This work presents the results of groundwater flow modeling in Abraka using the groundwater modeling software (GMS) which supports the MODFLOW as well as the MOD PATH. The model covers the three campuses of Delta State University and environs. A conceptual groundwater modeling approach was employed for the purpose of modeling; the source/sink coverage, recharge coverage, well extraction coverage, river leakage starting heads, Ibound, the top and bottom elevation, hydraulic conductivity and anisotropy; and later calibrated to get the residual of the computed heads verse the observed heads.
The hydraulic sensitivity likewise the effect of recharge and pumping rate was ascertained after calibration. The direction was ascertained as it moves in the direction of the Ethiope river with the velocity of the vector movement of the MODFLOW is given as 0.70016372204 m/day (8.1037465278×10-6 m/sec); likewise the MODPATH of which contaminant flows in the opposite direction of the river and few moving through the wells down to the aquifer with a porosity of 0.8 .volumetric analysis shows the total inflow of water is 138,069.96886253 and outflow -138,076.472868 with a difference of -6.504005432129.
The percent discrepancy value of the model is -0.0047% .This also shows the closeness the model is represents the groundwater condition in the study area The value of the total recharge rate on the aquifer is 12,728.870018005.
Table of Contents
1.0 INRODUCTION TO GROUND WATER AND AQUIFER SYSTEM
1.1 TYPES OF AQUIFERS
1.2 CLASSIFICATION OF AQUIFERS
1.3 AIM AND OBJECTIVES
1.4 LITERATURE REVIEW
2.0 GEOLOGY OF THE STUDY AREA
2.1 LOCATION OF STUDY AREA
3.0 MATERIALS AND METHODOLOGY
3.1 DIGITAL ELEVATION MODEL
3.2 FLOW SIMULATION
3.3 CREATING THE GRID
3.4 ASSIGNING IBOUND ARRAY
3.5 TOP AND BOTTOM ELEVATION
3.6 STARTING HEADS
3.7 LAYER PROPERTY FLOW (LPF) PACKAGE
3.8 ANISOTROPY
3.9 OPTIONAL PACKAGES
4.0 SIMULATION OF MODEL
4.1 VOLUMETRIC ANALYSIS
4.2 ZONE BUDGETING/ FLOW BUDGET
4.3 CALIBRATION
4.4 CONTAMINANT PREDICTION/ PARTICLE TRACKING
5.0 CONCLUSION
5.1 REFERENCE
CHAPTER ONE
1.0 INRODUCTION TO GROUND WATER AND AQUIFER SYSTEM
Exploration of groundwater has been the surest way to handle the ever increasing need for fresh and quality water used either for domestic, agricultural or industrial purpose. This is because of its relative abundance and quality with respect to many other sources. The development of this very important resource in Nigeria has not yielded a very impressive result that is commensurate with the financial resources expended on it (Edet and Okereke, 2014).This has therefore impeded the supply of quality water to a good percentage of the people of this country. (Perdomo et al. 2014), emphasize the fact that limited fund has also hampered the provision of water and the availability of necessary information to help assess this resource in developing countries. Assessing groundwater requires detailed geophysical exercise which includes geophysical well logging, seismic, magnetic, electrical method, inseam drilling and geographic information system. In a bid to effectively tap the groundwater resource, a method which is able to evaluate the aquifer layer, groundwater vulnerability, and quality is necessary (Ibrahim, 2013)
Groundwater is the water present beneath earth surface invokes on soil pore spaces on in the fractures of rocks formation. Unit of rocks or unconsolidated deposit is called an aquifer it can yield a usable quantity of water. The depth at which soil poor species or fractures unvoiced involves become completely saturated with water is called the water table. Groundwater is charged from the surface; it can discharge from the surface naturally at springs and seeps, unconfirmed Oasis or wetlands. Groundwater is also often withdrawn from agricultural municipal and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater in hydro geology is called groundwater hydrology (Gleeson et al 2016)
Groundwater is the most widely valuable natural resources in the world. It is known to occur within the earth sediments, rocks or sand formation. The occurrence and distribution of this natural resource are restricted to some geological formations and structures called aquifers. Groundwater encompasses water that exists in the subsurface and is contained in geologic formation called aquifers. Aquifers are geological formations that are porous and permeable which retained and released water (Wightman et al., 2003); (Todd and Mays,2005).The soils and rocks resistivity depend largely on properties of rocks which include permeability, soil porosity, ionic value of the pore fluids, and clay mineralization and these differ with time and space(Oseji,2010). Geophysical techniques have been applied for groundwater contamination studies (Kelly, 1976); (Arristodemou and Thomas-Betts, 2000);( Adepelumi et al., 2001) Geoelectrical methods were developed to demarcate locations prone to contamination ( Atakpo and Ayolabi, 2009)
