal

point in the eastern part. Therefore, the depositional

features indicate a truly west-directed longshore sedi-

ment transport. Due to the wave characteristics, the

coastline orientation is far from equilibrium, such that

shoreline stability is only achieved if there is a constant

sediment supply along the coast. While shoreline orien-

tation along the northern coast provides areas of

potential erosion and deposition just as a result of

morphology, potential erosional areas dominate, with a

coast highly sensitive to obstructions in sediment trans-

port. As a result, structures in the area have enhanced

extreme erosion problems. This is more evident in highly

urbanized areas, where the shore encroachments and the

structures of the small fishing harbors have interrupted

sediment transport and supply, creating critical erosion

problems downdrift. Moreover, sediment transport asso-

ciated with small changes of coastal orientation may play

a significant role in the critical areas heavily influenced

by man-made constructions.

(3) This study presents insight into the important phenom-

ena in the area and identifies the relevant processes that

need to be studied in detail for assessing erosion/

deposition problems in local areas. It has been evident

in the study that more complex problems arise when

considering the two- and three-dimensional effects of

coastal lagoons and coastal currents. The Q-alpha curves

could be used to analyze more detailed areas, for instance,

the areas of San Felipe, Holbox, or Dzilam de Bravo, in

order to identify erosion hotspots as a result of PLST

gradients given by shoreline orientation. However, a

more detailed analysis would be required considering the

two- and three-dimensional effects present along the

whole stretch of coast under study. Such phenomena

should be analyzed to provide further insight in the

coastal processes of Yucatan.

(4) The northern coast of the Yucatan Peninsula is an

extremely sensitive shoreline, vulnerable to activities on

the coastal zone, in particular, construction of littoral

barriers (including groins and housing). The sediment

transport patterns established in this study suggest that

shore protection should be oriented toward soft solutions

seeking sediment management such as dune stabilization

and sand bypassing. Still, both soft and hard solutions

will require much more detailed studies for successful

shoreline management actions.

(5) For a better understanding of the coastal processes in the

study area, the effects of coastal currents on sediment

transport, the effects of coastal structures and natural

inlets on the sediment budget, and the sources and sinks

of sediment must be assessed.

ACKNOWLEDGMENTS

The present study was supported by CONACYT FOMIX-

YUC project-106400 and PAPIIT IN 115411. We would like to

thank Ismael Marino-Tapia and Jorge Euan from the Center

for Research and Advanced Studies (CINVESTAV-IPN,

Merida Unit) for providing the wave and profile data, as well

as the orthophotograph. We also greatly appreciate the

valuable review of the manuscript done by Robert G. Dean

from the University of Florida. The authors would like to

thank Sergio Medellin and Rodrigo Medellin from Aerozoom

for the oblique aerial photographs and the Academia

Mexicana de las Ciencias for providing funding for the

organization of the First Workshop on Coastal Oceanography

of Yucatan, where this work was presented and discussed.

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% RESUMEN %

En este trabajo se presenta una evaluacion cualitativa de los procesos costeros a lo largo de la costa norte de Yucatan, en base a una metodologıa para la estimacion

del transporte potencial de sedimentos. A pesar de las condiciones de baja energıa de oleaje (Hs 5 1 m) en la zona, los problemas de erosion costera son crıticos en

varias localidades, incluyendo zonas urbanizadas. Se utilizaron 12 anos de datos (1979–2009) de un retroanalisis de oleaje (WAVEWATCH III) como condiciones de

frontera para un modelo de oleaje en la zona costera (MIKE 21 SW). Las series de tiempo de altura significante, periodo pico y direccion de oleaje se compararon con

mediciones in situ a 10 m de profundidad. Las condiciones de oleaje son muy afectadas por la amplia plataforma continental frente a la costa de Yucatan, mostrando

una tendencia a incrementar al acercarnos a la parte este de la penınsula donde la plataforma es reducida. El clima de oleaje determinado a lo largo de la costa fue

utilizado para evaluar el transporte potencial de sedimentos (modelo LITDRIFT) en la zona de estudio. Los calculos de transporte son consistentes con las

estimaciones en la zona (235,000 m3/ano). Se determino una tendencia dominante hacia el oeste para el transporte potencial de sedimentos en practicamente toda la

costa, con valores entre 220,000 y 280,000 m3/ano, siendo que unicamente al oeste de Holbox hay una inversion en la direccion del transporte. Los patrones de

erosion/acumulacion en las zonas no urbanizadas son consistentes con observaciones de campo. La dominancia del transporte de sedimentos con direccion al oeste

indica que es una costa muy sensible a las barreras litorales, lo cual es sustentado por las observaciones en las zonas densamente urbanizadas. Estas zonas no

muestran gradientes en el transporte de sedimentos, sin embargo la erosion es una caracterıstica comun como resultado de las barreras litorales. De esta manera, la

proteccion costera debera orientarse a estrategias de manejo de sedimento.



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