Browsing by Author "Mutua, Benedict M."

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Access to water in Kenya’s coast region
(2018) Ignatius, David O.; Hassan, Farida A.; Morara, George N.; Osore, Melckzedeck k.; Mutua, Benedict M.; Kitaka, Nzula K.
Water is considered a basic commodity and essential for life - living on planet earth is dependent on it. However, access to water has been and will continue to be a dilemma for a majority of the residents at the coast of Kenya. A close look at the window on “Coastal Resources and People” reveals that water is a key resource but despite its immense importance, many people especially in the rural areas and among the Vulnerable and Marginalized Groups (VMG’s) do not have adequate access to potable, reliable and convenient sources of water. Lamu, currently considered among water scarce counties in Kenya as per the Lamu County Integrated Development Plan (http://lamu.go.ke/wp-content/uploads/2016/03/LAMU_CIDP-Revised.June_2014-1.pdf), faces serious challenge of provision of potable water to its residents. With the influx of people from other parts of the country as a result of the implementation of the Kenya Vision 2030 flagship project - Lamu Port Southern Sudan Ethiopia Transport (LAPSSET) Corridor, the current water stresses is only expected to worsen. The Lamu County Government plans to address the ever-increasing demand for access to water but resources to actualise these plans are yet to be consolidated. To complement this situation, Kenya Coastal Development Project (KCDP), a World Bank funded project is working with local communities in Lamu in the development and implementation of community-led water projects targeting to increasing access to water at the household level. This paper will focus on community-based approaches to understand the water-web in Lamu East Sub-County to provide an assessment of opportunities, challenges and sustainability implications. Primary data is used on surveys, Social Assessment (SA),Vulnerable and Marginalised Group Plan (VMGP), observations and recommendations from the Lamu CIDP. It further proposes that direct usage of saline water, seawater or brackish water, for sanitation purposes could alleviate the freshwater shortage.
Analysis of drought and wet-events using SWSI-based severity-duration-frequency (SDF) curves for the upper Tana river basin, Kenya
(Science Publishing Group, 2018-06-12) Raphael Muli Wambua, Raphael Muli; Mutua, Benedict M.; Raude, James Messo
Drought and wet-event patterns in the Upper Tana River basin have significantly been changing due to variation of climatic and human-induced factors. This paper presents the analysis of drought and wet-events using Severity-DurationFrequency (SDF) curves for the Upper Tana River basin, Kenya based on Surface Water Supply Index (SWSI). The extreme value EV1 (Gumbel) frequency distribution function was used to formulate SDF curves. The developed SDF curves were used to develop isoseverity maps for the basin. From the results, the event-probability show that likelihood of drought events increased linearly with increase in magnitude of SWSI while the return period of drought events increased exponentially with decrease in magnitude of SWSI. The findings show that the probability and magnitude, the return period and magnitude of drought have linear and exponential regression coefficients of 0.984 and 0.980 respectively. On the other hand the probability of wet-period events decreased linearly with increase in magnitude of SWSI while the return period of the events increased exponentially with increase in magnitude of SWSI with regression coefficients of the linear and exponential functions of 0.804 and 0.881 respectively. This indicates that both the drought and wet-events probability and magnitude, and the return period and magnitude have a strong correlation. Spatially, it was found that generally the river basin exhibit an increasing pattern in cumulative SWSI in south-eastern areas than the north-eastern and generally a more increase in extreme wet-events than droughts in the basin. The developed (SDF) curves are critical for design of hydrologic, hydraulic and water resources supply systems while the spatial event-patterns can be incorporated in prioritized mitigation of extreme events.
Analysis of drought effect on annual stream flows of river Malewa in the lake Naivasha basin, Kenya
(Radiance Research Academy, 2014-09-15) Kyambia, Marshal M.; Mutua, Benedict M.
The main parameters of drought phenomenon are the longest duration and largest severity for a desired return period. These parameters form the basis for designing water storage structures to cope with drought effects. In this study, these drought parameters were estimated using the probability based theory. The sample estimates of the mean, coefficient of variation, skewness, correlation and information on the probability distribution of flow sequence, were used as the basic input parameters. The truncation level was considered at mean level of the annual flow sequences of River Malewa in Lake Naivasha basin. In this basin, 100, 50, 10, 5 and 2-year droughts may persist continuously for 6, 4, 3, 2 and 1 years respectively. From the probabilistic approach for a normal probability distribution function, high values of coefficient of variation resulted in high values of the actual severity. The results show that there is drought severity in Lake Naivasha basin especially in parts experiencing high inter-annual variability in annual flow regimes.
