Bank erosion and protection in the Niger delta

Abstract

A field study of erosion processes and local responses was carried out at representative sites of major soil groups in the Niger delta. The soils at these sites varied widely from plastic silty clays to silty sands of varying relative densities. Information on soil type, stratification and state of compaction together with tidal velocity distribution and pool level variation in river channels was used to establish predominant mechanics of erosion. The influence of vegetation on bank stability is dependent on the stage of growth of the vegetation, the relative location of the vegetation in the bank area, the bank steepness and its height. Although bamboo trees and raphia palms on lower parts of channel banks impede flow, thus aiding sedimentation, they may not be effective in checking bank recession. The difficulty of achieving an effective bank protection with raphia palms can be overcome by an improvement in bank protection design layout along the line of a filter which preferentially allows water to escape from the mesh. An upper bank protection may not be effective if low bank areas are scoured as this results in overhangs which readily fail. Consequently, bank protection measures must cover the entire bank profile. © 1993 Taylor & Francis Group, LLC.