Department of Civil Engineering

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Assessment of Hydro-climatic Trends and Variability over the Black Volta Basin in Ghana
(Springer Science and Business Media Deutschland GmbH, 2020) Abungba, J. A.; Khare, D.; Pingale, S. M.; Adjei, K. A.; Gyamfi, C.; Odai, S. N.
The present study examines the trends of hydro-climatic parameters over the Black Volta Basin in Ghana. Trend analysis was carried at different time scales (i.e., monthly, seasonal, and annual) from 1961 to 2016. Modified Mann–Kendall (MMK) test, Sen’s slope estimates, and Pettit–Mann–Whitney test were applied to compute the existence of a trend, the degree of change, and probable change point, respectively. The results revealed that there are warming trends over the entire Black Volta Basin. Both temperature extremes, i.e., highest and lowest (annual, seasonal, and monthly scale), for upstream and downstream region revealed an increasing trend. The annual rainfall in the upstream region depicted a downward trend, while downstream showed an increasing trend in the Basin. The seasonal trend analysis for rainfall depicted a falling trend (@ Sen’s slopes − 0.47 and − 0.69) with a percentage change over the 56 years − 19.66% and − 19.30%, respectively, for upstream and downstream regions during the dry periods. While, the rainy season showed a decreasing rainfall trend (@ Sen’s slope − 0.71 and percentage change − 4.41%) for the upstream region and increasing (@ + 0.71 & 4.39%) for the downstream. However, annual rainfall for the sites in the Basin depicted a decreasing trend (@ − 0.88 and − 4.76%) for upstream and an increasing trend (@ + 0.16 with 0.81% change) for downstream region. Annual streamflow revealed an increasing trend (@ + 0.02 with a 1.53% change) over the 43 years for upstream and a decreasing trend (@—0.41 and − 15.04% change) for downstream region at Chache-Bole. Therefore, this study output will be helpful for different stakeholders and policymakers within the Black Volta Basin of the West African sub-region toward improving decisions on water resources management.
Assessment of the quality of the Densu river using multicriterial analysis and water quality index.
(Applied Water Science, 2021) Ofosu, S. A.; Adjei, K. A.; Odai, S. N.
The natural resources, especially water in the Densu river basin, play signifcant roles in the socio-economic development of Ghana. The purpose of this study was to analyse the water quality of the Densu river using water quality index (WQI) and multivariate techniques. In this study, physico-chemical and bacteriological parameters were measured from surface water samples taken from eight (8) sampling stations in the study area. water quality index and multivariate techniques such as hierarchical cluster analysis and principal component analysis were utilized in the analysis of surface water quality data. The results indicated that the average WQI of the Densu river for the two sampling periods was sixty-one (61) which is classifed as Medium, based on the Solway WQI index. The pH levels of all the samples were within allowable limits of World Health Organization (WHO) guidelines. All the sampling stations for the two seasonal periods had bacteriological parameters higher than WHO guidelines, making the samples unsuitable for most domestic uses. The study revealed that six (6) principal components accounted for about 97% of the total variance of dataset and three (3) spatial clusters were classifed. This research has provided the basis for applying both WQI and multivariate techniques in analysing and classifying water quality in a river basin.
Big data challenges in transportation: A case study of traffic volume count from massive radio frequency identification (RFID) data.
(2017) Wemegah, T. D.; Zhu, S.
We are in an advancing stage of data acquisition and an even greater dynamic stage of dealing with big data. Data sizes have evolved over the years from a few kilobytes to Exabyte. The transportation engineer has also been caught up in the big data era and to efficiently analyze this massive data for maximum benefits, various challenges relating to data acquisition, data storage, data cleaning, data analysis and visualization has to be overcome. In this paper, we discuss these challenges and approaches to managing them with respect to massive Radio Frequency Identification data for traffic volume count in Nanjing, China. We recommended software, use analytical and visualization techniques like aggregation, graduated circular symbols and traffic count map to overcome big data challenges to produce peak hour, offpeak hour traffic volume counts and traffic count maps showing locations of low and high volume traffic. The paper, therefore, contributes to the management of big data by transportation engineers for traffic volume and congestion analysis.
Biotite influence on the binding properties of bituminous materials.
