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VOLTA LAKE

Spillways at Akosombo

Photo: N.B.Ayibotele

A. LOCATION

• Ghana.
• 6:15-9:10N, 0:20-1:40E; 85 m above sea level.

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B. DESCRIPTION

The Volta Lake is a man-made lake created after the River Volta was dammed at the Akosombo gorge. The lake is dendritic in shape and has a generally north- south orientation with an average length and width of 400 km and 25 km respectively. It has a catchment of 385,185 km², excluding its own area of 8,730 km². Nearly 60% of this area lies outside of Ghana. The lake was created to store up water primarily to generate hydro- electricity. Additionally it was envisaged that it would improve inland water transport, boost fishing, ensure enough water for domestic and industrial use and for irrigation, etc. The project was implemented by Impregilo (Italian Civil Engineering Firm) under the supervision of the Volta River Authority of Ghana, at the cost of £ 70 million, and was completed in 1966 (5).

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C. PHYSICAL DIMENSIONS

Surface area [km2]	8,502
Volume [km3]	148
Maximum depth [m]	75
Mean depth [m]	18.8
Water level	Regulated
Normal range of annual water level fluctuation [m]	2-3
Length of shoreline [km]	4,800
Residence time [yr]	4.3
Catchment area [km2]	385,180

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D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL

• Sketch map: Fig. AFR-16-0l.
• Names of main islands: Dodi, Dwarf and Kporve.
• Number of outflowing rivers and channels (name): 1 (Volta R.).

D2 CLIMATIC

• Climatic data at Kete Krachi

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Ann.
Mean temp. [deg C]*1	34.8	36.7	36	34.6	33.2	30.9	29.5	29.7	30.5	32.3	33.8	34.1	33
Precipitation [mm]*2	8	15	58	104	149	199	194	178	229	142	34	11	1,321

*1 1953-1963. *2 1950-1985.

Fig. AFR-16-01
Sketch map of the lake and its drainage area.

• Water temperature [deg C](2)

Ampem, 1974-1975

Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	26.9	27.7	29.0	30.1	27.7	28.4	28.6	27.6	28.0	29.4	29.9	28.5
1	26.8	28.1	29.0	30.1	29.7	28.9	28.4	27.6	28.0	29.3	29.8	28.5
5	26.7	27.9	29.0	29.8	29.6	28.9	27.9	27.6	27.5	29.3	29.8	28.5
10	26.7	28.1	28.7	29.7	29.5	28.7	27.9	26.9	27.2	29.0	29.0	28.5
B*2	26.7	27.5	28.6	29.3	24.2	28.6	27.9	27.3	27.2	28.1	28.2	28.1

*1 Surface. *2 Bottom.

• Freezing period: None.
• Mixing type: Polymictic.

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E. LAKE WATER QUALITY

E1 TRANSPARENCY [m](2)

Kete Krachi, 1968-1969

Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
3.40	-	-	3.00	-	-	2.25	2.30	0.20	0.70	0.95	2.50

E2 pH (2)

Akosombo, 1985-1988

Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*	6.9	7.1	7.1	6.9	7.1	6.9	6.9	6.9	7.1	7.1	7.7	6.9
* Surface.
Ampem, 1974-1975
S	7.5	7.7	8.1	7.7	7.8	7.4	7.2	7.3	7.5	7.7	7.9	7.3
1	7.5	7.6	8.1	7.7	7.8	7.4	7.2	7.3	7.3	7.7	7.9	7.2
5	7.4	7.3	8.1	7.6	7.8	7.3	7.2	7.3	7.2	7.7	7.7	7.2
10	7.3	7.3	7.4	7.45	7.7	7.2	7.15	7.1	7.1	7.4	7.4	7.2
B*	7.2	7.0	7.3	6.95	7.1	7.1	7.15	6.9	7.0	6.9	6.9	7.1

* Bottom.

E3 SS [mg l^-1](3)

Akosombo, 1986

Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*	99	30	23	52	27	70	60	92	23	82	72	85

* Surface.

E4 DO [mg l^-1](1)

Ampem, 1974-1975

Depth Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	5.55	6.5	6.9	6.75	6.7	6.3	5.5	6.2	5.8	6.2	6.6	4.8
1	5.25	6.45	7.2	6.65	6.5	6.2	5.6	6.2	5.7	6.2	6.7	4.7
5	5.25	6.0	7.2	6.45	6.3	5.9	5.3	5.7	4.7	6.2	6.1	4.7
10	5.10	5.7	6.0	5.1	6.1	5.4	4.9	4.8	3.4	5.0	4.8	4.0
B*2	4.25	2.05	5.4	0.55	2.7	3.8	4.3	2.3	2.3	1.1	0.2	0.0

*1 Surface. *2 Bottom.

