Flood and Food Security in the Benue Valley: Stylized Facts

The scientific consensus is that global climatic change is caused by human activities. Global climate variation has altered the pattern of annual rainfall in most parts of the world, resulting in annual flooding with devastating effects on humanity. With many rivers that crisscross the Nigerian landscape, the country has experienced a number of flood incidents along the river basins (valleys) with varying degrees of devastation. This paper, thus, focuses on the effects of flood on food security in the Benue Valley. The specific objectives of the study include: to examine the effects of flood on food supply; prices of agricultural output; and the level of public and private aids to flood victims within the study area. A sample of households and market leaders were interviewed for the purpose of data collection. Data was equally sourced from Non-governmental Organizations, State Emergency Management Agencies, and other written sources. The data was analyzed and presented using simple bar charts. Findings revealed that there is always a gross inadequacy of food supply during the years of devastating floods compared to years of normal annual rainfall. Prices of agricultural products increased by almost 200% and household income declined significantly during the flood disaster years. Findings also revealed that private organizations sometimes render more aids to flood victims than the public sector. To arrest the danger of annual devastating floods in the Benue Valley, the paper recommends better water infrastructure management strategies like the construction of more dams and dredging of River Benue

Representative elementary volume (REV) of cementitious materials from three-dimensional pore structure analysis

The representative elementary volume (REV) is a fundamental property of a material, but no direct measurements exist for cementitious materials. In this paper, the REV of cement pastes with supplementary cementitious materials (GGBS, PFA, SF) was determined by analysing the three-dimensional pore structure (> 0.2 μm) using laser scanning confocal microscopy (LSCM). The effect of axial distortion inherent to LSCM on 3D pore structure was also investigated. A range of 3D pore parameters was measured using skeletonisation, maximal ball and random walker algorithms. Results show that axial distortion has insignificant effects on most parameters except Euler connectivity, average pore and throat volumes and directional diffusion tortuosities. Most pore parameters become independent of sampling volume at ≈ 603 μm3 except diffusion tortuosities and formation factor. The REV for porosity calculated based on a statistical approach at eight realisations and 5% relative error was found to be ≈ 1003 μm3

Optimising confocal Raman microscopy for spectral mapping of cement-based materials

Raman spectroscopy combined with confocal imaging, i.e. confocal Raman microscopy (CRM) is a relatively new technique with huge potential for high-resolution chemical mapping of phase composition and spatial distribution in cement-based materials. However, the effects of sample preparation and various operating parameters on mapping quality has not been systematically studied. This paper optimises CRM for spectral mapping of carbonated and non-carbonated cement-based materials. The effects of sample preparation and scanning parameters on the detection of four main phases (calcite, portlandite, ettringite and unreacted cement) were investigated. Results show that although freshly cut cementitious samples can be analysed as-is, the Raman signals improve with short gentle drying and surface grinding/polishing prior to analysis. Increasing laser power, exposure time and scan accumulation, and short laser wavelength yields higher signal-to-noise (SNR) ratio in the obtained spectrum. The use of a 4.15 mW laser power, 2 s exposure time and scan accumulation of 2 with 532 nm laser represents a good operating condition for Raman analysis of cement-based materials. This produces SNR > 10 for all investigated phases at short testing time and low risk of laser-induced damage. Microcracking caused by localised heating during closely-spaced mapping can be limited by impregnating the sample with epoxy to protect the microstructure. We show for the first time that CRM can be used to quantify the volume fraction of calcium carbonate and portlandite at high resolution when combined with SEM. The advantages and limitations of CRM for mapping cement-based materials are discussed

The impact of green roof ageing on substrate characteristics and hydrological performance

