Morphological Characteristics of the Bonny and Cross River (Calabar) Estuaries in Nigeria: Implications for Navigation and Environmental Hazards - The Land/Ocean Interactions in the Coastal Zone of West and Central Africa - page 92

Fig. 7 Navigational chart of Bonny estuary showing several sandbars, sandbanks and other underwater obstructions (from British Admiralty
Chart 3286 1991 )

to drift and run aground. In the Bonny Estuary, surface
current velocity, which ranges between 1.8 and 2.5 m/s had
been recorded while the near bottom ranged between 0.9
and over 1.8 m/s (Table 1 and Fig. 5 ). In the Calabar
estuary, currents can exceed 1.87 m/s (Table 1 and Fig. 6 ).
These very fast currents superimposed on wave breakers
pose navigational hazards to boats and ships.

the estuary mouths and the immediate offshore area. The
large volumes of sediment reaching the coast and the
nearshore zone are worked and shaped by a combination of
waves and tides resulting in banks, shoals and ridges. Many
of these sandbars and shoals are under water during high
tides and hence present navigational problems for vessels.
In the Bonny estuary, the main navigational channel from
the ocean consists of a south-western north-eastern dredged
channel with depths ranging from 10 to 12.5 m. This is the
only navigable channel leading the ports of Port Harcourt,
Onne, Okrika and Bonny. Surrounding this main channel
are sandbars like the Baleur bank towards the east where
depths are less than 3 m, and breaker spit towards the west
where depths are less than 2.5 m (Fig. 7 ). Inside the estuary
are other isolated banks, sandbars and shoals (Fig. 7 ). Also

Sandbars and Shoals

Both the Bonny and the Cross River estuaries are fed by
numerous rivers, creeks and rivulets that carry huge amount
of sediments to the estuary and the nearshore zone. During
low tide and slack tides, plumes of sediments can be seen in