Browsing by Author "Wambua, Raphael M."

Now showing 1 - 10 of 10

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.
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
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.
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.
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.
Evaluation of streamflow response to agricultural water abstraction and its variability with rainfall for Thiba river watershed, Kenya
(KIBU, 2018-06-12) Omondi, Brian; Mutua, Benedict M.; Wambua, Raphael M.
The continuous increase of agricultural water demand in Thiba River Watershed as a result of the expansion agriculture especially in the Mwea Irrigation Scheme and other parts of the watershed has led to over abstraction of water from the scheme’s main water supplier, Thiba River, hence declining its flows. This river supplies a hydroelectric dam on its downstream and it is also depended upon by various livelihoods. This study sought to find out the potential impacts the expansion of agricultural lands would have on the stream flow of Thiba River and how it would affect the downstream users. The research was carried out by determining the streamflow response to agricultural water abstraction using Spearman’s rank correlation method. A relationship between streamflow and rainfall variability using regression analysis was also established. Different stream flow scenarios were simulated and their effects and impacts on the downstream users assessed. The results of the study showed that there was a very significant decline in the stream flow in the dry months compared to the wet months. The regression analysis of the variability between stream flow and rainfall provided a moderately strong but significant relationship between the two variables. Results from the model calibration showed a satisfactory efficiency with an NSE value of 0.50. The findings showed an increasing trend of water abstraction in Thiba basin. There was an increasing trend of water abstraction for the period between 2007 and 2014. The highest water abstraction was experienced in the dry months of January to February and June to October. Water abstraction analysis revealed that about 20,000 m3/day) is abstracted during the dry seasons whereas approximately 5000m3/day of the river’s flow is abstracted during the wet seasons. This represents about 35% of the dry season flow and only 3% of the wet season flow. This study is useful to water professionals and managers in developing a robust integrated water and land management system in the watershed. Key words: water demand, Thiba river watershed, water abstraction, dry months, wet months
Hydrological drought frequency estimation using stream flow drought index and modified gumbel method in upper Tana river basin
(Radiance Research Academy, 2015-11-15) Wambua, Raphael M.; Mutua, Benedict M.; Raude, James M.
Objective: To estimate the hydrological drought frequency for upper Tana River basin in Kenya using absolute Stream flow Drought Index (SDI) and modified Gumbel technique. The frequency of drought event of a defined severity for a defined return period is fundamental in planning, designing and operation of water storage systems in the basin. Materials and Methods: Based on a 41-year (1970-2010) stream flow data, hydrological droughts of 2, 5, 10, 20, 50, 100, 200, 500 and 1000-year return periods are evaluated based on the stream flows, Stream flow Drought Index (SDI) and a simplified mathematical model for hydrological drought estimation which is formulated using Gumbel’s technique. Results: The absolute SDI increases while the magnitude of the stream flow decreases with return period. The minimum and maximum drought events were exhibited in gauge stations 4AC03 and 4CC03 with absolute SDI ranging from 0.667 to 1.265 and 1.213 to 2.42, and corresponding stream flows of 4.341 to 2.719 and 18.246 to 1.021m3 /s for a 2 and 1000-year return period respectively. Conclusion: A simplified mathematical model for estimating hydrological drought event that uses mean flows of the annual minimum and average of the first three minimum stream flows as input variables is formulated for different return periods for the river basin.
Stochastic drought forecasting exploration for water resources management in the upper Tana river basin, Kenya
(IGI Global, 2016) Wambua, Raphael M.; Mutua, Benedict M.; Raude, James M.
This chapter presents the trend of drought as a stochastic natural disaster influenced by the climate variability for the upper Tana River basin in Kenya. Drought frequency, duration and intensity in the upper Tana River basin have been increasing over the years. To develop measures for mitigating impacts of drought, the influencing hydro-meteorological parameters and their interaction are necessary. Drought definitions, fundamental concepts of droughts, classification of droughts, types of drought indices, historical droughts and application of artificial neural networks in analyzing impacts of drought on water resources with special focus on a Kenyan river basin is presented. Gaps for more focused research are identified. Although drought forecasting is very vital in managing key sectors such as water, agriculture and hydro-power generation, drought forecasting techniques in Kenya are limited. There is need therefore to develop an effective drought forecasting tool for on-set detection, classification and drought forecasting. The forecasting is necessary for decision making on matters of drought preparedness and proper water resources planning and management.