Study on failure of flood control embankments in Bangladesh

Abstract

In Bangladesh, the main efforts in flood control has been through construction of embankments and polders. However frequent failure of embankments have resulted in doubts as to usefulness of embankments as an effective technology in flood mitigation projects. Embankments are often damaged during floods rendering them ineffective in providing protection. This study investigated on the nature, mode and extent of failure of embankments in Bangladesh. Main modes of failure of embankments are breaching,overtopping, public cut and river erosion. For indepth evaluation eight major flood control projects were taken up. It was found that breach of embankment section and erosion by river were the major causes of failure of embankments prior to 1987 flood. In major floods of 1987 and 1988 overtopping and public cut also. constitute major causes of embankment failure. Use of unsuitable construction materials, lack of proper maintenance, incomplete repair of damaged embankments and deviation from the design were found as other causes of failures. In the severe floods of 1987 and 1988 , 137.36 km and 35.69 km were damaged respectively out of a total of ,989.05 km of embankment in the selected projects. On the otner hand 10.09 km and 93.4 km bf protection works were damaged by the 1987 and 1988 floods indicating that major damage to embankment had occurred in 1988 due to failure of protection works. It was found that in 1987 flood main causes of embankment failure were: overtopping 62.22 km (45%), erosion 36.34 km (27%), public cut 25.11 km (18%) and breach 13.69 km (10%). Whereas in 1988 flood breach 21.51 km (60%) and erosion 8.63 km (24%) were the main causes of embankment failure; and overtopping 3.28 km (9%) and public cut 2.27 km (7%) constituted the other important causes. The study made detailed recommendation so that embankments can provide effective protection against floods.