Hydrogeological characterisation of regional faults and dolerite dykes in the Precambrian Basement and Karoo Supergroup (Tete Province, Mozambique)

2019 ◽  
Vol 122 (3) ◽  
pp. 343-356
Author(s):  
R.C. Minnaar ◽  
M.A. Dippenaar
Keyword(s):  
Groundwater Flow ◽  
Hydraulic Properties ◽  
Sequential Process ◽  
High Permeability ◽  
Vibrating Wire ◽  
Aquifer Testing ◽  
Groundwater Occurrence ◽  
Geophysical Surveys ◽  
Piezometric Surface ◽  
Level Monitoring

Abstract Faults and dolerite dykes within Basement- and Karoo-aquifers in northern Mozambique may increase groundwater occurrence but may also be barriers to groundwater flow. Should observation boreholes drilled into regional and local faults as well as dykes show a response to aquifer testing, it would be deduced that these hydrogeological discontinuities are not barriers to groundwater flow. The approach adopted for this study included a sequential process involving data acquisition through a hydrogeological fieldwork programme consisting of geophysical surveys, borehole drilling, aquifer testing, and groundwater level monitoring. The Zambezi Border and geological contact faults were characterised by high variability in hydraulic properties. Aquifer testing resulted in drawdown in observation boreholes as well as a reduction in piezometric surface in the installed vibrating wire piezometers located in different aquifer units, indicating the Zambezi Border- and geological contact-faults were not barriers to groundwater flow. Not all the northwest-southeast trending dykes acted as barriers to groundwater flow, as there were discreet intervals with relatively high permeability present.

scholarly journals Conceptual and Mathematical Modeling of a Coastal Aquifer in Eastern Delta of R. Nestos (N. Greece)

Hydrology ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 23
Author(s):  
Ioannis Gkiougkis ◽  
Christos Pouliaris ◽  
Fotios-Konstantinos Pliakas ◽  
Ioannis Diamantis ◽  
Andreas Kallioras
Keyword(s):  
Mathematical Modeling ◽  
Groundwater Flow ◽  
Coastal Aquifer ◽  
Flow Model ◽  
Meteorological Data ◽  
Field Measurements ◽  
Groundwater Flow Model ◽  
Aquifer System ◽  
Geophysical Surveys ◽  
The Mathematical Model

In this paper, the development of the conceptual and groundwater flow model for the coastal aquifer system of the alluvial plain of River Nestos (N. Greece), that suffers from seawater intrusion due to over-pumping for irrigation, is analyzed. The study area is a typical semi-arid hydrogeologic environment, composed of a multi-layer granular aquifers that covers the eastern coastal delta system of R. Nestos. This study demonstrates the results of a series of field measurements (such as geophysical surveys, hydrochemical and isotopical measurements, hydro-meteorological data, land use, irrigation schemes) that were conducted during the period 2009 to 2014. The synthesis of the above resulted in the development of the conceptual model for this aquifer system, that formed the basis for the application of the mathematical model for simulating groundwater flow. The mathematical modeling was achieved using the finite difference method after the application of the USGS code MODFLOW-2005.

Groundwater age from multi-level bores: What it can tell about the aquifers

2021 ◽  
Author(s):  
Uwe Morgenstern ◽  
Zara Rawlinson
Keyword(s):  
Groundwater Flow ◽  
Groundwater Recharge ◽  
Sea Level ◽  
Preferential Flow ◽  
Groundwater Age ◽  
Geological Processes ◽  
Recharge Sources ◽  
Transient Electromagnetic ◽  
Geophysical Surveys ◽  
Multi Level

<p>Geologic data to provide information on the functioning of aquifers is often scars. For the aquifers underlying the Heretaunga Plains, Hawkes Bay, one of New Zealand’s most important groundwater systems, we used groundwater age (tritium, SF6, 14C) to inform the geologic model and to provide information on groundwater flow through alternating strata of permeable river gravel beds and fine impermeable beds that form an interconnected unconfined–confined aquifer system with complex groundwater flow processes.</p><p>The aquifers are a result of geological processes responding to climate change cycles from cold glacial when sea level was more than 100m below present sea level, to warm interglacial periods with sea level similar to present day. Glacial climate strata are river gravel, sand and silt deposits and include the artesian aquifers. The interglacial strata form the aquicludes and are marine sand, silt, and clay deposits with interbedded estuarine, swamp and coastal fluvial silt, clay, peat and gravel deposits.</p><p>We have re-visited tracer data sampled during the drilling of multi-level observation well in the early 1990s, and collected new samples from these multi-level bores in order to understand in 3D the groundwater recharge sources, groundwater recharge and flow rates, connection to the rivers, and potential groundwater discharge out to sea. Consistently young water (c. 25 years) at depth greater than 100m indicates preferential flow paths, likely related to paleo-river channels. The flow pattern obtained from the water tracer data improves the geologic information from the drill-holes, and fits with information from recent airborne transient electromagnetic (SkyTEM) geophysical surveys.</p>

