COASTAL PROTECTION USING INTEGRATION OF MANGROVES WITH FLOATING BARGE

Abstract

Systems and methods of coastal erosion protection are disclosed, the system including at least one floating member, an anchor rode, an anchor, and a water-tolerant plant. The methods include placing at least one floating member in offshore waters, coupling an anchor rode to the floating member, coupling an anchor to the anchor rode, mooring the floating member to the sea floor, the mooring step further including placing the anchor on the sea floor and tightening the anchor rode until any slack in the anchor rode is removed, planting a water-tolerant plant in coastal soil, growing the water-tolerant plant to a pre-determined growth stage, and removing the floating member from offshore waters.

Description

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to systems and methods of coastal protection from erosion.

2. Description of Related Art

Coastal erosion occurs when rising sea levels, strong wave action, or flooding wear down the land along the coast. For example, coastal land subjected to the constant attack of incoming waves can experience severe erosion when rocks, soil, and sand are carried away by the strong ocean currents. In the United States alone, coastal erosion is responsible for over $500 million in property loss, including damage to ocean-front structures. [1]

Prior attempts have been made to prevent coastal erosion. For example, U.S. Pat. No. 9,644,334 (O'Neill) discloses methods and systems for controlling waterflow along waterways and coastal regions using a plurality of construction blocks to blunt tidal forces. The construction blocks may be arranged to form an impermeable wall to build structures such as river dams but may also be arranged to permit water to run past the blocks when used for controlling the force of water upon a shoreline. However, installation of the blocks is difficult because of their weight and often requires the use of hydraulic cranes, and the construction blocks are a permanent structure.

U.S. Pat. No. 4,498,806 (Szonnell) discloses the construction of curved jetties to prevent the vacuum effect which is often the cause of coastal erosion. The jetties may be constructed of suitable materials such as field rock and marl, but their installation requires intensive labor to arrange the rocks correctly in view of their weight. Further, the coastal area is left with a permanent man-made structure to curb erosion of the coastline.

Dai et al. discloses the use of permanent floating structures designed to disturb wave patterns and blunt the force of incoming waves. However, many floating man-made objects have a limited structural lifespan and have been criticized for their ability to resist waves of longer wavelength. [2]

Prior attempts at using natural resources to curb erosion have also been made. For example, studies have shown that mangrove trees may be effective at blunting tidal forces. [3] However, as tidal forces may often wash away or damage young mangroves before they reach a desired height and rooting level, using natural resources alone has not achieved maximum efficacy at protecting shorelines. Thus, there is a need for systems and methods to prevent coastal erosion in a way that may be efficiently implemented, reduce the need for permanent man-made structures, and resist long-term structural damage.

All references cited herein are incorporated herein by reference in their entireties.

BRIEF SUMMARY OF THE INVENTION

A first aspect of the invention is a system for preventing coastal erosion including at least one floating member, an anchor rode, an anchor, and a water-tolerant plant.

In certain embodiments, the at least one floating member is a floating barge.

In certain embodiments, the anchor rode comprises at least one of a rope, chain, cable, or belt.

In certain embodiments, the anchor is of a weight capable of preventing the floating member from drifting in water.

In certain embodiments, the system further comprises a plurality of water-tolerant plants.

In certain embodiments, the water-tolerant plant is capable of growing in coastal soil and reaching a height above water-level.

In certain embodiments, the coastal soil includes soil on a shoreline or water-logged soil proximate to the shoreline.

In certain embodiments, the water-tolerant plant is a halophyte.

In certain embodiments, the water-tolerant plant is a mangrove tree.

A second aspect of the invention is a method for preventing coastal erosion using the system of the invention including placing at least one floating member in offshore waters, coupling an anchor rode to the floating member, coupling an anchor to the anchor rode, mooring the floating member to the sea floor, the mooring step further including placing the anchor on the sea floor and tightening the anchor rode until any slack in the anchor rode is removed, planting a water-tolerant plant in coastal soil, growing the water-tolerant plant to a pre-determined growth stage, and, after said pre-determined growth stage is reached, removing the floating member from the offshore waters.

In certain embodiments, the floating member is a floating barge.

