DREDGING SUMMIT & EXPO ’18 PROCEEDINGS

BEACH DEVELOPMENT AND PROTECTION OF RESORT COASTLINE USING GEOTEXTILE TUBES C. D. Timpson1 and T. C. Stephens2

ABSTRACT Shore erosion is a serious problem that is present in many countries with coastal regions. Mexico is not an exception with coasts on the Pacific Ocean, the Gulf of Mexico, and the Caribbean Sea suffering from erosion. Climate change has played an important role in this matter, increasing the strength of storms that hit the Mexican coasts every year. These vulnerable coasts need to be protected to avoid beach retreat and property damage. Knowing how to design suitable coastal protection is important to help recover and stabilize a beach.

This paper will present the wave modeling and analysis to design and evaluate performance of structures incorporating geotextile tubes in protecting and stabilizing a 500 meter stretch of Caribbean beach at a resort in the state of Quintana Roo, Mexico. Also, after 9 years of observation of what has happened on the protected beach, this paper will detail how it has made it possible to better understand erosion protection projects more fully for this area and to incorporate the lessons learned to design projects for adjacent properties including beach renourishment dredging.

Keywords: Dredging, geotextile tubes, erosion, wave attack, shoreline.

INTRODUCTION The coasts of Quintana Roo, in Mexico have been experiencing increasing erosion, especially in the past 10 years, as storms have been more frequent and stronger than they have been historically. In October 2005, Hurricane Wilma (Category 5 on the Saffir-Simpson Hurricane Scale) passed over the northern part of the state, affecting the beaches of Cozumel, Playa del Carmen and Cancun.

All beaches were severely damaged and eroded with many hotels affected by damage to their structure, installations and furniture. This study is about a property where there was a hotel called Capitan Laffite, at coordinates 20º 40’30.7935” N, 087º o1’17.9711” W (fig. 1). The hotel lost around 20 m of beach and its’ foundations were submerged in the sea. As recovery would be too expensive, the land was sold to a developer, who planned to build a new hotel; the Gran Vela, Riviera Maya. This developer invested in hydrographic studies for a project to recover and stabilize the beach to the original extent of the seaward property line for the following reasons:

 The hotels in the Riviera Maya and Quintana Roo live from tourism and need wide white sand beaches for people from all over the world who come to see and enjoy them.  Seasonal storms develop medium to high waves with enough energy to make sand move and erode beaches. In winter, cold fronts generate waves from the Northeast that last up to a week in duration. In the summer, winds from the Southeast and East generate waves that for weeks. All this movement displaces the sand in front of the hotels, resulting in the narrowing of the beaches and which exposes the hotel facilities, especially public areas such as pools, restaurants, and bars. Protecting the beaches from erosion helps the hotels to maintain the hotels their facilities in good condition.  Mexican law states that the “Maritime Federal Zone” in 20 m from the High Sea Level, measured inland. Therefore, if the beach is eroded, the maritime Federal Zone moves, resulting in the hotel property becoming part of the Federal Zone. Then the property limits are adjusted and the hotel loses. It is important for developers to keep the width of the beach so that there is at least 20 m before the High Sea Level.

1 Engineer, TenCate Geosynthetics, 365 South Holland Drive, Pendergrass, Georgia 30567, USA, T:706-206-9683, Email: [email protected]. 2 Director, TenCate Geosynthetics, 365 South Holland Drive, Pendergrass, Georgis 30567, USA, T:404-660-2317, Email: [email protected].

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Mexico Yucatan Quintana Roo

Punta Bete

Figure 1. Location of Study

In the case of Gran Vela Hotel, bathymetric and topographic surveys were performed, and a project was initiated to protect, recover and stabilize the shoreline of 500 m of beach front. The project planned five 70 m breakwaters, parallel to the shoreline, with 30 m separation between the first four and 130 m between the last breakwater. In addition, a 600 m line of sand filled geotextile tubes were set parallel to the property line and covered with sand to form the core of a sand dune. The dune was vegetated with the objective being to catch sand moved by the wind and to fix the dune with roots of the plants.

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The project was finished in 2008 and has been working well. The beach has been widened. However, no salient due to sand accretion has been clearly formed, so the question is now being, “Was the design the best option?”.

The beach has been widening and narrowing a little with the different local wave conditions, so that it has now reached equilibrium. The sea bottom is rocky and no sand banks are found close to the project site. Sand moves only alongshore specifically from South to North. Neighboring beaches are still being eroded every year but the Gran Vela Hotel beach is wide and pleasant for the tourist to use.

