Introduction

The Rohmoria area is located 20 km north east of Dibrugarh town on the south bank of river Brahmaputra in the Dibrugarh district in Upper Assam. The Rohmoria area falls in the Kobo to Dehingmukh reach of the Brahmaputra river, just a few kilometers downstream of Kobo which is the starting point of river Brahmaputra. The gradient of the river is 1 in 3,700 in this reach. The area where the Brahmaputra river has caused extensive erosion, is surrounded by a number.

Problem

There is serious erosion in each year in Dibrugarh district, where particularly Rohmoria is the worst affected. It is found that the rate of erosion in the 16 km long section around Rohmoria in the south bank was 0.06 sq km per km during the period from 1915 to 1972, which is almost double of the overall rate (0.03) of river Brahmaputra. Again, the rate of erosion turned out to be.0.26 sq km per km for the period from 1972 to 1996, which is four times higher than the previous rate (0.06). This convincingly proves that the rate of erosion in Rohmoria area is increasing constantly and the situation is becoming very grave. The increasing rate of erosion in this place is due to direct action of the river flow as it takes a large concave turn and hits the bank directly. It to be added here that, during the flood of 2008, the Rohmoria area experienced tremendous flood pressure and erosion activity intensified. Specially at the D/S reaches of the existing pipe dampeners at Rohmoria, the erosion become devastating and eaten away huge shank of valuable homestead and tea garden areas. In the month of September 2008, the bank erosion again became aggravated due to activation of obliquely flowing sub-channels.

Provision

The provisions made in the DPR are:

• 9 nos. of land spurs
• RCC Porcupine Screens and Dampeners
• Construction of new embankment for tying the spurs (Connecting road cum bund)
• Approached Road, stack yards and others

Estimated Cost: Rs 5982 Crores.

Benefit Cost Ratio: 2.65:1

ROHMORIA AREA IN 2010 (Before implementation of work	Eroded villages up to Feb/ 2009 at Rohmoria	First phase work-plan of pro-siltation measures taken up at Rohmoria after floods of 2010

Implementation

The project is implemented as follows:

1. Pro-siltation measures with RCC porcupines were taken after floods of 2010.
2. During floods of 2011, the measures successfully diverted the flow northward and induced huge silt in the deep channel-bed near south bank.
3. Flow velocity in subsequent flood stage in the channel reduced considerably.
4. After floods of 2011, bank-protection works with sand-filled geo-bags in under-water apron and bank-slope pitching were taken up.
5. Apron work was executed by systematic dumping of the sand-filled geo-bags by boat.
6. Slope pitching with geo-bags were paneled with PVC coated crates, both in cross & long directions.

Post-flood view of another porcupine screen taken up at Rohmoria channel before 2010 floods	Post-flood view of another RC porcupines in screen and along bank of Rohmoria channel	Second phase bank-protection works of sand-filled geo-bags taken up at Rohmoria after floods of 2011, (excavation for apron-bed)

Conclusion

• Bank-protection with sand-filled geo-bags in under-water apron and revetment has completely controlled the erosion of Brahmaputra at Rohmoria.
• In last 5 years after completion of the project, river bank has converted to a natural sloppy bank with growth of vegetation.
• Use of sand-filled geo-bags in bank-protection of Brahmaputra has proved successful.

Flood-period view of Rahmoria bank in April/2012	Eco-friendly bank at Rohmoria in 2014	Stable bank of Rohmoria in July/2014