Eniola Damilola Ashaolu | University of Ilorin (original) (raw)

Papers by Eniola Damilola Ashaolu

Journal of Hydrology; Regional Studies, 2020

Study region: Osun Drainage Basin, Nigeria. Study focus: Estimating spatial and temporal pattern... more Study region: Osun Drainage Basin, Nigeria.

Study focus: Estimating spatial and temporal patterns of recharge is important for sustainable groundwater resources management. This is especially true for data poor regions, such as the Basement Complex in Nigeria, which has shallow aquifers, a proliferation of wells and no efficient groundwater monitoring network. This study evaluates the performance of a spatially distributed monthly water balance model (WetSpass-M) in estimating groundwater recharge. The WetSpass-M model has moderate data demands, which allows for comprehensive assessment of recharge.

New hydrological insights for the region: 27 % of the rainfall in Osun drainage basin becomes recharge, while the remaining is lost through evapotranspiration (43 %), surface runoff (21 %) and interception (9 %). September is the month with highest recharge, ranging between 0 and 73 mm in the north and 129 up to 213 mm in the south and northeast of the basin. The study revealed the significance of the applied water balance model in understanding the spatial and temporal status of recharge. Therefore, the spatial and temporal patterns of recharge should be taken into consideration in preparing a sustainable groundwater resources management plan for the Osun drainage basin. Artificial recharge might be adopted to store storm water runoff during wet periods to improve the groundwater supply in dry months. Also, monthly groundwater withdrawals should be regulated in relation to spatial and temporal recharge patterns.

Journal of Geology, Geography and Geoecology, 2019

Osun drainage basin is one of the regions in Nigeria experiencing increasing population growth an... more Osun drainage basin is one of the regions in Nigeria experiencing increasing population growth and rapid urbanization; and about 70% of the inhabitants rely on shallow groundwater resources of the region. Change in land use/land cover is one of the significant factors controlling regional hydrology and groundwater resources, thus the continuous change in land use and land cover of the drainage basin will significantly affect the basin's groundwater resources. There are 7 classified land use/land cover in the study area which are bare surfaces, built up area, crops/shrubs, forest, rock outcrops, water bodies and wetland. Applying WetSpass-M hydrological model, we predicted the effect of land use/land cover change on the groundwater recharge in Osun drainage basin, Nigeria between 1984-2015. The results revealed that the highest groundwater recharge of 48.56%, 33.64% and 37.29% occurred in forested area in 1984, 2000 and 2015, respectively. This result might be due to the influence of vegetation in slowing down the speed of running water across the forest area, that allows more infiltration and deep percolation into the water table to recharge the groundwater system. On the other hand, the least groundwater recharge of the total annual was on the rock outcrops, which are about 4% in 1984, 3% in 2000 and 2% in 2015. The least recharge found on rock outcrops is expected and may be attributed to the fact that infiltration can only occur around or on decomposed rock outcrop, which may result in minute recharge to the groundwater system. The mean annual groundwater recharge of the basin for the land use/land cover of 1984, 2000 and 2015 are 476.54, 411.07 and 430.06 mm/y, respectively. Overall, for the 32 years period of investigation, change in land use/land cover accounts for only 10% reduction in mean groundwater recharge occurrence between 1984 and 2015. Also, there is a change in recharge pattern in the study area during this period because most often, change in land use/land cover is a transition from one land use/land cover class to another, and the recharge pattern is influenced based on the degree of transition that took place and the characteristics of the dominant land use/land cover at a particular area of the basin. Although, the 10% reduction in mean annual recharge appears minute, this might become pronounced if the current rate of deforestation in the drainage basin continues unabated. Therefore, proper land use allocation, regulated land development and afforestation in terms of planting of native trees that were lost through anthropogenic activities in the basin should be policy option for groundwater sustainability. Вплив землекористування (зміни земного покриву) на поповнення запасів підземних вод в басейні річки Осун, Нігерія Е. Д. Ашаолу*, Дж. Ф. Олорунфемі, І. П. Іфабії Кафедра географії управління навколишнім середовищем, факультет соціальних наук, Університет Ілорін, Нігерія, *damash007@yahoo.com Анотація. Перші зВодосховище Осуна є одним з регіонів Нігерії, де спостерігається зростання населення і швидка урбанізація; і близько 70% жителів покладаються на неглибокі ресурси ґрунтових вод регіону. Зміна умов землекористування є одним з важливих факторів, що контролюють регіональну гідрологію та ресурси підземних вод. Таким чином, безперервна зміна використання землі та земельного покриву водозбірного басейну суттєво впливає на ресурси ґрунтових вод басейну. У досліджуваному районі є 7 класифікованих земельних ділянок (землекористування), якими є відкриті поверхні, забудовані території, сільськогосподарські угіддя, чагарники, ліси, відслонення гірських порід, водоймища та водно-болотні угіддя. За-стосовуючи гідрологічну модель WetSpass-M, ми прогнозували вплив зміни землекористування на живлення підземних вод

