(after Entz, 1984)
| LAKE KOSSOU | ||
| Geography | ||
| Country | Ivory Coast | |
| Latitude | 7° – 8°N | |
| Longitude | 5°25' – 5°45'W | |
| Altitude m a.s.l. | 206 | FAO/UNDP, 1976 |
| Vegetation-type | Forest and Guinean savannah | Balon and Coche, 1974 |
| Meteorology | ||
| Climate type (acc. to Köppen) | Amw - Aw | |
| Ambient temp. range (°C) | 13.0 – 40.0 | Balon and Coche, 1974 |
| Mean (ambient) values (°C) | 26.3 21.1 – 31.3 | Balon and Coche, 1974 Balon and Coche, 1974 |
| Rainfall (mm yr-1) | 1 150 – 1 400 846 | Balon and Coche, 1974 Kassoum, 1977 |
| Rainfall (km3) (m3/sec) | 204 (64.6) 1.43 | Balon and Coche, 1974 Balon and Coche, 1974 Kassoum, 1977 |
| Gross evaporation (mm) | 1 500 1 017 | Balon and Coche, 1974 Kassoum, 1977 |
| Evaporation (km3) | 2.4 .73 | Balon and Coche, 1974 Kassoum, 1977 |
| Humidity % | ||
| hydrology | ||
| Main river | White Bandama | |
| Other rivers | ||
| Catchment area above dam (km2) | 33 000 32 400 | Welcomme, 1972 Balon and Coche, 1974 |
| Range of annual inflow (km3) | 1.7 – 10.5 | Bazigos, 1971 |
| Range of annual inflow (m3/sec) | 5 – 525 55 – 334 | Iltis and Levêque, 1982 Bazigos, 1971 |
| Mean inflow (km3 yr-1) | 5.4 5.68 | Bazigos, 1971 Ita, 1979 |
| Max-min inflow (m3/sec) | 2 680 - 0 57 – 320 | Bazigos, 1971 Ita, 1979 |
| Mean inflow (m3/sec) | 171 179 | Bazigos, 1971 Ita, 1979 |
| Annual outflow range (km3) (m3/sec) | ||
| Mean outflow (km3) (m3/sec) | ||
| Max outflow (km3) (m3/sec) | (2 300) 72.6 | |
| River flow ratio min:max | Min. flow = nil 1:5.6 | Ita, 1979 |
| Outflow (yr-1): lake volume | 1:5.2 1:5 1:4.5 | Balon and Coche, 1974 Marshall, 1984a FAO/UNDP, 1976 |
| River flood season | Sept - Oct | Balon and Coche, 1974 |
| Suspended solids (mg/l) | ||
| Displacement time (years) | 5 | |
| Location of the dam | Kossou | |
| Length of the dam | 1 500 m | |
| Volume of the dam (m3) | 5.35 × 106 | |
| Dam closed | February 1971 | |
| Hydro-electric power (installed in MW) | 175 | Bazigos, 1979 |
| Working lake level reached | Not yet reached (1983) | |
| Main reasons for dam construction | Production of hydro-electric power | |
| Dam impacts | Power production during long drought endangered. Lake fisheries developed. Spread of water-borne diseases. Difficulties of resettlement. | |
| Start and termination of FAO project | May 1971 - Sep 1975 | |
| Purpose of the project | To place the multiple-use of the new water resource on a sound scientific and technical base. | |
| Main objectives | Fisheries, aquaculture | |
| Morphometry | ||
| Length max (km) | 180 170 | Balon and Coche, 1974 Welcomme, 1972 |
| Length mean (km) | ||
| Length min km) | ||
| Width max (km) | 30 | Welcomme, 1972 |
| Width mean (km) | 8.9 | |
| Surface area max (km2) | 1 600 1 855 | Welcomme, 1972 FAO/UNDP, 1976 |
| Surface area mean (km2) | 1 625 | FAO/UNDP, 1976 |
| Volume max (km3) | 29.5 | Balon and Coche, 1974 |
| Volume mean (km3) | ||
| Dead storage (km3) | ||
| Depth max (m) | 60 54 35 | Welcomme, 1972 Balon and Coche, 1974 Kassoum, 1977 |
| Depth mean (m) | 14.3 18.4 | Welcomme, 1972 Balon and Coche, 1974 |
| Shoreline length (km) | 3 500 | Welcomme, 1972 |
| Shoreline development | 247 | Marshall, 1984 |
| Hydrology | ||
| Water level max (m) | 206 | Balon and Coche, 1974 |
| Water level mean (m) | 204 | Balon and Coche, 1974 |
| Water level min (m) | ||
| Annual water level fluctuation (m) | 3 2 – 3 | Welcomme, 1972 Kassoum, 1977 |