Investigations in groundwater flow toward a spring in the Saphire area, Soufriere, Saint Lucia, West Indies

2019 ◽  
Vol 38 (6) ◽  
pp. 460-464
Author(s):  
Frank Dale Morgan ◽  
Saleh Al Nasser ◽  
Ruel Jerry ◽  
Ananias Verneuil
Keyword(s):  
Groundwater Flow ◽  
Geophysical Methods ◽  
Housing Development ◽  
Tree Cover ◽  
Flow Paths ◽  
Biological Contamination ◽  
Geophysical Surveys ◽  
Saint Lucia ◽  
Area Of Concern ◽  
Underground Flow

The Cocoa Grove Group is planning a housing development on approximately 5.5 acres in the area of Saphire, Diamond, Saint Lucia. Directly downhill of the property is a Water and Sewage Company (WASCO) spring that supplies drinking water to the town of Soufriere. This potable water is of high purity. Concern was expressed by WASCO as to the advisability of implementing development directly above the emanation of the spring. The obvious concerns were the possible change in flow volumes and chemical and biological contamination if a housing development was completed. F. D. Morgan and the Saint Lucia Water Resources personnel representing the Cocoa Grove Group discussed whether geophysical methods could be used to map the direction of groundwater flow into the spring. The group agreed that geophysical methods could be used in an attempt to delineate the underground flow paths into the spring. It was made clear that investigations could produce results that could be either favorable or unfavorable to the proposed development. Consequently, geophysical surveys were planned and executed in the area of concern to measure resistivity and self potentials. The geophysics did not indicate evidence of substantial fluid flow into the spring. However, we were able to locate the main water supply from the top of Terre Blanche down toward the spring. The flow comes downhill via a significant geologic fracture that is hidden from sight in the dense tree cover. Recommendations were made that it is relatively safe to develop the site as intended with respect to possible water contamination. In conclusion, we also recommended that WASCO take water from another point of a topographic step on Terre Blanche. Doing so would reduce the contamination risk essentially to zero from the planned housing development area.

scholarly journals The impact of faults on the hydrogeological conditions in the Roer Valley Rift System: an overview

2003 ◽  
Vol 82 (1) ◽  
pp. 41-54 ◽  
Author(s):  
V.F. Bense ◽  
R.T. Van Balen ◽  
J.J. De Vries
Keyword(s):  
Groundwater Flow ◽  
Hydraulic Properties ◽  
Great Influence ◽  
Hydraulic Head ◽  
Transport Processes ◽  
Rift System ◽  
Near Surface ◽  
Mining Areas ◽  
Vertical Permeability ◽  
The Impact

AbstractThe hydrogeology of the Roer Valley Rift System is strongly influenced by the hydraulic properties of faults. The hydrogeological impact of faults is illustrated by examples from the SE Netherlands and the adjacent lignite mining areas within the Roer Valley Rift System, near Bonn in Germany. Hydraulic head discontinuities over the main faults in the latter area can be up to tens of meters as a result of extremely large groundwater extractions in combination with the relatively low conductivity of the main faults. Within the Netherlands, outside the mining areas, such large groundwater extractions do not take place, and groundwater fluxes are smaller. In this situation natural hydraulic head differences over the main faults are limited to several meters. Hydraulic head profiles over faults provide a first estimate of fault hydraulic properties that can be quantified using simple analytical solutions. The impact of faults on near surface processes is reflected in vegetation patterns and the structure of drainage networks, aquifer structure and hydraulic head patterns. Faults can thus be of great influence on transport processes in the subsurface as well as on water-related phenomena at the surface, and should accordingly be taken into consideration in studies related to water-management, contamination and environmental impact. Faults that have an enhanced vertical permeability are difficult to detect when horizontal groundwater flow is studied, which is probably the main reason why they are rarely described. Though, these faults may form important preferential paths to vertical groundwater flow.

