Rwanda Journal of Engineering, Science, Technology and Environment

On 1 + 3 covariant perturbation with chaplygin-stiff fluid system in modified Gauss-Bonnet gravity

2025-03-24T16:32:50+00:00

The early stage of the evolution of the universe, when taken along with the recent observations that the current universe is dominated by dark energy, leads to at least a potential problem that modern cosmology must address. Cosmology still lacks a model to deal with the observed current cosmic acceleration. In this paper, a framework is proposed to address the current accelerated expansion of the universe via large scale structure formation. In this regards, we investigate cosmological perturbations of modified Gauss-Bonnet (f (G)) gravity in the presence of a stiff fluid and two different forms of chaplygin gas model, using the 1 + 3 covariant formalism. Gradient variables of respective fluids were defined to obtain the energy overdensity perturbation equations in redshift space, responsible for large scale structure formation. Using a particular functional form of f (G) model, together with two different forms of chaplygin gas, the perturbation equations were solved separately to study the growth of energy overdensity contrast with redshift. The numerical results for both considered forms of chaplygin gas models show that the energy overdensity contrast decays with redshift which might enhance the large structure formation scenario.

Mitigating RDO and MEC Complexity in H.26x Video Codecs using DWT

2025-03-24T16:37:11+00:00

The current rise of audiovisual content demand needs dynamic approaches for content compression. In video compression, the weakness of human visual system (HVS) is exploited to reduce spatial and temporal redundancies, hence reducing inherent bit content in video frame sequences. Nevertheless, processing involved pose new challenges of computation cost in terms of time, power and system design complexity especially in real-time video streaming. Mitigating the trade-off between compression ratios, video quality and computation cost continues to be the core area of research in video coding. In H.26x codecs, motion estimation (ME) and motion compensation (MC) algorithms, sometimes simply called motion estimation and compensation (MEC) are used in inter-frame prediction. Conventionally, MEC involves time consuming searching algorithms in macroblock and sub-block matching. Also, H.26x series employ rate distortion optimisation (RDO) in intra prediction (IP) modes which is repetitive and exhaustive. In this paper, we present two approaches to mitigate MEC and RDO complexities in H.26x codecs: (a) we present a Discrete Wavelet Transform-assisted intra prediction (DWTIP). DWTIP avoids exhaustive and blind evaluation of all possible intra prediction modes by restricting specific modes to a specific macroblock and sub-block size predetermined based on pixel homogeneity levels. This leads RDO relaxation. (b) We also present a DWT-assisted motion estimation and compensation (DWTMEC) for inter-frame prediction. DWTMEC limits the search window to DWT approximation sub-band and reduces the search area, hence reducing MEC computation time. Objective video quality metric is used to compare conventional MEC with DWTMEC and conventional IP with and DWTIP. Results showed that employing DWTMEC along with DWTIP, video coding rates are improved with negligible degradation in video quality.

Evaluating land degradation for sustainable silvopastoralism in Savanna Region: A case study in Matimba and Rwimiyaga sectors in Eastern Province of Rwanda

2025-03-24T16:39:51+00:00

Land degradation significantly affects the quality and productivity of land resources. It is caused by activities such as deforestation, soil erosion, desertification, pollution, overgrazing, and unsustainable agriculture. This study assesses land degradation in the Matimba and Rwimiyaga sectors of Nyagatare District, focusing on whether areas where silvopastoralism has been implemented correspond to regions experiencing significant land degradation from 2000 to 2022. Using the Good Practice Guidance (GPG) methodology, the study assessed changes in land cover, land productivity, and Soil Organic Carbon (SOC) as indicators of land degradation. The findings show significant changes in land cover over 22 years, with a reduction of 26,933 hectares in grassland (mainly used as rangeland) due to conversion to cropland. Deforestation, overgrazing, and expansion of built-up areas contributed to land degradation of 5,637 hectares over 22 years. Changes in land productivity indicate early signs of decline in about 40% of cropland, while the SOC remained relatively stable during the study period. Overall, from 2000 to 2022, the Matimba and Rwimiyaga sectors experienced land degradation of 7,347.4 hectares. The study discussed silvopastoralism sustainability and found that 46.7% of paddocks with this practice are in areas experiencing land improvement, 48.9% in stable areas, and only 4% in degraded areas. This implies that silvopastoralism is a promising strategy for improving land health. Therefore, the study recommends expanding silvopastoralism to other pastures with land degradation status and integrating this practice into Rwanda's National Adaptation Plan (NAP) for sustainability.

