THE HYDRODYNAMIC FLUXES OF THE ESCRAVOS AND FORCADOS RIVERS: IMPLICATIONS FOR TRANSPORT AND CIRCULATION PATTERNS OFF THE WESTERN

BY

IBITOLA MAYOWA PHILIPS

MASTER OF SCIENCE PHYSCIAL OCEANOGRAPHY AND APPLICATIONS , FACULTY SCIENCE & TECHHIQUE UNIVERSITY OF ABOMEY CALAVI,COTONOU REPUBLIC OF BENIN

NOVEMBER 2009

1 INTRODUCTIONINTRODUCTION

 The Escravos and estuaires are distributaries of the located in the western Niger Delta Niger River  These river systems are interconnected flowing at an average distance of 129km ending at the Bight of Benin of the where they open and discharge into the Atlantic ocean

 The River estuaries from a complex system where seawater is diluted with freshwater from Escravos River land runoff (Dyer 1997) Forcados River  The dilution process takes place at different mixing level due to many forcing mechanism like tides, tidal currents,currents, waves induced motion Forcados River  The River estuaries had served as navigation route for vessels and commercial activities of oil companies who have their terminal stations Bight of Benin along the River channel Bight of Benin  Due to periodic increase of navigation and commercial activities in the Rivers their water Atlantic ocean fluxes are affected this influencing the hydrodynamics of the River system

2 AIMAIM ANDAND OBJECTIVESOBJECTIVES

 The aim of this work is to evaluate water fluxes in Escravos and Forcados River estuaries

OBJECTIVES ARE:

 To analyse for current velocity and direction offshore western Niger Delta

 To analysis the water circulation from the Conductivity Temperature Depth (CTD) profiles (CTD) profiles

 To investigate the tidal fluxes influence on the river discharge.

3 OCEANOGRAPHIC CONDITIONS OF NIGER DELTA

 Tide

 Tidal current

 Waves

 Longshore current

 Ocean current

4 BATHYMETRIC MAP OF THE STUDY AREA WITH PATTERNS OF PREVAILING OCEANOGRAPHIC FORCES

5 DESCRIPTION OF THE STUDY AREA The Esrcavos River lie at the 5° 35′ 0″ N and 5° 10′ 0″ E and the Forcados River 0 0 0 at 5 18”30 and 6 25” E. The station S2 is located at 5 42 ” 10N and 0 Longitude 4 56’ 40”E offshore the Benin River.

Shallow water depth (15.8m)

Benin River. Escravos River

S2 Forcados River

Bight of Benin

S2 ADCP CTD lines

6 DATA COLLECTION

 ADCP, CTD and River discharge data for one year were extracted from database on shallow current measurement conducted along Nigerian coastline sponsored by Mobil Producing Unlimited in consultation with Evans Hamilton Incorporated (EHI) and the Nigerian Institute for Oceanography and Marine Research, Lagos and University of Calabar, Calabar

 Tidal data for Escravos and Forcados Rivers for one year was extracted from Tidal prediction table obtained from the Nigerian Hydrographic Survey, Apapa, Lagos

7 MATERIALS AND METHODS:  Field measurements were conducted using RD 300 KHz ADCP deployed at a Benin 0 0 River at station S2 (shallow water depth of 15.8m) within 4 56’ 40”E and 5 42’ 10” N near the mouth of Escravos and Forcados Rivers  CTD were done at cross shelf profiles at varying depth between 15m to 70m water

ADCP CTD

8  River discharge measurements was conducted using RD River Grand 600 KHz ADCP

mounted on the side of a boat and transect from bank–to-bank in the Escravos and Forcados Rivers to cover the low and high tide

ADCP

9 DATA ANALYSIS DATA ANALYSIS:  Matlab software was used for analysing the ADCP data acquired at Station S2(Shallow water) for current speed and direction  Win River software was used to view and compute the River discharge data to analyse for average intensity, water speed and velocity magnitude  Excel spread sheet was used to plot the tidal curve.