In certain embodiments, the method further comprises positioning a plurality of floating members in a linear formation.

In certain embodiments, the method further comprises positioning a plurality of floating members in a staggered formation.

In certain embodiments, the method further comprises positioning a plurality of floating members in a formation comprising multiple rows of the floating members.

In certain embodiments, the anchor rode may include at least one of a rope, chain, cable, or belt.

In certain embodiments, the anchor is of a weight capable of preventing the floating member from drifting to a different position once the mooring step is completed.

In certain embodiments, the method further comprises planting a plurality of water-tolerant plants.

In certain embodiments, the water-tolerant plant is a mangrove tree.

In certain embodiments, the pre-determined growth stage is when the water-tolerant plant reaches a root depth and height capable of withstanding the force of incoming water and curbing the force of the water without experiencing structural damage.

In certain embodiments, the floating members are removed after a period of time not exceeding two years.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in conjunction with the following drawings:

FIG. 1 is a side view diagram depicting an embodiment of the system of the invention comprising the integration of the floating members and water-tolerant plants.

FIG. 2 is an aerial view diagram of the embodiment of FIG. 1.

FIG. 3 is a side view diagram depicting another embodiment of the system of the invention comprising the integration of floating members in a formation using multiple rows of floating members.

FIG. 4 is an aerial view diagram of the embodiment of FIG. 3 depicting the integration of floating members in a staggered formation.

FIG. 5 shows a block diagram of an exemplary method of use of the system of the invention in accordance with examples.

FIG. 6 shows a side view diagram of a prophetic experimental setup using a series of moored floating members in a wave flume.

FIG. 7 shows an aerial view diagram of a prophetic experimental setup using floating members in a staggered formation.

FIG. 8 shows a side view diagram of an experimental setup of two floating members.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Coastal areas subjected to the constant attack of waves or tidal forces may experience severe erosion. Water-tolerant plants, such as mangrove trees, are effective in protecting the beach from becoming eroded by these tidal forces. The system and method of the invention uses the combined action of water-tolerant plants and floating members to protect the coastal area.

The floating member preferably includes a barge. Barges are rectangular floating bodies which are mainly used for offshore applications. In certain examples of the invention using barges, the barges are towed to the desired location in offshore waters and moored to the ocean floor using taut mooring. Offshore waters include the water between the shoreline and the transition point corresponding to the fair-weather wave base. The fair-weather wave base transition point is the vertical boundary from ocean surface to ocean floor at the minimum depth where the ocean floor is undisturbed by waves or surface current. To tautly moor the barge, an anchor is placed at the ocean floor that is connected to the barge by a rode, or tether. The rode connecting an anchor to the barge is tightened until any slack in the rode is removed. Once the anchor is placed and the rode is tightened, the barge will be able to remain stationary in the undulating waters. The floating members also attenuate the waves by damping. Waves will also break upon the barges, rather than the coast, and create a calm-water area in the space between the shoreline and the barges. The barges can be used in a specific area or can be used along the length of the beach depending on the desired portion of land to be protected.

In certain examples, once the shoreline is undisturbed by waves, water-tolerant plants may be planted in the coastal soil. The water-tolerant plants are preferably mangrove trees. After a predetermined period of time, such as one or two years, the mangroves will become rooted into the coastal soil. Once the mangroves have reached a predetermined growth stage where the mangroves are securely rooted and of a height capable of breaking the force of the waves, the barges are removed from the offshore waters. The mangroves blunt the force of the waves, preventing the beach from erosion. In certain examples, mangroves should be planted close to one another to firmly hold the surrounding coastal soil in place once the barges are removed and the mangroves are exposed to waves.

The invention will be illustrated in more detail with reference to the following Examples, but it should be understood that the present invention is not deemed to be limited thereto.

