Q. What is the significance of ‘Deltas’? What are the factors responsible for sinking of deltas in India? Suggest some strategies so as to deal with this issue. [Answer in 250 Words]
BRIEF DEFINITION OF DETAS
- Delta is a depositional feature of almost triangular shape at the mouth of a river debouching either into a lake or a sea.
- There are various features of ‘Deltas’ that make them very significant for the people. This is also evident from the fact that there were many ancient civilization that flourished around Deltas. These can be described as below:
- Being rich source of fertile soils, the Deltas have a crucial significance in terms of agricultural use. For example, the being one of the most fertile regions of the world – the Ganga-Brahmaputra delta in India and Bangladesh support various agricultural activities such as cultivation of rice, etc.
For Bio-diversity and Ecological Balance
- In addition to this, the deltas are also significant for sustaining ecological balance of the region as well as the biodiversity.
- River deltas are a some of the most bio-diverse areas on the earth and are a home to various species. This feature also makes them an attractive destination for tourists thereby aiding in development of economic activities.
For Disaster Management
- By providing an effective buffer against cyclones, hurricanes, and tsunami, deltas can help averting these natural disasters.
- For example, the deltas on the east coast of India with lots of mangroves have helped many Indian states during tsunamis and cyclones.
- There are various resources which are found in the in or near deltas. These resources can have great significance for various economic activities.
- For example, being a rich source of sand and gravel, the deltas can provide the raw material for the construction of raw material etc.
- In addition to this deltas can also prove to be an excellent sites for the developments of ports and harbors.
- They have significance for fisheries as well.
FACTORS RESPONSIBLE FOR SINKING OF DELTAS
According to some reports, it has been found that as a result of various factors both natural and man-made, Deltas of the world including those of India are sinking.
- Over a period of time, a natural subsidence of land (isostacy) takes place. This phenomenon is observed to be a natural factor behind the subsidence of deltas.
- However, sediment deposition and accretion by plant growth generally outpaces the natural subsidence, resulting in coastal land gain. Therefore, the natural subsidence of Deltas has generally been a rare event.
- Without land-building deposits from the river, subsidence dominates and massive areas of land sink and disappear below sea-level. (And here comes the role of Human Factors)
- Natural Sea level rise is also a factor responsible for sinking of deltas.
- Submergent Coast lines – Inundation of the sea will wash the deposited sediments. Example west flowing rivers in India do not make deltas.
A. Creation of Dams and Diversion of rivers
- As a result of dam building and diversion of rivers, much less sediments are able to reach the deltas
- Large reservoirs trap as much as 80% of the upstream silt. As a result, most rivers are carrying much less sediment, and some rivers (like Krishna, Indus, etc.) transport virtually no sediment
- The land building process therefore lags behind the process of natural subsidence and ultimately results in the sinking of delta.
B. Groundwater Mining
- Groundwater mining that causes land compaction is also a cause for sinking of deltas.
- Groundwater mining has led to a significant compaction and subsidence of land over the last 15 years in Ganga.
C. Clearing Natural Vegetation
- The rate of sediment deposition slows down significantly if the natural vegetation around the deltas is removed or cleared, thereby resulting in the sinking of deltas.
STRATEGIES TO ADDRESS THE ISSUE
- Sinking of deltas can lead to further damage to the natural environment such as inundation of coastal areas, saltwater intrusion into coastal aquifers, increased rates of coastal erosion, an increased exposure to storm surges, etc.
- Therefore, it is important that effective measure be taken to deal with the issue of sinking of deltas.
- Steps should be taken to conserve the natural vegetation around deltas, so that the rate of sediment deposition is not disturbed. For this strict guidelines need to be made to curtail illegal constructions around the deltaic region.
- Dependence on ground water should be reduced and reusing and recycling of water should be encouraged.
- Development of alternate sources of energy can reduce the dependence on dams which can go a long way in addressing the issue of delta sinking.
- Better water use methods in agriculture like drip irrigation etc. can reduce the need of creating dams and diverting rivers which can help in maintain the natural silt flow of rivers and prevent the sinking of deltas.
- The issue of sinking of delta can lead to critical ramifications if it is not timely addressed.
- The Godavari, Brahmani and Mahanadi deltas have seen a 40 per cent, 50 percent and 74 per cent reduction, respectively, in sediments delivered to them over the last three decades.
- It is hoped that the government of India will take due cognizance of this issue and come up with a fool proof plan to resolve this hazard.