Estuarine and Ocean Circulation Dynamics in the Niger Delta, Nigeria: Implications for Oil Spill and Pollution Management - The Land/Ocean Interactions in the Coastal Zone of West and Central Africa - page 81

Table 2 Summary circulation parameters in Forcados and Brass River Estuaries in the Niger Delta

Total discharge (m 3 /s) Estuary Tidal state Width of estuary along profile (m) Average current speed (m/s)

Forcados Ebb—dry season 3,484.17 1.0 29,571.10

Forcados Flood—dry season 3,557.57 0.75 22,391.73

Forcados Ebb—wet season 3,456.46 0.9 24,225.69

Forcados Flood—wet season 3,591.34 0.6 11,507.43

Brass Ebb—dry season 2,450.25 0.38 2,314.43

Brass Flood—dry season 2,329.46 0.32 9,797.25

Brass Ebb—wet season 2,441.90 0.95 20,637.63

Brass Flood—wet season 2,411.99 0.32 9,669.77

N

Fig. 12 Satellite imagery of part of the Niger Delta showing plumes off Nun, Brass and Sangana estuaries

Across-Shelf Circulation

Records from this ADCP (Fig. 13 ) show several days of
long-period oscillations. Tidal periods are averaged at
0.52 days with oscillation periods of between 13 and
14 days. The semi-diurnal tidal periods (0.5 days) contain
only relatively small amounts of current energy, mostly
confined within the across-shelf (north-south) component
(Fig. 13 ). Most of the energy in the tidal current resides
primarily in the fortnightly and long-period along-shelf
(north-western/south-eastern) component of the current.

The across-shelf circulation is principally driven by tides
and is in phase (north-south) with the tidal cycle. Acoustic
Doppler current profiler (ADCP) station number S2,
installed at a location offshore the Benin Estuary between
19/04/2000 and 04/02/2001 in water depth of 15.8 m lon-
gitude 00456 0 40 00 E and latitude 0542 0 10 00 N, shows the
characteristics of tides and the across-shelf circulation

(Fig. 13 ) (Evan Hamilton Inc 2001 ).