Analysis of manual and centralised supervisory control operations to improve level of service: a case study of pyramid hill no 1 channel, Victoria, Australia
(Kluwer Academic Publishers, 2001-02) Malano, Hector M.; Mutua, Benedict M.
The current challenge facing irrigation inAustralia is tofind ways to improve the operationalperformance of existing systems rather thanconstructing new ones. Unsteady flowsimulation models are often used as keytools to study and test improvedoperational scenarios for existing systems.While these models are generally notrecommended for real-time control, researchhas shown that they are able to simulatecanal response for different test scenariosfor operations planning. This paperpresents the results of two alternativemodes of operation for the Pyramid Hill No.1 Channel in northern Victoria, Australia.The channel is currently under manualoperation. Centralised control is the mostimmediate option considered by theirrigation authority to enable remotesupervision and control of the canal toimprove the channel operation and level ofservice standards. This type of control istermed Supervisory Control and DataAcquisition (SCADA). The two alternativeoperational scenarios were simulated andanalysed using the unsteady flow-simulationmodel DUFLOW. Specific performanceindicators were defined to compare the twomodes of operations based on the simulationresults. The results show that SCADAoperation has considerable potential toclosely match the discharges at thedownstream regulator with those ordered byfarmers while maintaining the water surfaceelevations within allowable fluctuationtolerance throughout the length of thecanal.
Analysis of spatial and temporal drought variability in a tropical river basin using palmer drought severity index (PDSI)
(Academic Journals, 2017-08-31) Wambua, Raphael M.; Mutua, Benedict M.; Raude, James M.
Analysis of spatial and temporal drought variability in the upper Tana River basin using Palmer Drought Severity Index (PDSI) was conducted. The drought is critical for formulation of mitigation measures in the river basin. A monthly temporal and 90-m spatial resolution was applied. This was achieved within ArcGIS environment. Climatic data for 1970 to 2010 was used for computation of the PDSI while the missing data sets were filled using Artificial Neural Networks (ANNs). The results of PDSI for dry and wet seasons at meteorological stations indicate that the time series plots for the PDSI values for dry season are generally lower than those for the wet seasons. The PDSI values for meteorological stations located at the lower elevation of the basin are lower than those located at higher elevation. On the other hand, spatially distributed drought severity based on PDSI show that the ranges of maximum and minimum drought severity values in 1970 are -0.868 to -0.804 and -0.675 to -0.610 respectively. These values of drought severity occur respectively in the north-western and south-eastern areas of the basin. PDSI values increased from the range -0.675 to -0.610 in 1970 and from -1.087 to 0.957 in 2010 for the north-eastern areas of the upper basin. The south eastern areas of the basin are more prone to drought risks than north-western parts. Use of the PDSI reflects the spatial heterogeneity and temporal variability of drought across the basin. The drought assessment offer technical approach for comprehensive understanding of drought for effective drought-induced disaster mitigation and its management, with a view to reducing adverse effects on livelihoods.
Analyzing the Mara river basin behaviour through rainfall-runoff modeling
(Scientific Research Publishing, 2017-09-14) Birundu, Anne M.; Mutua, Benedict M.
Hydrological models are considered as necessary tools for water and environmental resource management. However, modelling poorly gauged watersheds has been a challenge to hydrologists and hydraulic engineers. Research done recently has shown the potential to overcome this challenge through incorporating satellite based hydrological and meteorological data in the measured data. This paper presents results for a study that used the semi-distributed conceptual HBV Light Model to model the rainfall-runoff in the Mara River Basin, Kenya. The model simulates runoff as a function of rainfall. It is built on the basis established between satellite observed and in-situ rainfall, evaporation, temperature and the measured runoff. The model’s performance and reliability were evaluated over two sub-catchments namely: Nyangores and Amala in the Mara River Basin using the Nash-Sutcliffe Efficiency which the model referred to as Reff and the coefficient of determination (R2 ). The Reff for Nyangores and Amala during the calibration and (validation) period were 0.65 (0.68) and 0.59 (0.62) respectively. The model showed good flow simulations particularly during the recession flows, in the Nyangores sub-catchment whereas it simulated poorly the short term fluctuations of the high-flow for Amala sub-catchment. Results from this study can be used by water resources managers to
Assessment of water flow and sedimentation processes in irrigation schemes for decision-support tool development: a case review for the Chókwè irrigation scheme, Mozambique
(Multidisciplinary Digital Publishing Institute, 2019-02-28) Salvador de Sousa, Lateiro; Wambua, Raphael M.; Raude, James Messo; Mutua, Benedict M.