(International Journal of Engineering Research & Technology (IJERT), 2017) Aforla, B.; Woode, A.; Amoah, D. K.; AY, B. S.
The effect of biotite on rheological properties of bitumen was investigated using biotite extracted from gneiss rocks. The research methodology involves two phases. The first phase involves the separation of biotite from gneiss rock. The second phase involved tests carried out on bitumen- biotite blend to determine the effect of biotite on the rheological properties of bitumen. The biotite was ground to 75Âµm size and blended with bitumen AC-10 prepared in various proportions and the rheological properties determined in the laboratory. The results of this study shows that biotite improves the binding properties of bitumen. At low temperatures, the presence of biotite in bituminous mixtures in the proportion of 2 to 3.5% by weight of bitumen improves the binding properties. Conversely, at higher temperatures of about 135oC, the biotite bitumen mix showed best result at 2%. An increase of up to 3.5% by weight of biotite resulted in a drop in the kinematic viscosity values even though there was an improvement in the binding properties over the pure AC-10 bitumen results.
Causes of delays in highway construction projects in Ghana
(Civil and Environmental Research, 2016) Aforla, B.; Woode, A.; Amoah, D. K.
Delays in construction projects are a global phenomenon, causing a multitude of negative effects on the key project participants – clients, consultants, and contractors. The main purpose of this study is to identify the causes of delay of highway construction projects in Ghana to determine the most important to the key project participants. Literature review and semi-structured interviews of 12 key players in the implementation process were conducted. Thirty five possible causes of delay were identified and further grouped into ten categories. A questionnaire survey was conducted on the resulting list of delay causes for the identification of the most important causes of delay. The relative importance of the individual causes were determined and ranked by their Relative Importance Index. The findings revealed that the five most important causes of delay in road construction projects in Ghana are 1) Delay in honouring payment certificates 2) Equipment failure 3) Shortage of materials 4) Poor site management 5) Late delivery of materials on site. It is hoped that the findings of this paper will help project participants to act on critical causes to minimize delay of their projects.
Challenges and facilitators of public engagement with water, sanitation, hygiene and other environmental health issues in Ghana and Uganda: Perspectives of scientists
(Journal of Water, Sanitation and Hygiene for Development, 2020) Appiah, B.; Poudyal, A.; Anum, D. A.; Appiah, G.; Wesuta, A. C.; Akodwaa-Boadi, K.; Odai, S. N.
Despite many water, sanitation, hygiene (WASH) and other environmental health challenges in sub-Saharan Africa, little is known about interactions involving scientists, journalists and the public to aid public understanding of the relationship between WASH and health. Using purposive sampling, we conducted key informant interviews and focus group discussions with scientists, journalists and members of the public in Ghana and Uganda to identify issues associated with the promotion of public engagement with WASH and other environmental health issues. An inductive thematic analysis was used to explore the evidence, challenges and opportunities of public engagement. The effectiveness of public engagement was constrained by poor interactions between scientists and journalists and limited understanding among the public on WASH and other environmental health issues. Challenges identified included inadequate scientists–journalists collaborations, scientists' lack of time, pressure from media organizations and concerns about journalists' inadequate capacity to communicate environmental issues due to lack of training. Possible solutions included increased interactions, science communication training and using public information officers as knowledge brokers between scientists and journalists to boost public engagement with WASH and other environmental health issues. Our study contributes to the literature on the need to actively engage the public with WASH and other environmental health concerns.
Change and Analysis of Extreme Rainfall Indices During 1960–2010 and 2011–2100 in Abidjan District (Côte d’Ivoire).
(Climate Change Research at Universities, 2017) Danumah, J. H.; Odai, S. N.; Saley, M. B.; Akpa, L. Y.; Szarzynski, J.; Kouame, F. K.
