1.1.8

• Odisha is a state on the eastern coast coast of India, bordering on the Bay of Bengal. It is India’s 9th largest state by area and 11th by population (4.2 million in the 2011 census). 

  Odisha has a relatively straight coastline (480 km long) with few natural inlets and harbours. The narrow, level coastal strip known as the Odisha Coastal Plains supports the bulk of the state’s population.
• Chilika lake is a brackish salty lagoon. 

  A barrier spit near Palur due to littoral drift and creation of a sand bar along the eastern shore have transformed the lake gradually to a shallow lagoon. 

  Silt of the Mahanadi river drains into the northern end of the lake, and the northerly currents in the Bay of Bengal, have formed a sandbar along the north eastern shore.

  During the monsoon season the lake becomes less saline, being diluted by the freshwater rainfall, and occupies a larger area than during the rest of the year.
• Mahanadi delta is an important ecological zone, providing important habitats for a wide variety of wildlife. It covers a coastline of 200 km and is formed by the network of three major rivers: Mahanadi, Brahmani and Baitarini. 

  The central part of the delta is distinct for its extensive plains, the coastal parts contain lakes, creeks, swamps, beaches, tidal flats and mangroves.
• Bhitarkanika mangrove is a salt tolerant, complex ecosystem, lying in the estuarine region of Brahmani- Baitarani in the North-Eastern corner of Odisha.
• role of wave energy 

  It has been observed that the same beach experiences a changing profile on an annual cycle due to variations in wave steepness.

  • As wave steepness decreases, beach slope angle increases. 

  The more energetic waves of winter erode and transport sediment offshore, forming an offshore bar, leaving a gentler beach profile.

  During the summer, lower energy waves move material onshore, building the beach up into a steeper profile. 

  This is a simplification as high energy waves also occur in summer and low energy ones in winter.
• Monsoons (May- September)

  Coasts affected by monsoons, which bring high energy waves and heavy rainfall, often show clear cliff profile changes with the wet and dry seasons, such as around the Indian sub-continent. 

  • The heavy rainfall saturates the soils  and cliffs, leading to a reduction in the shear strength and an increased chance of slope failure and mass movement. 

  High energy waves driven by the strong onshore winds lead to higher rates of erosion.
• Sea level change (eustatic change)

  These are changes in the absolute seawater level, they are global in scale because all the seas and oceans are interconnected. 

  The hydrosphere is a system, so change in one part will affect other components.  

  If all the land based ice melted, sea levels would rise by 90 metres (Antarctica would contribute 57 metres, and Greenland 7 metres).
• Isostatic change (land)

  These are changes in the absolute level of the land, this is localised

  • The land can be depressed when great weight is added, such as the accumulation of ice (during ice ages) or sediment. The Mississippi delta has sunk by some 165 m in the past 100,000 years due to deposition of sediments transported by the river from its basin.

  Tectonic activity can also cause the rise and fall of land. Movement along fault lines can lift land by several metres in a sudden event. Alaskan and Californian coastlines, lengths of the coast have been elevated by tectonic forces.
• A relative rise (eustatic) sea level can result from

  • sea level rising, while the land subsides, remains stationary or rises at a lower rate than the sea
  • sea level remaining stationary while the land subsides
  • sea level falling while the land subsides at a faster rate
• A relative fall in the sea level (eustatic) can result from

  • sea level falling while the land surface rises, remains stationary or subsides at a slower rate than the sea
  • sea level remaining stationary while the land rises
  • sea level rising while the land rises at a faster rate
• Sea level change associated with glaciation

  • The last major ice advance peaked at around 18,000 years ago. 
  • Huge ice sheets extended across vast swathes of the northern hemisphere, covering both land and marine areas. 

  The Scandinavian ice sheet covered the Baltic, Irish and North Seas. The Holocene (11,700 years ago) is the time since the end of the last ice age.
• During ice ages

  • Ice builds up on the land, crustal depression occurs (land is pushed down).

  End of the ice age

  • When the ice melts the weight is removed from the land, and the land adjusts upwards, a process known as glacio-isostasy/ isostatic readjustment.

  When the land based ice melts, the freed water flows back to the coast, causing sea level rises. This is called glacio-eustasy.
• Glacio-eustasy is relatively rapid in geological terms
• • Glacio-isostasy is a very slow process

  Isostatic readjustments are still continuing since the end of the last ice age (11,700 years ago). The land continues to ‘rebound’ at about 10 mm /yr across the Baltic region. In the UK (where the ice sheet was not as thick) the rebound is lower ar 2 mm /yr.
• effects on coastal landforms

  • When sea levels are low (glacial), marine processes are no longer dominant and sub-aerial weathering is a more important factor affecting the coastline. 

  During interglacials (now) the sea level rises, and marine processes once again act on former shorelines
• Transgressive conditions = drowning (submergence/ submergent landforms) of coastal areas and/or migration onshore of some landforms such as fjords.
• Regressive = falling sea levels, and emergent landforms develop as the coastline, such as raised beaches.