Water flow and sedimentation processes have been significantly erratic at the Chókwè Irrigation Scheme (CIS) and have affected its hydraulic performance. Given its expansion there is need to understand these processes taking place on-site and along the channels of the scheme. CIS being the biggest project of its kind in Mozambique requires proper management of water flow and sedimentation processes. Therefore, the effect of water flow, sediment transport and deposition parameters on the performance of the CIS is needed. In order to determine the effect of spatial and temporal water flow and sediment distribution trends along the irrigation canals, there is need to establish a correlation between these parameters. Determining the influence of water flow velocity on sediment settling rate at different depths along the canal reaches is important in managing the CIS. In addition, a developed decision-support tool to predict sediment deposition is required. For this reason, it is therefore crucial to carry out a timely assessment of water flow and sedimentation processes in CIS in a review concept. From the current review, some gaps that exist for more focused research on Chókwè Irrigation Scheme have been identified. In this regard therefore, there is need to develop an effective support tool for managing water flow and sediment deposition along the canal reaches with a view to increasing crop production in CIS
Bathymetric survey of lake Naivasha and its satellite lake Oloiden in Kenya; using acoustic profiling system
(wileyonlinelibrary.com/journal/lre, 2018-10-23) Raude, James M.; Maina, Caroline W.; Sang, Joseph K.; Mutua, Benedict M.
Lakes and reservoirs play important roles as freshwater sources for domestic, indus-trial, agricultural, fisheries and recreational purposes. However, for the lakes to be sustainably exploited, there is need to understand their bathymetric characteristics by conducting bathymetric surveys. This aids in generating information that can guide lakes stakeholders and managers in establishing the volume of available water. It is recommended, therefore, that bathymetric surveys be conducted at ten-year intervals. Such continuous bathymetric information is lacking in many lakes, espe-cially in developing countries. One example is Lake Naivasha in Kenya, which is largely exploited for various socio-economic purposes. Despite its importance, its most recent published bathymetric data were collected in 1991. The goal of the pre-sent study, therefore, was to conduct a bathymetric survey of Lake Naivasha and its satellite Lake Oloiden, using an Acoustic Profiling System (APS) to generate Depth–Area–Volume relationships for the lakes. The survey results indicate the in the year 2016 mean depth, volume and surface area of the lake were 4.68 m, 722 × 106 m3and 154.17 × 106 m2, respectively. Because of limited information from the 1991 sur-vey, the 2016 survey results were comparable with those of 1983. The difference in the lakes mean, and maximum depth for the 1983 and 2016 survey was less by 0.23 and 2 m, respectively. This could be an indicator the lake is being affected by anthro-pogenic activities or environmental changes. The established Depth–Area–Volume relationships are crucial since they provide invaluable information to lake and water resources managers for making informed decisions regarding management of the lake’s water resources.
Challenges of sustainable financing of sanitation in Nakuru municipality, Kenya
(WEDC, Loughborough University, 2009-05-22) Ojwando, K.O.; Mutua, Benedict M.
Adequate sanitation is of great importance in addressing public health and plays an important role with respect to poverty alleviation. A large proportion of population in Nakuru is not served with adequate sanitation facilities. Worldwide experiences on financing of sanitation are widely scattered, and influenced by very dif erent local circumstances. Little, if any, real linkage and upscaling has taken place, to draw conclusions that would fit all circumstances. A study was conducted in Nakuru municipality using structured questionnaires. Results from the data analysis indicated that majority of the households interviewed had low monthly incomes ranging between Kshs. 500010000. Sanitation therefore was not a priority with this meager income. The finding indicated that the only way these residents were willing to contribute to sanitation would be in kind labour, 44%. Majority of Nakuru residents, 65% admitted that they don’t pay for garbage collection services, reason being that of poverty and the notion that this is the responsibility of the municipal council. On household improvement priority, many respondents, 35% would prefer to have water in their residence followed closely with sanitation. They argue that with water availability, sanitation is guaranteed. Potential financial constraints were identified as unwillingness and inability to pay due to poverty, lack of political will and poor governance and low priority for sanitation in public sector spending due to competing interest with other sectors such as health and education.