Resilience and sustainability in African Cities: Exploring residents’ living environment across Kigali City neighbourhoods

2025-03-24T16:46:10+00:00

Rapid urbanization is intensifying inequality in cities, particularly in Africa, where informal neighbourhoods present significant challenges, often exposing vulnerable residents to precarious living conditions. Building resilient communities and ensuring satisfaction with livelihoods are fundamental to determining quality of life. This study examines the living environments and satisfaction levels of residents across Kigali’s neighbourhoods, based on the premise that the neighborhood is a key framework for analysing residents’ livelihoods and their distinct characteristics. Using spatial data, 130 residential neighbourhoods were mapped and analysed, while a quantitative survey collected information on residents' living conditions from 1,092 households. The results revealed significant differences in neighborhood living environments. However, contrary to common perceptions, residents of informal areas reported high levels of satisfaction with their neighbourhoods. The study concludes that, despite disparities, living conditions across Kigali’s neighbourhoods are generally adequate. Drawing from detailed evidence, it further confirms that the neighborhood scale is a valuable framework for studying resilience and sustainability in African cities.

Implementing SDGs in Rwanda's rural housing: Lessons from Karama Model Village

2025-03-24T17:03:17+00:00

Rwanda has shown a strong commitment to localizing the Sustainable Development Goals (SDGs) by incorporating them into its national development plans and strategies, particularly the 1^st National Strategy for Transformation 2017-2024, the 2^nd National Strategy for Transformation 2014-2029 and Rwanda’s Vision 2050. Within the Vision 2050, the urbanization is identified as a key driver of economic transformation and urban development. This emphasis has further promoted the development of grouped villages, locally known as ‘imidugudu,’ which have become a central element of the government’s Integrated Development Programme (IDP) and the Economic Development and Poverty Reduction Strategy (EDPRS). Since 2010, over 60 IDP model villages have been established in Rwanda, guided by the principle of leaving no one behind, with the goal of resettling vulnerable households from high-risk areas. Karama, a model village located in the peri-urban area of Kigali and completed in 2019, serves as a case study for this research. A post-occupancy appraisal was conducted between 2021 and 2022 through direct participant observation and interviews with residents, including an assessment of their satisfaction with the new housing. In addition, a critical discourse analysis of national policies was carried out. The findings from this fieldwork are discussed in particular in relation to SDG 11, highlighting the tension between the overarching SDG discourse and its local, grassroots implementation. The qualitative data from the post-occupancy interviews, combined from the results of a satisfaction questionnaire is used to explore the potential and relevance of the SDGs in housing. By mapping the global policy framework alongside its local application, and the trend of SDG 11 targets and measures, from respondents’ reflections about their daily life before and after relocation, this research identifies the extent to which context-specific projects, such as Rwanda’s IDP model villages, can provide opportunities for the local implementation of the SDGs, ultimately contributing to a more resilient future for Rwanda’s communities.

Awareness and compliance of construction employers with the National Occupational Safety and Health (osh) regulation of Rwanda

2025-03-24T17:10:20+00:00

The construction industry is an important sector of every economy as it contributes to the continual growth of developing and developed countries. It is however challenged by many issues that lead to poor project performance. One of such challenges is the perennial occurrence of accidents and fatalities on construction sites due to lack of awareness and compliance with relevant OSH regulations. This study investigates the level of awareness and compliance of construction employers with the national OSH regulation of Rwanda. The quantitative survey research design was adopted for the study. The study’s questionnaire was distributed to 178 construction employers using the random sampling technique. The result indicated that construction employers are aware of the OSH regulation but are only compliant to nine of the nineteen items in the OSH regulation. There is also no significant difference in the level of awareness of the respondents of OSH regulation. However, there is a significant difference in the level of compliance of the consulting and contracting organisations with the OSH regulation. Also, there is a significant relationship between the awareness and compliance of construction organisations with the OSH regulation. It was recommended that the government should introduce stricter laws to enforce compliance with the OSH regulation and other construction stakeholders should prioritise health and safety practices on construction site.