CHARACTERISTICS OF THE STUDY AREA The study area is vulnerable to hurricanes and it is necessary to consider that year after year tropical storms hit the area. The Gran Vela Hotel location has the typical characteristics of Quintana Roo coasts; flat and low. The average elevation at the dune is about 2 m above sea level, rising slowly inland. The beach slope is 20:1 and the sea bottom is rocky continental platform with sandy areas of between 5 cm and 2 m. Small reef heads may be present on the sea floor. The sea bottom gradually deepens slowly up to about 50 or 55 m offshore where a ledge appears and the bottom drops to 400 m deep. The average tidal range between the Mean High Water and Mean Low Water is about 30 cm.

Predominant waves and winds are from Southeast and East, with winds from the Northeast in winter due to cold fronts.

Several field studies were carried out such as a topography survey, a bathymetric survey, current measurements, and exploration dives with SCUBA equipment to look for marine sand banks. Figure 2 provides details of the field work being conducted.

Figure 2. Examples of Field Work

Work was carried out using computer programs to determine wave patterns. The surveys provided the following information:  Topography and bathymetry  Currents mainly travel from Southwest to Northeast  No nearby sand banks of importance for beach nourishment  Good movement of sand parallel to the beach from South to North for most of the year with some episodes in the opposite direction in winter due to the cold fronts that last between 2 and 7 days From the mathematical model Wave Watch III, information based on 9 years of measurements made by NOAA at a deep-water points North of Cozumel Island with coordinates 21º n, 86.5º W, and using program STWAVE (Figure 3). Table 1 was obtained (http://polar.ncep.noaa.gov/waves/index2.shtml).

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Figure 3. Deep Water Wave Characteristics

Table 1. Characteristic of Waves in Deep Waters

Wave propagation from the numerical simulation provided wave heights and periods in front of the property at a distance of 100m offshore according to Table 2 and Figure 4.

Table 2. Shallow Water Wave Characteristics

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Figure 4. Wave Directions, Wave Period, and Wave Height

SHORELINE PROTECTION ALTERNATIVES The following possible solutions for shoreline protection were taken into consideration when developing the mitigation strategy for the beach at the Gran Vela Hotel.  Beach Nourishment: This option represents a solution with a low-impact on the coastal ecosystem and tourism. However, it requires a sediment supply source (e.g. a big sand bank close to the beach). It is obvious that it would be necessary to continue this nourishment, since sand will continue to be mobilized under storm wave conditions and go downdrift or move out to sea. For this reason, a structure retaining the sand would be preferable.  Jetty: The local ecological authority does not allow the building of jetties or any other structure that stops the long shore sediment transport. Therefore, this alternative was not considered.  Breakwaters parallel to shore: Breakwaters parallel to the shoreline were the only option that could be authorized, so this was the solution that was adopted. Additionally, an artificial dune made of the sand filled geotextile tube and aligned in front of the hotel is perfect for vegetation, protecting the sand from erosion caused by wind and providing a barrier in case of extraordinary storm waves. The geotextile tube line should be heavy enough to withstand wave impact and should have an anti-scouring apron to prevent the geotextile tube from rotating forward. This solution selected is the construction of several breakwaters parallel to the shoreline. This system would help dissipate wave energy, and capture sand. No side effects would impact neighboring properties. There would be no interruption of longshore sediment transport. The quantity, size, and separation between breakwaters would be determined by formulas to obtain the optimum results for wave energy reduction.

MODELING OF WAVE CONDITIONS IN FRONT OF THE PROTECTED COAST Modeling of different wave conditions was performed using Genesis software (Gravens et al 1991) with four of the breakwater structures. The wave conditions modeled a) Height = 0.7 m, Time = 6.6 s and Direction = 259º, b) Height = 0.7 m, Time = 6.6 s, and Direction = 281º, c) Height = 0.7 m, Time = 6.6 s, and Direction = 238º, and d) Height = 2.45 m, Time = 6.6 s, and Direction = 333º. Tide was considered zero. Normal range is less than 1.0m. The software basically modeled two different responses. Figure 5 demonstrates the salients that were expected to form under normal wave conditions and Figure 6 demonstrates the salient formation under storm wave conditions.

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Figure 5. Beach Response Under Normal Wave Conditions

Figure 6. Beach Response Under Storm Wave Conditions

DESIGN OF PROTECTIVE STRUCTURES The Dally and Pope (1986) formula from the Costal Engineering Manual (2006) was used to find a mathematical relation between offshore distance and the structure length. See Table2.

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Table 3 Conditions for the formation of salients.

Ls represents the length of structure, Y the distance from shore to the breakwater and b the minimum beach width at MHW after nourishment (Ward, 2006).

According to the length of the breakwater and its’ distance offshore, based on Figure 7, the structures create salients, which is the desired response of the beach.

Ls represents the structure length, Lg the length of gap, Y is the distance from shore and ds is the depth at which the structure is located.