10 RESULTS Current polar plots for stationS2 (15.8m water depth) between 19 April 2000 and 4 February 2001. Bin 3 is 2. 3 from sea bottom, Bin 13 is 7.3m above the sea bed. Bin22 is 11.8m above the sea bed 0 0 0 30 330 30 330 30 330 60 300 60 300 60 300 2 1.5 1 3 0.5 20 2 15 10 90 1 270 5 90 90 270 270 240 120 240 120 240 120 210 150 210 150 210 150 180 180 180

Bin 3( 2.3m) Bin 13( 7.3m) Bin22(11.8m)

Bin 22 show higher amplitude and long period of oscillation, compared to the Bin3 and Bin13 with a mean velocities of 0.12m/s 11 Temp (° C) Salinity (PSU)

16 21 26 31 36

CruiseConductivity 1, Line 2 Temperature Depth Plot Temperature, Salinity VS Depth CTD Profile at Cruise1, Line2 (April)

0

Name Convention: (day)(month)(line)(site) 10  Homogenous surface layer with temperature 1904201 S (PSU) 20 0 0 1904201 T (°C) ranging from 29 C-30 C

30 1904202 S (PSU)

1904202 T (°C) 40 1904203 S (PSU)  Salinity range of 29PSU 50 1904203 T (°C) to 34.5 PSU within the 1904204 S (PSU) 60 mixed layer 1904204 T (°C) mixed layer

1904205 S (PSU) 70 1904205 T (°C)

80 1904206 S (PSU)  Thermocline is about

1904206 T (°C)

et (m) Depth 20m-30m corresponding 90 20m-30m corresponding 1904207 S (PSU) to the pycnocline 1904207 T (°C)

1904208 S (PSU) 100 1904208 T (°C)

1904209 S (PSU)

1904209 T (°C)

Evans Hamiliton (2001) 12 Temp (° C) Salinity (PSU) 15 20 25 30 35 Conductivity Temperature Depth Plot for Rainy Season

Cruise 2, Line 2 Temperature, Salinity VS Depth CTD Profile at Cruise2, Line2 (July)

0  Homogenous surface layer Name Convention: with temperature ranging (day)(month)(line)(site) 10 from 25 0C-260C 2507201 S (PSU)

2507201 T (°C) 20 2507202 S (PSU) Salinity range of 30 PSU to 2507202 T (°C) 30 34 PSU within the mixed 2507203 S (PSU) layer 2507203 T (°C) 40 2507204 S (PSU) ) m ( 2507204 T (°C) Thermocline is about 28m th50 2507205 S (PSU) p to 40m corresponding to De 2507205 T (°C) the pycnocline 2507206 S (PSU) 60

2507206 T (°C)

2507207 S (PSU) 70 2507207 T (°C)

Evans Hamiliton (2001) 13 Temp (° C) Salinity (PSU) 15 20 25 30 35

Cruise 3, Line 2

Temperature, Salinity VS Depth Conductivity Temperature Depth Plot

0 CTD Profile at Cruise 4 Line 2 (October) Name Convention: 10 (day)(month)(line)(site)

2910201 S (PSU) 20  Homogenous surface 2910201 T (°C) layer with temperature 30 2910202 S (PSU) ranging from 270C-280C 2910202 T (°C)

40 2910203 S (PSU)

2910203 T (°C)  50 Salinity range of 23PSU 2910204 S (PSU) to 34 PSU within the 2910204 T (°C) 60 mixed layer 2910205 S (PSU)

et (m) Depth 70 2910205 T (°C)

2910206 S (PSU)  Thermocline is about 60- 80 2910206 T (°C) 70m deep corresponding

2910207 S (PSU) to the pycnocline

2910207 T (°C)

Evans Hamiliton (2001)

14 Temp (° C) Salinity (PSU) 15 20 25 30 35 Conductivity Temperature Depth Plot

Cruise 4, Line 2 Temperature, Salinity VS Depth CTD Profile at Cruise 4 Line 2 0 (February)

Name Convention:  Homogenous surface layer with (day)(month)(line)(site) 0 10 temperature ranging from 27 C- 0402201 S (PSU) 290C 0402201 T (°C) 20 0402202 S (PSU)

