03/11/2016
Sri. K. N. BALAGOPAL FORMER MEMBER OF PARLIAMENT (UPPER HOUSE) GOVT.OF INDIA Email : [email protected]
Land subsidence is the gradual settling or sudden sinking of the Earth's surface owing to subsurface movement of earth materials.
Subsidence is the motion of a surface (usually, the Earth's surface) as it shifts downward relative to a datum such as sea- level. The opposite of subsidence is uplift, which results in an increase in elevation.
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Climate change and sea level rise Ground water extraction Mining and erosion Extraction of natural gases Movement of Tectonic plates Dissolution of limestone Earthquakes Geological faulting Isostatic subsidence Seasonal changes and associated effects
Shape shifting of 33 reef islands in the Solomon Islands was reported between 1947 and 2014 . It was found that five had been washed away completely and six more had been severely eroded.
Solomon Island
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Kiribati,acountryconsistingofachainof33atollsand islands with a maximum elevation of 266 feet above sea level is reported to be sinking.
Kiribati
The Maldives: Like several other South Asian and Oceanic archipelagos, the Maldives’s topography suffers from a lethal combination of high surface erosion and rising sea levels. The former stems from the islands’ soft soils, but most scientists agree that the latter is a direct consequence of global warming
Maldives Other important islands sinking are Fiji, Micronesia, Palau, Republic of Cape Verda, Mauritia etc.
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The largest river island Majuli in Assam is submerging due to excessive sediment discharge caused by frequent low magnitude seismic disturbances. It has been reported that the surface area of the island got reduced from 1100 sq km has shrunk drastically to 352 sq km within a short span of time.
The earthquake that caused the Tsunami of December 2004 has altered the topography and ecology of the Andaman and Nicobar Islands.
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Lohachara Had been sinking and was finally lost in 2006. The first inhabited island to be submerged as a result of climate change. Was located in India’s Sundarbans, where the rivers Brahmaputra and Ganges empty their contents into the Bay of Bengal. The island was once inhabited by as many as 10,000 people. As it gradually sunk into the sea, most of the residents fled to the neighboring Sagar Island, which is also under threat of sinking.
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Munroe Island (Malayalam : Munroe thuruthu) Named after Colonel Munroe, the British Resident of erstwhile Travancore State
A major tourist attraction in the State
Located at the confluence of Ashtamudi Lake and Kallada River, in Kollam District, Kerala, South India .
25 kilometers away from Kollam, the District Capital by road.
Latitude and longitude : 9°0′0″N &76°37′0″E Area: 13.4 sq km Height Above Sea Level: 3.32 m Population :10380 (as of 2011) Density :776 /km2
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GPS View of Munroe Island
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There are two types of lands constituting the Munroe islands: The already formed land area Delta formed by the Kallada River Other features
Earlier, the inhabitants used to reclaim the land by filling the marshy delta with soil during low tide to support their coconut cultivation. They started prawn farming 25 years ago,
Fishing
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Backwater fishing is one of the major income sources. Freshwater prawns, lobsters, crabs, clams and oysters which find a ready market overseas are caught from these backwaters Important fishes: Pearl-spot, Milk fish, Mullets, Tilapia, Murrels etc. Fishing methods Gill net Hook and line Chinese dip nets Cast net Traps etc.
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Murrel Mullet Milk fish
Pearl spot Lobster Tilapia
Shrimps Clam Crab
Traditional hand picking of clams
Chinese Dip net
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Over 70% of the Panchayath is the delta formed by the Kallada river and the people mostly depend on prawn farming (even named as ‘prawn village” of the State.
The island is noticed to be sinking after the Tsunami in 2004, endangering the lives of the inhabitants. Low-lying areas of the Island are now under the threat of Submergence during high tides. May sink and vanish in the near future!!
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Contd.
Most of the nearby islands are seen permanently inundated to by about 1.25 m since a few years. The islands including Kidapram North and South, Kandramkani, Pattamthuruthu East and West and Nenmeni North have been found to be severely affected by tidal floods. Water level has risen to over a feet during the high tides recently. Over 300 families abandoned the place because their houses got flooded permanently.
Water intrusion is really horrible
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Due to change in climatic conditions caused by global warming. Unscientific constructions. The post-tsunami tectonic shift and dam construction-across River Kallada (Dr. Sainudeen Pattazhi and Shasthra Sahithya Parishad). Downward movement of minor tectonic plates in the area (3 m high areas sunk by 0.5 to 1 m). The reduced silt accumulation in the island after the dam construction.
National Centre for Earth Science Studies (NCESS), Kerala State Council for Science, Technology and Environment (KSCSTE), and the State Disaster Management Authority (SDMA) inferred that the flooding is caused by spring tide or subsidence (spring tide theory)
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There is a possibility of structural or land subsidence on the artificially created island (?)
Railway bridge over the area led to some internal adjustments of earth plates and associated subsidence (?)
The saline water intrusion - everywhere! Reduced availability of drinking water Reduced land availability for agriculture and allied activities Diminished space for house building Decline in agriculture production levels and day to day economy Abandoned shrimp ponds Severe drainage problems including non-working of toilet flush systems.
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This might be a unique case in the world?
In most of the other cases, the sinking islands (Caribbean and Pacific Islands) are surrounded by sea while Munroe Island is located in the backwaters!
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The issue has been raised in many forums including the Parliament of India by the speaker. The concern about the possibility of drowning of the island has been well discussed.
Anyway, we have to protect the Island and it’s population- need of the hour is to formulate location specific protocols for constructing buildings of high adaptability to the given situation! (light roof/ raised basements/ water proofed wall) To ensure the livelihood of the local community adaptable methods of agriculture, aquaculture and allied activities have to be introduced.
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CONCLUSION Munroe island is alarmingly sinking; which is a serious issue to be addressed.
It is very important to assess the sinking rate of Munroe island scientifically and to find out solutions to conserve this precious land.
GPS surveys, LiDAR, InSAR, Field observations using Extensometers and using Optical leveling methods are the methods suggested.
Afforestation of different types of mangroves around the Island may help to control further erosion and sinking.
Global attention from FAO, NACA and other Organizations is highly solicited.
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