Figure 7. Conditions for formation of salients and tombolos

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Five 70 m long breakwaters were designed to be built in front of the property, four parallel to the shoreline and on the same axis, with 30 m wide separation and the fifth with an angle of 131 degrees from the rest with a gap of 131 m, as shown in Figure 9. The crown width is 2.0 m, the base 5.0 m and side slopes 1:1.

The material used for the construction of the breakwaters was “bolsacreto” which is a geotextile bag that is filled with concrete. Several bags are filled to form a pyramid with an angle of 45º. The bags of bolsacreto are 2 m wide by 3 m long by 0.5 m high. Figure 9 shows the cross section of the breakwater with the crown of the structure at Mean High Sea Level s to provide protection for the majority of the time but not to be visible from the shore.

Figure 8. Coastal Protection Project with Five Breakwaters and Artificial Dune

Figure 9. Breakwater Cross Section

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The height of the artificial dune was determined by reproducing the geometry of a natural dune and adding extra height, taking into consideration that tide level rises by 1.0 m under storm wave conditions. Thus, the final height of the dune was 2.7 m over Mean Sea Level. Figure 10 shows the cross section of the artificial dune. The total length of the dune was 502 m, with the dune core constructed of sand filled geotextile tube. The geotextile tubes were 6.8 m circumference and filled to a height of 1.4m with a width of 2.7 m. A 5.5m wide scour apron was attached to bottom of the tube and extended seaward of the structure 4.0 m. The scour apron provides protection from erosion undermining the structure in severe storm events. Sand from the site was used to fill the tubes and cover the structure to form the “Artificial Dune”. Spermacoce laevis, a native plant, was selected to be planted in the sand cover of the geotextile tube core of the sand dune. The roots will provide additional erosion protection from a storm surge and high winds.

Geotextile Tube

Scour Apron

Figure 10. Artificial Sand Dune Cross Section

CONSTRUCTON OF PROTECTIVE STRUCTURES The artificial dune and the breakwaters were built in 2008 - 2009. Figure 11 shows the building stages and Figure 12 show the final view of the dune after vegetation.

Figure 11. Geotextile Tube Core of Artificial Dune Installation

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Figure 12. Artificial Sand Dune after Construction in 2010

It was expected that a prominent salient would be formed, but although the beach response was good, no well- defined salient has appeared.  In 5 years the shoreline has recovered 20 m in the middle and most critical part of the property  In other areas, the beach has recovered 14 m on average.  The beach at the North point of the property did not recover as much width which is believed to be caused by the effect of the separation of 130 m between the fourth and fifth breakwater which is too great of a gap.  It is believed that the salients were not prominent because the separation of 30 m for the other four breakwaters, may be too small  Comparing old and new topography, the amount of sand captured by the structures was calculated to be 20,100 m3 over five years. This volume appears to be stable during most of the year. Figure 13 shows the shoreline evolution over time. The thick red line represents the old “zero” line five years ago. The green line represents the new “zero” line today. The orange wavy line represents the prominent salient that was expected to form due because of the installation of the breakwaters.

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Figure 13. Gran Vela Master Plan

Figure 14 compares the stabilizing affect between 2009 and 2010. In the left photo taken in 2009, the salients were formed, while in the right photo taken in 2010 shows the more even shoreline with small salients observed. In the 2009 photo you can see the formation of the wide beach with space for chairs and hotel guest. Note that the protected area is a lot wider than the unprotected beach at the South and North of the protected area. Salients are visible and the North point appears wide but not as wide as the rest of the protected beach. Also in Figure 14, in the 2010 photo, a stable wide beach is visible but with no prominent salients.

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2009 2010

Figure 14. Evolution of the Gran Vela Beach

LESSONS LEARNED From analysis of the performance of these marine geotextile bag breakwater structures we can say that the fifth Breakwater should be relocated parallel to the other four breakwaters to provide protection against most of the annual wave conditions. Also, we must be aware that in winter the protection will be less effective due to the presence of Northeast waves.

The separations between the breakwater structures should be the same for all breakwaters. Nevertheless, it seems that the breakwater separation should be larger than the 30 m which was the smaller separation of four of the five breakwaters. The only way to confirm the optimum separation would be to conduct several models with different breakwater length and different separation lengths and compare the results.

Another alternative that could be adopted is to nourish the beach with more sand from the offshore marine sand bank to obtain a robust beach and protect the new beach from downdrift and up draft. This would hold more sand in place and make the system more stable even during seasonal storm conditions.

As for the artificial sand dune with the geotextile tube core, the method of installation with the natural vegetation appearance is providing a stable defense of the physical structures and amenities of the property. This is an excellent barrier in case of an extraordinary storm hits the coast.

In summary, both the concrete filled geotextile bag breakwaters and the geotextile tube of the artificial sand dune are performing as designed to protect the property and provide exceptional wide and calm beach environment recreation for their guest.

