Geo tubes to be modified to counter strong sea waves

Thiruvananthapuram: An unexpected technical hurdle has slowed down the shore protection works using geo tubes at Poonthura. Kerala State Coastal Area Development Corporation Limited which is implementing the project has now sought a modification in tube design to withstand strong waves during inclement weather.
A bathymetric study conducted by the officials, after two layers of geo tubes were laid, revealed undulations along the second layer.This indicated erosion of sand from the tubes after filling ports had ruptured. It was found that strong waves during monsoon battered the tubes causing the stitched portions of filling ports to come off. Slurry of sand and water is pumped into the tubes through the filling ports.
An official associated with the project said that while the first layer remained intact, the second layer showed undulations and steps have been taken to address this issue. “We used material of the same design and dimensions. The wave action caused the filling ports to open and sand oozed off. This was not anticipated. The divers did physical inspection and the technical opinion of experts from the National Institute of Ocean Technology was also sought. We have now decided to either use a bolt and screw method or other options like bottle cork mechanism to keep the filling ports intact. Once the roughness of the sea subsides by the end of the monsoon, we will resume work with suitable modification in design,” the official said.
The next sets of geo tubes are to be procured in July. These tubes will be procured with modified design. Bathymetric studies will be conducted again and work will resume after that. The final option for a modified design will be submitted in two to three weeks.
The officials said the project is already yielding good results. Waves which used to lash over the seawall did not reach the houses once the two layers of geo tubes were laid. “There has been a significant reduction in wave overtopping near the project site. The residents have given us positive feedback. We will address the technical hurdles and speed up the works,” the official said.
The work on one segment is now being done and each segment measures 100 metres in length. The total work includes four gaps and five segments. Geo tubes have to be laid in three layers in each segment. The change in location from the actual project design has added to the challenge. The initial plan was to lay the tube in front of the beach. However, demand arose that it be done near the settlement which is close to the seawall. Waves lash hard at the seawall during harsh weather making the work extremely difficult.
As per the project document, Poonthura sandbank where the Killiyar discharges into the sea which is situated at the south side of the coast line has to be protected. Unprotected beach measuring 750 m lies north of the existing sandbank. This beach is being used by the fishermen community.