Key triggering factors in the clogging process of Nyarutarama hybrid ponds treating municipal wastewater in Kigali

2025-03-24T17:13:43+00:00

Constructed wetlands are man man-made wetlands or ponds that use the natural processes involving wetland vegetation, gravel, sand and their associated microbial assemblages to treat and improve the quality of wastewater effluent. The major operational challenge faced by natural wastewater treatment systems including constructed wetlands or hybrid ponds is the clogging process of porous media resulting from the accumulation of various solids types such inorganic solids from chemical precipitation, sludge from sedimentation and biological process like plant detritus and biofilm formation. The present study was carried out to determine the level of clogging process of Nyarutarama natural ponds system treating sewage from neighboring estate. Data were collected through the key informant interview about the key triggering factors in clogging process of that treatment system. This system is made by a combination of three series of constructed ponds that were built in Kigali. The assessment results indicated the clogging level of 78%, 60%, and 75% for primary facultative pond, water lettuce covered pond and free water surface flow pond respectively. Those results indicated that the ponds system clogging was due to the accumulation of solids materials resulting from the lack of operational, monitoring and maintenance plans. The well operated and managed constructed wetlands can effectively be used for environmentally and friendly treatment of wastewater rather than using conventional treatment systems since constructed wetlands are inexpensive. The constructed wetlands and hybrid ponds can easily be operated and maintained. In addition, when they are well designed they can serve as touristic and field study areas.

The effect of meteorological factors on extreme COVID-19 infection in Rwanda: The generalized additive extreme value modeling approach

2025-03-24T17:17:21+00:00

The novel human coronavirus disease, COVID-19, was first identified in China in 2019 and has since spread throughout the world becoming a global pandemic of great concern. High daily new cases have brought a heavy burden on health facilities and health workers helping patients and fighting the spread of this pandemic. Understanding the behavior of extreme cases of COVID-19 and associated factors is crucial to devise strategies to flatten the pandemic curve. This study used generalized additive modeling and extreme value theory approaches to analyze weekly maximum positive cases of COVID-19 together with three climate covariates (temperature, rainfall, and solar radiation) with the purpose to evaluate the predictive power of climate factors on extreme COVID-19 cases. According to the findings, a Generalized Extreme Value distribution with a constant location parameter, a linear model for the shape parameter with rainfall as a predictor, and a non-linear model for the scale parameter with temperature and rainfall as predictors fits the weekly maximum positive cases the best. As a result, both temperature and rainfall have a significant effect on the spread of the COVID-19 pandemic. The findings of this study make a significant contribution to the existing knowledge about the COVID-19 pandemic.

Characterization of microbes responsible of potato off-flavor in Rwandan Arabica coffee

2025-03-24T17:30:24+00:00

Coffee is a key socio-economic commodity worldwide due to its exportation and role in generating income for farmers and countries. However, potato taste defect (PTD) in coffee beans affects the taste quality of brewed coffee, impairing the commercial value of coffee across the East African region. Despite numerous suggested causes of PTD in coffee beans, microbial identification using culture-dependent methods remains largely unexplored and poorly understood. This study isolated bacteria and fungi taxa linked with PTD in Arabica coffee beans from three districts (Muhanga, Rwamagana, and Gicumbi) in Rwanda between May and July 2024. Culture-dependent methods (culturing, microscopic examination, and biochemical tests) revealed the presence of bacterial and fungal taxa. Specifically, bacterial isolation on Nutrient Agar (NA), Mannitol Salt Agar (MSA), and MacConkey Agar (MCA) revealed the presence of S. aureus and E. coli. These bacteria were catalase-positive, oxidase-negative, indole-negative, and urease-positive. Additionally, S. epidermis and Micrococci colonies were detected, appearing pink or red (without a yellow halo) and small bright yellow, respectively. Fungal isolation on SDA (Sabouraud Dextrose Agar) and PDA (Potato Dextrose Agar), along with microscopic examination, showed yeasts (Saccharomyces species) and molds (Aspergillus and Penicillium) in the Arabica coffee bean samples. This work suggests that these microbes may produce chemical compounds in Arabica coffee that affect its taste and odor. The study provides insight into microbes associated with PTD through culturedependent methods.

Mathematical modeling of methane gas extraction from Lake Kivu

2025-03-24T17:35:03+00:00

Lake Kivu, located on the border of Rwanda and the Democratic Republic of Congo, contains vast reserves of dissolved methane gas, offering significant opportunities for energy generation. However, improper extraction could destabilize the lake's stratification, potentially triggering catastrophic gas eruptions. The challenge lies in developing an efficient and sustainable method for methane extraction that maximizes energy recovery while maintaining the stability of the lake. This study develops a mathematical model to describe the process of methane gas extraction from Lake Kivu. The model focuses on key aspects of extraction while omitting detailed considerations of the lake's stratification physics and gas-water chemistry. It accounts for the rate of methane gas generation in the resource zone, the extraction of methane from deep water via bubble-driven tubes, and processes occurring in the separation and washing zones. Furthermore, the model incorporates the rate at which methane is released into the deep layers from these zones. It also examines the effects of extraction rates, well placement, and operational strategies on lake stability. From the results, the extraction system will be stable when the yearly average extraction of methane gas from Resource Zone is 0.1704 km³/year , 0.1672km³/year in the separation zone and 0.1464km³ /year in the washing zone. Numerical simulations were conducted to explore various scenarios related to methane gas extraction rates. To better understand the conversion of extracted gas into electrical power, a separate two-compartment model was developed, comprising the production zone and the electricity zone. Overall, the mathematical model serves as a valuable tool for analyzing and optimizing methane gas extraction from Lake Kivu, offering insights to enhance efficiency and sustainability in resource utilization

