Groynes

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Context: Poonthura region, irrigation department is all set to construct eight groynes at a cost of Rs 17.5 crore.

Details

Introduction

To mitigate the risk of flooding and coastal erosion there are both hard and soft coastal engineering methods. Groynes are a form of hard engineering - they are easy to construct and have long term durability and are low maintenance.

Groynes

Groynes are low lying wood or concrete structures which are situated out to sea from the shore.

How they works

• They are designed to trap sediment, dissipate wave energy and restrict the transfer of sediment away from the beach through long shore drift.
• Longshore drift is caused when prevailing winds blow waves across the shore at an angle which carries sediment along the beach.
• Groynes prevent this process and therefore, slow the process of erosion at the shore.

Permeable or impermeable Groynes

• Permeable groynes allow some sediment to pass through and some longshore drift to take place.
• However, impermeable groynes are solid and prevent the transfer of any sediment.

Advantages

• Groynes are easy to construct.
• They have long term durability and are low maintenance.
• They reduce the need for the beach to be maintained through beach nourishment and the recycling of sand.

Disadvantages

• Wooden groynes are less durable than rock groynes.
• They can have a negative, visual effect on the landscape.
• Groynes prevent sediment being transported to beaches further down the coast and therefore increase the amount of erosion and sediment loss at those beaches.
• The down drift erosion caused by the groynes may cause the need for regular maintenance and beach nourishment on the downstream side.

Examples of groynes from around the world.

Kerala Case

• The irrigation department is all set to construct eight groynes at a cost of Rs 17.5 crore.
• The groynes bearing a length of 60, 40 and 20 meters will be constructed at a distance ranging from 150 to 200 meters.
• Tetrapods will be used at the sides of the groynes and rocks will be used to build it.
• In 2020, Kerala State Coastal Area Development Corporation (KSCADC) had constructed four groynes to curb coastal erosion. But due to unscientific construction, all the groynes got destroyed by strong waves and coastal erosion has become rampant again in this area.

Coastal Erosion data of India by National Centre for Coastal Research (NCCR)

• It is observed that 33.6% of the Indian coastline was vulnerable to erosion, 9% was under accretion (growing) and 39.6% was in stable state.
• The study by NCCR reveals that the shoreline changes are combined effect of natural and human activities.
• Kerala is worst affected State by coastal erosion in India.

Sources:

TimesofIndia, PIB,TheGeographyteacher.com.