Characterization of greywater from urban and peri-urban areas of Nakuru municipality, Kenya
(Loughborough University, 2009) Raude, James M.; Mutua, Benedict M.; Chemelil, Mathew C.; Sleytr, Kirsten
Kenya faces serious challenges regarding water and sanitation services. Despite many years of government investment, existing facilities continue to deteriorate and have also failed to meet the demand of increasing population. These challenges are particularly severe in rapidly growing settlements of urban poor. One such settlement is Nakuru municipality which has an average annual population growth of about 8%. The municipality’s sewerage connection is inadequate (11% coverage) and only serves middle and high income areas. This study used a semi-structured questionnaire aiming at characterizing and determining the composition of greywater, besides identifying existing water supply and lifestyle characteristics. The total suspended solids range in greywater was 200-3500 mg/l and faecal coliform (FC) count 105 -106 100mL-1. High values of FC concentration in greywater can be associated with life style characteristics and the settlement patterns. These results were used to develop site specific greywater treatment systems ideal for peri-urban areas.
Classification of catchment risk areas using spatially distributed event-based soil erosion: a case of upper Njoro river catchment, Kenya
(WIT Press, 2008-12-19) Wambua, R.M.; Mutua, Benedict M.; Nyaanga, D.M.; Kundu, P.M.
Human-induced soil erosion and drastic change in land use practices have adversely infl uenced the land degradation and surface runoff response in upper Njoro River catchment. The drainage area is approximately 127 km2. Due to human activities, the land has been exposed to accelerated erosion and low land productivity, water scarcity, decline in ground water recharge, siltation of Lake Nakuru and other sediment sinks. This study was conducted to establish event-based risk areas for prioritized conservation within the catchment. Spatially distributed soil erosion map was created as a ratio of sediment yield to sediment delivery ratio (SDR). Modifi ed Universal Soil Loss Equation (MUSLE) integrated within a Geographical Information Systems environment was used to create the sediment yield map. Spatial data layers for the MUSLE were derived from a 20-m resolution Digital Elevation Model, soil property, land use maps and climatic data of the catchment. Land use map was derived from Landsat imagery via its processing using Integrated Land and Water Information Systems software. The results show that the spatially distributed soil erosion ranged from 0.06 to 0.51 t/ha for a 43.2-mm rainfall event. Spatially distributed SDR ranged from 0.09 to 0.82, while the average SDR for the whole catchment was 0.72. These values were derived using an empirical equation. A new contribution was made by developing spatially distributed slope length factor, SDR, runoff volumes, MUSLE parameters and classifi ed erosion risk areas for prioritized catchment conservation. This means that the event-based soil erosion classifi cation can be adopted for prioritized soil and water conservation within Njoro catchment.
Comparative assessment of the effect of climate change and human activities on streamflow regimes in central rift valley basin, Ethiopia
(Science and Education Publishing, 2019) Gadissa, Takele; Nyadawa, Maurice; Mutua, Benedict M.; Behulu, Fiseha
Climate change and anthropogenic activities are the main driving factors for changes in hydrological processes of a given watershed. This research was conducted to assess the relative contribution of climate change and human activities to streamflow change. The ensemble mean of five regional climate models (RCMs) in the coordinated regional climate downscaling experiment (CORDEX)-Africa was considered for the purpose of this study. Two emission scenarios, the Representative Concentration Pathways, RCP4.5 and RCP8.5, were considered for the future scenario period (2041–2070). Streamflow change due to climate change and human activities was assessed using coefficient of elasticity method and SWAT hydrological model. A change due to climate change was further split into change due to precipitation and evapotranspiration. Climate change contributed 46.7% while human activities contributed 53.3% to changes in streamflow. It was found that a 10% decrease in precipitation caused a reduction of 25.1% in streamflow, while 10% increase in potential evapotranspiration caused a reduction of 15.5% in streamflow. The results from ensemble mean of Regional Climate Models (RCMs) show that the average projected precipitation will decrease by 7.97% and 2.55% under RCP4.5 and RCP8.5 respectively. On average, temperature will increase by 1.9°C and 2.7°C under RCP4.5 and RCP8.5 respectively. This corresponds to 4.89% and 6.59% increase in potential evapotranspiration under RCP4.5 and RCP8.5 respectively. Using coefficient of elasticity method, the estimated values of streamflow change were – 26.9% and – 15.8% under RCP4.5 and RCP8.5 respectively. The results of this study show that the reduction in streamflow due to human activities was higher than the reduction due to climate change. The streamflow change induced by anthropogenic factors can be associated with factors such as water abstraction, land use change, ground water abstraction, and the other catchment properties. Hence, further research is recommended to separate changes from these factors.
