Difference between revisions of "Dynamics, threats and management of dunes"
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Damaged coastlines are not attractive locations for tourism or leisure. Dune system vulnerability is defined as a set of conditions producing an acceleration of the erosion rhythm and system degradation. It is really important to not block natural processes which could destroy the system (Bodéré ''et al.'', 1991<ref>BODERE J.C., CRIBB R., CURR R., DAVIES P., HALLEGOUET B., MEUR C., PIRIOU N., WILLIAMS A., YONI C., 1991. La gestion des milieux dunaires littoraux. Evaluation de leur vulnérabilité à partir d’une liste de contrôle. Etude de cas dans le sud du Pays de Galles et en Bretagne occidentale. Norois n°151. Poitiers-France. 279‐298.</ref>) and to take into consideration all the dune system with [[beach]] and [[foreshore]]. The natural dune- rebuilding process can take several years, and it may be desirable to rebuilding a storm-eroded dune quicker than natural processes O’Connell, 2008). Dune damaging accelerates sand transit towards inland and then this sand cannot nourish the beach anymore (Pinot, 1998<ref>PINOT, J.-P., 1998. La gestion du littoral: 1. Littoraux tempérés: côtes rocheuses et sableuses. Collection Propos. Institut Océanographique: Paris. ISBN 2-903581-20-7. 399 pp. Available from: [http://www.vliz.be/imis/imis.php?module=ref&refid=198656]</ref>). There are different ways to protect or restore dunes. Firstly, the protection of wildlife is important because fauna and flora are an integral part of dune system: vegetation stabilizes sand whereas fauna control plants growing and interactions. Sand dunes provide unique wildlife habitat. We must limit the trampling of visitors by paths and beach access setting up with fences. People walk through the dune because it is difficult to go on the sand. As they are looking for a hard surface to walk, we must provide them one. A marked pathway (by fences and why not with educative panels) is already dissuasion.</br> | Damaged coastlines are not attractive locations for tourism or leisure. Dune system vulnerability is defined as a set of conditions producing an acceleration of the erosion rhythm and system degradation. It is really important to not block natural processes which could destroy the system (Bodéré ''et al.'', 1991<ref>BODERE J.C., CRIBB R., CURR R., DAVIES P., HALLEGOUET B., MEUR C., PIRIOU N., WILLIAMS A., YONI C., 1991. La gestion des milieux dunaires littoraux. Evaluation de leur vulnérabilité à partir d’une liste de contrôle. Etude de cas dans le sud du Pays de Galles et en Bretagne occidentale. Norois n°151. Poitiers-France. 279‐298.</ref>) and to take into consideration all the dune system with [[beach]] and [[foreshore]]. The natural dune- rebuilding process can take several years, and it may be desirable to rebuilding a storm-eroded dune quicker than natural processes O’Connell, 2008). Dune damaging accelerates sand transit towards inland and then this sand cannot nourish the beach anymore (Pinot, 1998<ref>PINOT, J.-P., 1998. La gestion du littoral: 1. Littoraux tempérés: côtes rocheuses et sableuses. Collection Propos. Institut Océanographique: Paris. ISBN 2-903581-20-7. 399 pp. Available from: [http://www.vliz.be/imis/imis.php?module=ref&refid=198656]</ref>). There are different ways to protect or restore dunes. Firstly, the protection of wildlife is important because fauna and flora are an integral part of dune system: vegetation stabilizes sand whereas fauna control plants growing and interactions. Sand dunes provide unique wildlife habitat. We must limit the trampling of visitors by paths and beach access setting up with fences. People walk through the dune because it is difficult to go on the sand. As they are looking for a hard surface to walk, we must provide them one. A marked pathway (by fences and why not with educative panels) is already dissuasion.</br> | ||
| − | In case of dune landscape restoration, totally or partially destroyed, it could be necessary to stimulate natural vegetation regeneration by planting indigenous species, and preferably plants characteristic of the first step of dune colonisation: builder sand plants like ''Ammophila arenaria'', or ''Elymus fractus'' because they permit sand stabilization and input. Moreover, it is fundamental to avoid invasive species and to limit them when there are already here.</br> | + | In case of dune landscape restoration, totally or partially destroyed, it could be necessary to stimulate natural vegetation regeneration by planting indigenous species, and preferably plants characteristic of the first step of dune colonisation: builder sand plants like ''[http://www.marinespecies.org/aphia.php?p=taxdetails&id=403902 Ammophila arenaria]'', or ''Elymus fractus'' because they permit sand stabilization and input. Moreover, it is fundamental to avoid invasive species and to limit them when there are already here.</br> |
The protection of implanted root native vegetation against wind erosion with weed permeable fences (“ganivelles”) and biodegradable geotextiles (Heurtefeux ''et al.'', 2007) is also a priority.</br> | The protection of implanted root native vegetation against wind erosion with weed permeable fences (“ganivelles”) and biodegradable geotextiles (Heurtefeux ''et al.'', 2007) is also a priority.</br> | ||
