Morphological Structure and the Anthropogenic Dynamics in the Lake Naivasha Drainage Basin and its Implications to Water Flows. | DAAD Alumni Summer School 2005 - Topics of Integrated Watershed Management, Proceedings.

Throughout its length, the Kenyan Rift Valley is characterized by Quaternary volcanoes. At Lake Naivasha drainage basin, the Eburru (2830m) and Olkaria (2434m) volcanic complexes and Kipipiri (3349m), Il Kinangop (3906m) and Longonot (2777m) volcanoes mark the terrain. Remote sensing data and field survey were used to make morphostructural maps and to determine the structural control and the land use impacts on the drainage systems in the basin. Lake Naivasha is located at the southern part of the highest part of Kenya’s Rift Valley floor in a trough marked to the south and north by Quaternary normal faults and extensional fractures striking in a N18°W direction. The structure of the rift floor influences the axial geometry and the surface process. Simiyu and Keller (2001) interpret the rift floor structure as due to thickening related to the pre-rift crustal type and modification by magmatic processes. The rift marginal escarpments of Sattima and Mau form the main watershed areas. From the marginal escarpments the Rift Valley is formed by a series of down-stepped fault scraps. These influence the nature of the soils and the rainfall regime. The drainage is also influenced by the fault trends. At the Malewa fault line for example the drainage is south-easterly influenced by the trend of the Malewa fault line (Thompson and Dodson, 1963). The morphotectonic control on the drainage has implications on ground water recharge in the Naivasha basin. This may also influence the spring water supply and geothermal reservoirs. The nature of the terrain, human development processes and their impact on the lake was visualized using Landsat TM satellite data (path 169/Raw 060) from three dates (28/1/1986 L5, 1/3/1989 L4 and March 2000 L5) and a mosaic of the data based on satellite data of various dates from 1989. The image data was compared with elevation models of the terrain and the normalized difference vegetation index (NDVI) data.

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