Impact of Dredging on Coastal Infrastructure: Case Studies from Okrika and Port Harcourt, Niger Delta

Sand excavations in river beds have compromised the safety of several bridges recent years. Large scale sand mining from is now common Niger Delta, due to necessity reclaiming land for development purposes and meet construction needs region. There currently no regulation as where can be mined channels because lack adequate understanding risks coastal infrastructure involved with its abstraction. The phenomenon bridge Abutment bank failure induced by excessive dredging bed considered. Two types instability were distinguished, one relating equilibrium slope riverbed other riverbank instability. An empirical relationship form Xs = 3Htan(90 - α) has been developed through analysis, supported examples that a minimum distance 94 m (for beds) should observed abstraction order guaranty foundation. For clay riverbeds, slightly shorter distances considered safe. study further shows capacity borrowing generate dependent on composition stratigraphy beneath bed.