By Akintola Omigbodun
The River Benue has its origins in the Adamawa Plateau of Northern Cameroon. The Lagdo Dam, a 40m high dam, has been built across the river about 50km upstream of Garoua, a major town on the river in Northern Cameroon. The water releases from this dam has continued to create floods in Cameroon and in Nigeria over the years and the resulting devastation reached all the way to the Niger Delta in Nigeria during 2012. Two major tributaries, River Mayo Kebi and River Faro, join the Benue in Northern Cameroon downstream of the Lagdo Dam.
The Cameroon has an extremely dry north but a very wet high attitude western region. River Katsina-Ala rises in the western region of Cameroon before entering Nigeria, it passes through Katsina-Ala before joining the River Benue about 40km east of Makurdi. The River Donga, which provides up to 20% of the Benue flow, starts in the Adamawa Highlands of Nigeria, adjacent to the Cameroon. The River Donga joins the River Benue at Jibu. The River Taraba also has its origins in the Adamawa Highlands and it joins the River Benue about 20km northeast of Jibu.
The Rivers Katsina Ala, Donga and Taraba drain a part of the western region of Cameroon and an area in Nigeria south of the River Benue. The River Gongola has its origins in Plateau State of Nigeria and it drains an area north of the River Benue before joining the River Benue at Numan.
Essentially, these major rivers just mentioned above contribute to the flow observed in the River Benue at Makurdi. The basic approach for the control of the flooding caused by a river is to provide a dam at some suitable point on the river so as to contain the peak flood waters within the dam reservoir. Water stored in the dam reservoir is released in such a manner as to reduce high flows and increase low flows resulting in a stable flow regime downstream of the dam.
Currently, contracts have been awarded for the construction of dams on the River Donga in the region near Gembu for hydro-electric power generation. When in operation, the hydro-electric power project would stabilise flows on the River Donga.
There is a dam, Kashimbilla Dam, under construction on the River Katsina Ala. This dam should also stabilise flows on the River Katsina Ala if it is properly operated. The Federal Ministry of Water Resources which is responsible for the construction of this dam has not been giving adequate direction for the operations of other dams under its control and hence this dam may not have any significant effect on the River Benue floods.
There have been reports that Cameroon and Nigeria intend to enter into a Memorandum of Understanding with respect to the River Benue basin. The only significant flood control structure in the River Benue basin is the Lagdo Dam. This dam has a substantial hydroelectric power potential of about 700MW, it has an installed capacity of 84MW and only one turbine for 21MW is in use. We have to take a look at the electric power sector in Cameroon such that we understand why the existing installed capacity at Lagdo Dam is under-utilised and why the overall potential for hydropower at Lagdo Dam is not considered in planning for the future.
AES-Sonel is the company responsible for electric power supply to the public in Cameroon. It came into being in 2001 following partial privatisation of the existing company with AES Corporation holding 56% of the equity and the Cameroon Government 44% of the equity. The electric power network consists of a western grid and an eastern grid which are connected together while there is a northern grid which is independent of the other two.
There is surplus power available from the northern grid which is connected to the power station at Lagdo Dam. However, AES Sonel has concentrated on building new power stations in the west and the east and it has concentrated its efforts on optimizing the hydropower obtained from River Sanaga which has existing hydropower schemes at Song Loulou, 384MW, and Edea 264MW.
It is unlikely, in the immediate future, that the hydropower potential at Lagdo Dam would be put to better use. If Lagdo Dam is to serve as a flood control structure, less water would have to be stored in the reservoir behind the dam. The present maximum operating level of the dam, the full supply level, is 216m above sea level. This should be lowered to 208m above sea level and the lowered level should be incorporated into the Memorandum of Understanding between Cameroon and Nigeria.
It should be noted that peak flow in the River Benue at Garoua is usually in the month of September. Average flow observed in the river at Garoua in September is about 1670 cubic metres per second. However a flow of 6130 cubic metres per second was observed in the river at Garoua in August 1948. If such a flow should occur now, the effects would be catastrophic on the Rivers Benue and Niger through to the Niger Delta.