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. Erosion littorale et la protection des rives dans le delta du NigerRésumé Une étude de terrain des processus érosifs et de leurs effets locaux a été menée en divers sites du delta du Niger, représentatifs de différents types de sols, allant des argiles plastiques aux sables vaseux de densités variées. Les principaux processus d'érosion ont été identifiés grâce aux données concernant les types de sols, leur stratification et leur état de compaction, la distribution des vitesses des courants de marée et la variation des niveaux dans les différents biefs. L'influence de la végétation sur la stabilité des berges dépend du niveau de développement de cette végétation, de sa localisation sur les rives, de la pente et de la hauteur de celles ci. Bien que les bambous et les raphias situés à l'aval des biefs ralentissent le courant, favorisant ainsi la sédimentation, ils peuvent s'avérer incapable de prévenir le recul des berges. La protection des berges pourrait être améliorée grâce à un filtre permettant le passage préférentiel de l'eau à travers ses mailles. Des mesures visant à protéger le sommet des berges peuvent se révéler inefficaces si leur base est affouillée, provoquant des surplombs instables. Les mesures de protection des berges doivent donc concerner celles ci dans leur totalité.

Indigenous knowledge for disaster risk reduction: An African perspective

“…Local people in Nigeria have used indigenous plants to tackle bank and gully erosions. Abam ( 1993 ) carried out a study in the Niger Delta region of Nigeria, which led to the knowledge that river banks, where bamboo plants and raffia palms had been planted by local people, prevented the washing away of soil which causes bank erosions. These plants serve as current breakers for the water and over time, strengthen the materials that make up the river banks.…”

“…The application of local methods to solve local problems in the community can be called soft technology. Soft technologies, which in this sense are community-led disaster risk reduction (DRR) approaches, are critical to disaster management at the local level (Abam 1993 ; Domfeh 2007 ). It involves the use of local laws and experiences to alter nature to promote human development and management of the society.…”

Traditional ecological knowledge and flood risk management: A preliminary case study of the Rwenzori

“…Because of their fibrous root, rhizome and extensive leaf systems, (1) they hold soil together and reduce hydraulic conductivity, and (2) their canopies intercept rain water and fibrous roots take-up large quantities of intercepted water and releases it through transpiration. Furthermore, they improve hydrological systems such as the wetlands (these in turn improve the storage of the excess water in the river) – altogether, over time, these indigenous ecological processes strengthen the local riparian biotic and abiotic diversity that make up the riverbanks and hydrological systems and thereby reduce the chances of a flood disaster (Abam 1993 ; Barbedo et al 2014 ; Brody et al 2007 ; Calder & Aylward 2006 ). This would mean that FRM approaches that support planting of the traditional ecological plants and related practices would be most suited to address the impacts and risks posed by floods.…”

Geotechnical, Geological, and Hydrologic Characterization of a 52 km Electrical Power Transmission Line Alignment Route in Southeastern Nigeria

“…g = Acceleration due to gravity. Co = a coefficient with 0.13 Abam and Omuso (1999), carried out a sensitivity analysis of various parameters in the above equation and concluded that the flow velocity is the most important variable followed by the unit weight of water.…”