The Beach-Dune System and Management Concepts
The Beach-Dune System and Management Concepts
Picturesque though they are, coastal sand dunes serve a more important purpose than beauty. Dunes act as flexible barriers to ocean storm surges and waves, protect low-lying backshore areas, and help preserve the integrity of low barrier islands. In addition, they provide a habitat for many animals, including migratory birds. With proper planning and management, their functions may be enhanced. This publication discusses the features of coastal dunes, restoration of damaged dunes, and construction of new dunes using vegetation.
Functions, Values and Limitations
Coastal barrier dunes are formed by wave and wind action. The waves bring sand to shore from the adjacent inner continental shelf, and it is transported landward by onshore winds. Obstacles, such as driftwood, a sand fence, or vegetation, reduce wind speed, causing sand to accumulate. As sand accumulates, plants adapted to the beach environment emerge, stabilizing the surface and promoting further dune formation. In the absence of stabilizing vegetation, blowing sand may drift into large "live" dunes that move back and forth with the wind.
Dunes formed as a result of establishing vegetation act as flexible barriers to storm tides and waves and serve as sand reservoirs for beach nourishment. During storms, sand erodes from the beach-dune system and re-deposits as shallow sandbars offshore. In a stable beach- dune system, the sand moved offshore during storms is returned during calm weather. Thus, the dunes, beach, and near-shore sandbars act as a dynamic, integrated unit, often referred to as the beach-dune system.
Although dunes serve as temporary protective barriers during storm tides of short duration, they are not effective against persistent beach recession caused by rising sea level, migrating inlets, or changing shoreline dynamics. Therefore, they cannot be considered permanent structures that will "hold off the ocean."
The value of dunes and their fragile nature are often misunderstood or not appreciated. Excessive use often upsets the natural balance, damaging the vegetation and deteriorating the dune system. Today, shoreline development and the pounding of dunes by feet and vehicles pose serious threats to dune vegetation and dune stability. Intensive beach use increases the need to restore, construct, protect, and manage dunes.
Restoration of Slightly Damaged Dunes
Dune sands are readily moved and shaped by wind and water action. Consequently, disturbed dunes revert rapidly to unstable conditions, regardless of their stage of development at the time of disturbance. As a result, dune restoration usually begins with the establishment of pioneer plants.
Dunes that are only slightly damaged may be repaired by planting vegetation in bare areas, giving stressed grasses a judicious amount of fertilizer, and protecting the area from trampling and traffic.
Vegetation is critical to dune formation and stabilization. Without vegetation, blowing sand will migrate inland.
Selection of plant species is of paramount importance when restoring vegetation in bare areas of existing dunes. Dune plants must be able to survive sand blasting, sand burial, salt spray, saltwater flooding, heat, drought, and a limited nutrient supply. Only a few plant species can tolerate these stresses.
Planting stock may be acquired as seedlings from commercial producers, or, with permission on private property, transplants can be dug from existing stands.
The best transplants are 1- to 3-year-old seedlings often found in small clusters seaward of the frontal dune.
Construction of Dunes
When barrier dunes are absent, they may be rebuilt by bulldozing, dredging, or, preferably, by encouraging the natural process of dune building by trapping blowing sand with sand fences and vegetation. Building dunes with vegetation is more economical than using heavy equipment and discourages placement of the dune too close to the ocean or in other unsuitable locations.
Bulldozing and Dredging
Bulldozing and dredging are extremely expensive as well as damaging to the coastal environment. Usually these activities only result in short-term benefits and will need to be continued in the future.
Sand Fences and Vegetation
Barrier dunes are best located as far from the ocean as practical to allow for normal ocean tidal fluctuations. As the dune accumulates sand, it expands seaward, allowing plants to spread into freshly deposited sand. Some severely eroding beaches do not have sufficient space to successfully use vegetation for dune building. Where adequate distance exists between the ocean and property to be protected, well-vegetated dunes will provide valuable protection from storm waves.
The first step to dune establishment is providing a barrier to trap sand. Sand fences create areas of lower wind speed both in front of and behind the fence, which encourages sand deposition. The amount of sand trapped depends on the fence height, the size of spaces between fence slats, and the wind speed. Wooden slat fences are most commonly used and are generally preferable to fabric fences.