| Mean water level before dam (m) | ||
| Water exchange ratio | 1:5 2 | Balon and Coche, 1974 |
| Sections of reservoirs with: | ||
Riverine conditions | ||
Semi-riverine conditions | Northern part | |
Lacustrine conditions | Southern part | |
| Water Physics | ||
| Annual mean temp at surface (°C) | 28 | Kassoum, 1977 |
| Mean temp of whole water column (°C) | Apr-May 28.5 Jul-Aug 27.3 Sep-Oct 27.7 Dec-Jan 27.2 | |
| Surface temp range (°C) | 23.8 – 34.1 | Balon and Coche, 1974 |
| Bottom temp range (°C) | 26 – 27 | Kassoum, 1977 |
| Surface temp summer range or mean (°C) | 26 – 28 | Kassoum, 1977 |
| Annual variation of surface temp (°C) | Apr-May 30–32 Jul-Aug 27–28 Sep-Oct 29–30 Dec-Jan 26–27.5 | |
| Surface temp winter range or mean (°C) | 28 – 29 | Kassoum, 1977 |
| Type of mixing | Warm dimictic | |
| Period(s) of homothermy | Dec-Feb + Jul-Sep | Balon and Coche, 1974 |
| Homothermic at (°C) | 27 | Balon and Coche, 1974 |
| Periods of thermal stratification | Mar-Jun; Oct-Nov No strong stratification | Balon and Coche, 1974 |
| Location of metalimnion (m) | 5 – 10 | Balon and Coche, 1974 |
| Temperature of metalimnion (°C) | 27 | |
| Depth of euphotic zone (m) | 3 – 6 | Kassoum, 1977 |
| Secchi disc transparency (cm) | 20 – 300 10 – 300 155 (mean) | Kassoum, 1977 Balon and Coche, 1974 |
| Transparency (annual cycle) | Mar 160–200 cm Jul 80–160 cm Oct 120–210 cm Dec 60–190 cm | Kassoum, 1977 |
| Global radiation | Approx. 400 cal/cm2/day | |
| Water chemistry | ||
| pH | 6.8 – 9.0 | Balon and Coche, 1974 |
| Conductivity range (μS cm-1) | 35 – 50 (river inflow) 36 – 128 90 – 200 35 – 95 | FAO/UNDP, 1976 Balon and Coche, 1974 Marshall, 1984 FAO/UNDP, 1976 |
| Conductivity mean (μS cm-1) | Approx. 75 – 80 Surface 72 Bottom 108 Increasing from N to S | Marshall, 1984 |
| Total dissolved solids (TDS) | ||
| Morpho-edaphic Index (MEI) | ||
| Suspended solids | ||
| Dissolved O2 at surface (mg/l) range | 1 – 10 0.2 – 0.4 (Jul) 2 – 9 | Balon and Coche, 1974 Iltis and Levêque, 1982 Kassoum, 1977 |
| Dissolved O2 at bottom | Below 10 – 20 m; 0 mg/l 0 mg/l at stratification | Kassoum, 1977 FAO/UNDP, 1976 |
| Surface dissolved O2 annual variation (mg/l) | Apr-May 5–8 Jul-Aug 3–6 Sep-Oct 4–8 Dec-Jan 2–6 | |
| O2 present at homothermy (m) | 15 – 20 | |
| O2 present during stratification (m) | 5 – 16 | |
| H2S conditions | Decreasing in hypolimnion since 1973 0.1 – 0.5 mg/l on the bottom max 2.0 mg/l | FAO/UNDP, 1976 Kassoum, 1977 Kassoum, 1977 |
| Oxygen stratification | Oct-Nov and Mar-Jun | Balon and Coche, 1974 |
| Typology of water (acc. to Maucha) | Ca-Mg-HCO3 | |
| Na (mg/l) (meq/l) | 4.6 5.8 – 6.4 Bandama 5 – 5.3 | Marshall, 1984 |
| K (mg/l) (meq/l) | 3.52 1.6 – 2.5 Bandama 2.3 – 2.5 | Marshall, 1984 |
| Ca (mg/l) (meq/l) | 11.22 4.4 – 5.0 Bandama 4.6 – 4.7 | Marshall, 1984 |
| Mg (mg/l) (meq/l) | 4.01 Bandama 2.0 – 2.2 | |
| Ca + Mg : Na + K | 1.87 | |
| HCO3 (mg/l) (meq/l) | 57.96 24 – 36 18.6 Bandama Confluence 36 – 37 | Kassoum, 1977 Marshall, 1984 Nicolas, 1972 |
| CO3 (mg/l) (meq/l) | ||
| Cl (mg/l) (meq/l) | 2.13 1.0 – 35 Bandama 4.6 | Marshall, 1984 |
| SO4 (mg/l) (meq/l) | 9.12 0.2 – 1.0 Bandama 0 – 0.26 | Marshall, 1984 |
| P total (mg/l) | ||
| PO4 (mg/l) | 0.2 – 0.8 | Iltis and Levêque, 1982 |
| PO4-P (mg/l) | (0.66) | Kassoum, 1977 |
| NO2 (mg/l) | ||
| NO3 (mg/l) | ||
| NO3-N (mg/l) | (0.32) | Kassoum, 1977 |
| Mn (mg/l) | 1.6 | |
| Fe (mg/l) | 1.4 | |