Revision as of 10:58, 6 July 2012
UNDER CONSTRUCTION
Contents
Processes and mechanisms driving natural dynamics & ecosystem development
Vulnerability & threats
During the last thirty years, almost 75% of Mediterranean coastal dunes have been damaged or destroyed, principally by tourism consequences (Géhu, 1985; Salman & Strating, 1992; in Van Der Meulen & Salman, 1993[1]). There are different kinds of destruction causes. First, the natural vents which are erosion by storms or/and sea level rise, overwash, and sea flooding events. The vulnerability of coastal dunes to flooding depends on the characteristics of the dune system itself: height, width, conservation status etc. It also depends on the intensity and impact of the event (e.g. sea level rise, storm intensity). The taller dunes are more resistant to flooding but possibly more susceptible to erosion while the shorter dunes might be more vulnerable to flooding. In the next century, climate change will lead to a rise of mean sea‐level, a likely increase of storms intensity and frequency and a more contrasted distribution of wetness between winter and summer (GIECC 2001, 2007, in Vinchon et al., 2008[2]). These changes will modify the coastal erosion and sea‐flooding hazards. Dune dynamics are driven by naturally occurring disturbances, which can be both common and recurrent. However when these disturbances increase in intensity or frequency or are removed there can be substantial alterations in community dynamics (Martinez and Psuty, 2004[3]). Dunes are thought to be fragile because only a slight disruption (either natural or human induced) may lead to change and long‐term progressive alteration (Carter, 1988[4]) and their natural diversity might be compromised easily.
For thousands of years, human activities have been impacting the coastal environment of the Mediterranean Basin through agriculture, husbandry and the deliberate use of fire. In recent decades, tourism has caused important damages on coastal landscapes with the urbanization of the coast, the increase of summer visitors, and the introduction of invasive or exotic species. The most heavily affected habitats are the sandy coastal systems and coastal dunes in particular (Tzatzanis et al., 2003[5]). The pedestrian and motorized pathways all over dunes lead to vegetation destruction and therefore enhanced weathering and erosion (Moulis and Barbel, 1999[6]). Waste deposits and invasive species introduction are also destruction factors. The potential for dune recovery is dependent on the sediment supply in each area and on the intensity of human impact. Dune plants are especially sensitive to disturbance and are heavily affected by humans. Without dune plants, the integrity and preservation of a stable dune complex cannot exist. Anthropogenic impacts combined with the natural regression process of the coastline induce the acceleration of the destruction of the dune vegetation (Araujo et al., 2002[7]) ultimately leading to to dune destruction.
Key processes to focus on for maintaining ecosystems integrity
Damaged coastlines are not attractive locations for tourism or leisure. Dune system vulnerability is defined as a set of conditions producing an acceleration of the erosion rhythm and system degradation. It is really important to not block natural processes which could destroy the system (Bodéré et al., 1991[8]) and to take into consideration all the dune system with beach and foreshore. The natural dune- rebuilding process can take several years, and it may be desirable to rebuilding a storm-eroded dune quicker than natural processes O’Connell, 2008). Dune damaging accelerates sand transit towards inland and then this sand cannot nourish the beach anymore (Pinot, 1998[9]). There are different ways to protect or restore dunes. Firstly, the protection of wildlife is important because fauna and flora are an integral part of dune system: vegetation stabilizes sand whereas fauna control plants growing and interactions. Sand dunes provide unique wildlife habitat. We must limit the trampling of visitors by paths and beach access setting up with fences. People walk through the dune because it is difficult to go on the sand. As they are looking for a hard surface to walk, we must provide them one. A marked pathway (by fences and why not with educative panels) is already dissuasion.
In case of dune landscape restoration, totally or partially destroyed, it could be necessary to stimulate natural vegetation regeneration by planting indigenous species, and preferably plants characteristic of the first step of dune colonisation: builder sand plants like Ammophila arenaria, or Elymus fractus because they permit sand stabilization and input. Moreover, it is fundamental to avoid invasive species and to limit them when there are already here.
The protection of implanted root native vegetation against wind erosion with weed permeable fences (“ganivelles”) and biodegradable geotextiles (Heurtefeux et al., 2007) is also a priority.