Journal of Environmental Geography , 2019

Over the years, Osun drainage basin has witnessed tremendous increase in population, and urbaniza... more Over the years, Osun drainage basin has witnessed tremendous increase in population, and urbanization that have changed the landscape of the area. This study evaluated the spatio-temporal pattern of land use/land cover change (LULC) in the study area, and made hydrological inferences. Landsat imageries were acquired from USGS-EROS satellite image database for the period 1984, 2000 and 2015, while the Digital Elevation Model (DEM) was obtained from Shuttle Radar Topography Mission (SRTM) of the National Aeronautics and Space Agency (NASA). Supervised image classification using the Maximum Likelihood Algorithm in Erdas Imagine was adopted to classified the land use/land cover of the study area into seven classes. Elevation, aspect and slope of the study area were processed from DEM using ArcGIS. Modules for Land Use Change Evaluation (MOLUSCE) plugin in QGIS was used to simulate the basin future LULC change, using change driving factors of population, elevation, aspect and slope of the study area. There was about 234% increase in built up areas and 89.22% in crop/shrubs between 1984 and 2015. The most significant decrease in LULC occurred in forest (58.75%) and wetland (84.69%) during this period. The predicted future LULC change suggests that only about 12% of the basin will remain under forest cover by the year 2046. The results underscored the increasing anthropogenic activities in the basin that influenced recharge rate, surface runoff, incidences of soil erosion, etc., in Osun drainage basin. The planting of the lost native trees was recommended for the sustainability of the basin's ecosystem.

Ruhuna Journal of Science, 2018

This study examined the climatic water balance and aridity in the Western Lithoral hydrological z... more This study examined the climatic water balance and aridity in the Western Lithoral hydrological zone of Nigeria. Monthly climatic data from 1976-2015 collected from six Nigeria Metrological Agency (NIMET) stations located in Ikeja, Ibadan, Akure, Abeokuta, Osogbo and Ilorin were used. The climatic variables are rainfall amount, temperature, sunshine hour, relative humidity and wind speed. The FAO Penman-Monteith method was adopted in estimating the potential evapotranspiration (PET). Water balance was determined from PET and rainfall amount. The spatial and temporal pattern of rainfall amount and PET were evaluated using universal kriging interpolation method, Mann-Kendall and regression trend analysis. The results of the Mann-Kendall and regression trend analysis revealed a statistically significant (Z= 2.74, P= 0.005) upward trend in rainfall amount between 1976 and 2015. Similarly, a statistically significant (Z= 4.40, p= 0.001) increasing trend was observed in PET during the same period. Six months of water surplus (May-October) and six months of water deficit (November-April) were identified. Overall, 27 years of water deficit was discovered over the 40 years period. Water balance pattern revealed the highest annual mean water surplus (324.51 mm) in the hinterland of Idanre, Akure, and Owo rather than the coastal city of Ikeja which can be attributed to orographic effect in the hinterland. The study area with a mean Aridity index (AI) of 0.94 can still be regarded as humid environment, although the spatial variability of AI indicates that the northern part is tending towards a dry sub-humid condition (AI= 0.76). This study recommends conservation of water surplus in the wet months for the augmentation of deficit in the dry months; this will not only boost agricultural production, but also alleviate water supply problem in the study area

