2015, Koech, Richard

In the gravimetric calibration method of water meters, the volume of water that has passed through the equipment under test (EUT) is generally collected into a tank and the quantity (mass) determined by weighing. The mass of water collected is then converted into a volume. This conversion of mass into volume requires knowledge of the water density, which can be estimated, measured directly or determined by other means. The error of measurement of the EUT is determined by comparing the volume recorded by the EUT and the volume collected in the tank. The density of water is, therefore, one of the major causes of measurement uncertainty in laboratory calibration of water meters using the gravimetric method. Water meter calibration facilities commonly use density formulations proposed by the International Standards Organisation (ISO) and the Organisation for International Legal Metrology (OIML). In Australia, additional guidance in water density determination is provided by the National Measurement Institute (NMI). In this study, testing was undertaken using ten positive displacement water meters arranged in series in the test rig to evaluate some of the common water density formulations used in Australia. The effect of these different formulations on the water meter error measurement was determined, as well as the effect on the measurement uncertainties. The results shows that the use of these different density formulations evaluated do not significantly affect the water meter error of measurement or the uncertainty of measurement. There was no apparent correlation between the water meter error and the meter position in the test rig. It was also determined that if the water density was adjusted only for temperature effects, a maximum of 0.05 and 0.15% drift in meter error and measurement uncertainty respectively, can be expected.

2019-02-12, Langat, Philip Kibet, Kumar, Lalit, Koech, Richard, Ghosh, Manoj Kumer

Ecohydrological changes in large rivers of the world result from a long history of human dimensions and climate. The increasing human population, intensified land use, and climate change have led to a decline in the most critical aspect of achieving sustainable development, namely, that of water resources. This study assessed recent hydromorphological characteristics of the tropical Tana River in Kenya using flow duration curve, and geospatial techniques to gain a better understanding of human impacts over the last two decades and their consequences for new development projects. The results show that all extremal peak, low, and mean discharges exhibited significant increasing trends over a period of 17 years. Dam construction represents a 13% reduction of the maximum discharge and a 30% decrease in low flows, while post-regulation hydrological changes indicated an increase of 56 and 40% of high flows and low flows respectively. Dominant flow was observed to be higher for the current decade than the previous decade, representing a rise of the dominant streamflow by 33%. The assessment of four morphologically active sites at the downstream reach showed channel adjustments which support the changes in the flow regimes observed. The channel width increased by 8.7 and 1.9% at two sites but decreased by 31.5 and 16.2% for the other two sites under study during the time period. The results underscore the contribution of other main human modifications, apart from regulation, such as increased water abstraction and inter basin transfer, up-stream land use and anthropogenic climate change to assess the ecohydrological status in this river basin. Such streamflow regime dynamics may have implications on water resource management, riverine environments, and development of new water projects.

2016, Koech, Richard, Pires de Camargo, Antonio, Molle, Bruno, Saretta, Ezequiel, Frizzone, Jose Antonio, Benhu, Gao, Pezzaniti, David

The International Network of Irrigation Testing Laboratories (INITL) undertook a sprinkler intercomparison testing exercise to generate data for an objective comparison of the performances of the different facilities and identify opportunities for further improvements. Three impact sprinklers were tested in four laboratories in accordance with established standards. The plots of flow rate-pressure profiles were found to be consistent, and correlated to those obtained from previous studies. Although there were slight variations in the measured flow rate data, the mean flow rates at each pressure level were the same for the three sprinklers, and the shapes of the radial distribution profiles were similar. The deviations of reconstituted flow rates (from the measured) of at least two tests in each facility were found to exceed the recommended limit. The sprinkler software developed by INITL was found to have a good correlation with a related commercial software program.

