The Tamil Nadu Fisheries Department will soon begin work on laying geotextile tubes filled with slurry (mixture of sand and water) as a shore protection measure to prevent beach erosion and reclaim the shoreline at Bommayarpalayam.
The National Institute of Ocean Technology (NIOT), which has experience in laying geotextile tubes at Kadalur Periyakuppam in Chengalpattu district, has prepared a Detailed Project Report (DPR) for the Bommayarpalayam project.
“Tenders for the project, costing ₹19 crore, have been opened and the contractor has been finalised. This project has already been proved successful and Bommayarpalayam will be the first pilot project to be taken up by the Fisheries Department in the State,” a senior official said.
Funds for the project have been sanctioned from the National Bank for Agriculture and Rural Development (NABARD). The Fisheries Department has already completed the Bathymetry survey and shared the details with NIOT. The alignment will be finalised by NIOT through GPS (Global Positioning System) and the offshore submerged dyke using geotextile tubes will laid at a distance of four metres from Chart Datum Level offshore.
The structure will reduce the intensity of the waves and prevent erosion and, allow beach enhancement, the official added.
“NIOT has already proved this technology at Kadalur Periyakuppam village. The submerged dyke will reduce wave activity and allow sand to freely move from south to north and vice-versa and prevent erosion along the coastline. The structure will be mainly effective during natural calamities especially cyclones, and ensure that there is no land loss,” M.V. Ramanamurthy, Director, National Centre for Coastal Research (NCCR) told The Hindu .
According to an official, the proposed dyke will comprise seven segments, each with 18 geo-synthetic tubes. Each geotube spans 25 metres in length, 15 metres in circumference and rises to a height of 3.5 metres after it is filled with sand. Each geotube will be filled with 450 cubic metres of sand and will cover a stretch of 1.35 km of the coast. Each segment will be situated 50 metres apart to facilitate navigation of fishing vessels through these gaps.
The geotubes will be attached to concrete blocks submerged under the sea. The structure will also be equipped with reflectors for easy identification of their location by fishermen at night.
The structure will be a double barrier with one geo-tube supported by two tubes below. The tubes on the first layer will rise to a height of 2-2.5 metres while the tube on the second layer will rise to a height of 1-1.5 metres. The tubes will hold sand and release water. The work is expected to be completed in nine months.
According to Vijaya Ravichandran, scientist, NIOT, “While conventional shore protection measures like groynes and sea walls protect the coast where they have been installed, they also transfer the accretion of sand towards adjacent coasts on the northern side. However, geotextile tubes are environment-friendly and more efficient as they will be laid at a significant distance offshore. The structure will interact with the incoming wave energy to produce a calm region landward of the structure.”
The tubes will be placed in required positions and will be filled with locally-dredged sand to the required level. The tubes are flexible and can adjust to the bed profile during filling and stabilise once the excess water flows out from the tube. The structure will also reduce the hydraulic loading on the coastline and maintain its dynamic equilibrium, she added.
Fisheries Department officials estimate that the sea has advanced about 500 metres at Bommayarpalayam over the last two decades. As many as 75 houses have been damaged due to erosion. In addition, fishermen have been unable to berth their boats due to frequent damage to boats.
Over the last few years, the coast has been hit by erosion and the project is expected to result in the reclamation of sand levels and the restoration of the coast by 50 metres.