Flood risk occurrence is very often related to heavy precipitation. The availability of analysis of weather data is a potential source for long term flood risk prediction and management. The aim of this paper was to determine and analyse trends of observed and future rainfall indices from 1961 to 2010 and 2011 to 2100 using rclimdex model in Abidjan District. This work was based on the integration of daily weather data within rclimdex model throughout quality control test, homogeneity test and indices calculation of ten (10) rainfall indices. The results showed an overall decrease trend of the rainfall indices namely through a negative trend in the annual total rainfall, maximum number of consecutive wet days, and number of extremely wet days during the period from 1961 to 2010. Exception was made from 1995 to 2010 where the same indices showed a positive trend. However, the results have showed also an increase trend of consecutive wet days (CWD), Simple daily intensity index (SDII) and Number of heavy precipitation days (R10) indices from 2011 to 2100. Thus these findings explain the nowadays flood occurrence and indicate that rainfall extreme under flood risk events will continue in the future. Therefore it call decision makers for preparedness and mitigation strategies in Abidjan District.
Characterisation of fractured carbonate aquifers using ambient borehole dilution tests.
(Journal of Hydrology, 2020) Agbotui, P. Y.; West, L. J.; Bottrell, S. H.
Fractured carbonate aquifers derive their transmissivity essentially from a well-developed network of solutionally-enhanced fractures and conduits that can lead to high groundwater velocities and high vulnerability to contamination of water quality. Characterisation of the variation of hydraulic properties with depth is important for delineating source protection areas, characterising contaminant fate and transport, determination of the effectiveness of aquifer remediation, and parameter estimation for models. In this work, ambient open borehole uniform and point injection dilution tests were conducted on observation boreholes in the unconfined Cretaceous Chalk aquifer of East Yorkshire, UK, and interpreted in conjunction with other data via the implementation of a new work flow. This resulted in the characterisation of flow in these boreholes and the inference of properties such as groundwater flow patterns and velocities in the surrounding aquifer formation. Our workflow allowed sections of open boreholes showing horizontal versus vertical flow to be distinguished, and the magnitude of such flows and exchanges with the aquifer to be determined. Flow within boreholes were then used to characterise: i) presence and direction of vertical hydraulic gradients; ii) nature and depth distribution of flowing features; iii) depth interval porosity and permeability estimation of the flowing features from overall borehole transmissivity and geophysical image or caliper logs; iv) groundwater velocity estimation in the surrounding aquifer. Discrete flowing features were distributed across the range of depths sampled by the observation boreholes (typically up to 45–60 mbgl), but the majority were located in the zone of water table fluctuation marked by solutionally enlarged flow features. Quantitative interpretation of both uniform injection (tracer distributed throughout the open borehole section) and point injection (slug of tracer introduced at targeted depth) yielded vertical velocities within the borehole water column in broad agreement with those measured by flow logging. Depth specific fracture kinematic porosities inferred from the ambient dilution data combined with long-interval pump test and geophysical log data ranged between 3.7 × 10−4–4.1 × 10−3 with an average of 2.1 × 10−3; these values were in excellent agreement with those from other methods applied to the same aquifer such as larger scale pumping tests. A new approach to estimation of groundwater velocities from the dilution test data using externally measured hydraulic gradients gave inferred horizontal groundwater velocities ranging between 60 and 850 m/day, in full agreement with those from previously conducted borehole-to-borehole tracer tests. These results confirm that the studied aquifer is karstic, with rapid preferential pathways which have implication for flow and transport modelling, and pollution vulnerability. Our study results indicate that ambient single-borehole dilution approaches can provide an inexpensive and reliable approach for the characterisation of fractured and karstic aquifers.
Characterization of a fractured aquifer using open-well dilution tests.
(80th European Association of Geoscientists & Engineers (EAGE) Conference and Exhibition, 2018) Agbotui, P.Y.; West, J.; Bottrell, S.
An approach to characterization of multilayer aquifer systems using open well borehole dilution is described. The approach involves measuring observation well flow velocities while a nearby extraction well is pumped by introducing a saline tracer into observation wells and collecting dilution vs. depth profiles. Inspection of tracer profile evolution allows discrete permeable layers within the aquifer to be identified. Dilution profiles for well sections between permeable layers are then converted into vertical borehole flow velocities and their evolution, using an analytic solution to the advection-dispersion equation applied to borehole flow. The dilution approach is potentially able to measure much smaller flow velocities that would be detectable using flowmeters. Vertical flow velocity data from the observation wells are then matched to those generated using a hydraulic model of the aquifer system, "shorted" by the observation wells, to yield the hydraulic properties of the constituent layers. Observation well flow monitoring of pumping tests represents a cost-effective alternative or preliminary approach to pump testing each layer of a multilayer aquifer system separately using straddle packers or screened wells and requires no prior knowledge of permeable layer depths and thicknesses. The modification described here, of using tracer dilution rather than flowmeter logging to obtain well flow velocities, allows the approach to be extended to greater well separations, thus characterizing a larger volume of the aquifer. An example of the application of this approach to a multilayer Chalk Aquifer in Yorkshire, Northeast England, is presented.
