THE current floods being experienced along the River Benue and River Niger should not be allowed to occur in future. A new operations regime that will ensure safe operations at dams and their associated reservoirs should be put in place for all dams in Nigeria.
Dam owners/operators in Nigeria include the River Basins Development Authorities, RBDAs, PHCN successor companies, State Water Boards/Corporations.
The Federal Ministry of Environment held a round-table meeting with dam owners/operators in Abuja on May 23, 2012 and I addressed the participants at this gathering on the role and responsibilities of dam owners/operators in flood early warning system operations.
Dam owners/operators were told that their primary responsibility was to exercise control over the water behind their dams such that in years of heavy rainfall and for singular rainfall events, water going past the dam does not damage dam infrastructure or create floods.
In the first place, dams should not store water that is not required. One of the problems with dams under the control of the RBDAs is that some of them are designed for electric power generation but the existing law, the River Basins Development Authorities Act, does not include electric power generation in the functions of each Authority.
Thus the budgets of the RBDAs cannot include funds for power generation and distribution. Besides amendments to the law to permit RBDAs to generate and distribute electricity, procedures for safe operations of dams such that floods are not inflicted on interests and communities downstream of dams should also be specified in the law.
Communities downstream of a dam should be allowed by law to jointly monitor water levels behind the dam with the RBDA.
The release of water from Lagdo Dam on the River Benue in Cameroon leads to floods each year along the River Benue, both in Cameroon and in Nigeria. Again, it is emphasized that water which is not required should not be stored behind a dam.
The Cameroonian authorities should be approached to lower the critical operating water level in the Lagdo dam by 8m from 216m above sea level to 208m above sea level. With respect to Kainji Dam, PHCN has been operating this dam for over 40 years and PHCN should by now have a good hydrological model for operations at the dam.
Water entering Kainji Lake takes an average of 76 days before going past the dam. Some of the water reaching Kainji Lake takes about six months to arrive at the lake from Guinea. It should be possible to plan water release from Kainji Lake such that there are no significant floods in areas downstream of the dam.
The floods that occurred along the River Ogun in Lagos State and Ogun State during 2007, 2010 and 2011 should also not be allowed to occur again.
The Ogun-Oshun River Basin Development Authority should lower the critical operating water level at Oyan Dam by 4m from 63m above sea level to 59m above sea level. Gates should also be provided at the Ikere Gorge Dam on the River Ogun as this will lead to better control of water releases into the main channel of the River Ogun.
An assessment of flood risk along the River Ogun in Lagos State and Ogun State shows that water release from Oyan Dam in the region of 10,000 million litres per day leads to the formation of a lake on the river between Magbon and Hate, that is between latitude 6Â°49’30Ã¢â‚¬Â³ N and 6Â°48’00Ã¢â‚¬Â³ N. A second channel takes off from this lake to the east of the main channel of the River Ogun and this channel carries water directly to the concrete viaduct on the Lagos to Ibadan Expressway at latitude 6Â°40’00Ã¢â‚¬Â³, then onwards into River Owuru which flows into Majidun Creek which discharges the water into the Lagos Lagoon.
The flood path from the main channel of River Ogun and the lake covers parts of Ogun State and Lagos State; it is over 27km long and it is up to 4km wide in places. It is, therefore, necessary to plug the second channel and other channels along the River Ogun through appropriate embankment construction.
Flood control studies should be carried out from Oyan Dam to Lagos Lagoon which studies will assess the needs of communities along the River Ogun, especially Abeokuta metropolitan area.