An aquifer is explained as a subsurface formation which is capable of storing and transmitting water at a pace fast enough to provide sufficient quantity to wells (Fetter, 2007). The presence of water in a formation does not in any way imply that the water quality is good enough for domestic consumption. However, groundwater that occurs in formations which are properly sealed by a non porous formation is known to provide good quality water (Todd, 2004).Sometimes a confining layer of less porous rock might occur above and below the aquifer layer. When this happens, the aquifer is referred to as a confined aquifer. In such a situation, the rocks surrounding the aquifer confine the pressure in the porous rock and its water. The pressure inside the aquifer might just be enough to move the water to the surface if a borehole is sank into the aquifer. When this occurs, the well is called an artesian (Todd, 2004).The depth to the groundwater aquifer varies and sometimes could be as deep as 50m and above. Therefore, exploring this resource requires proper planning and technique. Some of the techniques that have been used to source groundwater includes aerial, surface, subsurface and esoteric (Fetter, 2007). The most common procedures are the surface and subsurface methods (Anomohanran, 2014). The surface methods are made up of geophysical, geological, geomorphologic, hydro-geological, geobotanical and geochemical methods
1.1 TYPES OF AQUIFERS
Aquifers may be classified by whether they are confined or unconfined and by their geologic composition. Confined aquifers exist between two impermeable layers, often comprised of clay or clay-derived rock. Unconfined aquifers lack a confining layer above the water table, and are thus vulnerable to pollution from the surface. Unconsolidated aquifers consist of sand, gravel, and other materials that have not been cemented together, and where water fills up spaces between the particles. In contrast, water-bearing formations that have been cemented together are termed consolidated aquifers. Relatively large pore spaces in unconsolidated aquifers and solution channels in carbonate aquifers can hold significant amounts of groundwater with high hydraulic conductivity. In contrast, only the presence of fractures and joints in igneous and metamorphic rocks allow water to enter and move through the formations. Sand and gravel aquifers are generally unconfined, and can be several hundred feet thick. They are comprised of alluvial or glacial deposits and found in valleys, depressions, and lowlands. Alluvial aquifers were formed over hundreds to thousands of years by water deposition of sand, silt, and clay particles. These alluvial deposits can contain large groundwater reserves that are fairly accessible and easy to withdraw. Sand and gravel aquifers of glacial origin may also have large reserves of groundwater that are fairly easy to withdraw, but hydraulic conductivity in such aquifers may be quite variable due to lack of sorting in glacial till.
1.2 CLASSIFICATION OF AQUIFERS.
A confined aquifer is one that is bounded from above and from below by impervious formations, and the water pressure in it is such that the level of water in a well that is open in it will be at, or will rise above the upper impervious bounding surface. In other words, the piezometric surface of a confined aquifer is above the latter’s impervious ceiling.
An aquifer that is bounded from above by a phreatic surface is called a phreatic aquifer, or an unconfined aquifer. For an aquifer with essentially horizontal flow, the water table is also the piezometric surface of the aquifer. A special case of a phreatic aquifer is the perched aquifer The phreatic aquifer of limited areal extent, formed on a semipervious, or impervious, layer that is present between the persistent water table of a phreatic aquifer and ground surface. A perched aquifer may exist only for a limited period of time, seasonal or ephemeral, as its water drains into the underlying phreatic aquifer.
A leaky phreatic aquifer, is a phreatic aquifer that is bounded from below by a semipervious layer, usually referred to as an aquitard.
A leaky confined aquifer is a confined aquifer, except that one or both confining layers are aquitards, through which leakage may take place. (Dillon,P.J. 2002) Abbildung in dieser Leseprobe nicht enthalten Fig 1.0 classification of aquifer. ( Dillon, P.J. 2002)
One way to address groundwater flow is through the use of models. Groundwater models are computer models of groundwater flow systems, and are used by hydrologists, hydrogeologists and hydrogeophysicist.
1.3 AIM AND OBJECTIVES
The aim of this research work is use GMS to better understand the process governing the groundwater flow in and out of the aquifer.
The specific objectives are;
i. To simulate the groundwater flow(magnitude and velocity)
ii. To determine volumetric analysis/flow budget in the model
iii. To determine the contaminant presence and particle tracking.
iv. To determine the effect of pumping rate on hydraulic conductivity
v. To determine the effect of recharge rate on hydraulic conductivity
1.4 LITERATURE REVIEW
Groundwater resources are hidden systems and dynamic; their quality and quantity are often hard to measure and understand. The state of any hydrogeological system can change over time. In this regard, model designers and operators are repetitively developing new scientific models and solution techniques to evaluate these systems. Groundwater models can help to explain the behaviour of the whole or a part of a groundwater system, understand the processes, make predictions, make management decisions, and test a hypothesis.