Comparison of missing data infilling mechanisms for recovering a real-world single station streamflow observation
(International Journal of Environmental Research and Public Health, 2021) Baddoo, T. D.; Li, Z.; Odai, S. N.; Boni, K. R. C.; Nooni, I. K.; Andam-Akorful, S. A.
Reconstructing missing streamflow data can be challenging when additional data are not available, and missing data imputation of real-world datasets to investigate how to ascertain the accuracy of imputation algorithms for these datasets are lacking. This study investigated the necessary complexity of missing data reconstruction schemes to obtain the relevant results for a real-world single station streamflow observation to facilitate its further use. This investigation was implemented by applying different missing data mechanisms spanning from univariate algorithms to multiple imputation methods accustomed to multivariate data taking time as an explicit variable. The performance accuracy of these schemes was assessed using the total error measurement (TEM) and a recommended localized error measurement (LEM) in this study. The results show that univariate missing value algorithms, which are specially developed to handle univariate time series, provide satisfactory results, but the ones which provide the best results are usually time and computationally intensive. Also, multiple imputation algorithms which consider the surrounding observed values and/or which can understand the characteristics of the data provide similar results to the univariate missing data algorithms and, in some cases, perform better without the added time and computational downsides when time is taken as an explicit variable. Furthermore, the LEM would be especially useful when the missing data are in specific portions of the dataset or where very large gaps of 'missingness' occur. Finally, proper handling of missing values of real-world hydroclimatic datasets depends on imputing and extensive study of the particular dataset to be imputed.
Delineation of preferential flow pathways in a tropical crystalline rock aquifer in Tarkwa, Ghana using integrated hydrogeophysical methods
(IWA, 2023) Agbotui, P. Y.; Ewusi, A.; Seidu, J.; Brookman-Amissah, M.; Woode, A.
In Ghana, crystalline rock aquifers with secondary hydraulic features and preferential flow pathways serve as very important aquifers. Protecting and managing these geological porous media require identifying preferential flow pathways and hydraulic characteristics. In this study, preferential flow pathways and hydraulic parameters were characterised for two boreholes (Hilly and Valley) located in Tarkwa, Ghana via the integrated use of borehole dilution testing (BDT), slug testing, and geological mapping. The geological fieldwork mapped a relatively sparsely fractured Sandstone Unit overlying a heavily foliated and fissile Phyllite Unit. Geology influenced groundwater flow in boreholes. The BDT confirmed the geology by showing a stratified flow system with preferential flow pathways. The Hilly/recharge area borehole shows relatively low downward flow, whereas the Valley/transition area borehole is dominated by the concentrated diffuse horizontal flow. These flow patterns are in agreement with the borehole locations and their dominant geologies. The estimated hydraulic conductivity, transmissivity, and storage coefficient ranged between 5.1 104 –7.7 102 m/d, 4.0 102 –3.2 m2 /d, and 107 –105 , respectively. The cheap integrated hydrogeophysical methods used in this study are applicable for characterising, protecting, and managing other crystalline aquifers in the West African sub-region and other tropical terrains.
Delineation of preferential flow pathways in a typica crystalline rock quifer in Takwa, Ghana using integrated hydrogeo
(IWA Publishing, 2023-04-29) Agbotui, P.Y, Ewusi, A., Seidu J., Brookman-Amissah, M., Woode, A., Aforla, B.
Ecological vulnerability of the Densu River Basin due to land use change and climate variability
(Cogent Engineering, 2020) Ofosu, S. A.; Adjei, K. A.; Odai, S. N.