Benthic macroinvertebrate diversity as biological indicators of health status of Kibumba urban wetland, Kigali City, Rwanda

2025-03-24T17:39:11+00:00

Kibumba wetland is one of the urban wetlands in Kigali City, Rwanda. Human settlements surround the wetland and some anthropogenic activities take place within it. Its hosted biodiversity including benthic macroinvertebrates (BMIs) is unknown, while its protection would rely on knowledge of its biodiversity. In that regard, a study to document its hosted benthic macroinvertebrates was designed to assess its benthic macroinvertebrate diversity and its health status. The study's objectives were specifically to i) assess the diversity of benthic macroinvertebrates in the Kibumba urban wetland and ii) assess the health status of the wetland based on the sensitivity of benthic macro-invertebrates to pollution. Data collection was conducted in April 2024. Benthic macroinvertebrate specimens were collected using a kick net, stored in 70% alcohol, and identified using available identification keys on African aquatic fauna. Sixteen benthic macroinvertebrate families of the pollution tolerant category were identified from collected samples. The pollution of the wetland mainly results from anthropogenic activities including agriculture, waste disposal, and wastewater from surrounding human settlements, especially from industry complexes, and sand extraction. This was the first study at the wetland and its findings serve as baseline data on which protection measures of the wetland should be based on.

Assessment of factors limiting agricultural mechanization in Rwanda

2025-03-24T17:43:08+00:00

Agricultural mechanization is an important symbol of agricultural modernization, andagricultural equipment is the carrier of agricultural modernization and thus an important tool used to promote agricultural mechanization. This study evaluated limiting factors to agricultural mechanization in Rwanda and carried out on key informants from the state, Machinery AssemblyWorkshops and garages, private companies delivering Agri-mechanization services andpilot farmers.The results showed that agricultural mechanization has a great positive effect onagriculture and socioeconomic development. The results showed that 100%of AMoperators, and technicians received general training on site, they did not attend any training centreorspecialized training and 57% of farmers reported that AM equipment is not easily accessiblebecause all equipment is located far away from their farms and have to pay for fuel to transport the tractor to their farms, which increases the production cost Moreso, even if thereisasignificant role of government in agricultural mechanization, there are several factors that limit the adoption of agricultural mechanization in Rwanda like high cost of agricultural machinery, lack of spare parts, inadequate low skills and knowledge of technicians, operators andsomeagricultural mechanization stakeholders. The government should facilitate the availabilityofspare parts locally and make them easily accessible to the tractor owners, capacity buildingoftechnicians as well as garages reserved for only agricultural machines. The Agricultural Mechanization Centers should be strategically located in mechanization potential areastosupport the beneficiaries. Rwanda should establish standards and certification schemes andschemes regulations for Agricultural mechanization equipment for both imported agricultural machines and locally manufactured.

Unveiling the resilience of unprotected wetlands through a comprehensive wetland health index assessment, Rwanda: The case of Kiyonga wetland.

2025-03-24T17:47:05+00:00

Wetlands are vital ecosystems providing numerous ecological services, yet they face increasing threats from anthropogenic activities and environmental changes. Thus, monitoring and evaluation of their status is crucial to ensure sustainable uses. This study focuses on assessing wetland health in Kigoya wetland located in the western province of Rwanda by employing the Wetland Health Index, a multivariable approach integrating Geographic Information Systems (GIS) and remote sensing by analyzing land use and land cover (LULC) spanning four decades (1990-2023). Moreover, a comprehensive Wetland Health Index was developed using Analytic Hierarchical Processes (AHP) amalgamating environmental and climatic factors to assess wetland resilience and vulnerabilities. Significant transformations in the wetland landscape were unveiled, including notable expansions of built-up areas and declines in bare land. Significant transformations in the wetland landscape were unveiled, due to dynamic conversion from natural conditions to man-made environment. Statistical analyses of the index revealed diverse wetland health statuses, with fair health comprising 76.89 Ha (45.35% of total area), good health covering 32.27 Ha (19.03%), poor health occupying 53.24 Ha (31.40%), and critical health encompassing 0.63 Ha (0.37%). These findings provide information on the status, health, and restoration potentials of Kigoya wetlands and similar ecosystems. The WHI index is useful for advocating for integrated conservation efforts to safeguard the wetland’s ecological integrity and resilience.