0402202 T (°C) Salinity range of 29.7PSU to 34

30 0402203 S (PSU) PSU within the mixed layer

0402203 T (°C)

0502104 S (PSU) ) 40  Thermocline is about 40m-50m m 0502104 T (°C) ( deep corresponding to the th 0402205 S (PSU) p 50 pycnocline 0402205 T (°C) De

0402206 S (PSU)

60 0402206 T (°C)

0402207 S (PSU)

0402207 T (°C) 70

Evans Hamiliton (2001)

15 Temp (° C) Salinity (PSU) 15 20 25 30 35

Conductivity Temperature Depth Plot

Cruise 5, Line 2 Temperature, Salinity VS Depth CTD Profile at Cruise 4 Line 2 (May)

0  Homogenous surface layer with temperature ranging from 290C- 0 Name Convention: 30 C (day)(month)(line)(site) 10

0805201 S (PSU)  Salinity range of 30PSU to 0805201 T (°C) Salinity range of 30PSU to 20 35PSU within the mixed layer 0805202 S (PSU)

0805202 T (°C) 30 0805203 S (PSU) Thermocline is between 20m- 0805203 T (°C) 40m deep corresponding to the 40 0805204 S (PSU)

) pycnocline m 0805204 T (°C) (

th50 0805205 S (PSU) p

0805205 T (°C) De

60 0805206 S (PSU)

0805206 T (°C)

0805207 S (PSU) 70 0805207 T (°C)

Evans Hamiliton (2001)

16 Escravos River Discharge for rainy season 23/07/2000

height(m) time(hr)

09 35 21 35 1.6 1.4 ) 1.2 m (

ht 1 g 15 45

hei 0.8 0.6 03 02 0.4 0.2

0

03 02 09 35 15 45 21 35

time(hr) Flood Ebb Tidal curve Total Q =12,358.24m3/s Total Q=16,142.98m3/s

17 Escravos River Discharge for dry season 19/12/2000

time(hr) height(m)

1.6 24 08

1.4 12 08 1.2

1

0.8 06 19 height(m) 18 15 0.6

0.4

0.2 0 Tidal Curve

06 19 12 08 18 15 24 08

time(hr)

Ebb tide Flood tide Tidal curve Total Q =9,938.58m3/s Total Q =5893.62m3/s

18 Forcados River Discharge for dry season (22/12/2000)

time(hr) height(m)

12 12

1.6 24 42 1.4

) 1.2 m (

ht 1 g

hei 0.8 05 38 0.6 18 52

0.4

0.2

0

05 38 12 12 18 52 24 42

time(hr) Ebb tide Flood Tidal curve Total Q Total Q =10,427.35m3/s =8,851.79m3/s

19 Forcados River Discharge for rainy season 26/07/2000

time(hr) height(m)

02 06

1.6 14 53

1.4

1.2 ) m ( 1 ht g 0.8 hei 20 36 0.6 08 43 0.4

0.2

0

02 06 08 43 14 53 20 36

time(m)

Flood tide Ebb tide Tidal curve Total Q Total Q=10,513.48m3/s =10,421.38m3/s

20 SUMMARY OF FINDINGS

 The near surface currents observed offshore in the western Niger Delta shows that long period of oscillating current was observed at Bin 22 (11.8m) when

compared to other Bin 3 and Bin 7

 The variation in the mixing level observed from the CTD plot show that the river discharge and tidal currents are forcing mechanism controlling the estuary circulation.

 The evaluation of the Escravos and Forcaodos water fluxes show that river discharge during rainy season has higher value compared to that of Dry season discharge during rainy season has higher value compared to that of Dry season

21 CONCLUSION

 The results from the study shows that the current offshore are observed to be moving parallel direction to the coastline . While the river discharge and tidal generated current mixes the river estuaries progressive toward the offshore.

 Thus, the understanding of the dynamics of along shelf current and tidal current can be used to trace the path of the water transport, dispersal, deposition of pollutants, sediments and nutrients across and offshore the rivers.

22  THANKSTHANKS FORFOR LISTENINGLISTENING

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