Detection of spatial, temporal and trend of meteorological drought using standardized precipitation index (spi) and effective drought index (edi) in the upper Tana river basin.
(Scientific Research Publishing, 2018-07-17) Raude, James M.; Wambua, Raphael M.; Mutua, Benedict M.
Drought events across the world are increasingly becoming a critical problem owing to its negative effects on water resources. There is need to understand on-site drought characteristics for the purpose of planning mitigation measures. In this paper, meteorological drought episodes on spatial, temporal and trend domains were detected using Standardized Precipitation Index (SPI) and Effective Drought Index (EDI) in the upper Tana River basin. 41 years (1980-2016) monthly precipitation data from eight meteorological stations were used in the study. The SPI and EDI were used for reconstruction of the drought events and used to characterize the spatial, temporal and trend distribution of drought occurrence. Drought frequency was estimated as the ratio of a defined severity to its total number of events. The change in drought events was detected using a non-parametric man-Kendall trend test. The main drought conditions detected by SPI and EDI are severe drought, moderate drought, near normal, moderate wet, very wet and extremely wet conditions. From the results the average drought frequency between 1970 and 2010 for the south-eastern and north-western areas ranged from 12.16 to 14.93 and 3.82 to 6.63 percent respectively. The Mann-Kendall trend test show that drought trend increased in the south-eastern parts of the basin at 90% and 95% significant levels. However, there was no significant trend that was detected in the North-western areas. This is an indication that the south-eastern parts are more drought-prone areas compared to the North-western areas of the upper Tana River basin. Both the SPI and the EDI were effective in detecting the on-set of drought, description of the temporal variability, severity and spatial extent across the basin. It is recommended that the findings be adopted for decision making for drought-early warning systems in the river basin.
Detection of trends in extreme streamflow due to climate variability in the lake Naivasha basin, Kenya
(2014-11-17) Kyambia, Marshal M.; Mutua, Benedict M.
Variability of streamflow has far-reaching impacts especially in developing countries. This is aggravated by climate change which has adversely affected the water resources and food security. This paper presents the characterization trends in extreme streamflow regimes with a view to providing information for planning local coping mechanisms to climate variability and change using streamflow data recorded from 1959 to 2008 in the Lake Naivasha basin in Kenya. The maxima and percentiles of streamﬂow distributions were investigated to identify changes in extreme intensity and frequency, respectively, using the Mann–Kendall test. The results indicate significant increases in annual maxima at all gauging stations. The flows in the month of November increased significantly at gauging stations 2GB4 and 2GC4. Flow percentile exceedance revealed that the annual 95th percentile exceedance increased significantly at gauging stations 2GB1 and 2GB5 with a decrease in annual 90th and 97th percentile exceedance at gauging stations 2GB4 and 2GC4. The results presented in this paper are useful for climate change adaptation planning and management especially in water supply, hydropower generation and agriculture.
Determination of discrete particles optimum design parameters for surface irrigation system settling basin
(2018-06-05) Namu, Patrick n.; Raude, James M.; Mutua, Benedict M.; Wambua, Raphael M.
Irrigated agriculture is faced with challenges that include sediment loading in the river basins and dams. The management of sediments in river basins and waterways has been an important issue for water managers throughout history. Water managers are faced with similar challenges caused by siltation of water reservoirs and irrigation water conveyance systems. As a copping strategy to counter the low irrigation application efficiency for surface irrigation systems, designs of settling tanks are typically oversized with an aim of having enough detention time for the sediment particles to settle. To settle discrete particles an optimum settling tank is important so as not to have problems over overdesigning and consequently costly projects. The optimum hydraulic design parameters for a settling basin were calibrated using a physical model prepared in the Civil Engineering laboratory at Jomo Kenyatta University of Agriculture and Technology. Using a dataset from a model a quartic equation 1.5844 42.341 385.56 1350.8 1188.8 4 3 2 T   x  x  x  x  was developed to calculate turbidity drop in a small-scale settling basin when the flow rate is known. Finally, a quadratic equation 0.0906 1.0975 5.7338 2 Y  X  X  was developed for calculating optimum surface area required for settling discrete particles for different flow rates. For this research the optimum design surface areas were Q1 = 2.42m2 , Q2 = 3.04 m2 , Q3 = 3.75 m2 , Q4 = 4.20 m2 and Q5 = 4.71 m2 corresponding to 5.7, 8.7l/min, 9.9 l/min, 10.5 l/min and 11.1 l/min respectively.