APPLYING KNOWLEDGE TO NEW PROJECTS Performance of the Gran Vela project over the past 9 years has developed the confidence of property owners that if a master plan is well conceived and supported with available design models, they too can utilize the economical geotextile tube technology for marine structures.

In 2014, the 1.6 km long beach front MayaKoba Resort located adjacent to and just north of the Gran Vela Resort and the Kanai Resort located approximately 2.4 km north of MayaKoba hired Tecnoceano, the same marine engineering company in Cancun that designed the protection for Gran Vela, to develop beach development and

12 DREDGING SUMMIT & EXPO ’18 PROCEEDINGS protection plans for both properties. Using the collected data and lessons learned from observing Gran Vela for the past 9 years, Tecnoceano applied this knowledge to develop the master plans for each property.

In 2015, MayaKoba started a four-stage construction sequence following the master plan for beach development and protection. See Figure 15. First, in 2015 they installed stage one of property protection that consisted of a 1.8m high geotextile tube core for what would become the sand dune protection. See Figure 16. Second, in 2016, MayaKoba installed five geotextile tube breakwaters protection the entire 1.6 km shoreline of the property. See Figure 17 and 18. This was followed by completing the geotextile tube sand dune core for the same length. In June 2017, with the first two stages comprising the protection structures in place, MayaKoba will start the beach renourishment dredging program which will include dredging from an offshore bank +500,000 m3 of sand onto the beach. The final stage, scheduled for completion in late 2017, will incorporate the construction of several artificial reef sections comprised of prefabricated concrete pyramids. See fig. 18 for the detailed design.

The Kanai Resort project master plan is almost identical to the MayaKoba four stage plan except making the adjustment to accommodate the unique features of the site bathymetry and wave climate. The first stage incorporating the geotextile tube sand dune core protection will start in June 2017 in conjunction with the second stage of the geotextile tube breakwaters installation. The concrete artificial reef units will be installed in 2018 followed by the renourishment dredging.

Figure 15. Proposed MayaKoba Master Plan

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Figure 16. MayaKoba Geotextile Tube Sand Dune Core

Figure 17. MayaKoba Geotextile Tube Breakwaters Installation Oct. 2016

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Figure 18. MayaKoba Shoreline at Geotextiel Tube Brakewater #4 Formation of Beach Salients Jan. 2017

Figure 19. MayaKobe Beach Renourishment Dredging Jan. 2018

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Figure 20. Proposed Kanai Resort Master Plan

Figure 21. Kanai Resort Shoreline 2017

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Figure 21. Kanai Resort Beach Geotextile Tube Shoreline Protection Installation 2018

Figure 22. Kanai 2 – 1 Pyramid Geotextile Tube Breakwater 2018

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CONCLUSIONS There are five conclusions that can be drawn from this paper:  Performing detailed studies of the site conditions and collecting accurate information is critical.  There is existing modeling software available that can use the data collected to accurately predict the performance of geotextile structures like breakwaters in coastal application.  Geotextile tube Structures are economical solutions for shoreline protection.  Geotextile tube structures are environmentally friendly solutions  Geotextile tube structures are flexible and easy to modify

ACKNOWLEDGEMENTS Special thanks to the owners of Gran Vela, MayaKoba, and Kanai Resorts, their engineering and project management teasm; to Control de Erosión, the breakwater and artificial dune installation contractor; and to the Tecnoceano professional team of engineers and technicians who provided the Master Plans designs, jobsite QC and collection of data.

REFERENCES Gray E., Lopez R., Stephens T. C., (2016) Modeling Wave Conditions and Analysis For Coastal Design of Beach Restoration Incorporating Geotextile Tubes At Riviera Maya, Mexico. GeoAmericas 2016

Ward D. L. (2006) Shore protection projects. Coastal Engineering Manual, V-3.

Gravens, M. B.; Kraus, N. C.; Hanson, H. (1991): GENESIS: Generalized Model for Simulating Shoreline Change. Technical Report CERC-89-19, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg, MS.

Model web page WaveWatch III from NOAA: http://polar.ncep.noaa.gov/waves/index2.shtml, date; 17/NOV/07.

Noormets, R.; Felton, E. A.; Cook, K. A. W. (2002): Sedimentology of Rocky Shorelines: 2. Shoreline Megaclasts Emplacement and Transport of a Shore Platform, Oahu, Hawaii. Sedimentary Geology 150, 31 – 45.

Zona Federal Maritimo Terreste: (1991), Directiva Exjecutiva, Article 119, Fracc. I, Ley General de Bienes Nacionales

CITATION Timpson, C. D., and Stephens, T. C., “Beach Development and Protection of Resort Coastline Using Geotextile Tubes”, Proceedings of the Western Dredging Association Dredging Summit & Expo ‘18, Norfolk, VA, USA, June 25 – 28, 2018.

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