TITLE:
Impact of Dredging on Coastal Infrastructure: Case Studies from Okrika and Port Harcourt, Niger Delta
AUTHORS:
Tamunoene Kingdom Simeon Abam, Ferdinand Dumbari Giadom, Robert Egwu Otu Iduma
KEYWORDS:
Dredging, Impacts, Coastal Infrastructure, Niger Delta
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.11 No.5,
May
31,
2023
ABSTRACT: Sand
excavations in river beds have compromised the safety of several bridges in
recent years. Large scale sand mining from river beds is now common in the Niger
Delta, due to the necessity of reclaiming land for development purposes and to
meet construction needs in the region. There is currently no regulation as to
where sand can be mined in river channels because of the lack of adequate
understanding of the risks to coastal infrastructure involved with its
abstraction. The phenomenon of bridge Abutment and bank failure induced by
excessive dredging of sand river bed is considered. Two types of instability
were distinguished, one relating to the equilibrium slope of the riverbed and
the other riverbank instability. An empirical relationship in the form Xs = 3Htan(90 - α) has
been developed through analysis, supported by examples that a minimum distance
of 94 m (for sand river beds) from a bridge should be observed for sand
abstraction in order to guaranty the safety of bridge foundation. For clay
riverbeds, slightly shorter minimum distances can be considered safe. The study
further shows that the capacity of sand borrowing in river channels to generate
bank instability is dependent on the composition and stratigraphy beneath the
river bed.