Drought forecasting under climate change scenarios using artificial neural networks for sustainable water resources management in upper Tana river basin, Kenya
(Elsevier, 2018-07-10) Mutua, Benedict M.; Wambua, Raphael M.; Raude, James M.
Climate change has continued to impact negatively on water resources globally. For instance, extreme weather conditions especially the drought phenomena have become frequent in Africa. This has prompted water engineers and hydrologists to formulate mitigation and adaptation measures to address these challenges. The frequency of drought event of a defined severity for a defined return period is fundamental in planning, designing, operating and managing water resources systems within a basin. This paper presents an analysis of the hydrological drought frequency for the upper Tana River basin in Kenya using the absolute Stream flow Drought Index (SDI) and modified Gumbel technique. The study used a 41-year (1970-2010) stream flow data and forecasted hydrological droughts for 2, 5, 10, 20, 50, 100, 200, 500 and 1000-year return periods in relation to the selected stream flows. The results provide an overview of drought trends within the river basin and therefore would be very useful in applying drought adaptation policies by water resource managers.
Drought forecasting using indices and artificial neural networks for upper Tana river basin, Kenya-a review concept
(OMICS Publishing Group, 2014-01-01) Wambua, Raphael M.; Mutua, Benedict M.; Raude, James M.
Due to increased impact of drought on water availability at different scales there is need to understand droughts especially in upper Tana River basin which is a critical and largest water system in Kenya. There is need to correlate trends of drought as influenced by the climate variability of the present times. Drought frequency, duration and intensity in the basin have been increasing. The influencing hydro-meteorological parameters and their interaction are necessary in developing measures for mitigating impacts of droughts. It is important to have a timely review of drought definitions and fundamental concepts of droughts, classification of droughts, types of drought indices, historical droughts and artificial neural networks with special focus of Kenyan a basin. Out of the review, this paper draws conclusions where gaps for more focused research especially for a typical river basin in Kenya exist. By developing effective.
The effect of climate change on loss of lake volume: case of sedimentation in central rift valley basin, Ethiopia
(Multidisciplinary Digital Publishing Institute, 2018-12-11) Gadissa, Takele; Nyadawa, Maurice; Behulu, Fiseha; Mutua, Benedict M.
Evaluating the impact of climate change on sediment yield has become one of the major topics in climate research. The purpose of this study was to investigate sediment yield contribution to lake volume change under changing climatic conditions in the Central Rift Valley Basin. The ensemble mean of five regional climate models (RCMs) in the coordinated regional climate downscaling experiment (CORDEX)-Africa was considered for the purpose of this study. The climate variables (precipitation, minimum and maximum temperatures) in RCMs were bias corrected against observed data (1985–2016) using linear scaling (LS), power transformation (PT), variance of scaling (VS), and quantile mapping (QM). Two emission scenarios, the Representative Concentration Pathways, RCP4.5 and RCP8.5, were considered for the future scenario period (2041–2070). Better results were obtained when the ensemble values of the bias correction methods were used. Hence, the projected values of climate variables after bias correction were used in the Soil and Water Assessment Tool (SWAT) hydrological model to estimate the sediment yield contribution to lake volume change due to climate change. The results show that the average projected precipitation will decrease by 7.97% and 2.55% under RCP4.5 and RCP8.5, respectively. On average, the maximum temperature will increase by 1.73 ◦C and 2.36 ◦C under RCP4.5 and RCP8.5, respectively, while the minimum temperature will increase by 2.16 ◦C and 3.07 ◦C under RCP4.5 and RCP8.5, respectively. The average annual sediment yield contributions to Lake Ziway were 431.05 ton/km2 and 322.82 ton/km2 for the Meki and Ketar rivers, respectively, in the historical period (1985–2010). The study also reveals that the annual sediment yield that was estimated for the Meki River was 323 ton/km2 and 382 ton/km2 under RCP4.5 and under RCP8.5, respectively. The sediment estimations for the Ketar River were 157 ton/km2 and 211 ton/km2 under RCP4.5 under RCP8.5, respectively. This will decrease the rate of volume change in Lake Ziway by 38% under RCP4.5 and by 23% under RCP8.5. The results show that the life expectancy of the lake is likely to increase under climate change scenarios. This will help water resources managers make informed decisions regarding the planning, management, and mitigation of the river basins.