| Cu (mg/l) | 0.4 Bandama 15.9 – 16.7 | Iltis and Levêque, 1982 |
| SiO2 (mg/l) | ||
| NH3 | ||
| Salinity | ||
| CaCO3 alkalinity (mg/l) | ||
| Limnobiology | ||
| Lake phase at present | Filling phase | |
| Trophic grade | Oligotrophic | |
| Chlorophyll content | 8.4 – 41.3 23.8 (mean) mg/m2 | Kassoum, 1977 Kassoum, 1977 |
| Primary production | Gross: 4.4 g O2/m2/day in wet season 10.0 g O2/m2/day in dry season | |
| Phytoplankton (spp.) | ||
| Periphyton (Aufwuchs) | Important as fish food | |
| Dry weight of Aufwuchs and macrophytes | ||
| Main floating weeds | Pistia stratiotes (only) | |
| Bush clearance | 95 hm2 = 6% | |
| Areas covered by floating weed mats | ||
| Submerged vegetation | ||
| Sudd vegetation | ||
| Emerged vegetation | ||
| Shore vegetation | ||
| Production of macrophytes | ||
| Organisms of the second | ||
| Production level: | ||
Plankton | Rotifers diminish Copepods increase | |
Benthos | ||
Zoobiomass data | ||
| Fishes and fisheries | ||
| Number of fish species known | 83 | FAO/UNDP, 1976 |
| Most important species (max length in cm) | First: Labeo coubie, Alestes baremose later: tilapias | FAO/UNDP, 1976 |
| Introduced species | ||
| Herbivores | ||
| Plankton feeders | ||
| Omnivores | Increasing | FAO/UNDP, 1976 |
| Invertebrate predators | Decreasing (e.g. Clariidae) | |
| Fish predators | Decreasing (but Lates nil. increase) | |
| Clupeids | Pellonula afzeliusi (present) | |
| Changes in species or groups important for fisheries | 1974: tilapias; Chrysichthys, Distichodus, Labeo spp.; Lates; Alestes spp., Siluridae 1975: same spp. but proportion of tilapias increased from 35 to 40%; Labeo decreased from 15 to 7% | |
| Changes of species or groups in the yield (weight) | ||
| Maximum expected yield | 13 500 t/yr 11 – 16 000 t 40 kg/ha/yr | Gaudet, 1979 FAO/UNDP, 1976 Welcomme, 1972 |
| Possibilities for further yield increase | Cage culture of Heterotis niloticus (already successful) | |
| Catch per unit effort | 1.4 – 6.0 g/m2/h (max 10g/m2/h) Pellonula 25 g/m2/h; 17 – 300 g/m2/day | |
| Changes in CPUE | Highest in the north Decreasing: Confluence →dam | |
| Seasonal changes in the catch | ||
| Total fish landings in tons | 1972: 5 680 1973: 4 905 1974: 7 355 1975: 8 000 | FAO/UNDP, 1976 |
| Mean distance between fish landing places | 3.18 km | FAO/UNDP, 1976 |
| Landings of introduced species | Oreochromis niloticus Heterotis niloticus | |
| Landings of fish (kg/ha/yr) | 1972: 109 1973: 84 1974: 106 | FAO/UNDP, 1976 |
| Ichthyomass (kg/ha) | ||
| Catch in tons/boat/year | ||
| Catch in kgs/boat/day | ||
| Catches on experimental basis | ||
| Catch/fisherman/day | ||
| Catch/fisherman/yr | ||
| Number of fishermen | 1 370 – 3 120 ± 4 000 not more than 3/km2 | FAO/UNDP, 1976 |
| Types of boats | ||
| Number of fishing boats | ± 2 000 | Welcomme, 1972 |
| Main types of nets | Gillnets. Monofilament nets catch about twice as much as multifilament | |
| Useful mesh sizes | 10 – 60 mm | |
| Fresh fish/processed fish landings in different seasons | ||
| Main diseases of the area and changes caused by flooding | Malaria, polyomyelitis and schistosomiasis; danger of spreading of onchocerciasis and trypanosomiasis | Waddy, 1973 |
| Vector organisms | ||
| Number of people resettled | Many problems of resettlement 1 000 000 | Gaudet, 1979 |
| Drawdown agriculture | ||
| Areas with irrigation potential | 3 158 ha 253 000 ha | FAO/UNDP, 1976 |
