Estimation of water losses in Ngaciuma-Kinyaritha Sub-catchment, Upper Tana Basin, Kenya
Kirera, Samuel J.M.
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Soil is an important component of a watershed. It is important to understand how soils relate to management; planning and conservation of water resources in the watershed in order to make water availability a reality for both present and future generation. In this regard, there is need to understand soil physical properties together with other components such as biophysical and human environment in order to achieve comprehensive conservation of resources, management and planning of the watershed. Development of soil sampling and analysis programs are crucial for this purposes. It is important in a biologically mega-diverse country that is undergoing rapid human landscape transformation, to understand modes of the water patterns in the sub- catchment. This helps in developing conjunctive water management which controls geomorphology and hydromorphology of Ngaciuma-Kinyaritha sub--catchment. The main objectives of this study were: - (i) To· determine selected soil physical properties of the sub-catchment. (ii)To investigate the losses of water due to poor water abstraction and hydro morphology threats of riparian land. (iii) To investigate the water losses in unlined furrow conveyance system in Ngaciuma-Kinyaritha sub-catchment. Soil sampling was done on any observed colour changes on the land surface and at the crest, at the middle of slopes and valleys which was used for soil texture and soil moisture content analysis. Soil texture analysis was done in the laboratory using mechanical machine and sieves as per United States Department of Agriculture (USDA) standards to determine the precise soil texture. Moisture content was determined in the laboratory using oven dry at 105°C for twenty-four hours. Soil profile was measured in situ using survey leveling staff and tape measure. Direct flow measurement was done using current meter and drop rod to ascertain progressive water losses in canals. Further, the overcrowding of water abstraction structures and their sizes relative to the width of river was determined using tape measure and tabulated estimate threat posed on riparian land. The data were analysed using Excel computer package and results tabulated in tables. Strength, weakness, opportunities and threats (SWOT) tool was used in the analysis of riparian land threats in. the whole sub-catchment. Correlation was performed to examine relationship between soil texture and water losses in the furrow conveyance system and on soil particles distribution and water losses in the furrow conveyance system. The both test proved that correlation is statistically insignificant. The soil texture in the all zones was found to be loamy sand and sandy loam which have high infiltration rate but poor soil consolidation which are susceptible to erosion. Water losses in furrow conveyance system were very high in all zones which are the main source of emerging water conflicts in the watershed. Riparian land is threatened by high concentration of water abstraction structures which has resulted in over trenching of river banks. Also, riparian was further threatened by shamba system, encroachment of wetland and poor waste management among others. Therefore, there is need for holistic conjugative watershed planning, management and conservation in order to make water availability a reality for intergenerational equity in Ngaciurna-Kinyaritha sub-catchment