Ruhuna Journal of Science , 2016

In Basement Complex rocks where rainfall is seasonal, water provision in dry season depends on re... more In Basement Complex rocks where rainfall is seasonal, water provision in dry season depends on regolith aquifer. For effective exploitation of groundwater resources, it is reasonable that geophysical investigation be conducted before development of well. In many instances, geophysical surveys may be expensive or nonexistent. Hence, there is a need for spatial analysis which might advise water engineers within such environments. Vertical Electrical Soundings (VES) data of 53 locations conducted with ABEM SAS-1000 terrameter using Schlumberger electrode configuration were obtained from the hydrogeology Department of Kwara state Ministry of Water Resources and Lower Niger River Basin and Rural Development Authority, Ilorin. VES locational coordinates were recorded using handheld GPS device. Sound curves were evaluated by partial curve matching approach and computer iteration using WinResist. The results depict six geo-electric regional successions, namely: top soil, lateritic clay, weathered basement, fairly-hard basement, thin fractured and hard basement. The geo-electric succession identified was plotted in Surfer 12 environment, using kriging interpolation method to show spatial distribution pattern of this zone. The spatial pattern is expected to give an insight to the nature of spatial variability of geo-electric layers and assist drillers as well as water resources policy makers in their operations.

The importance of drainage basin as a planning unit for water resources development and managemen... more The importance of drainage basin as a planning unit for water resources development and management cannot be overemphasized and this requires accurate characterization of the drainage basin. This study takes a closer look at the Osun drainage basin with a view to updating the existing records, estimate the morphometric features and make hydrological inferences. The data used in this study include a 30m resolution Digital Elevation Model (DEM) acquired from the United State Geological Survey (USGS), geology map of Nigeria acquired from Nigeria Geological Survey Agency (NGSA), Harmonized World Soil Database (HWSD) prepared by the Food and Agricultural Organization (FAO), and the 1991 locality population data of Nigeria acquired from National Population Commission (NPC). Remote sensing and GIS techniques were adopted in the analysis of the data using ArcGIS 10.2. The acquired DEM was used to delineate Osun drainage basin and 21 morphometric parameters were estimated. The results revealed that Osun drainage basin is a 4th order drainage basin, with an area of 9926.22km 2 , and a length of 213.08km. The area covered by the two geology types and the four soil types were quantified and it revealed that 93.28% of the basin is underlain by the Basement Complex rocks, while 50.89% of the basin is covered by sandy clay loam soil. All these will influence the basin discharge rate, chances of flood occurrence, peak flow, infiltration rate and recharging of the Osun basin groundwater system among others. Based on these results, this study serves as a scientific database for further detailed hydrological investigation of Osun drainage basin while benefiting the sustainable drainage basin management and development programmes of the Ogun-Osun Rivers Basins Development Authority.

Present paper tries to understand the influence of hydrogeological characteristics on groundwater... more Present paper tries to understand the influence of hydrogeological characteristics on groundwater yield of shallow wells in regolith aquifer, Ilorin, Nigeria. The data on hydrogeological characteristics such as drawdown, water level, depth of borehole, depth of overburden and well yield for 78 borewells were collected from Kwara State Ministry of Water Resources and Lower Niger River Basin Development Authority in Ilorin. While the aquifer transmissivity and well specific capacity was calculated from this data. The data obtained were subjected to Pearson moment correlation, multiple and stepwise multiple regression analysis. The results of the stepwise multiple regression (R 2 of .929) indicates that aquifer transmissivity and drawdown contributed 92.9% to the variability in well yield in the study area. It is concluded that while constructing wells, aquifer transmissivity and the rate of drawdown be taking into account for the purpose of having productive well in the study area.

Rainfall varies over time and space and the study of its variability cannot be over emphasized. T... more Rainfall varies over time and space and the study of its variability cannot be over emphasized. This paper examines spatio-temporal patterns of rainfall in Ilorin metropolis, Nigeria. 30 years data were collected in 3 locations [Nigeria Meteorological Agency (NIMET), Lower Niger River Basin Development Authority (LNRBDA) and Kwara State Water Corporation (KWWC)]. The analytical procedure includes trend analysis, reduction analysis, and ordinary kriging with Gaussian semivariogam model. The results showed that June and September recorded the highest amount of rainfall in Ilorin across the three stations. An upward trend of rainfall of about 0.30mm, 0.40mm and 0.2mm respectively, were recorded in the 3 stations. The reduction pattern analysis revealed the variability and percentage change in the amount of rainfall received in Ilorin over the 30 years of study. Nine regional pattern were also revealed from the kriging analysis, and a variability of 50mm were recorded over the 12km 2 sized metropolis. The southwestern part of Ilorin recorded more rainfall than the other parts. It was concluded that spatial distribution of annual rainfall in Ilorin, varied from one part to the other. The increasing upward trend might increase water supply, increase chances of urban flooding, erosion and sedimentation. The paper recommends that wet season rainfall be properly managed to boost water supply in dry season.