E7 NITROGEN CONCENTRATION (1)

• NH₄-N [mg l^-1]

Ampem, 1974-1975

Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	.06	.05	.03	.03	.03	.05	.03	.03	.04	.03	.03	.03
1	.06	.05	.03	.03	.03	.05	.03	.03	.04	.03	.03	.03
5	.06	.05	.03	.03	.03	.05	.03	.03	.04	.03	.03	.03
10	.05	.05	.03	.03	.03	.05	.03	.03	.04	.03	.03	.04
B*2	.06	.08	.06	.09	.29	.24	.05	.35	.12	.58	.56	1.22

*1 Surface. *2 Bottom.
Data for NH₄-N only.

E8 PHOSPHORUS CONCENTRATION (2)

• Total-P [mg l^-1]

Adjena, 1969

Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
40	-	.08	.07	.08	.07	.09	.15	.05	.27	-	-	-
45	-	.10	.09	.10	.09	.11	.19	.06	.26	-	-	-
50	-	.12	.11	.13	.10	.14	.23	.07	.34	-	-	-
55	-	.14	.12	.16	.12	.16	.27	.08	.43	-	-	-
60	-	.16	.13	.19	.13	.19	.32	.10	.51	-	-	-
65	-	.18	.15	.21	.15	.21	.36	.11	.60	-	-	-
70	-	.20	.16	.24	.16	.24	.40	.12	.68	-	-	-

E9 CHLORIDE CONCENTRATION [mg l^-1](3)

Akosombo, 1986

Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*	10	11	8	3	8	8	8	9.5	10	14	8	5

* Surface.

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F. BIOLOGICAL FEATURES

1969-1974

F1 FLORA (4)

• Emerged macrophytes
  Cyperus articulatus, C. digitatus, Echinochloa pyramidalis, Typha australis, Polygonum seneyaleus, Ficus congensis.
• Floating macrophytes
  Pistia stratiotes, Azolla africana, Salivinia nymphellula, Lemna paucicostata, Wolffia arrhiza, Spirodela polyrhiza, Wolffiella welwitschii.
• Submerged macrophytes
  Ceratophyllum demersum, C. submersum, Utricularia inflexa, U. reflexa, U. gibba, Vallisneria spiralis, Najas pectinata, N. meiklei, Nitella mucronata, N. microcarpa.
• Phytoplankton
  Actinastrum gracilimum, Ankistrodesmus falcatus, Scenedesmus bijuga, Cryptomonas erosa, Peridinium africanum, Synedra acus, Lyngbya limnetica, Microcystis aeruginosa, Aphanocapsa pulchra, Oscillatoria limosa, O. princeps, Volvox tertus, Pandorina, Glenodinum quadridens, Navicula, Fragillaria crotonensis, Synedra fasciculata.

F2 FAUNA (4)

• Zooplankton
  Anuraeopsis, Polyarthra, Trichocera, Keratella, Filina, Cyclops, Diaptomus, Diaphanosoma, Ceriodaphnia, Bosmina, Moina, Bosminopsis.
• Benthos
  Povilla adusta, Chironomus formosipennis, Amphipsyche, Ecnomus, Bulinus spp., Nilodorum fractilobus.
• Fish
  Pellonula, Tilapia zillii*, T. galiloea*, Oreochromis niloticus*, Chrysicthys velifer*, Lates nilotica*, Synodontis, Labeo, Alestes.
  * Economically important.

F3 PRIMARY PRODUCTION RATE (1)

• Net primary production rate [mg C m^-3 hr^-1]

Ampem, 1975
Depth [m]	NPP
S*	81.4
5	31.4
10	8.4

* Surface

F5 FISHERY PRODUCTS (4)

• Annual fish catch [metric tons] 1980: 40,000.

F6 PAST TRENDS (14)

Date	Annual fishery production [metric tons]
May 1969	37,676
May 1970	24,664
May 1971	26,446
May 1972	24,546

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G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA (Q)

1985
	Area [km2]
Agricultural land Crop field	22,374*

* Data are based on the part of the catchment within Ghana.