Another action of dune rehabilitation could be sand input to ensure dune system dynamics. The nourishment of the lowest part of the white dune will restore a homogeneous altimetry of the dune barriers in order to make it less sensitive to natural aggressions (waves and marine wind), and to limit the risk of marine submersion. This must be adapted to the morphology of the dune with consideration for the sensitivity of the natural environment (Heurtefeux et al., 2007).
Current management practises
According to Heurtefeux et al. (in press), there are different coastal management modes which have been used and are yet to be employed. In the last twenty years, four global approaches to manage coast have been developed (Error! Reference source not found.). First, there is the approach by holding the line. As presented above, it has persisted to be used. Traditionally, the goal is to protect developed area using hard structures (Klein et al., 2001). The “do the minimum” approach corresponds to the use of natural processes to reduce risks but permitting coast natural changes. Some of the techniques used with this approach attempt to limit rather than to stop coastal erosion and cliff’s retreat. The “do nothing“ approach, which is rare but can be found is one of the more famous cases of “do nothing” approach is the municipality of Happisburg, in the county of North Norfolk (UK). The storm waves reached the coast with important damages on the bottom of the cliff, the cliff fell with major impact on the houses which were totally destroyed. Do nothing is one of policy adopted when it is too late, when any decision has been thought before, when the cost benefit analysis shows than the defense front to the sea exceeds the value of the properties. Finally, the Managed Realignment (M.R.) approach is quite recent. Its definitions and its particularities will be presented below.
The M.R.’s aim is to avoid heavy structures to respect dune‐beach system and its intrinsic transfers in order to not damage ecosystem functionalities. It’s necessary to consider dune-beach system in its totality, and thus its natural capacity to return at an initial state after a perturbation.
There are many special features of Managed Realignment. One of these features is to move back the economic assets on the coast to the hinterland. It is also to create a new defense line behind the beach and facing the sea to restore natural areas and to create a buffer between the sea and the economic assets. Another feature is to avoid the construction of new economic assets in areas where they would be vulnerable (Heurtefeux et al., in press).
References
- ↑ VAN DER MEULEN F. And SALMAN A.H.P.M., 1993. Gestion des dunes côtières de Méditerranée. The first International Conference on the Mediterranean Coastal Environment. 167‐183.
- ↑ VINCHON C., BALOUIN Y., IDIER D., GARCIN M., MALLET C., 2008. La réponse du trait de côte au changement climatique: Evolution des risqué côtiers en Aquitaine et en Languedoc‐Roussillon dans le siècle à venir. The littoral : challenge, dialogue, action. Lille-France. 11pp.
- ↑ MARTINEZ M.L. and PSUTY N.P., 2004. Coastal Dunes. Ecology and Conservation. Ecological Studies. 171, 386pp. Available from: [1]
- ↑ CARTER R.W.G., 1988. Coastal environments. An introduction to the physical, ecological and cultural systems of the coastlines. Academic Press, New York.617pp. Available from:[2]
- ↑ TZATZANIS M., WRBKA T., SAUBERER N., 2003. Landscape and vegetation responses to human impact in sandy coasts of Western Crete, Greece. J. Nat. Conserv. 11, 187‐195.
- ↑ MOULIS D., and BARBEL P., 1999. Restauration des dunes. Réhabilitation et gestion des dunes littorals Méditerranéennes Françaises. Collection: Manuels et Méthodes. BRGM Ed., 75-91.
- ↑ ARAUJO R., HONORADO J., GRANJA H. M., NEVES DE PINTO S., BARRETO CALDA F., 2002. Vegetation complexes of coastal sand dunes as an evaluation instrument of geomorphologic changes in the coastline. Littoral 2002, The changing Coast: 337-339. EUROCOAST/EUCC, Porto-Portugal : 337‐339.
- ↑ BODERE J.C., CRIBB R., CURR R., DAVIES P., HALLEGOUET B., MEUR C., PIRIOU N., WILLIAMS A., YONI C., 1991. La gestion des milieux dunaires littoraux. Evaluation de leur vulnérabilité à partir d’une liste de contrôle. Etude de cas dans le sud du Pays de Galles et en Bretagne occidentale. Norois n°151. Poitiers-France. 279‐298.
- ↑ PINOT, J.-P., 1998. La gestion du littoral: 1. Littoraux tempérés: côtes rocheuses et sableuses. Collection Propos. Institut Océanographique: Paris. ISBN 2-903581-20-7. 399 pp. Available from: [3]
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