Material parameters effect and optimization of rail clip design for heavy haul subjected to different axle loads and speeds

2025-03-24T17:52:40+00:00

The fastening system, a critical component in railway engineering, serves the dual purpose of transferring the load from the rail to the sleeper while ensuring the rail’s steadfast position. Due to increase of annual tonnage, concrete sleepers and fastening systems have been experiencing a wide variety of failures that include rail seat deterioration, insulator wear, shoulder deterioration, and worn rail pads. The mechanical behavior of fastening system is not fully investigated and further research need to be done. The primary objective of this research is to analyze the impact of varying axle loads and speeds on rail clips, considering various mechanical properties. The study aims to comprehensively assess their overall influence on the performance of the railway system. Finite element method is used for this analysis. Modal analysis is utilized to pinpoint areas of maximum deformation, specifically at the point of contact with the rail (front toes) and the lower two arches. Further insight is gained through frequency response analysis, conducted across varying speeds and axle loads. Additionally, the analysis extends to exploring the impact of altering mechanical properties such as density, Young’s modulus, and Poisson’s ratio. The results demonstrate that increasing the values of the mechanical properties leads to an increase in both the amplitude and corresponding frequencies. The relationship between speed, axle load, and the corresponding frequencies and amplitudes is determined. The results not only confirm expectations but introduce novel observations, providing a comprehensive understanding of how these factors interplay in the railway system.

Critical success factors contributing to road project success in Tanzania. A case study of Tanzanian National Roads Agency - TANROADS

2025-03-24T17:56:04+00:00

In Tanzania, there is a knowledge gap in critical success factors for the implementation of road projects. This study aimed to assess how project critical success factors are evaluated in Tanzania. Semi-structured questionnaires were used to collect primary data from the Tanzania National Roads Agency (TANROADS). The top ten (10) critical success factors from the research findings are appointing a competent project manager, allocating sufficient resources, top and general management support, on-site project manager, client consultation, project mission, goals, philosophy, client acceptance, communication and procedures, goal commitment of the project team and schedule. It was recommended that effective communication and procedures, commitment to the project goals, cutting-edge knowledge to do cost estimations to increase efficiency, the appointment of competent project managers, the existence of on-site project managers, stakeholder engagement, sufficient resources, top and general management support and less political influence be strengthened to achieve road project performance.

Spatio-temporal erosion modelling for gullies control in Kigali city: Case of Kigali Sector

2025-03-24T18:00:24+00:00

Due to land scarcity, hilly topography, and the presence of a significant urban poor population in Rwanda, urban expansion driven by population growth in Kigali city has encroached upon vulnerable ecological areas, resulting in gully erosion. Given the intersection between erosion processes, urban dynamics, and specific locations in urban areas, monitoring temporal variations in erosion is essential for prioritizing resources for controlling gully in areas experiencing the highest erosion. This study aims to model the spatio-temporal patterns of soil erosion to support gully control efforts in Kigali, specifically focusing on the Kigali sector. Potential gully sites were identified using a Digital Elevation Model (DEM) and field measurements. The Integrated Valuation of Ecosystem Services and Tradeoffs-Sediment Delivery Ratio (InVEST-SDR) model was applied to quantify erosion intensity over the period from 2000 to 2022. Data analysis used Pearson’s correlation to evaluate the relationship between estimated erosion levels and observed gully measurements. Zonal statistics analysis was conducted to assess the annual variation in soil erosion intensity at the cell level, aiming to identify areas prone to high erosion. The results indicate that both temporal and spatial erosion intensities increased during the 2010 period, rising to 43 and 150 tons/ha/year, up from 45 and 145 tons/ha/year in 2000. However, in 2015, these rates decreased to 38 and 103 tons/ha/year, before rising again in 2022 to 49 and 133 tons/ha/year. The results from field validation reveal a positive correlation (0.6) between gullies and soil erosion that is exacerbated by rapid urbanization. The findings and analytical approach of this study can support policy and decision-makers in developing cost-effective interventions to manage gullies and reduce soil erosion in the region most affected by soil degradation.