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.
8-637: The Malewa River catchment of 1,730 square kilometres (670 sq mi) 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 3,700 metres (12,100 ft) in the Nyandarua (Aberdare) mountains. Its tributary the Wanjohi is fed by several small rivers running from
16-429: Is 60 kilometres (37 mi) and maximum drop is 873 metres (2,864 ft). Just north of the lake, the river opens into a broad floodplain, through which channels have been dug to support irrigated farming. The river's inlet to Lake Naivasha is cloaked with Papyrus, other sedges and Typha. The Gilgil and the much larger Malewa are the main sources of water for Lake Naivasha. Both carry large amounts of sediment into
24-470: Is common and poverty is widespread. Improvements to resource management practices could cause major improvements in reducing pollution and erosion. Gilgil River The Gilgil River drains part of the floor of the Great Rift Valley, Kenya and the plateau to the east of the valley, flowing from the north into Lake Naivasha . The river runs to the east of the town of Gilgil , which is on
32-425: Is towards more intensive cultivation of food crops and cash crops. The river is threatened by deforestation and siltation, increasing diversion of water for irrigation, and pollution by fertilizers and pesticides. In August 1997 sediment-laden plumes of Malewa river water extended about 500 metres (1,600 ft) into Lake Naivasha. Access to natural resources and markets is not equitable in the region. Water conflict
40-642: The height of land between the Lake Naivasha and Lake Elmenteita basins. The river has its origins above 2,500 metres (8,200 ft), where rainfall is around 1,100 millimetres (43 in) annually. It has water year round. The Gilgil has three main headwaters. The Morindati rises at 2,700 metres (8,900 ft), the Kiriundu at 2,710 metres (8,890 ft) and the Little Gilgil at 2,400 metres (7,900 ft). The maximum horizontal channel length
48-582: The rocks. Sulphate in the water comes from the atmosphere. The floor of the Rift Valley gets just 600 millimetres (24 in) 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. The Malewa River is fed by streams that run through the Kinangop Plateau . At one time the plateau
56-531: 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 1,200 millimetres (47 in) 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
64-416: Was almost completely covered in tussocky grassland with very few trees. The stream valleys had many tussocky bogs. The plateau has been settled by Kikuyu farmers since the 1960s. They have ploughed much of the land to grow maize, wheat, cabbage and potatoes. The wetlands have mostly been drained. Where drainage has not been deliberate, the trees planted for poles and firewood have absorbed the water. The trend
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