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Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Yihdego Y.,University of Twente | Becht R.,University of Twente
Journal of Hydrology | Year: 2013

Aquifers near Lake Naivasha, Kenya are important water resources and are used extensively for irrigation and for municipal and domestic water supplies. Head data for a 79-year period (1932-2010) were analyzed to develop a conceptual model of aquifer-lake interaction and used to develop a three-dimensional numerical model. A three-dimensional groundwater flow model with four layers was used to simulate ground-water flow in the aquifers and lake-aquifer interaction. The lake is simulated by specifying a high hydraulic conductivity for lake-volume grid cells. The 90. m Digital Elevation Model (DEM) that includes the bathymetry improved the 3-D representation of the lake in the groundwater system and helped to define the deformed layer that honors the stratigraphy. The calibration process was carried out using PEST in conjunction with pilot points and regularization. The finite difference groundwater model results were comparable with measured head data and isotopic and hydro-chemical data. The sensitivity of the computed lake level was tested using the "high-K" method to the choice of K2/K1, where K2 and K1 are the hydraulic conductivity of the lake node and the aquifer (respectively). Higher values of K2/K1 should be used with higher regional gradients on the order of 0.002 to ensure mainly accurate calculations of seepage rates to and from the lake. © 2013 Elsevier B.V.


Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.,La Trobe University
Journal of Environmental Management | Year: 2012

In southwestern Victoria a large number of lakes are scattered across the volcanic plains; many have problems with increasing salinity. To identify the hydrologic components behind this problem, three lakes, Burrumbeet, Linlithgow and Buninjon, were selected for detailed water and salt budget modelling using monthly values of rainfall, evaporation, surface inflow and outflow, and groundwater inflow and outflow (using the new modified difference method developed in this study). On average, rainfall begins to exceed evaporation with the onset of winter rainfall in May, so lake levels rise and lake salinities decline. The modelled lakes have become more saline over the last decade, a time of drought with below average rainfall, and all eventually dried out, their salinities rising to very high levels as they shallowed. Lake Burrumbeet is generally much less saline than Lakes Linlithgow and Buninjon, because it has substantial groundwater outflow, probably due to leakage through one or more volcanic necks. This limits the amount of time the lake water is subject to evaporation, and also allows significant salt export. The other lakes do not leak. The modelling indicates that when the lakes dry out, salt is lost from the lake-beds, probably due to wind deflation of salt crusts and leakage into the underlying groundwater. The removal of salt during drying-out phases resets the salinity of the lakes, limiting their ability to become more saline with time. Drying-out phases may therefore be essential in preventing the increased salinisation of lakes and wetland environments across the volcanic plains. © 2012 Elsevier Ltd.


Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.,La Trobe University
Water Resources Management | Year: 2013

In western Victoria, Australia the water table and lake level in the Glenelg-Hopkins catchment have been declining for the last 15 years, and this is attributed to either the low rainfall over this time and/or a substantial change in land use. Stream flow modelling was carried out using monthly empirical water balance model (modified tanh function together with double mass curve analysis), on 37 stream gauges to assess whether the impact of land use change could be detected by a change in the magnitude of the resulting runoff. The empirical hydrological model was able to distinguish impact of land use change on stream flow from the climatic variables. There were substantial decreases in stream flow in the 1970s-1980s, probably related to increasing livestock densities in the region. Furthermore, the methodology can be a powerful tool to monitor and evaluate the possible impacts of future land use changes. It can be concluded that the use of such empirical hydrological modelling greatly improves the ability to analyse the impact of land use on catchment runoff. The model is a practical tool that can be readily used for identifying and quantifying the effect of landuse changes on catchment for water resource decision-making, which could be hardly possible using the time consuming, data hungry and expensive physical process models available. © 2013 Springer Science+Business Media Dordrecht.


Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.A.,La Trobe University
Environmental Earth Sciences | Year: 2014

Lake Burrumbeet, which is located in the basalt plains of western Victoria, Australia, has a much lower salinity than other lakes in the region. To determine the factors causing the freshness of this water body, an assessment was carried out using existing geological information to reconstruct the palaeotopography beneath basalt flows, and using hydrogeological data, bore hydrographs and hydrological data together with a time variant lake water balance analysis calibrated from 1998 to 2008. The calibrated water balance of Lake Burrumbeet shows that groundwater outflow has a major influence on lake levels (31 % of water losses). The lake water budget analysis confirms that the interaction of Lake Burrumbeet with the surrounding groundwater system is volumetrically significant. Geological re-construction of the course of the buried river valley sediments (Deep Lead underlying the basalt) shows that they run directly beneath Lake Burrumbeet. Groundwater leakage into these sediments is sufficient to transfer enough salt from the lake to maintain a low to moderate lake salinity. The conceptual hydrogeological model of Lake Burrumbeet, coupled with the time variant water budget analysis, show that the difference in salinity among the lakes in the region can be explained by variations in the configuration and hydrogeological setting of the lakes, and this hypothesis provides new understanding of the relative freshness of the lake. © 2014, Springer-Verlag Berlin Heidelberg.


Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Al-Weshah R.A.,University of Jordan
Environmental Earth Sciences | Year: 2016

Site characterization was performed on an area of 580 km2 around the strategically vital freshwater aquifers of the Al-Rawdhatain and Umm Al-Aish to assess the status of groundwater pollution as the result of Iraq invasion to Kuwait in 1991. Advanced data analysis and visualization software (EVS-Pro) was used for groundwater contamination assessment analytes: total petroleum hydrocarbon (TPH) and total dissolved solids (TDS). This will reduce the number of samples needed (saves time and money) and provide a superior assessment of the analytes distribution. Based on the “minimum–maximum plume technology” analysis, the nominal plume area with a threshold of 0.031 mg/kg TPH is estimated at about 0.47 km2. This is the difference between the maximum and minimum predicted plume sizes. EVS-Pro also computed 3.3775 × 109 and 4.0788 × 106 for the plume volumes and masses (dollars per volume and mass), respectively. Also, new sampling locations were determined for further detailed site assessments based on the confidence and uncertainty analysis, which is more defensible and cost-optimized approach. This will reduce the number of samples needed (saves time and money) and provide a superior assessment of the analytes distribution. These tools prove to be effective in assessing remediation costs of clean-up versus benefits obtained and in developing a cost-effective monitoring programme for insights into processes controlling subsurface contaminant transport that impact water quality. © 2016, Springer-Verlag Berlin Heidelberg.


Al-Weshah R.A.,University of Jordan | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC
Environmental Earth Sciences | Year: 2016

An oil flow from the oil wells damaged during the 1991 Gulf War and the sea water used for extinguishing the resulting oil fire have contaminated the freshwater aquifers of Raudhatain and Umm Al-Aish water fields in north Kuwait. The numerical flow modelling of the aquifers was undertaken to create a calibrated and validated model that could be used in the future to explore a viable remediation strategy for the aquifers. The Environmental Visualization Software (EVS-pro) 3-D data presentation program was used to construct a conceptual model as a preliminary step. A 3-D numerical model was developed using the MODFLOW-SURFACT code that overcame the limitations of the classical MODFLOW. This model was able to combine both freshwater lenses in one model domain simulating the vadose zone together with the saturated zone. The model domain covered an area of 580 km2 encompassing the Al-Raudhatain and Umm Al-Aish basins. A steady-state model was developed first to study regional flow patterns in the aquifer. A transient model was developed subsequently to assess seasonal recharge on groundwater and investigate their effects on flow patterns. Analysis of the calibrated steady-state model output indicated that the model simulated the groundwater elevation and flow direction across the model domain to an acceptable level. The calibrated transient flow model is of significant importance to assess the vertical and lateral plume migration in the area and helps to come up with a plausible remediation strategy. © 2016, Springer-Verlag Berlin Heidelberg.


Yihdego Y.,Snowy Mountains Engineering Corporation SMEC
Geotechnical and Geological Engineering | Year: 2016

Hydraulic in situ measurement of rock mass permeability by packer (Lugeon) testing is an inherent and integral element of many engineering, hydrogeological and mining investigation. This paper describes and discusses geotechnical testing in the design process from a consulting practitioner’s perspective. This study focuses on the Packer testing planning, procedure, results & interpretation. Packer test system is an optimum method for obtaining values of hydraulic conductivity in wells that are difficult to analyse using conventional slug test systems. Packer tests are carried out to assess the variability of a borehole as it intersects various hydrogeological units. It gives vertical distribution of hydraulic properties and water quality in the aquifer and usually cheaper than a nest of wells and gives more continuous record and this knowledge can often be essential for a proper design. The role, objectives, types and interpretation of testing, limitations and recommended good practices as part of the geotechnical design process are outlined through the examination of test data from a case record. © 2016 Springer International Publishing Switzerland


Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Drury L.,Snowy Mountains Engineering Corporation SMEC
Environmental Monitoring and Assessment | Year: 2016

Analytical and empirical solution coupled with water balance method were used to predict the ground water inflow to a mine pit excavated below the water table, final pit lake level/recovery and radius of influence, through long-term and time variant simulations. The solution considers the effect of decreased saturated thickness near the pit walls, distributed recharge to the water table and upward flow through the pit bottom. The approach is flexible to accommodate the anisotropy/heterogeneity of the real world. Final pit void water level was assessed through scenarios to know whether it will be consumed by evaporation and a shallow lake will form or not. The optimised radius of influence was estimated which is considered as crucial information in relation to the engineering aspects of mine planning and sustainable development of the mine area. Time-transient inflow over a period of time was estimated using solutions, including analytical element method (AEM). Their primary value is in providing estimates of pit inflow rates to be used in the mine dewatering. Inflow estimation and recovery helps whether there is water to supplement the demand and if there is any recovery issue to be dealt with in relation to surface and groundwater quality/eco-system, environmental evaluations and mitigation. Therefore, this method is good at informing decision makers in assessing the effects of mining operations and developing an appropriate water management strategy. © 2016, Springer International Publishing Switzerland.


Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Drury L.,Snowy Mountains Engineering Corporation SMEC
Environmental Monitoring and Assessment | Year: 2016

The efficient use of water resources in arid region has become highly relevant in the evaluation and mining planning, since the exploration phase to closure. The objective of the numerical groundwater model was to assess the potential for groundwater extraction to meet mine water demand from one of the driest area in the world. Numerical groundwater models were used to assess groundwater resource. Modelling was undertaken using MODFLOW-SURFACT code, an advanced MODFLOW based code, within the framework of Visual MODFLOW version 4.6. A steady state model was developed to assess the regional groundwater flow pattern and to calibrate the recharge and hydraulic conductivity parameters in the model. The model was calibrated with a correlation of coefficient of 0.997, and root-mean-squared error is 0.3 m. A transient simulation model was used to predict the impact of 1.5 million cubic metre/year extraction for 10 years on the main aquifer hydrogeological regime, including after cession of pumping. Modelling simulated four hydrogeological scenarios. Model results for the ‘worst case’ scenario suggested that the Saq Sandstone aquifer should be capable of supplying the mine water demand (1.5 million cubic metre (MCM)/year) for 10 years. However, the long-term water-level drawdown shows a continuous decrease without achieving steady state conditions; thus, the majority of water is being taken from aquifer storage, and in the long term, there will be a mutual interference from a borefield located to the north of the model area. In this area, the hydraulic gradient is relatively steep and over-pumped for more than 28 years. Other scenario shows that there will be a recovery of around 8 m out of the 11.6-m drawdown, after 18 years of cession of pumping, implying that the aquifer will be stressed and a large percentage of water taken from aquifer storage. To minimise hydrogeological impacts, it is recommended to laterally spread out production bores, bores should be located where the Saq Sandstone is deepest, and operate the bores at low extraction rates. Overall, this study presents a useful numerical model output for mine water supply assessment and will contribute towards improving water resources management under different conditions in one of the world driest area. © 2016, Springer International Publishing Switzerland.


Yihdego Y.,Snowy Mountains Engineering Corporation SMEC
Geotechnical and Geological Engineering | Year: 2016

In this study a vertical barrier forming the exclusion system in relation to partials extending into an impermeable stratum was analysed using a 3-D numerical modelling used to quantify the effect of a hydraulic barrier on flow which allows taking the anisotropy and heterogeneity of the site in a complex hydrogeological context and hydraulic barrier into account. A simulation in this study shows that for 0 % cut off the % reduction in flow is 0 and for 100 % cut off the % reduction in flow is 96, 94 and 92 % at 5, 10 and 15 days respectively due to leakage through the sheet piles, even with 100 % of the aquifer cutoff, the % of groundwater inflow impounded never reaches the 100 %. Also the change in trend where the % reduction in flow increases significantly with % cut off occurs at around 60 % cut off. That is, the reduction in flow through the aquifer only becomes significant after 60 % cut off by the sheet piles. The sensitivity analysis allows determining the factors of influence. A sensitivity analysis indicates the relationship appears relatively less sensitivity to varying the hydraulic conductivity, but very sensitive to the % cut-off. Therefore the effect of the sheet piles start to be significant after cut off exceeds 80 % and that the total profile length matters, i.e. the 60 % cut off must be applied to the whole width of the aquifer and not a portion of the aquifer, i.e. the minimum required to adequately reduce flow under the levee is 80 % cut off. From this study it can be derived that less water flows to a levee structure surrounded by sheet piles, depending on the depth of the sheet piles in proportion to the depth of the water bearing layer. The relationship is independent for the hydraulic conductivity but dependent on the ratio between the installation depth of the sheet piles beneath the Piezometric level and the depth of the bottom of the water bearing layer beneath the same Piezometric level. This study demonstrated the major influence of the technical design of the barrier on the simulated flow disturbances. The current approach can be applied elsewhere in related field for variety of application including formulating a resource management strategy, contamination containment and settlement risk. Overall, the capacity of decision makers to understand flow systems, how they function and respond to the placement of hydraulic barriers in the area they manage will form the basis for the operational management of the resources and infrastructure. © 2016 Springer International Publishing Switzerland

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