Coastal Sand Dunes
Sand dunes are formed at the interface between the sea and land. They are formed from sand which is eroded and ground rock, derived from terrestrial (e.g., glacial or river) and oceanic sources (e.g., coral reefs). The form of dune systems will be dictated by a number of factors, including the shape of the coastline, shape of the beach, currents and swell of the ocean, prevailing wind, frequency of storm events, and particle size of the sand.
Reference
Dr.Ramesh.R. and Dr.Purvaja Ramachandran. 2007,’ENVIS – MoEF on Coastal Zone Management and Coastal Shelter belt Vol(6)’,pp 25.
There are seven requirements for dune formation
1. Wind
2. Sand supply
3. Topographical degree of coastal exposure
4. Rainfall
5. Plant colonization
6. Sea (wave action)
7. River mouth dynamics
The vegetation that is native to sand dunes is very unique and is tolerant to:
• Saltwater spray from sea waves
• Can sustain high and salty wind
• Can stand high daytime temperatures when the sand gets very hot
• Has special roots that can find footing even in loose sand and reach the soil underneath
Parts of a Sand Dune
• Secondary Dune-second line of dunes heading inward
• Hollow- dry depression between dunes
• Leeward Side- steep sloping side
• Primary Dune- first line of dunes from the ocean
• Inclined Windward Side- gently sloping side facing the ocean
• Dune Base- compact base of a dune
One of the most important things to realize with the coastal and dune environment is that it is dynamic, like the forces that shape it, so these environments are always changing. Accepting change can be a difficult for humans to accept (such as the common perception that damage to established forest in storms is bad) but it is important to acknowledge that change is a natural and health part of this ecosystem, and helps to maintain biodiversity.
Due to the extensive coastal development that characterizes much of our beaches now, stabilization has been a large focus. This has lead to the extensive planting of marram grass that form high densely covered dunes that prevent most sand moving beyond the foredunes, affording protection to developed areas. This form of planting has proven successful for human habitation but has come at the expense of the native sand binders and associated plants. This section intends to outline the values associated with the coastal dune environment as well as the processes associated with dune building and the dynamics of the different
Sand dune formation
Dunes develop at the back of beaches where there is sufficient sand supply and wind energy to transport it landwards. Sand from the dry portion of the beach is transported inland until the wind energy is dissipated, or a physical barrier (such as vegetation) causes the sand to be deposited
Coastal Plantation
Cyclones and tsunamis mostly originate from the sea and move towards the land, the wind – generated reduced, reflected, deflected and dissipated, when they pass through obstacles such as coastal forest, mangroves, offshore islands, coral reefs, head lands, sea cliffs, sand pits, mud flats, sand dunes, creeks etc.
Other than the above natural features, manmade structures along the coastal line such as offshore platforms, sea wall constructions, harbour and plantations also help in energy dissipation.
Coastal habitats such as mangroves and other wetlands, coral reefs, coastal barrier islands and lagoons are often recognized by experts as the best defenses against wind, waves and erosion by deflecting and absorbing much of the energy of winds.
Coastal habitats such as mangroves and other wetlands, coral reefs, coastal barrier islands and lagoons are often recognized by experts as the best defenses against wind, waves and erosion by deflecting and absorbing much of the energy of winds.
http://www.keralaagriculture.gov.in/htmle/bankableagriprojects/fw%5Ccasuarina.htm
Casuarina
Casuarina equisetifolia is the most popular farmforestry tree in the coastal lands of Andhra pradesh, Orissa, Tamilnadu, West Bengal, Maharashtra, Gujarat & Karnataka. Casuarina resembles feathery conifer in general appearance. Almost all of the approximately 35 casuarina species produce top-quality firewood. They are rapid-growing, carefree species for sites and climates as varied as coastal sand dunes, high mountain slopes, the hot humid tropics and semi-arid regions. They tend to be salt tolerant, wind resistant and adaptable to moderately poor soils.
Casuarina Plantations in Orissa
Links
http://www.mssrf.org/tsunami/mangrove_toolkit_final.pdf