Green roofs contribute to stormwater management through the retention of rainfall and the detention of runoff. However, there is very limited knowledge concerning the evolution of green roof hydrological performance with system age. This study presents a non-invasive technique which allows for repeatable determination of key substrate characteristics over time, and evaluates the impact of observed substrate changes on hydrological performance. The physical properties of 12 green roof substrate cores have been evaluated using non-invasive X-Ray Microtomography (XMT) imaging. The cores comprised three replicates of two contrasting substrate types at two different ages: unused virgin samples; and 5-year-old samples from existing green roof test beds. Whilst significant structural differences (density, pore and particle sizes, tortuosity) between virgin and aged samples of a crushed brick substrate were observed, these differences did not significantly affect hydrological characteristics (maximum water holding capacity and saturated hydraulic conductivity). A contrasting substrate based upon a light expanded clay aggregate experienced increases in the number of fine particles and pores over time, which led to increases in maximum water holding capacity of 7%. In both substrates, the saturated hydraulic conductivity estimated from the XMT images was lower in aged compared with virgin samples. Comparisons between physically-derived and XMT-derived substrate hydrological properties showed that similar values and trends in the data were identified, confirming the suitability of the non-invasive XMT technique for monitoring changes in engineered substrates over time. The observed effects of ageing on hydrological performance were modelled as two distinct hydrological processes, retention and detention. Retention performance was determined via a moisture-flux model using physically-derived values of virgin and aged maximum water holding capacity. Increased water holding capacity with age increases the potential for retention performance. However, seasonal variations in retention performance greatly exceed those associated with the observed age-related increases in water holding capacity (+72% vs +7% respectively). Detention performance was determined via an unsaturated-flow finite element model, using van Genuchten parameters and XMT-derived values of saturated hydraulic conductivity. Reduced saturated hydraulic conductivity increases detention performance. For a 1-hour 30-year design storm, the peak runoff was found to be 33% lower for the aged brick-based substrate compared with its virgin counterpart

Moisture content behaviour in extensive green roofs during dry periods: the influence of vegetation and substrate characteristics

Evapotranspiration (ET) is a key parameter that influences the stormwater retention capacity, and thus the hydrological performance, of green roofs. This paper investigates how the moisture content in extensive green roofs varies during dry periods due to evapotranspiration. The study is supported by 29 months continuous field monitoring of the moisture content within four green roof test beds. The beds incorporated three different substrates, with three being vegetated with sedum and one left unvegetated. Water content reflectometers were located at three different soil depths to measure the soil moisture profile and to record temporal changes in moisture content at a five-minute resolution. The moisture content vertical profiles varied consistently, with slightly elevated moisture content levels being recorded at the deepest substrate layer in the vegetated systems. Daily moisture loss rates were influenced by both temperature and moisture content, with reduced moisture loss/evapotranspiration when the soil moisture was restricted. The presence of vegetation resulted in higher daily moisture loss. Finally, it is demonstrated that the observed moisture content data can be accurately simulated using a hydrologic model based on water balance and two conventional Potential ET models (Hargreaves and FAO56 Penman–Monteith) combined with a soil moisture extraction function. Configuration-specific correction factors have been proposed to account for differences between green roof systems and standard reference crops

Characterising the microstructure of cement-based materials using laser scanning confocal microscopy