Groundwater models are used to simulate and predict aquifer conditions. Models allow the analysis of present conditions of the groundwater systems as well as its temporal development. From the water quality perspective models are useful tools to understand and predict the behaviour of flowing groundwater. This can also helps to reliably assess the risks arising from groundwater contamination problems, and to design alternative remediation measures. Models are also useful tools to understand the dynamics of ground water surface water fluxes exchange. We have several models namely Analytic Element Method, FEFLOW, SVFlux, FEHM, HydroGeoSphere, MicroFEM, GMS, SahysMod, Spatial agro-hydro-salinity-aquifer model, online US Geological Survey Water Resources Ground Water Software. ZOOMQ3D.
It is also a visualized groundwater numerical simulation software based on finite difference method, integrating various modules such as Modular Finite-Difference Flow (MODFLOW) and Modular Three-Dimensional Transport (MT3DMS). The source of River Ethiope in Umuaja has been simulated by Delta State, Nigeria by Okocha and Atakpo (2013) to determine groundwater-river interaction within the study area. Duke and Ayenigba (weber& Aukoru 1975) also used GMS to model groundwater flow model for Otokiti area of the River Meme catchment, Lokoja. GMS was used to examine the aquifer and its response to abstractions under different pumping conditions. Ohwoghere-Asuma et al. (2021) revealed from the simulation of saltwater intrusion into coastal area of the western Niger Delta that the saltwater freshwater interface is less than 200m from the coast Model practically used for this project work is the Groundwater Modeling System (GMS)
CHAPTER TWO
2.0 GEOLOGY OF THE STUDY AREA
2.1 LOCATION AND EVOLUTION OF NIGER DELTA BASIN
Niger Delta according to (Klett et al 1997) is situated within the Gulf of Guinea province with extension throughout the Niger Delta Province. It is situated on the West African continental margin at the apex of the Gulf of Guinea, which formed the site of a triple junction during continental break-up in the Cretaceous (Doust & Omatsola 1990) . It is a clastic fill of 12,000m with an aerial extent of 75,000sqkm and extending more than 300km from the Apex to the mouth (Evamy et al 1978); (Reijers et al 1997).It has a single petroleum system- the Tertiary Niger Delta (Akata-Agbada) petroleum system (Tuttle et al 1990). The Niger Delta is a prolific hydrocarbon belt in the world whose formation was initiated during the tertiary (Ekweozor & Doukoru 1994). ; (Bustin 1988) . The delta proper began developing in the Eocene, accumulating sediments that are now over 10km thick (Tuttle et al 1990). From the Eocene to the present, the Delta has prograded southwards, forming depobelts that represents the most active portion of the Delta at each stage of its development (Doust & Omatsola 1990)
Abbildung in dieser Leseprobe nicht enthalten
Fig 2.0 map showing the location of the Niger delta basins (Doust & Omatsola 1990)
2.2 STRATIGRAPHY OF THE NIGER DELTA BASIN
The caustic Niger Delta has three major lithostratigraphic units which include Akata, Agbada and Benin Formations depositional environments range from marine, deltaic to fluvial environments (weber & aukoru 1975)
Akata Formation is about 6400 m thick at the center of the clastic wedge; the lithologies include dark gray shale and silts, having streaks of sand which their origin could be from turbidite flow. the age of this Formation ranges from Paleocene to Recent. theirs Formation grades vertically into the Agbada Formation with abundant plant remains and micas in the transition zone (Doust & Omatsola 1990) .
Agbada Formation extends throughout Niger Delta clastic wedge and has a maximum thickness of about 3962 m. thee lithologies of this Formation include alternating sands, silts and shales. Strata in this Formation are believed to have been produced in fluvial–deltaic environment. Agbada Formation ranges from Eocene to Pleistocene in age.
