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The Malewa River rises in the western slopes of the Aberdare Range in Kenya and flows south and west into Lake Naivasha in the Great Rift Valley. Lake Naivasha is an important source of water in a semi-arid environment, and supports export-oriented horticulture and floriculture businesses as well as tourism. Malewa River water quality has deteriorated because of more human activities in the upper catchment. Long-term effects of this on the percentage of rainfall getting into Lake Naivasha are not clear. Possibly in low-rainfall years the percentage will drop because of water abstraction, while in high-rainfall years the percentage will go up because of cultivated soils having a lower water-holding capacity and the introduction of more 100% runoff surfaces like tarmac roads and iron sheets, etc. ==Catchment== The Malewa River catchment of provides about 90% of the water flowing into Lake Naivasha, with most of the remainder coming from the Gilgil River. The headwaters of the main channel of the Malewa originate at an elevation of in the Nyandarua (Aberdare) mountains. Its tributary the Wanjohi is fed by several small rivers running from the slopes of the Aberdares. Other tributaries are the Turasha, Simba, Nyairoko and Ol Kalou. The rivers in the Malewa basin are relatively shallow but are all perennial. The Aberdare range receives about of rain annually and has large areas of dense forest. The highlands drained by the Malewa are volcanic and contribute sodium and calcium to the water through chemical weathering of the rocks. Sulphate in the water comes from the atmosphere. The floor of the Rift Valley gets just each year and is mainly covered by scrub, with some bare soil. Rainfall peaks between April and June and again in October and November. Erosion is highest in these months. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Malewa River」の詳細全文を読む スポンサード リンク
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