More than 50% of Nigeria is underlain by basement complex rock which is a poor aquifer unit and e... more More than 50% of Nigeria is underlain by basement complex rock which is a poor aquifer unit and evidences abound that the climate of Nigeria is changing. The posing question is how this poor aquifer will respond to the vagaries of climate variability and change. However, understanding the response of groundwater to climate variability and change in Nigeria will be hampered by dearth of data, because the nature of change in groundwater is not monitored. On this basis, the study tried to understand how groundwater responds to weather variability in a poor aquifer unit of Ilara-mokin and its environs in the tropical area of Nigeria. Rainfall and temperature data for forty years (1973–2012) were collected from NIMET and groundwater level were monitored in the area for two years (2012–2014).The general trends in rainfall and temperature received in the last forty years were examined using regression analysis and moving average. The dry and wet episodes were also examined using Standard Rainfall Anomalies Index (SAI). Also, the percentage changes in the rainfall and temperature received were determined using reduction pattern analysis. The response of groundwater to weather variability was however established using Pearson Moment Correlation and multiple regression analysis. The results of the analyses revealed an average of six years dry episode every decade in the last 40 years. The temperature of the study area is increasing in the last 20 years. Groundwater responded negatively to temperature but positively to rainfall in the area. Rainfall and temperature accounted for 67% of variability in monthly groundwater level. This study is a good starting point in understanding groundwater response to climate in poor aquifer units of Nigeria despite the dearth of data.

Geografia, Sep 15, 2015

Basement aquifers are usually developed within the weathered, over-burdened and fractured bedrock... more Basement aquifers are usually developed within the weathered, over-burdened and fractured bedrock of crystalline
rocks which can provide a sizeable amount of groundwater if the overburden is relatively thick enough to store
percolating water. This study assessed the static water level and overburden pattern for sustainable groundwater
development and management in Ilorin city, Nigeria. The data on depth of boreholes, depth to water, water level of
100 boreholes and the Vertical Electrical Soundings (VES) data conducted before the borehole were drilled, were
collected from Kwara State Ministry of Water Resources and Lower Niger River Basin Development Authority,
Ilorin. All the Vertical Electrical Soundings (VES) data collected were conducted with ABEM SAS-1000 Terrameter
using the Schlumberger electrode configuration, and the electrode spacing (AB/2) varied from 10m to 200m. From
the manual interpretation of each VES curve, we estimated the overburden thicknesses. Field work was embarked on
to get the coordinates (locations) of the sampled points using handheld GPS. Pearson Moment Correlation
Coefficient was applied to determine the level of association between borehole parameters and thickness of
overburden. The static water level and contour map were computed with the data on depth to water and the
coordinates to show the pattern of water level in Ilorin, using ArcGIS 10.2 and Surfer 12 GIS software. The depth of
overburden and the point location collected were also used to plot the overburden map using IDW interpolation. This
study classified Ilorin into poor (overburden <10m), marginal (10m-19m overburden) and good or high zone
(overburden ≥ 20m) of groundwater potentials. The spatial pattern of overburden depth revealed that the majority of
Ilorin city was underlain by marginally thick overburden. The study concluded that sustainable groundwater
development and management in Ilorin city could only be attained by controlling the indiscriminate drilling of
boreholes (wells), continuous mapping and regular updating of the available records on groundwater resources.

Momana Ethiopian Journal of Science, 2014

This study characterize groundwater yield and flow pattern on a shallow overburden aquifers of a ... more This study characterize groundwater yield and flow pattern on a shallow overburden aquifers of a basement complex rock in Ilara-mokin and its’ environs, southwestern Nigeria. A total of 40 wells were sampled by using a handheld GPS and well estimator to collect data on the wells parameters and the physiographic characteristics of the well’s locations. The data collected include: elevation, longitude, latitude, well depth, depth to water and well diameter of the sampled wells. The mean yield of the well has revealed by this study is 1.21m3, with high variability in yield depending on the nature of the underlying overburden aquifers of the sampled well. The static water level, groundwater flow direction, surface profile and 3-D elevation model of the study area were produced from the data collected using ArcGis 9.3 and surfer 8 GIS software. The groundwater flow direction in the study is towards the southwestern part of the study area with few exceptions as the case of Ikota in the eastern part of the study area. The study concluded that Ilara-mokin and it’s’ environs have poor groundwater yield that can sustain the increasing population. It is therefore recommended that there should be proper development, management and advance exploration of the groundwater in areas where water level is close to the surface especially within the lowland areas and isolated marginally thick overburden as confirmed by a previous hydro-geophysical studies carried out in the area.

