Japheth O. Onyando

The Effects of Groundwater and Surface Water Use on Total Water Availability and Implications for Water Management: The Case of Lake Naivasha, Kenya

This study discusses the effects of water abstractions from two alternative sources on the available water volume around Lake Naivasha, Kenya: the lake itself and a connected aquifer. An estimation of the water abstraction pattern for the period 1999–2010 is made and its effect on the available water volume in Lake Naivasha and its connected aquifer is evaluated using a simple water balance modeling approach. This study shows that accurate estimates of annual volume changes of Lake Naivasha can be made using a simple monthly water balance approach that takes into account the exchange of water between the lake and its connected aquifer. The amount of water that is used for irrigation in the area around Lake Naivasha has a substantial adverse effect on the availability of water. Simulation results of our simple water balance model suggests that abstractions from groundwater affect the lake volume less than direct abstractions from the lake. Groundwater volumes, in contrast, are much more affected by groundwater abstractions and therefore lead to much lower groundwater levels. Moreover, when groundwater is used instead of surface water, evaporation losses from the lake are potentially higher due to a larger lake surface area. If that would be the case then the overall water availability in the area is more strongly affected by the abstraction of groundwater than by the abstraction of surface water. Therefore water managers should be cautious when using lake levels as the only indicator of water availability for restricting water abstractions.

Evaluation of Plant Growth on Expanded Black Cotton Soil

In aggregate hydroponics, the suitability of a particular medium is often guided by its physical properties. However these may not provide adequate evaluation. By growing a crop, the growth characteristics can also be used to guide medium preparation and selection. Tomatoes ( Anna F1 variety) were grown in containers under a greenhouse and provided with equal amount of nutrient solution. The expanded black cotton soil was prepared by mixing with rice husk at a ratio of 90:10, fired at 750 o C for 30 minutes and size reduced to various textures. The crops planted in the expanded clay aggregates performed better than the black cotton soil both in terms of stem elongation and enlargement due to improved drainage, nutrient flow and aeration conditions. The root length density was 25654 m m -3 in black cotton soil, being the highest and lowest in the coarse aggregates which had 9433 m m -3 .

Chapter 5 – Climate

Climatic characteristics, factors influencing them and effects on agro-climatic zonation and crop productions is discussed. It is recognized that climate plays a key role in agricultural production which is the mainstay of the Kenyan economy. Factors influencing climatic characteristics are notably latitude, altitude, characteristics of prevailing winds, distance from water body, topography, vegetal cover and pressure belts. Air masses, their sources and influence on dry and rainy seasons for various regions of the country are described. Rainfall and temperature distribution in various parts of the country are observed to have significant influence on agricultural practices. Variations in rainfall and temperatures are attributed to differences in characteristics that influence these climate variables. Subsequently, seven climatic regions are identified as residing in various sections of the country. Based on rainfall and temperature which determine moisture availability and evaporation rates, distinct agro-climatic zones are have been established and which play a significant role in determining appropriate land use practices for various regions of the country as well as serving as a tool for assessing suitable crops to be grown in these distinct zones. The effects of climate extremes resulting into natural disasters like floods and droughts are further discussed and strategies for their management proposed to minimize their effects on agricultural production. The role of meteorological network in monitoring weather information is noted to be important for predicting weather related disasters.