EXAMPLES

Referring to the Figures, FIG. 1 is a side-view diagram depicting a working nonlimiting example of the integration of the floating members 2 and water-tolerant plants 10. In this example, the floating member 2 is positioned in offshore waters 8. In certain examples, the floating member 2 is placed in a location in offshore waters 8 between the shoreline 16 and the location where waves break 18. The floating member 2 also attenuates the waves by damping. The floating member 2 is coupled to a rode 4 which tethers the floating member to an anchor 6. To moor the floating member 2 to the ocean floor 20, the anchor 6 is placed at the ocean floor. The rode 4 is then tightened until any slack is removed from the rode, keeping the floating member 2 in a stationary position despite encountering waves or currents. In certain examples, a plurality of floating members 2 are used. Floating members 2 can be used in the ocean, but can also be used in lakes, rivers, streams, or other bodies of water that experience tidal forces or have currents that could cause erosion. In certain examples, the floating members 2 include floating barges.

Once the floating member 2 is securely moored to the ocean floor 20, a water-tolerant plant 10 is preferably planted in the coastal soil 12. The water-tolerant plant 10 will be permitted to grow because waves will break upon the floating members 2 instead of on the shoreline 16, creating a calm-water area 14 between the floating members and the shoreline 16. The water-tolerant plant 10 is preferably a halophyte that is capable of growing in at least one of low-oxygen, brackish, and salt-water conditions. In certain examples, water-tolerant plants 10 are mangrove trees, which have an average lifespan of one hundred years. However, as the type of vegetation that may grow in coastal soil varies by geographic area, the water-tolerant plant 10 can also include other plants capable of growing in the coastal soil 12. A plurality of different water-tolerant plants 10 can be used. The water-tolerant plants 10 should preferably be planted closely together, as the roots of the water-tolerant plans will eventually anchor the coastal soil 12 in place. Thus, in certain embodiments, each plant is planted 1, 2, 3, 4, 5, 6, 7, 9, 10, 15, 25, 50, 75 or 100 cm from adjacent plants.

The floating member 2 should preferably be left in place until the water-tolerant plants 10 reach a predetermined growth stage. In certain examples, the predetermined growth stage is when the water-tolerant plants 10 become securely rooted in the coastal soil 12 to an extent where the water-tolerant plants will not become uprooted if the water-tolerant plants encounter waves or strong currents. Further, the predetermined growth stage also includes when the water-tolerant plants 10 reach a height taller than the average highest water level at the shoreline 16, including the average crest of any incoming waves. In certain environments, such as lakes, rivers, or streams that may not experience strong waves, the predetermined growth stage can be at a lower height or rooting level than in an ocean-front area that experiences waves and storm surges.

Once the predetermined growth stage of the water-tolerant plants 10 is reached, the floating member 2 is preferably removed from the offshore waters 8. Any waves or currents will attenuate and then break upon the water-tolerant plants 10 once the floating member 2 is removed. As these waves or currents are no longer breaking upon the shoreline 16, the shoreline is protected from erosion. In examples using mangroves as the water-tolerant plants 10, the lifespan of the mangroves is approximately one hundred years in comparison to permanent man-made ocean structures which remain structurally sound for approximately ten to twenty years. Thus, the use of water-tolerant plants is not only eco-friendly and avoids the creation of permanent man-made structures, but also offers a longer-term solution than many man-made structures.

FIG. 2 is an aerial view diagram depicting a working, nonlimiting example of the integration of the floating members 2 and water-tolerant plants 10. In this example, a plurality of floating members 2 are positioned in an orientation where the floating members 2 are in a linear formation 22. The floating members 2 are preferably floating barges. The floating members 2 should be positioned in close proximity to one another. In certain examples, the floating members 2 should be positioned as close as possible to one another without creating the possibility for collision in undulating offshore waters 8. In certain embodiments, the distance between adjacent floating members is 0.5, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 75 or 100 meters.

Once the floating members 2 are positioned in the desired location, the floating members are tautly moored to the ocean floor 20 (FIG. 1) by placing an anchor 6 (FIG. 1) on the ocean floor 20 (FIG. 1) and tightening the rode 4 of each floating member which is coupled to the floating member and the anchor. In certain examples, floating member 2 has a plurality of rodes 4 and anchors 6 (FIG. 1). Once the mooring step is complete, the floating members 2 will be able to maintain their position and linear formation 22 in the offshore waters 8 even when encountering waves or currents.