• Types of important vegetation (9) Moist semi-deciduous forest, wooded savanna and open grassland.
• Main kinds of crops and cropping systems (9) Guinea corn, millet, maize, rice, yams and tomatoes; Bush fallowing and compound farming are the main cropping systems.
• Levels of fertilizer application on crop fields: Light.
• Trends of change in land use in recent years Pressure on land leading to desertified conditions in NE part of the catchment in Ghana and Burkina Faso. More land being brought under rainfed rice farming.

G3 POPULATION IN THE CATCHMENT AREA* (10)

	Population	Population density [km-2]	Major cities (population)
Urban	268,9		Bolgatanga, Tamale, Sunyani
Rural	5,420,305
Total	5,689,205	36

* In Ghana only.

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H. LAKE UTILIZATION (11)

H1 LAKE UTILIZATION

Source of water (Volta River), navigation and transportation (44,285 passengers/21,066 tons of cargo in 1986), sightseeing and tourism (no. of visitors in 1986: >15,000) and fisheries.

H2 THE LAKE AS WATER RESOURCE

1986
	Use rate [mill. m3 yr-1]
Domestic & industrial	9.312
Irrigation	0.494
Power plant	25,500 [MCM (20.7 MAF) yr-1]

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I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (Q)

I1 ENHANCED SILTATION

• Extent of damage: Not assessed but seems not serious.

I3 EUTROPHICATION

• Nuisance caused by eutrophication Unusual algal bloom: Microcystis aeruginosa.

I4 ACIDIFICATION

• Extent of damage:
  None.

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J. WASTEWATER TREATMENTS

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA (Q)

b) No sources of significant pollution.

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K. IMPROVEMENT WORKS IN THE LAKE (Q)

None.

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L. DEVELOPMENT PLANS (2)

1. Improvement and expansion of the on-lake transport including the construction of an inland port at the lake head at Buipe.
2. Extension of hydro-electric power supply to the northern regions of Ghana - the northern electrification and system reinforcement project.

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M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS (Q)

M1 NATIONAL AND LOCAL LAWS CONCERNED

• Names of the laws (the year of legislation)
  1. Volta River Development Act, Act 46 (1961)
  2. River, Lake and Beach Law (under review), Act 46
  3. Volta River Development Act (1961)(amended in 1962, Act 95)
• Responsible authorities
  1. Volta River Authority
• Main items of control
  1. Water obstruction
  2. Low flow releases downstream of dam
  3. Disease control

M2 INSTITUTIONAL MEASURES (the year of establishment)

1. Volta River Authority, Accra (1961)(monitoring and control)
2. Institute of Aquatic Biology, CSIR, Accra (1965)(monitoring)
3. Volta Basin Research Project, University of Ghana, 1963 (monitoring)

M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES

1. Volta Basin Project Research Institute
2. Institute of Aquatic Biology
3. Water Resources Research Institute

N. SOURCES OF DATA

Questionnaire filled by Dr. N. B. Ayibotele, Director, Water Resources Research Institute, Accra, Ghana.

1. Obeng-Asamoa, E. K. (1977) A limnological survey of the Afram Arm of Volta Lake. Hydrobiologia, 55: 257-264.
2. FAO (1971) Volta Lake Research, Ghana. Physicochemical Conditions of the Lake Volta, Ghana, Based on the Work of CW, Czernim-Chudenitz. SF GHA 10, Technical Report 1.
3. Gordon, C. Unpublished data.
4. Smithsonian Institute (1974) Environmental Aspects of a Large Tropical Reservoir. A Case Study of the Volta Lake, Ghana. A Report for the Office of Science and Technology Agency for International Development. 340 pp. Washington D. C.
5. Obeng, L. (ed.)(1969) Man-made Lakes, Accra Symposium. Ghana Universities Press.
6. Akosombo, V. R. A. Personal communication.
7. Meteorological Services Dept. Personal communication.
8. Atlas Project, CSIR (1985) Crop-Area Maps.
9. Benneh, G. & Dickson, K. A New Geography of Ghana. Longman, London.
10. Ghana Preliminary Census Report (1984).
11. V. R. A. Annual report (1986).
12. V. R. A. Brief on Volta Lake Transport System.
13. Council for Law Reporting (1978) Index to Acts and Statutes.
14. Volta Lake Research Project, UNDP/FAO/Ghana Government (1973) Quarterly Progress Report. Phase II, October-December.

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