Geo-textile in Riverbank-Embankment Protection from Flood Flow Erosion

Abstract

Bank erosion of rivers, e.g. Bagmati, Burhi Gandak, Kosi and Kamla-Balan, all originating in the Himalayan hills of Nepal and flowing through the alluvial plains of North Bihar, is a chronic and common phenomenon. Cutting and deposition result in shifting or meandering of the river endangering the embankment, road, bridge, barrage, and countryside. Anti-erosion and maintenance require huge investment. The river Kamla-Balan faces bank erosion throughout its embanked length, but stretches at km 37 and 62 are highly unstable and vulnerable. This paper deals with the problem, presents the hydrological details responsible for the hazard, and demonstrates the effectiveness of supplementary geo-textile with conventional sand filter pitching to protect the soil and slope of the riverbank. Estimated flood discharge and velocity at 100 years of return period is nearly 2100 cumecs and 0.9 m/sec, respectively. Riverbed and bank material is represented by silt with d50 of 0.018 to 0.05 mm while 0.02 mm of silt may get eroded and transported by flow above 0.15 m/s. Launching apron is also required due to local scour. Model study test shows its suitability under various hydraulic conditions. Study reveals the effectiveness of woven type geo-textile reinforced revetment irrespective of cost and environmental consideration.