Ecological hazards such as floods, drought and poor water quality remain notable disparaging natural catastrophes of climate variability in West Africa. Associated hazard manifestation is an amalgamation of various factors, which require enhanced knowledge of its spatio-temporal extent. This work aims at the identification and mapping of areas prone to ecological vulnerabilities in the Densu River Basin of Ghana. This research utilized a combination of Analytical Hierarchical Process (AHP) and multicriteria methods (MCM) using dataset such as land use land cover, type of soil, slope, drainage density, rainfall variability and the community distribution in the basin, using Geospatial Technology. Vulnerability mapping models were developed for flooding, drought and surface water quality. The resulting analysis revealed that about 15% of the basin was highly vulnerable to flooding, about 1% was prone to drought and 6% was prone to poor surface water quality. It was revealed that the southernmost part of the basin was susceptible to flooding whilst communities along the tributaries of the Densu river were predisposed to flooding and poor water quality. The study further displayed the extent of vulnerability of the communities within the Densu basin. Uniquely, a combination of AHP and MCM was successfully used to map the vulnerability of a river basin. Therefore, it is now possible to extend the procedures to other river basins for the development of effective mitigating strategies for future hazards
Enhancing food waste compost quality with nutrient amendments.
(Journal of Recycling Organic Waste in Agriculture, 2022) Nkansah, J. B.; Oduro-Kwarteng, S.; Essandoh, H. M. K.; Kuffuor, R. A.
Purpose Recycling of food waste fraction of municipal solid waste into compost for use in agriculture is seen as an effective environmentally–friendly option. In developing countries, however, there are few commercial composting facilities producing composts whose use in agriculture is low, mainly due to their low nutrient content compared to chemical fertilizers. Method This study investigated the effect of the food waste (FW) nutrient-amendment ratio on compost quality using amendments such as Cocoa Pod Husk Ash (CPHA), poultry manure (PM), and cow manure (CM). Six treatments (T1, T2, T3, T4, T5, and T6) and control were composted for 70 days. Results The total Nitrogen, total Phosphorous, and total Potassium content ranged from 0.96–1.42%, 0.19–0.78%, and 0.86-1.42%, respectively, for the different compost types. In all treatments, the C/N ratio reduced significantly, while concentrations of heavy metals (Pb and Zn) were within the acceptable international limits. Toxicity of composts to cucumber (Cucumis sativus) was ascertained. Germination index (GI) was the highest in T5 (FW amended with PM only) whereas the control (FW only) recorded the least GI. Conclusion This study shows that the use of PM, CM, and CPHA seems to be beneficial for the enrichment of food waste compost.
Estimating the spatial distribution of evapotranspiration within the Pra River Basin of Ghana
(Elsevier Ltd, 2021) Nsiah, J. J.; Gyamfi, C.; Anornu, G. K.; Odai, S. N.
It is important in water resource planning to accurately estimate the spatial distribution of evapotranspiration (ET) as an input parameter for hydrological studies. Although, conventional pan evaporation, lysimetric and eddy covariance techniques have been used, they only estimate point values. Hence, this study aimed at estimating the spatial distribution of ET within the Pra River Basin (a forest ecological zone) of Ghana, using cloud-free Landsat 8 (OLI/TIRS) satellite images employing the SEBAL methodology. The study further estimates the spatial distribution ET in relation to major climatic variables, Land Use Land Cover (LULC) types and energy balance components. The overall spatial distribution of ET had a mean value of 5.63 mm/day. Spatial distribution of ET (mm/day) for water body (5.51–7.81) and uncultivated forest (5.10–7.71) were high, while moderately average values were observed for logged forest (4.80–7.51). Settlement and bare landscapes observed low rates ((2.05–5.10) mm/day). Spatially, ET was higher in the upper western, central and the eastern parts of the basin, but lower in the northern part and pockets of areas at the southern part of the basin where settlement/bare landscape and logged forest dominate. Areas with high temperature and high solar radiation experiences high ET, while low wind speed, low to average temperature and solar radiation areas experience low ET. Also, areas with both high net radiation and ground heat flux but low to average sensible heat flux experiences high ET and vice versa. Linear regression analysis showed good fit with slope of 0.76 and R2 of 0.93 indicating that 93 % of the variations in observed field measurement of ET fitted perfectly well with ET distributions generated by the SEBAL model.