After the floating members 2 are tautly moored to the ocean floor 20 (FIG. 1), a calm-water area 14 is created in the space between the floating members 2 and the shoreline 16. Water-tolerant plants 10, such as mangrove trees, are then planted in the coastal soil 12. Once the pre-determined growth stage is met where the water-tolerant plants 10 reach a height and root depth capable of withstanding tidal forces and blunting the force of incoming waves and currents, the floating members 2 are preferably removed from the offshore waters 8. The water-tolerant plants 10 then are able to protect the shoreline 16 from incoming waves, storm surges, or currents.

FIG. 3 is a side view diagram depicting another working and nonlimiting embodiment of the system of the invention comprising the integration of floating members in a formation using multiple rows 24 of floating members 2. In preferred embodiments, the floating members 2 are tautly moored to the ocean floor 20. Floating members 2 can include floating blocks, floating barges, or other similar floating structures capable of breaking the force of incoming waves moving toward the shoreline 16. In certain examples, the floating members 2 are arranged in a formation using multiple rows 24 of floating members to increase the ability of the floating members to break the force of any waves or currents. Once the floating members 2 are in place, a calm-water area 14 is created between the floating members and the shoreline 16, permitting water-tolerant plants 10 to be planted in coastal soil 12 and experience minimal disturbance from waves or currents while growing. The floating members 2 remain in place until the water-tolerant plants 10, such as mangrove trees, reach a predetermined growth stage. Once the predetermined growth stage is reached, the floating members 2 are removed, and incoming waves or currents break upon the water-tolerant plants 10 as opposed to the floating members. Thus, the water-tolerant plants 10 blunt the force of waves or currents and protect the shoreline 16 from erosion.

FIG. 4 is an aerial view diagram of the embodiment of FIG. 3 depicting a working example of the integration of floating members 2 in a staggered formation 26. In this example, a plurality of floating members 2 are positioned in a staggered formation 26 in offshore waters 8 such that multiple rows of floating members are used, and each floating member in one row is aligned where a space 28 between floating members exists in another row. The staggered formation 26 not only uses multiple rows of floating members 2 to blunt the force of incoming waves, but also avoids exposure of any spaces 28 between floating members to prevent strong tides from permeating into the calm-water area 14 created between the floating members and the shoreline 16. Once the floating members 2 are in place and a calm-water area 14 is created, water-tolerant plants 10 are planted in coastal soil 12. The water-tolerant plants 10 then grow undisturbed by strong tidal forces until their root structures and height reach a predetermined growth stage capable of blunting tidal forces without the water-tolerant plants experiencing damage. Once the predetermined growth stage is met, for example, one to two years after the water-tolerant plants 10 are planted, the floating members 2 are removed.

FIG. 5 shows a block diagram of an exemplary working method of use of the system of the invention in accordance with examples. The method includes first placing at least one floating member 2 (FIG. 1) in offshore waters 8 (FIG. 1), coupling an anchor rode 4 (FIG. 1) to the floating member, coupling an anchor 6 (FIG. 1) to the anchor rode, mooring the floating member to the sea floor 20 (FIG. 1), the mooring step further including placing the anchor on the sea floor and tightening the anchor rode until any slack in the anchor rode is removed, planting a water-tolerant plant 10 (FIG. 1) in coastal soil 12 (FIG. 1), growing the water-tolerant plant to a pre-determined growth stage, and removing the floating member from the offshore waters.

The floating members 2 preferably includes floating blocks or floating barges, among other similar floating structures. The number of floating members 2 used is preferably based on the desired length of shoreline 16 to be protected from erosion. For example, if one kilometer of shoreline 16 must be protected from erosion, four floating barges can be used as floating members 2, each barge measuring 250 meters×250 meters in length and breadth. The floating barges can then be arranged in orientations including but not limited to a linear formation 22 (FIG. 2), formation using multiple rows 24 (FIG. 3), or staggered formation 26 (FIG. 4) in offshore waters 8 parallel to the shoreline 16 with minimal spacing between the barges. The spacing of any floating members 2 such as floating barges should be decided based on the maximum amount of surge and sway a floating member 2 is able to move in the x and y directions once moored to the ocean floor 20 (FIGS. 1 and 3) and contacted by waves or currents. In certain examples, floating members 2 are arranged in a linear formation 22 (FIG. 2) in waters that do not experience strong waves or storm surges or a formation using multiple rows 24 (FIG. 3) or a staggered formation 26 (FIG. 4) in waters that do experience strong waves or storm surges.

