CHAPTERCHAPTERCHAPTER 111 BACKGROUNDBACKGROUNDBACKGROUND OFOFOF THETHETHE PROJECTPROJECTPROJECT Figure 1-3 Locations of Weather Station (left) and Annual Rainfall Distribution (right) Table 1-2 Observation Periods of Collected Data of Each Weather Station Name of the Elevations Annual Rainfall (mm) Period Weather Stations (m) Katimok 2,286 1415 1983-2009 Kabarnet 2,042 1340 1995-2005 Nakuru 1,901 967 1995-2010 Barwasa 1,676 884 1983-2010 Snake farm 975 755 1984-2010 Nginyang 914 541 1983-1996 Kapedo 762 497 1983-2000 Monthly Rainfall 275 Katimok 250 Kabarunet 225 Nakuru 200 Barwesa Snake Farm 175 Nginyang 150 Kapedo 125 100 75 Rainfall (mm/month) 50 25 0 1 2 3 4 5 6 7 8 9101112 Month Figure 1-4 Monthly Rainfall Variation in the Project Area These Figures and Table show the following tendencies: · Monthly rainfall is larger from April to August, and smaller from December to February. · Rainy season starts in March. · November has a little bit larger rainfall than October. · Annual rainfall in the highland area is larger than in the lowland area, which means that annual rainfall in Tugen Hills is larger than those in lowland areas such as Marigat and Chemolingot. · Southern sub-basins have larger annual rainfall than the northern sub-basins in the project area. b. Air Temperature Monthly averages of daily maximum and minimum air temperature at Nakuru Weather Station are as shown in Figure 1-5. The observation period of collected data is from 1996 to 2009. The data shows that 1-5 CHAPTERCHAPTERCHAPTER 111 BACKGROUNDBACKGROUNDBACKGROUND OFOFOF THETHETHE PROJECTPROJECTPROJECT annual average of daily maximum air temperature is 26°C, and annual average of daily minimum air temperature is 12°C. Monthly change of daily maximum air temperature is higher in January to March and lower in July, and monthly change of daily minimum temperature is higher in April to May and lower in December to February. However, the difference among the air temperatures is small. 35 Daily Maximum 30 Daily Minimum 25 20 15 10 Temperature (℃) Temperature 5 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 1-5 Monthly Change of Daily Maximum and Minimum Air Temperature c. Sunshine Hours Monthly averages of daily sunshine hours at Nakuru Weather Station are as shown in Figure 1-6. The observation period of collected data is from 1996 to 2009. The data shows that annual average of daily sunshine hours is about 7.5 hours, and the months from December to March and May to September have longer sunshine hours (more than 7 hours). On the other hand, sunshine hours are less than 6 hours in November. It should be noted that there are many months with no observation data. Sunshine Hours 10 9 8 7 6 5 4 3 Daily Sunshine Hours Sunshine Daily 2 1 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 1-6 Monthly Change of Sunshine Hours d. Wind Speed 1-6 CHAPTERCHAPTERCHAPTER 111 BACKGROUNDBACKGROUNDBACKGROUND OFOFOF THETHETHE PROJECTPROJECTPROJECT Monthly averages of daily wind speed at Nakuru Weather Station are as shown in Figure 1-7. The observation period of collected data is from 1996 to 2009. The data shows that annual average of wind speed is about 3.1 m/sec. Wind speed is higher from December to May; however, the difference is small and wind speed is slow throughout the year. Wind Speed 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Wind Wind Speed (m/sec) 0.5 0.0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 1-7 Monthly Change of Wind Speed 1-2-2 Topography Kenya is located at the east coast of the African Continent and the equator crosses the country. It has a variety in topographical features such as glaciated high mountains, the Great Rift Valley abundant in faults and volcanoes, hilly highland, plain dessert and coastal landform. The project area is located in Elgeyoescarpment Uasin Gishu highland Uasin Gishu the Great Rift Valley. East Pokot Figure 1-8 shows the boundary and lowland topography of the project area. The topographical characteristics of the area are Kerio lowland escarpment Laikipia governed by the Great Rift Valley System which extends to the north–south direction, and Tugen hills the distinctive features are classified to Marigat highland areas and low-lying areas. The lowland highlands are the Mochongai (Laikipia) escarpments, the Tugen hills (Kamasia block), the Elgeyo escarpments and the Uasin Gishu highland from east to west of the project area. Figure 1-8 Topography of the Project Area 1-7 CHAPTERCHAPTERCHAPTER 111 BACKGROUNDBACKGROUNDBACKGROUND OFOFOF THETHETHE PROJECTPROJECTPROJECT Low-lying areas such as Marigat lowland, East Pokot lowland and Kerio lowland lie among them. One of the other characteristics is the existence of lakes: Lake Bogoria is located at south of Marigat lowland, and Lake Baringo is in the Marigat lowland. Both lakes are located at the lowest part of each internal drainage basin. Another characteristic is the existence of newly formed volcanoes such as Korosi, Paka and Silali in the East Pokot lowland. These three volcanoes were formed in Quaternary Era, and are expected for geothermal exploitation. 