Estimation of Shipping Emissions in Developing Country: A Case Study of Mohammad Bin Qasim Port, Pakistan.
(International Journal of Environmental Research and Public Health, 2022) Hussain, I.; Wang, H.; Safdar, M.; Ho, Q. B.; Wemegah, T. D.; Noor, S.
Transportation has the highest dependence on fossil fuels of any sector and accounts for 37% of carbon dioxide (CO2) emissions. Maritime transportation is responsible for around 940 million tons of CO2 and approximately 3% of global emissions annually. The significant increase in shipping activities around the globe has magnified the generation of toxic pollutants. In recent years, shipping emissions have received significant attention in developed countries due to global climate change, while in developing countries, researchers are making enormous efforts to tackle this catastrophic and pressing issue. This study considers Muhammad Bin Qasim Port (MBQP), Karachi, Pakistan as a case study. This study employed an activity-based or bottom-up approach with a standard procedure to estimate the various anthropogenic pollutants emissions including particular matters (PM10 and PM2.5), nitrogen oxide (NOx), sulfur dioxide (SO2), carbon monoxide (CO), CO2, methane (CH4), non-methane volatile organic compound (NMVOC), and hydrocarbon (HC) under different operational modes, i.e., hoteling, maneuvering, and reduced speed zones. The results indicated that CO2 was the highest contributor with a proportion of 92%, NOx 5%, and SO2 1.5% for all three operational modes. Moreover, the results indicated that container ships account for 64% of overall emissions, followed by tankers for 24%. Regarding the monthly trend, the findings revealed that November and December had the highest emission rates, with over 20% of the total emissions recorded. This study’s findings will assist stakeholders and policymakers to prioritize maritime emissions in developing countries.
Evaluating the impact of an agricultural land‐use change adaptation strategy on household crop production in semi‐arid Ghana.
(Singapore Journal of Tropical Geography, 2021) Badmos, B. K.; Villamor, G. B.; Agodzo, S. K.; Odai, S. N.; Badmos, O. S.
In this study, the Land Use Dynamic Simulator model was applied to investigate the impact of farm credit as an adaptation strategy to cope with effects of climate variability on agricultural land-use change and crop production in the Vea watershed in Ghana. The authors identified the determinants of crop choices within the landscape (e.g., farm household and biophysical characteristics of farm plot). The crop choice sub-model was then linked to the crop yield sub-model to determine the yields of selected crops. In adapting to the impacts of climate variability, the maize credit adoption sub-model under the maize cultivation credit scenario was integrated into decision-making. This was simulated for a 20-year period, and compared with the business-as-usual scenario. Under the simulated maize credit scenario, maize adopters increased from about 20 per cent to about 50 per cent and the area allocated for maize cultivation significantly increased by about 266 per cent. Consequently, the average annual aggregated household crop yield increased by 6.3 per cent higher than in the business-as-usual scenario. This simulation study shows that access to maize credit can significantly influence agricultural land-use change and food availability in the study area. However, although access to farm credit may translate into food availability, the sustainability of this strategy is questionable.
Evaluation and Comparison of Satellite Rainfall Products in the Black Volta Basin
(Springer Science and Business Media Deutschland GmbH, 2021) Logah, F. Y.; Adjei, K. A.; Obuobie, E.; Gyamfi, C.; Odai, S. N.
This study evaluated the performance of five satellite rainfall products (CHIRPS, PERSIANN, TRMM, RFE, and ARC) in the Black Volta Basin (BVB) using four performance evaluation methods: pairwise statistics, categorical statistics, rainfall intensity distribution, and extreme rainfall indices. In all, 21 rainfall stations distributed across the BVB with daily data spanning from 1981 to 2010 were used in the study. A high linear relationship was observed between observed and satellite rainfall data at decadal and monthly time scales as compared to weak relationship at the daily and annual time scales. The rainfall amount was least underestimated by CHIRPS at all the time scales. CHIRPS, PERSIANN and RFE performed well with the least deviation (BIAS ≤ 10%) from the observed rainfall amount at all time scales. Considering the high correlation coefficient and good NSE at decadal, monthly, and annual time scales, rainfall in the BVB is best represented by CHIRPS, followed by PERSIANN, RFE, ARC, and TRMM in that order. Though the probability of correctly detecting rainfall events is high (POD = 0.57–0.94), the satellite products were not able to adequately detect rainfall events in the basin at the daily time scale. The TRMM product was better in reproducing a very high rainfall amount (R ≥ 5 mm/day) in the basin as compared to CHIRPS, PERSIANN, RFE, and ARC. Extreme rainfall indices (R20, R99p, CWD and SDII) in the study basin were best represented by CHIRPS. Generally, precipitation in the BVB is best represented by CHIRPS, followed by PERSIANN, TRMM, RFE, and ARC in that order.