2021, Kogo, Benjamin Kipkemboi, Kumar, Lalit, Koech, Richard

The western region of Kenya is experiencing remarkable land changes resulting from population growth and related impacts. The study used remote sensing and GIS techniques to analyze the land use/cover changes in the years 1995, 2001, 2010 and 2017. Multi-spectral Landsat (TM, ETM + and OLI) images were pre-processed and classified using maximum likelihood algorithm in ENVI version 5.4. The overall classification accuracies in all the images were more than 80%. The results revealed major conversions of each land use/land cover type in varying trends and magnitudes. Between 1995 and 2001, there was an increase in built-up areas by 71%, forest cover by 43%, farms by 5%; and decrease in grassland by 47%. By 2017, the built-up areas had increased by 225% and farms by 17%; the forestland, grassland and water reduced by 38, 10 and 11%, respectively. The observed changes are characterized by increased settlements and encroachment of sensitive ecosystems.

2019-11-08, Kogo, Benjamin Kipkemboi, Kumar, Lalit, Koech, Richard, Kariyawasam, Champika S

Climate change and variability are projected to alter the geographic suitability of lands for crop cultivation. In many developing countries, such as Kenya, information on the mean changes in climate is limited. Therefore, in this study, we model the current and future changes in areas suitable for rainfed maize production in the country using a maximum entropy (MaxENT) model. Maize is by far a major staple food crop in Kenya. We used maize occurrence location data and bioclimatic variables for two climatic scenarios-Representative Concentration Pathways (RCP) 4.5 and 8.5 from two general circulation models (HadGEM2-ES and CCSM4) for 2070. The study identified the annual mean temperature, annual precipitation and the mean temperature of the wettest quarter as the major variables that affect the distribution of maize. Simulation results indicate an average increase of unsuitable areas of between 1.9–3.9% and a decrease of moderately suitable areas of 14.6–17.5%. The change in the suitable areas is an increase of between 17–20% and in highly suitable areas of 9.6% under the climatic scenarios. The findings of this study are of utmost importance to the country as they present an opportunity for policy makers to develop appropriate adaptation and mitigation strategies required to sustain maize production under future climates

2019-04, Kogo, Benjamin Kipkemboi, Kumar, Lalit, Koech, Richard

Deforestation poses a threat to sustainability of forest ecosystem services and socio-economic development in many parts of Kenya. Understanding the trend and extent of forest cover changes and the underlying driving forces over time is pertinent for sustainable management of ecosystems. However, in many parts of the country, such information is still somewhat unknown due to limited data availability for multi-temporal analysis. This paper focuses on western Kenya, a major agricultural region of biodiversity and water catchments that are under threat from forest cover dynamics. The study analyses the status of the forests in the region with the aim of determining the areal extent of coverage, trends in forest cover, drivers of change and associated impacts of deforestation. To achieve these objectives, remote sensing techniques were used to undertake supervised classification on Landsat images of 1995, 2001, 2010 and 2017 with classification scheme of forest and non-forest land cover classes. The results of the study showed that the changes in forest cover varied over time and space. There was considerable net gain in forest areas by about 43% between the period 1995–2001, and thereafter, a continuous decrease ending in a 12.5% loss by 2017. Deforestation in the region is caused by a combination of complex factors that include population pressure, politics and failures in implementation of policy. This study determined the forest cover dynamics and driving forces across diversified sub-basins, an approach that had not been used by previous studies in the region. Thus, the findings will provide valuable information for decision making pertaining to integrated land use and catchment management in order to realize the enormous benefits of sustainable forest ecosystems. The information will not only be important to the study area, but equally applicable to similar tropical regions.

2020-11-22, Kogo, Benjamin Kipkemboi, Kumar, Lalit, Koech, Richard

This study examined the impact of land use/cover changes on soil erosion in western Kenya in the years 1995 and 2017. The study used the GIS-based Revised Universal Soil Loss Equation (RUSLE) modelling approach and remote sensing assessment. The results showed that the average soil loss through sheet, rill and inter-rill soil erosion processes was 0.3 t/ha/y and 0.5 t/ha/y, in the years 1995 and 2017, respectively. Of the total soil loss, farms contributed more than 50%, both in 1995 and 2017 followed by grass/shrub (7.9% in 1995 and 11.9% in 2017), forest (16% in 1995 and 11.4% in 2017), and the least in built-up areas. The highest soil erosion rates were observed in farms cleared from forests (0.84 tons/ha) followed by those converted from grass/shrub areas (0.52 tons/ha). The rate of soil erosion was observed to increase with slope due to high velocity and erosivity of the runoff. Areas with high erodibility in the region are found primarily in slopes of more than 30 degrees, especially in Mt. Elgon, Chereng’anyi hills and Elgeyo escarpments. This study forms the first multi-temporal assessment to explore the extent of soil erosion and seeks to provide a useful knowledge base to support decision-makers in developing strategies to mitigate soil erosion for sustainable crop production.