1-2-3 Geology (1) Geology of Kenya The geology of Kenya consists of Pre-Cambrian, Paleozoic, Mesozoic and Cenozoic rocks and sediments. The geology of Pre-Cambrian belongs to the Mozambique belt. It covers large parts of central and west Kenya, and some of northeast Kenya. The Mozambique belt falls generally into three systems called as the Nyanzian-Kavirondian system, Basement system and Bukoban system from the old system in order. Among these, the Basement system occupies a large portion of Pre-Cambrian in Kenya. The Basement system was thought as base rock in Kenya in the past; however, in the second half of 1966, it became apparent that the Basement system was formed in a newer period than the Nyanzian and Kavirondian systems. Paleozoic and Mesozoic sedimentary rocks are distributed in northeast and southeast areas of Kenya. These consist of two kinds of rock: one is a peculiar terrestrial deposit correlated with the Karoo system formed from late Paleozoic to early Mesozoic, the other is a marine deposit such as limestone and sandstone formed from Jurassic to Cretaceous. The geology of Cenozoic consists of volcanic rocks (mainly distributed in the Great Rift Valley) and sedimentary rocks (distributed in a belt continuing to the coast at the east side and around Lake Turkana). Lithological character of intrusive rocks widely changes from acidic to ultra-basic rocks. Intrusive rocks were main products by igneous activities during pre-synorogenic and synorogenic stages, and the rocks are more or less metamorphosed. On the other hand, there are non-metamorphosed intrusive rocks which formation might be during late synorogenic stage to post synorogenic stage. These intrusive rocks exist as forms of rock sheets, stocks, and dikes. Large scale rock bodies such as batholith were not recognized. Volcanic rocks were formed with movements of the Great Rift Valley, and it began from activities of basalt during Miocene, and it accompanied eruptive activities of nephelinite and carbonatite in Kenya. In addition, at late Miocene, fissure eruptions formed lava plateaus of phonolites, and also formed trachy-welded tuff. Caldera formation with volcanic activities continued even in Quaternary era. 1-8 CHAPTERCHAPTERCHAPTER 111 BACKGROUNDBACKGROUNDBACKGROUND OFOFOF THETHETHE PROJECTPROJECTPROJECT Sedimentary rocks consist of marine sand of Tertiary era and sand/coral reef of Quaternary era at eastside, and lacustrine sediment during late Miocene to Pliocene around Lake Turkana. (Source: METAL MINING AGENCY OF JAPAN, 1984) (2) Geology of the Project Area The geology of the project area consists of: the basement system of Pre-Cambrian; phonolites, trachytes, basalts of Miocene and Pliocene; trachytes, basalts, pyroclastics of Pleistocene; colluvial and flood deposits of Holocene. Figure 1-10 shows the outline of geology of the project area. The project area is almost located in the Great Rift Valley, and the movement formed many faults in north-south and east-west directions. 35°40'0"E 36°0'0"E 36°20'0"E 05 10 20 30 40 km 4 Study Area 1°20'0"N 1°20'0"N Chomolingot ! 1°0'0"N 1°0'0"N Kabartonjo 0°40'0"N 0°40'0"N ! Kabarnet ! Marigat ! 0°20'0"N 0°20'0"N 35°40'0"E 36°0'0"E 36°20'0"E Figure 1-9 Geology of the Project Area 1-9 CHAPTERCHAPTERCHAPTER 111 BACKGROUNDBACKGROUNDBACKGROUND OFOFOF THETHETHE PROJECTPROJECTPROJECT Table 1-3 Stratigraphic Classification of the Project Area Symbol of Geological age Rocks and Sediments facies Geology Cenozoic Colluvial deposits、red soils、lacustrine deposits、and flood deposits; these deposits are distributed in lowland. Red sols along Holocene Kerio river, lacustrine deposits in lowland. Colluvial deposits at Quaternary the end of hilly area, food deposits along rivers. Trachytes, basalts, pyroclastics. Representative rocks are Baringo Pleistocene trachytes and Baringo basalts, and these geologies can be seen at west side of Lake Baringo. Intrusive rocks. Trachytes, phonolites, basalts, and sedimentary rocks interleaved Pliocene in igneous rocks. Representative geology is Kabarnet trachytes, Neogine which can be seen around Kabarnet. Trachytes, phonolites, basalts, and sedimentary rocks interleaved Miocene in igneous rocks. Representative geology is Samburu Basalt, which is widely distributed around Laikipia and Tugen hills. Mozambique belt (Basement system). The source rocks were Pre Cambrian sand, clay and limestone, and those were metamorphosed to gneiss, schist and marble stone. 1-2-4 Hydrogeology (1) Distribution of Springs Existing spring data are provided from the counterpart team, and the locations are as described in the following figures with topological map and rainfall distribution maps.