Water is a vital resource, and the importance of its management, use and allocation cannot be ove... more Water is a vital resource, and the importance of its management, use and allocation cannot be overemphasized.
Water is either use for domestic, industrial or agricultural purposes to satisfy human needs and development in a
society. This study attempts to look into household water use behaviour in Irepodun Local Government Area of
Kwara State, Nigeria with a view to determine who sources, allocates and uses most indoor water in the
households, and for what purpose. A tool known as water diary was modified and incorporated into this study to
be able to gather the necessary information that would serve the purpose of the study. Irepodun LGA has eleven
wards, 30 households were sampled at random in each of these wards to give a total of 330 households.
Percentages and charts were used in the analysis which revealed that 53.25% and 47.65% of the surveyed
households were female and male respectively. The result shows that female sources 76.67%, allocates 91.82%
and uses 78.07% of the total indoor household’s water resource. It is therefore concluded that female are the
principal actors in household water use/management and should be at the center of regional domestic water

Research Article, Feb 2014

"This study looks into the water and poverty situation in Oyun Local Government Area, North-centr... more "This study looks into the water and poverty situation in Oyun Local Government Area, North-central Nigeria. A well-structured questionnaire is used to collect data at household level. Thirty households were sampled at random in each of the 11 wards in the LGA, giving a total of 330 households. The data were analyzed using percentages, Kendall’s correlation coefficient and WPI (Composite Index Method). The results revealed that Ojoku scored highest (62.4) while Igbonna scored lowest (52.0), which shows that it is the most water poor in the area. The result of the overall WPI (58.34) shows that the water and poverty situation in the whole of the LGA is slightly above average. The study concludes that the overall water and poverty situation in Oyun LGA is fair. It is therefore recommended that appropriate measure should be taken to improve the overall water accessibility and usage in the LGA by creating more water supply points in the community and renovating/upgrading the existing water works in the area for improved pipe borne water supply. Also, water use should be extended beyond domestic usage into other sectors that can increase productivity and hence, the overall poverty level in the area.
"

Environmental Issues, 2016

Several studies have revealed the impacts of rainfall variability on water resources across the w... more Several studies have revealed the impacts of rainfall variability on water resources across the world. This paper makes an analysis of the impacts of rainfall variability on public water supply in Ilorin. The data used in this
study are mainly rainfall amount for 30 years (1981-2010), which was obtained from NIMET and the quantity of water supplied by Kwara State Water Corporation, which was only available for 11 years (2001-2011). These data were interpreted using both descriptive and analytical methods. The analytical procedures include time series analysis, reduction pattern analysis and Pearson moment correlation. The results of the trend analysis show that rainfall and water supply in Ilorin have been on the increase at the rate of 0.27mm per annum and 0.20 million (m3) per annum respectively over the period of study. The results of reduction pattern analysis carried out revealed the variability and the percentage changes in rainfall and water supply over time in Ilorin. The result of Pearson moment correlation coefficient revealed that strong negative relationship (-0.6) existed between monthly rainfall and monthly water supply at 0.05 significant level. This shows that as rainfall increases, water production in the treatment plant decreases. This is expected in view of the increasing cost of water treatment in rainy seasons. It was concluded that increase in
rainfall poses water treatment challenges. It was therefore recommended that the capacity of treatment plants be increased. This would enable proper management of the abundant surface water and in turn increase water supply in the city.

Books by Eniola Damilola Ashaolu

J. F. Olorunfemi (Ed.) Kwara State: A Geographical Perspective. Unilorin Press, Ilorin, Nigeria (2017), 2017

Geography in Development: Issues and Perspectives. Edited by Dr. S.L. Tilakasiri. Stamford Lake Publication, Sri Lanka , 2017