2020-07-20, Islam, Md Aminul, Warwick, Nigel, Koech, Richard, Amin, Md Nurul, Lobry De Bruyn, Lisa

Coastal salinity causes substantial adverse impacts on agricultural productivity and food security. Farmers' choice of salinity adaptation strategies might depend on how they perceive the problem. This research examined rice farmers' perceptions of salinity, adaptation strategies, and its implications for policy initiatives to sustain rice production in the affected coastal areas of Bangladesh. Boro rice growers (n = 109) randomly selected from two coastal sub-districts were interviewed using a semi-structured survey. Awareness of salinity and its increase over the past 20 years was widespread among rice farmers. A high proportion of farmers (90%) perceived the reproductive (e.g. booting, heading, and flowering) stages of the rice plant as the most sensitive to salinity problems. Salinity (ECe) was measured in the farmers' fields and were categorized according to farmers' perceptions and scientific interpretation (e.g. high or low). Farmers perceived a field affected by high salinity at a lower EC reading than the scientific interpretation of the salinity level. Most of the farmers (67%) were undertaking early transplanting and applying irrigation in order to adapt to salinity problems which occur later in rice crop growth during Boro season. Thus, farmers' actions demonstrated that their perceptions of salinity and adaptation responses were pre-emptive of when salinity was most likely to have an impact on the rice crop. Farmers' perceptions of salinization and measures to manage salinity need to be considered in research prioritization and policy formulation by the government. This action could potentially secure rice production and thus contribute to the achievement of Sustainable Development Goals (SDG-1, 2 and 3).

2015, Koech, Richard, Mossad, Ruth, Smith, Rod, Gillies, Malcolm

The hydraulic performance of large-diameter gated fluming, commonly used in furrow irrigation, was investigated using computational fluid dynamics (CFD). The continuity and the momentum equations governing the fluid in the system were solved numerically for a steady incompressible and turbulent flow using a realizable software model. The CFD results were compared with the laboratory measured results and those obtained using a hydraulic simulation model. The CFD results showed a good correlation with the measured data and those generated using the software. The velocity head in the pipeline had no influence on the magnitude of the outflows possibly due to the unique shape of the outlet. The pressure head recovery across the outlets was greater than the energy loss along the pipe; hence, the pressure and discharge increased towards the downstream end. The CFD approach was found to be an appropriate tool for detailed analysis of the hydraulic characteristics of gated irrigation pipelines.

2021-01, Kogo, Benjamin Kipkemboi, Kumar, Lalit, Koech, Richard

Climate change and variability are a major threat to the agricultural sector globally. It is widely accepted that the changes in temperature, rainfall patterns, sea water level and concentration of CO₂ in the atmosphere will have the most devastating impacts on agricultural production. This paper examines the past and future crop production and food security in Kenya under variable climate. From the review, it is evident that the country is already experiencing episodes of climate change, manifested by seasonal changes in precipitation and temperature of varying severity and duration despite overreliance on rain-fed agriculture. The findings also reveal that climate change would continue to negatively affect crop production and food security to the already vulnerable communities in the arid and semi-arid areas. Future projections also indicate that climate variability will likely alter cropping patterns and yields in several regions. As the country is faced with a high population growth rate and rapid urbanization, crop production and food security systems need to become more adaptive as uncertainties of projected climate variability and change unfold. This study is important in providing decision makers and interested stakeholders with a detailed assessment of climate impacts and adaptation strategies geared towards improved crop production and food security.