Catchment hydrology
Lake Naivasha is a “lake on the edge” situated between fertile upland soils and lowland drylands. The eastern portion of its basin (Wanjohi and Turasha sub-basins) comprises well-watered highlands draining the Nyandarwa Range, one of the 5 Water Towers. Western and southern portions are covered in lowland dry savannah grasslands and have no permanent river. This great difference between different parts of the basin, and the fact that precipitation is dominated by monsoonal rains, contribute to great local climate instability in the Lake Naivasha Basin.
The name “Naivasha” derives from the Maasai “enaiposha” meaning “moving waters”, which refers to the rapidly changing water levels that characterise the lake. Lake Naivasha has been completely dry sometime between 200 and 150 years ago, but then reached very high water levels at the beginning of the last century.
Only the Malewa River flows permanently into the lake, carrying the drainage of the Nyandarwa Range. The Gilgil River instead, coming from the Bahati Highlands, tends to dry out during the dry season. The Karati River comes from the Southeast and flows only during rain events. The Marmanet River drains the lower western slopes of the Eburu Highlands and disappears underground around Ndabibi, before reaching the lakeshore.
Farmers (mostly small-scale) living in the upper catchment, flower farmers around the lake and Naivasha Town residents use most of the water resources available in the Basin. A small amount of water is diverted towards Nakuru, while some water is utilised for generating steam in Olkaria Geothermal Power Plant.
Lake Naivasha has no surface outlets, but has underground outflow in the South and in the Northwest. The exit of water carries away also salts and allows Naivasha to persist as a freshwater lake. Rift valley lakes with no outflow, such as Nakuru, Bogoria, Elementeita, Magadi and Natron, are salty “soda lakes”.
The Lake Naivasha Basin (Catchment). The dotted yellow line represents the limit of the catchment (= the surface receiving all the rainfall that will eventually drain into the lake).