Benin Formation is the top of the clastic wedge Niger Delta. The top of this Formation consists of the recent sub aerially exposed delta top surface. The shallow part of Benin Formation is made up of non-marine sands that were deposited in either upper coastal plain or alluvial depositional environments (Doust & Omatsola 1990) . Benin Formation ranges from Oligocene to Recent in age (Short & Stauble 1965). Agbada Formation is the main reservoir in the Niger Delta clastic wedge. The ratio of gas to oil tends to increase toward the south within the depobelts in the Niger Delta. this is because of the complexity in the distribution of hydrocarbons in the basin (Doust & Omatsola 1990) .thee source rock in the Niger Delta consists of marine shale of Akata Formation. It could also consist of marine interbedded shales in the Agbada Formation as well as the underlying Cretaceous shale (Doust & Omatsola 1990) the primary seal rocks are the interbedded shale that occur in the Agbada Formation
Abbildung in dieser Leseprobe nicht enthalten
Fig 2.1 stratigraphy of the Niger delta basin (Doust & Omatsola 1990)
2.1 LOCATION OF STUDY AREA
Due to copyright issues, this figure is not part of this publication.
Fig 2: map showing the study area
The Abraka area, situated between latitude 5° 45’ and 5° 50’ N and longitude 6° and 6° 15’ E is located on the south bank of the River Ethiope and is an agglomeration of several communities that are aligned linearly along the New and Old Sapele– Agbor highway. These communities include from the west, Oria, Ajalomi, Abraka PO, Ekrejeta, Urhuoka and Umeghe. Ajalomi, Abraka PO, Ekrejata and Urhuoka have grown in size and are now conjoined to form what is loosely referred to as Abraka Urban, the seat of all three sites of the Abraka Campus of the Delta State University. Southwards, the rural communities of Ugono, Aragba, Abraka Inland and Ughere - Uragbesa are as well, bona fide Abraka communities
2.1.1 TOPOGRAPHY, RELIEF AND DRAINAGE OF THE STUDY AREA
The topography of the study area is low lying without remarkable hills, and falls within the interior coastal lowlands of Western Nigeria. The study area is well drained by river Ethiope, which flows West direction from Umuaja in Ndokwa L.G.A of Delta State, through Ethiope East L.G.A to empty itself water into the Atlantic Ocean at Sapele in Okpe L.G.A. The river is a fast flowing body of water which has a high velocity rate of about 1.65m/sec at the Abraka region and lower at Umutu (1.85m/sec) the upper course of the river which is very close to the source of the river at Umuaja. This study area falls within the humid tropical climate of AF Koppen classification; with mean annual rainfall and 0 temperature of 30.6% and 30 C respectively. According to the USDA soil classification taxonomy, the soils of the study area fall under the oxisols, alfisols and psalment. (Richards, 2012)
Due to copyright issues, this figure is not part of this publication.
fig 2.3 regional map showing the relieve and drainage of the study areas
2.1.2 GEOLOGY OF THE STUDY AREA
The area is located in the Niger Delta Basin, a much studied and important petroleum province. Briefly, there is general agreement that the basin was formed as a result of an aulacogen type development that was triggered by the separation of the African and South American plates in the Jurassic. The resulting trough has been filled by a series of marine transgressions, regressions and deltas, the present Niger delta being the most recent. The basin fill has been described by (Short& Stauble 1967), (Reijers et al.1996), (Nwajide 2006), among many others and consists of three formations, namely, from the oldest to the youngest, the Akata Formation, Agbada Formation both of Eocene to Recent and the Miocene to Recent Benin Formation. However, west and just south of Abraka the Benin Formation is masked by the younger Holocene deposits of the Sombreiro-Warri Deltaic Plain, the Mangrove Swamp and Freshwater Swamp wetlands. These deposits which have not been assigned formal geological names because they are universally considered to be recent expressions of and a continuation of the Benin Formation are only identified by the physiographic terrains in which they occur. The aerial distribution of these delta top deposits coincides somewhat with the associated physiographic subdivisions .The inferred boundary between the Sombreiro–Warri Deltaic Plain and the Benin Formation outcrop as can passes through the Abraka area such that the southern part of the area is underlain by Sombreiro-Warri Deltaic Plain deposits while the north rests on Benin Formation outcrop. The Ethiope River, the most important physiographic feature in the area flows almost exclusively on the outcrop of the Benin Formation. The Benin Formation in the Abraka area is overlain everywhere by reddish brown colored ferruginized regolith that is usually no less than 2 m thick. This can be observed clearly at two locations on the Abraka – Ugono road The first site is a large borrow pit located just before the bridge on the River Ethiope and from where material is being excavated for building and road construction and the second at the rail road crossing near the overpass on the Abraka – Ugono Road. At both locations, the formation is massive and deeply weathered.
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- Citar trabajo
- Imosili Christopher Osemudiamen (Autor), 2022, Ground Water Modeling Using the GMS Software. Specified Areas in Abraka Delta State Nigeria, Múnich, GRIN Verlag, https://www.grin.com/document/1313093
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