GUWAHATI, Aug 29 � Serious concerns have been expressed by the water resources engineers here on the safety of the five-kilometer-long geo-tube dyke laid at Matmora area of Dhakuwakhana Revenue Circle in the North bank district of Lakhimpur at a total cost of Rs 142 crore. Foreign technology was used to lay the dyke that contains compressed river sand in geo-tubes.
River engineers here maintain that the general scour-depth of the Brahmaputra is at least 25 meters. At places like Majuli and Matmora, the scour-depth of the river may be more than 25 metres.
When the geo-tube dyke was envisioned, it was suggested that the scour apron depth should be kept at 45 metres in the Matmora area and boulders should be used for the purpose, as, geo-tubes can never be an alternative to boulders so far as checking erosion is concerned.
But the Central Water Commission (CWC), the apex body in such matters, did not approve this scour-depth, which was worked out basing on the Bureau of Indian Standard (BIS) code. The boulder apron provision was also dropped by it. The CWC instead asked the implementing agencies to install geo-tubes as �scour aprons� with 16 meters depth for low-lying areas and 12 meters depth for level ground.
Water resources engineers fighting the Brahmaputra flood and erosion for decades, are of the opinion that 16 meters and 12 meters of geo-tube �scour aprons� are not sufficient to prevent scouring of the Brahmaputra where the minimum scouring depth of the river is beyond 25 meters. In fact, the geo-tubes used as �scour aprons� can in no way act as the scour aprons.
Once the river bank touches the geo-tube aprons in this area, the aprons will be vulnerable to erosion. The river will erode away the geo-tubes used in the scour aprons and subsequently, the geo-tube dyke will be in peril. The geo-tubes of the dyke have been laid at the cost of Rs 100 crore and the rest of the total amount of Rs 142 crore was spent on installing the �scour aprons� and the porcupine screens to provide protection to the unconventional dyke.
The porcupine screens installed at both ends of the dyke have silted up the river channel closer to the bank and now the river has been pushed away from the bank by more than one kilometer. But possibility is there that the subsequent floods may revive the silted up channel if the porcupine screens are not strengthened. If the silted up channel gets reactivated, it will pose serious threat to the geo-tube dyke, said the water resources engineers.
They have called for immediate measures to strengthen the porcupine screens and installation of boulder scour aprons to permanently protect the geo-tube dyke against erosion of the Brahmaputra for saving the Matmora area in Lakhimpur district and the famous river island Majuli in Jorhat district.