FIG. 6 shows a side view diagram of a prophetic experimental setup using a series of moored floating members 2 in a wave flume 30. In this exemplary setup, two floating members 2 will be moored with a plurality of anchor rodes 4 to the sloping floor 32 of the wave flume 30 using taut mooring. A plurality of wave gauges 34 will be used to measure wave height. In this nonlimiting setup, six wave gauges 34 will be used. On one side of the wave flume, a wave generator 36 will be placed to generate waves mimicking those found in the ocean. Wave gauges 34A and 34B will measure incident wave height and wave reflection from the floating member 2 positioned closest to the wave generator 36. Wave gauges 34C and 34D will measure the transmitted wave height by the floating member 2 positioned closes to the wave generator and wave reflection from the floating member 2 positioned closest to a simulated shoreline 38. Wave gauges 34E and 34F will measure the transmitted wave height behind the floating member 2 positioned closest to the simulated shoreline 38. In this nonlimiting example, each floating member 2 will be a barge. The slope of the sloping floor 32 will be varied to study the effect of beach slope on the transmitted wave heights. The motion response of the two floating members 2 will be measured for regular and random wave conditions. The experimental setup in the wave flume will simulate wave-on-floating member 2 responses, anchor rode 4 line forces, and transmitted wave heights. Further, the wave transmission coefficient of the setup will shed information on the reduction of wave height behind the floating member 2 positioned closest to the simulated shoreline 38, which in turn can be used to determine the effective growth of water-tolerant plants 10 (FIG. 1) such as mangroves providing protection from beach erosion on an actual shoreline 16 (FIG. 1).

FIG. 7 shows an aerial view diagram of a prophetic experimental setup in a shallow wave basin using floating members 2 in a staggered formation 26. The expected results of this experimental setup reflect the performance of working exemplary floating members 2 proposed to be installed in a body of water. Three floating members 2 will be considered for this example. A wave generator 36 (FIG. 6) will also be used. Four wave gauges 34 will be used to measure the wave height at the respective location, further classified as wave gauges 34A-34D. Wave gauges 34A and 34B will measure incident wave height and reflected wave height, respectively. Wave gauge 34C will measure the wave height between the two floating members 2 positioned closest to a wave generator (FIG. 6) in a shallow wave basin 40. Wave gauge 34D will measure wave height behind the floating member 2 positioned closest to the simulated shoreline 38. The anchor rodes 4 of the floating members 2 will be moored to the sloping floor 32 (FIGS. 6 & 7) using taut mooring. The slope of the sloping floor 32 will be varied to match environmental conditions. The study will consider the phenomenon of wave diffraction, reflection, and transmission by the floating members 2. The motion response of the three floating members 2 and anchor rodes 4 will be measured for regular and random wave conditions.

The prophetic experimental setups conducted in the shallow wave basin 40 (FIG. 7) and wave flume 30 (FIG. 6) illustrate expected performance of floating members 2 with waves. The expected results from the experimental studies outlined in FIGS. 6 and 7 further illustrate the effectiveness of floating members in permitting water-tolerant plants 10 (FIG. 1) such as mangroves to grow and minimize beach erosion.

FIG. 8 shows the preliminary design of the floating members 2 for a working exemplary barge-assistant mangrove coastal protection system including two floating members 2 each with a length of 100 m, width of 100 m, and depth of 5 m. The draft of both the floating members 2 is 2.5 m. The water depth considered was 10 m. The two floating members 2 are arranged in a formation including multiple rows 24 of floating members along with the incoming wave direction. The distance between the floating members 2 is an important factor in the design, which influences whether the motion of the water between the floating members is of a piston-type or sloshing-type. The distance between, draft, and breadth of the floating members 2 influence the resonant frequency of the water between the floating members. As the distance between the floating members 2 increases, the water oscillation changes from a sloshing-type to a piston-type when the water depth and the draft of the floating members remain constant. Table 1 shows the dependency of distance (gap width) in meters (m) on resonant frequency of the water between the floating members 2.

