Study of Flood Embankment Deterioration of Omchhu

Abstract

Omchhu basin has a catchment area of about 22.52 km². Omchhu runs across the heart of Phuentsholing town with tremendous discharges during monsoon. Past events of floods along Omchhu posed considerable losses and damages. The construction of embankment in 2001 have aided in reducing the damages, however the flood embankments along Amochhu and Omchhu still suffers greater deteriorations. The main causes for the deteriorations are intense rainfall, slope instability, high river bed incision rate, shorter span of river width and the quality of embankment protection works. A proper engineered, efficient and effective protection works are desired. A proper concept on embankment construction, rectification of existing structures and determination and monitoring of embankment deterioration factors are essential. Field investigations and inspections with photographic evidences were used to determine the deteriorating factors. River survey using total station (TSO6) was extensively carried out along the simulation stretch to get the cross sectional details for the design. The iRIC software (Nays2D Flood) was used to simulate flood for the identification and determination of flood prone areas. Therefore, this study is oriented to determine the maximum flood level that have occurred in Omchhu in order to suggest appropriate embankment protection works so that the Phuentsholing City remains safe and protected from any future flood events. The factors that leads or contributes to the deterioration of embankments are studied such as scour prediction and slope instability problems. A brief geotechnical studies and laboratory test on soil and bed materials were also carried out to study the subsoil characteristics and to determine the parameters required for scour depth computation and design. Proper rectification to the existing embankments and design of new embankments at flood prone areas are suggested incorporating the factors causing embankment failure.