Introduction

Matmora situates beside Sissi-Tekeliphuta B/dyke at Dhakuakhana in Lakhimpur Dist. The dyke length was 27.15 km, constructed in 1955-56 at bank margin of 3 km from the river.The river Brahmaputra formed a bank-ward spill channel near Matmora after 1950’s E/quake.The channel eroded away the bank margin till 1964 along with portion of the dyke. The channel further caused subsequent chronology of breaches, requiring closure works every time. The Reported area lost in erosion at Matmora was 200 hectre up to 1992 and 600 hectres next up to 2008. Flood damage loss in each of consecutive years from 2006 to 2008 was Rs.123 Cr. Flood damage occurred in 10,117 hect. area at immediate vicinity, 41,883 hect. at far downstream. Total villages affected: 200 in Dhakuakhana & Majuli with about 5 lakh population. In 3 consecutive years from 2006 to 2008, total loss was Rs.669 Cr.; and therefore cost dimension of the project justified enough the benefit it would yield.

Brief on the Project

The project provisions and specifications Construction of a 5 km long breach closing retirement with sand filled geo-textile tubes in form of 1 over 2 (each tube being 40m long. Bank-protection measures with 11 Nos. spurs with similar sand filled geo-textile tubes. Strengthening of existing earthen dyke lengths at up & down streams of the geo-retirement. Use of Non-Woven Geo-Textile tubes was proposed both in retirement. and spurs.

Further on the recommendation of CWC the following changes were finalized:

• Stability design for composite dyke section reqd. to replace the original provision of 1 over 2 tubes with new provision of 1 over 2 over 3.
• Use of non-woven geo-textile tubes was replaced with woven geo-textile tubes as required to sustain filling pressure by sand pumps.
• CWC suggested provision of submerged vanes was reviewed on reason that vanes may effect adversity in absence of stable channel configuration (existing spill channel’s flow-direction may change or new formation may undergo during recede of high flood wave or waves).
• Provision of geo-spurs was ultimately replaced with limited number of permeable screens & spurs (with RC porcupines) at salient locations.
• River-side slope of the geo-dyke was provisioned to be covered with sand filled geo-textile mattress, anchored at toe and crest. Anchorages were hooked with smaller sand filled geo tubes.
• Riverside toe apron was provisioned to encounter probable scour by over-bank flow of flood beside the geo-dyke.

Implementation

Geo-dyke component was globally tendered in single package.100 days physical completion time had to be stipulated on urgency to complete before the next year’s flood, biders were fixed to primarily produce: Manufacturing capability of geo-textile quantum required in the project to conform physical completion within 100 days, Construction methodology, list of deployable machineries & key personnel's, Site-supply delivery-schedule of geo-text tubes/mattress, Construction schedule with details for installation of machineries,Track record of successful similar constructions, Contract was awarded to Emaskira Company of Malaysia. Geo-textile tubes and sand-pumps including accessories and certain deployed machineries were brought from Malaysia through sea-route to Kolkota port, then road-transported to Matmora project site. Completion of tube-fillings required minimum 3 stages, in each stage the pumping of slurry by sand pumps inflated the tube to its maximum volume, then pumping was halted until the water pours out from inside the tube. Such stages continued until the fill height attained the designed value of 2.5m.Due to certain reasons, installation progress of tubes deviated down from the periodic schedule for stipulated completion (before the next flood of Brahmaputra); but all RCC porcupine screens & spurs were completed. The reason of interruption in progress of geo-tube installation was natural obstruction in the sea-route of material transportation (reported as low water condition of the sea near Kolkota port). On attaining about 20% progress of installation of the tubes, the construction was held up due to flood of 2009.During floods, huge siltation was observed in the river channel, totally eliminating the bank erosion at Matmora. On recede of flood water, damages of installed tubes were thoroughly inspected, under-constructions were rectified and further installation work was resumed.

Conclusion

In spite of hurdles faced, the Geo-dyke construction was completed in all respect well before the floods of 2010 and was finally dedicated by the Govt. to the people of Assam on 3rd December’2010. Erosion at the Matmora reach was totally controlled by the permeable measures. The completed Project benefits 52,000 Hectares of Land having 200 villages & 5,00,000 population, definitely improving the socio-economy of the entire flood hit area of Dhakuakhana & Majuli. Matmara Geo-dyke stands as a paradigm of sustainable protection against flood-devastation by the mighty Brahmaputra at Matmora.