TABLE 1
Effect of gap width between the floating
members on resonant frequency
Gap width (m) Resonant Frequency (Rad/s)
8             0.3
5             0.38
2             0.58

Resonant frequency is calculated using the following equation, which is a modification of the pumping mode frequency suggested by Moradi et al. [5].

$\omega =\sqrt{\frac{g}{\frac{d*B}{h-D}+D}}$

where ω is the resonant frequency, g is the acceleration due to gravity, B is the width of the floating member, d is the gap width between the floating members, h is the water depth and D is the depth of the floating member.

As the gap width between the floating members increases, the resonant frequency decreases. The fluid motion between the floating members changes from a sloshing-type motion to a piston-type motion as the gap width between the floating members increases. This increase in the gap width will contribute to a reduction in the fluid motion as well as the floating member motions.

While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

REFERENCES

• [1] United States Government (Apr. 1, 2021). Coastal Erosion, U.S. Climate Resilience Toolkit, https://toolkit.climate.gov/topics/coastal-flood-risk/coastal-erosion.
• [2] Dai et al. (2018). Review of recent research and developments on floating break waters. Ocean Engineering 158:132-151.
• [3] Spalding et al. (2014). Mangroves for coastal defence. Guidelines for coastal managers & policy makers. Wetlands International and The Nature Conservancy.
• [4] Raju & Arockiasamy (2022). Coastal Protection Using Integration of Mangroves with Floating Barges: An Innovative Concept. Journal of Marine Science and Engineering, 2022, 10, 612. https://doi.org/10.3390/jmse10050612.
• [5] Moradi et al. (2015) Effect of inlet configuration on wave resonance in the narrow gap of two fixed bodies in close proximity. Ocean Eng. 103:88-102.

Claims

1. A system for preventing coastal erosion, the system comprising: at least one floating member,an anchor rode,an anchor, anda water-tolerant plant.

2. The system of claim 1, wherein the at least one floating member is a floating barge.

3. The system of claim 1, wherein the anchor rode comprises at least one of a rope, chain, cable, or belt.

4. The system of claim 1, wherein the anchor is of a weight capable of preventing the floating member from drifting in water.

5. The system of claim 1, comprising a plurality of water-tolerant plants.

6. The system of claim 1, wherein the water-tolerant plant is capable of growing in coastal soil and reaching a height above water-level.

7. The system of claim 6, wherein the coastal soil includes soil on a shoreline or water-logged soil proximate to the shoreline.

8. The system of claim 1, wherein the water-tolerant plant is a halophyte.

9. The system of claim 1, wherein the water-tolerant plant is a mangrove tree.

10. A method of preventing coastal erosion using the system of claim 1, the method comprising: placing at least one floating member in offshore waters,coupling an anchor rode to the floating member,coupling an anchor to the anchor rode,mooring the floating member to the sea floor, the mooring step further comprising placing the anchor on the sea floor and tightening the anchor rode until any slack in the anchor rode is removed,planting a water-tolerant plant in coastal soil,growing the water-tolerant plant to a pre-determined growth stage, andremoving the floating member from the offshore waters.

11. The method of claim 10, wherein the floating member is a floating barge.

12. The method of claim 10, further comprising positioning a plurality of floating members in a linear formation.

13. The method of claim 10, further comprising positioning a plurality of floating members in a staggered formation.

14. The method of claim 10, further comprising positioning a plurality of floating members in a formation comprising multiple rows of the floating members.

15. The method of claim 10, wherein the anchor rode may include at least one of a rope, chain, cable, or belt.

16. The method of claim 10, wherein the anchor is of a weight capable of preventing the floating member from drifting to a different position once the mooring step is completed.

17. The method of claim 10, further comprising planting a plurality of water-tolerant plants.

18. The method of claim 10, wherein the water-tolerant plant is a mangrove tree.

19. The method of claim 10, wherein the pre-determined growth stage is when the water-tolerant plant reaches a root depth and height capable of withstanding the force of incoming water and curbing the force of the water without experiencing structural damage.

20. The method of claim 10, wherein the floating members are removed after a period of time not exceeding two years.