Three-dimensional (3D) pore characterisation of cement-based materials is essential for understanding the influence of topological pore parameters such as connectivity and tortuosity on transport processes. The main objective of this thesis was to develop laser scanning confocal microscopy (LSCM) for 3D imaging and quantification of pore structure of cement-based materials at submicron resolution. To enable this, a novel approach to reconstruct large volumes of cement-based materials at submicron resolution was developed by combining serial sectioning with LSCM. The method uses a series of Z-stacks with overlapping regions for stitching based on phase correlation. With this method, no information is lost and the spatial resolution is maintained with increase in image size. The effects of axial distortion in LSCM images caused by mismatch of refractive indices between immersion medium and different phases within cement-based materials on various pore attributes were examined. Results indicated that parameters including porosity, specific surface area, percolation connectivity, scalar diffusion tortuosity and formation factor are not significantly affected by axial distortion. A generic correction method was proposed based on measuring the aspect ratio of pulverised fuel ash (PFA) particles in hardened blended pastes. The representative elementary volume for 3D pore characterisation of different cementitious systems was also investigated using a statistical approach. For a given number of realisations, an image volume of 1003 μm3 was found to give comparable porosity to that measured by 2D backscattered electron (BSE) microscopy. BSE signal variation across pore-solid boundaries was simulated using a 3D Monte Carlo technique to enhance image analysis of the pore structure. It was found that a single pore of down to 1 nm can be resolved with field emitters under ideal imaging conditions. The Overflow method was also found to be able to accurately segment pores larger than 1 μm with errors of ~1% and randomly inclined pores with an average error of ~5.2%. Effects of supplementary cementitious materials including silica fume (SF), pulverised fly ash (PFA) and ground granulated blastfurnace slag (GGBS) on the 3D pore structure of cement pastes were investigated using LSCM in conjunction with BSE microscopy. Generally, results from both techniques showed that SF enhances the pore structure (i.e. decreased porosity and percolation connectivity, and increased diffusion tortuosity) from early ages whereas PFA and GGBS show improvements at later ages. The percolation connectivity decreases while diffusion tortuosity increases drastically, as porosity reduces to ~15%. Measured 3D pore characteristics were used as inputs to simple analytical equations for predicting transport properties. Predicted results agreed reasonably well with measured values, mostly within a factor of five. An exploratory study into the application of fluorescence LSCM for real-time imaging of early cement hydration is also presented. Qualitative and quantitative analyses of microstructural developments in different hydrating cementitious systems were made. The advantages and limitations of LSCM for such application are also discussed.Open Acces

TRADE AND EMERGENCE OF ENTREPRENEURSHIP IN TIVLAND (1900 – 2020)

Trade and entrepreneurship are inextricably linked in all societies. Humans do not only engage in trade. They do so to profit, and when they can distinguish themselves in specific areas, they become successful entrepreneurs in those sectors. This research investigates the relationship between trade and entrepreneurship in Tivland from pre-colonial to post-colonial periods. The study contends that trade has existed among the Tiv people of Central Nigeria since far before colonialism. However, colonialists' integration of the Tiv economy into the global capitalist market increased trade in Tivland, resulting in the rise of many Tiv traders and entrepreneurs. However, from the late 1990s to the present, Tivland has seen a significant drop in trade and business. Several factors have been identified as contributing to the decline, including a drop in agricultural and industrial productivity in Benue State, a lack of adequate business education, a lack of financial discipline among younger generations, a lack of a good business succession plan, cultural impediments, and poor government policies, among others. To overcome hurdles, the government must establish an enabling climate for businesses to prosper, and citizens must have a favourable business mentality to stimulate trade and entrepreneurship. The study employs a historical approach to analysis, drawing on both secondary and primary sources

Improvements in the LLNL objective analysis scheme for deriving forcing fields for single-column models using ARM data

The objective analysis method use for deriving Single-Column Model (SCM) forcing fields with ARM data (Leach, et al., 1996) is undergoing continual improvement. Several improvements were identified at the SCM Workshop held at LLNL in April 1996. These include incorporating large-scale analyses in the objective analysis, and time-filtering input data streams

Experimental analysis of green roof detention characteristics

Green roofs may make an important contribution to urban stormwater management. Rainfall-runoff models are required to evaluate green roof responses to specific rainfall inputs. The roof's hydrological response is a function of its configuration, with the substrate – or growing media – providing both retention and detention of rainfall. The objective of the research described here is to quantify the detention effects due to green roof substrates, and to propose a suitable hydrological modelling approach. Laboratory results from experimental detention tests on green roof substrates are presented. It is shown that detention increases with substrate depth and as a result of increasing substrate organic content. Model structures based on reservoir routing are evaluated, and it is found that a one-parameter reservoir routing model coupled with a parameter that describes the delay to start of runoff best fits the observed data. Preliminary findings support the hypothesis that the reservoir routing parameter values can be defined from the substrate's physical characteristics