The effect of climate change on loss of lake volume: case of sedimentation in central rift valley basin, Ethiopia
(MDPI, 2018-12-11) Behulu, Fiseha; Mutua, Benedict M.; Gadissa, Takele; Nyadawa, Maurice
Evaluating the impact of climate change on sediment yield has become one of the major topics in climate research. The purpose of this study was to investigate sediment yield contribution to lake volume change under changing climatic conditions in the Central Rift Valley Basin. The ensemble mean of five regional climate models (RCMs) in the coordinated regional climate downscaling experiment (CORDEX)-Africa was considered for the purpose of this study. The climate variables (precipitation, minimum and maximum temperatures) in RCMs were bias corrected against observed data (1985–2016) using linear scaling (LS), power transformation (PT), variance of scaling (VS), and quantile mapping (QM). Two emission scenarios, the Representative Concentration Pathways, RCP4.5 and RCP8.5, were considered for the future scenario period (2041–2070). Better results were obtained when the ensemble values of the bias correction methods were used. Hence, the projected values of climate variables after bias correction were used in the Soil and Water Assessment Tool (SWAT) hydrological model to estimate the sediment yield contribution to lake volume change due to climate change. The results show that the average projected precipitation will decrease by 7.97% and 2.55% under RCP4.5 and RCP8.5, respectively. On average, the maximum temperature will increase by 1.73 ◦C and 2.36 ◦C under RCP4.5 and RCP8.5, respectively, while the minimum temperature will increase by 2.16 ◦C and 3.07 ◦C under RCP4.5 and RCP8.5, respectively. The average annual sediment yield contributions to Lake Ziway were 431.05 ton/km2 and 322.82 ton/km2 for the Meki and Ketar rivers, respectively, in the historical period (1985–2010). The study also reveals that the annual sediment yield that was estimated for the Meki River was 323 ton/km2 and 382 ton/km2 under RCP4.5 and under RCP8.5, respectively. The sediment estimations for the Ketar River were 157 ton/km2 and 211 ton/km2 under RCP4.5 under RCP8.5, respectively. This will decrease the rate of volume change in Lake Ziway by 38% under RCP4.5 and by 23% under RCP8.5. The results show that the life expectancy of the lake is likely to increase under climate change scenarios. This will help water resources managers make informed decisions regarding the planning, management, and mitigation of the river basins.
Effect of streamflow on hydro-power generation in the upper Tana river basin, Kenya
(KIBU, 2018-06-12) Francis K. Musyoka, Francis K.; Wambua, Raphael M.; Mutua, Benedict M.
Hydro-power is one of the Kenya’s important energy sources. The main hydro-power project in Kenya is located in the Upper Tana River basin. There has been a fluctuation of power generation due to climate change over the years. The main objective of this research was to assess the effect of streamflow on hydro-power generation under climate change scenarios. Hydro-power generation is estimated by relating the runoff changes to hydro-power generation through the ArcGIS software, in conjunction with ArcSWAT model based on 30-year hydrometric data. Results showed a peak discharge in May, with gradual decrease, the first decade registering a peak flow of 82.74 m3/s in Tana-Sagana River followed by 80.65m3/s. The annual average dam inflows declined at the rate of 0.7992 m3/s annually. For the 30 years, dam inflow decreased by 23.98 m3/s. The minimum inflow rates increased with the years 2000 and 2009 having the lowest inflows of 21.4 m3/s and 22.8 m3/s respectively. The highest inflow and lowest inflow occurred in 1998 and 2009. A decreasing trend in the amount of hydro-power produced in the scheme from 1990 to 2010. The driest years, which were 1999-2000 and 2009, recorded the lowest levels of hydro-power generation. Decreasing amounts of precipitation and increasing temperatures have led to declining Masinga dam inflow rates. Results from this study are useful in explaining the trend in hydropower generation in the basin. The findings show how the hydro-power generation is correlated to dam inflows, which in turn is linked to the amount of precipitation and can be incorporated for planning of hydro-power supply.