RIVER REGIMES

The seasonal variation in the volume of water in a river is known as the regime. A knowledge of the regime of a river is important to man in controlling possible floods, storing up water for irrigation and human consumption, and also in planning hydro-electric production.

The regime of a river will depend on a number of factors, such as the seasonal distribution of precipitation (both snow and rain), the nature of the rocks (whether they are permeable or not), the size of the catchment area (a very large catchment area such as that of the Niger benefit from rainfall occurring in different parts of the basin) and the vegetation cover.

The Niger, which is 4160 km long (2600 miles), passes through nearly all the climate zones of West Africa – from a wet region through a semi-desert into a wet climate again. It rises from Guinea, an area of heavy rainfall, where it is joined by the Niantan, the Milo and the Tinkisso rivers which, apart from the rains of Southern Mali, add to its volume.

The flood-waters of the Niger reach their highest in May- June in this upper course and then flow into Mali, an arid country, where they are spread over the level inland delta and delayed until October when they reach Timbuktu. Much of the flood is lost in the delta through evaporation and use for irrigation.

The slackened floods continue their journey and reach Niger Republic in January when that country is experiencing a dry season, a blessing to the Niger farmers along the banks of the river.

The Niger comes into another region of comparatively heavy seasonal rainfall in Nigeria. Local rains as well as its tributaries particularly the Benue, swell its water. The highest water from the local rains flood- waters that left Guinea in May-June reach Nigeria between February and April the following year.

That is, it takes the flood water about 8-10 months to reach Nigeria from Guinea. The Niger thus experiences a very low water level in Nigeria from April to June/July when local rains will begin to swell its water level again. The Niger has a varied regime.