The initial dune crest is located by installing a 2- foot-high sand fence several hundred feet behind and parallel to the high tide line to accumulate wind-blown sand. Install the fence several months before transplanting vegetation to allow the sand to accumulate without burying the transplants.
The best transplants are 1- to 3-year-old seedlings often found in small clusters seaward of the frontal dune.
Construction of Dunes
When barrier dunes are absent, they may be rebuilt by bulldozing, dredging, or, preferably, by encouraging the natural process of dune building by trapping blowing sand with sand fences and vegetation. Building dunes with vegetation is more economical than using heavy equipment and discourages placement of the dune too close to the ocean or in other unsuitable locations.
Bulldozing and Dredging
Bulldozing and dredging are extremely expensive as well as damaging to the coastal environment. Usually these activities only result in short-term benefits and will need to be continued in the future.
Sand Fences and Vegetation
Barrier dunes are best located as far from the ocean as practical to allow for normal ocean tidal fluctuations. As the dune accumulates sand, it expands seaward, allowing plants to spread into freshly deposited sand. Some severely eroding beaches do not have sufficient space to successfully use vegetation for dune building. Where adequate distance exists between the ocean and property to be protected, well-vegetated dunes will provide valuable protection from storm waves.
The first step to dune establishment is providing a barrier to trap sand. Sand fences create areas of lower wind speed both in front of and behind the fence, which encourages sand deposition. The amount of sand trapped depends on the fence height, the size of spaces between fence slats, and the wind speed. Wooden slat fences are most commonly used and are generally preferable to fabric fences.
The initial dune crest is located by installing a 2- foot-high sand fence several hundred feet behind and parallel to the high tide line to accumulate wind-blown sand. Install the fence several months before transplanting vegetation to allow the sand to accumulate without burying the transplants.
Plant small areas and steep slopes by hand, as described in the earlier section on the ‘Restoration of Slightly Damaged Dunes’.
Plant large, flat areas with tractor-drawn tobacco or vegetable Tran planters with extended planting shoes to make furrows 8 to 10 inches deep. Space the furrows at least 18 inches apart. When building a dune, plants should be closely spaced, 18 inches by 18 inches, in several rows where the crest of the dune is to be located. Then spacing should be increased to 2 feet and then 3 feet for several rows on each side to allow sand to penetrate to the centre of the planting.
Protection of Dunes
Although dune plants tolerate harsh beach conditions, they cannot withstand foot and vehicular traffic. These activities crush plant shoots and roots.
Protection of Dunes
Although dune plants tolerate harsh beach conditions, they cannot withstand foot and vehicular traffic. These activities crush plant shoots and roots.
Trampling by pedestrians and traffic such as four- wheel-drive vehicles and trail bikes often lead to greater sand removal by wind.
In addition, soil compaction often results from vehicular traffic and decreases water infiltration, leading to erosion from rain and increased damage during droughts.
Restricting or banning access to dunes can reduce the need for other sand control measures. However, some dunes will have to bear traffic, and to protect them, crosswalks and beach access areas should be designated.
Conclusion
Human activity has accelerated the loss of dune vegetation along our beaches. Recreational and commercial development, off-road vehicles, and population pressures associated with urban growth in coastal areas have altered the natural seashore. The building of streets and structures near the sea disrupts normal beach and dune processes. The procedures recommended here can help restore, enhance, and protect dune vegetation.
Conclusion
Human activity has accelerated the loss of dune vegetation along our beaches. Recreational and commercial development, off-road vehicles, and population pressures associated with urban growth in coastal areas have altered the natural seashore. The building of streets and structures near the sea disrupts normal beach and dune processes. The procedures recommended here can help restore, enhance, and protect dune vegetation.
 |
 |
 |
| | ||
 |
 |
 |
Internatioal Surfing News:
Surfing News and Contests, Surf Reports, Wave Forecasts |
||||
|---|---|---|---|---|
| 1. Surf-News exclusive! -- Google style News-Alerts daily24 | ||||
|
||||
| 2. Redman Carr wins Billabong Pro Tahiti for 3 in a row24 | ||||
|
||||
| 3. Edge of the seat 'day of drama' at Billabong Pro Tahiti24 | ||||
|
||||
| 4. Kana Bask Tour est reporté au weekend 10 et 11 juin24 | ||||
|
||||
| 5. Dramatic upsets continue at the Quiksilver ISA WJSC24 | ||||
|
||||
| Records 1 to 5 of | ||||
|