Hydraulic properties calibration by high resolution monitoring data and 1D to 3D groundwater flow modeling of the Carozzo Landslide

2021 ◽  
Author(s):  
Alberto Previati ◽  
Giuseppe Dattola ◽  
Gabriele Frigerio ◽  
Flavio Capozucca ◽  
Giovanni B. Crosta
Keyword(s):  
Steady State ◽  
Groundwater Flow ◽  
Material Properties ◽  
Hydraulic Properties ◽  
Transient State ◽  
Primary Concern ◽  
Piezometric Level ◽  
Piezometric Head ◽  
Storage Function ◽  
Rainfall Recharge

<p>A reliable modeling of a landslide activation and reactivation requires a representative geological and engineering geological characterization of the affected materials. Beyond the material strength, landslide reactivation is sensitive to groundwater pressure distributions, that are generated by some external perturbation (recharge) and by the hydraulic properties of the materials. Drainage stabilization works generally involve drilling of a large number of drains and, therefore, minimize the total length is of primary concern to reduce the costs.</p><p>Aim of this work was the calibration of material properties for the optimization of drainage elements to be built for the slope stabilization and the construction of a shallow tunnel crossing a landslide. The case study is represented by the 4.0 · 10<sup>5</sup> m<sup>3</sup> Carozzo landslide (La Spezia, Liguria, Italy) which affects some marly and sandstone formation. During the tunnel excavation a monitoring network consisting of five DMS columns for displacements and piezometric head multilevel measurements was installed. The monitoring provided a series of piezometric head recession curves following some recharge events. The series of data generated in response of a unique perturbation (rainfall recharge event) were chosen to calibrate the material properties through a multi-step approach, starting from a 1D model and progressively approaching a complete 3D model.</p><p>The 1D simplified approach applies the solution by Troch et al. (2003) that considers a homogeneous landslide material, with constant slope and a progressive change in the slope width. In this model a storage function considers the amount of water stored in a slope section. By imposing the continuity equation and the Darcy law a second order of partial differential equation is solved by integration in space and time. By taking the initial conditions from piezometric measurements and assuming a constant rainfall recharge, the piezometric level and the outflow rate were computed and compared with the local piezometric level time history, by changing the hydraulic conductivity and the storage function value.</p><p>Successively, a groundwater flow FEM numerical model (in 2D and 3D) was developed considering the landslide geometry and internal zonation, including the presence of the excavated part of the tunnel. The model domain was divided into sub-zones according to the available geological surveys to account for internal variations of the material properties. The steady-state simulation of the water flow allowed to estimate the equivalent hydrogeological parameters of each subdomain. The hydraulic head distribution obtained under steady-state conditions was used as initial condition for the transient-state simulation. The recharge from precipitation was also included in the water balance by means of daily rainfall time-series. Finally, the model parameters were calibrated in transient state by comparing measured data and simulated results.</p><p>The minimum error between simulated and measured piezometric heads under transient conditions was obtained through the 3D configuration. Calibrated hydraulic conductivities in the 3D solution are up to an order of magnitude lower than the 1D solution because of the homogenous assumption of the model. The internal zonation of the landslide body and the modeling of a low-conductivity shear zone were essential to explain the pressure differences inside the body.</p>

Megascopic Controls on Radionuclide Transport in Groundwater Flow Systems

1982 ◽  
Vol 15 ◽  
Author(s):  
Leslie Smith ◽  
Franklin W. Schwartz
Keyword(s):  
Groundwater Flow ◽  
Hydraulic Properties ◽  
Stochastic Simulations ◽  
Radionuclide Transport ◽  
Geologic Structure ◽  
Macroscopic Scale ◽  
Groundwater Flow Systems ◽  
Significant Control ◽  
Key Factor ◽  
Wide Scale

ABSTRACTIn this paper we investigate how the geologic structure of a basin influences the reliability with which predictions of radionuclide transport within a depository horizon can be made. Results from a series of stochastic simulations show that, in some cases, transport predictions are sensitive to perturbations in the hydraulic properties of surrounding layers, indicating megascopic effects on a basin-wide scale exert a significant control on transport at the macroscopic scale. Other cases are identified where transport is not sensitive to perturbations in the hydraulic properties of surrounding layers. A key factor in this response is the distribution of the hydraulic gradient in the basin.

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