Evaluation of potential evapotranspiration assessment methods for hydrological modelling with SWAT in the Densu river basin in Ghana.
(International Journal of Environmental Science and Technology, 2022) Adjei, F. O.; Obuobie, E.; Adjei, K. A.; Odai, S. N.
Accurate estimation of evapotranspiration (ET) is required for a good estimation of available water for use in any catchment as ET constitutes major means by which water is lost in any catchment. SWAT model uses climate data in estimating potential evapotranspiration (PET). The PET together with other parameters is then used in estimating actual evapotranspiration (AET). SWAT model provides three different methods in estimating PET which are Penman–Monteith (PM), Hargreaves (H) and Priestly–Taylor (PT). These three PET methods were evaluated in a limited available spatial and temporal data Densu river basin to assess their impact on the resulted model water balance. The missing data in the 8 climate stations that were used in this study were estimated using a WXGEN weather generator. The results showed that the accuracy of the water balance from the SWAT model was defined by how well the PET method selected for the SWAT was able to estimate an accurate spatial and temporal distributed PET in the basin. A discharge at Nsawam, a town within the basin, was used for the model calibration and validation. Hargreaves PET method had the best Nash–Sutcliffe model efficiency coefficient (NSE) values of 0.70 for the calibration and 0.74 for validation period, while the PM PET method had the worse NSE value of 0.66 for calibration and 0.62 for validation. These results were attributed to the limited available data within the basin. The discrepancies in the resultant water balance model could be attributed to the three different PET methods used in relation to the climate data that were available for the calibration and validation of the SWAT model.
Evaluation of RFE Satellite Precipitation and its Use in Streamflow Simulation in Poorly Gauged Basins
(Springer Science and Business Media Deutschland GmbH, 2021) Darko, S.; Adjei, K. A.; Gyamfi, C.; Odai, S. N.; Osei-Wusuansa, H.
Abstract: The performance of satellite Rainfall Estimates (RFE, version 2.0) at daily resolution was evaluated in comparison with ground-based meteorological datasets (GBD) by applying statistical and hydrological modeling approaches. In-situ daily rainfall observations from 5 stations in and around the periphery of the Nasia river basin in Ghana, covering a period of 15 years (2001–2015), were used in this research. Comparison of the observed rainfall data with satellite-based estimates revealed a strong positive correlation, which yielded the highest correlation coefficient (R2) of 0.74 at the monthly timescale as against the weak positive linear relationship with the highest R2 of 0.41 at the daily timescale. Mean annual precipitation computed from both datasets also showed close correspondence yielding 978.83 mm/annum and 977.12 mm/annum for RFE and GBD, respectively. Calibration at the daily timescale showed that the ground-based data (GBD) performed better in simulating the observed streamflows compared to the satellite-based (RFE) simulations yielding a Nash Sutcliffe Efficiency (NSE) of 0.81 and 0.67 for the GBD and RFE, respectively. At the monthly timescale, the performance of both datasets improved, resulting in an NSE of 0.89 and 0.80 for the GBD and RFE, respectively. Although the RFE-based simulations could not perfectly reproduce the observed discharge, it can be used to supplement traditional in-situ gauge data to address the problem of non-availability of observed rainfall data for hydrological applications such as water resources planning and assessment. Future research into the usability of the RFE in other medium scale river basins could be carried out to compare with these results. Highlights: • There is a strong correlation between RFE version 2.0 and ground-based monthly rainfall data • RFE-based simulations appear to underestimate the observed hydrographs compared to ground-based data simulations • RFE could be used to supplement in-situ observations of rainfall for hydrological analysis

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