Husam Musa Baalousha

Using Monte Carlo simulation to estimate natural groundwater recharge in Qatar

Rainfall is the only source of groundwater recharge in arid countries, where no surface water exists. Quantification of the total volume of rainfall recharge is essential for water resources management, development and protection, but it is challenging. Numerous recharge estimation methods can be found in the literature, but the selection of the most appropriate one depends on the hydrogeological setting of the area of study and on the available data. Qatar is an arid country as rainfall is very little and surface water is non-existent. Aquifer is the only conventional source of water, which has been over-exploited in the last few decades. One of the main country’s grand challenges is to implement an aquifer storage and recovery scheme, which requires understanding of the flow regime and quantification of the natural rainfall recharge. This study uses a water balance model coupled with Monte Carlo Simulation to quantify rainfall recharge. Using a historical groundwater piezometric map, the flow to the sea was calculated by applying Monte Carlo Simulation to the Darcy’s Law. The natural recharge was calculated considering all water budget components. Results reveal the groundwater rainfall recharge amounts to 58.7 million m3, which is close to literature values obtained by other means.

Vulnerability, probability and groundwater contamination risk

In many articles and publications in sub-surface sciences, the terms probability, vulnerability and risk are used incorrectly and interchangeably (i.e. Dao and Peduzzi 2003; Harter and Rollins 2008; Wen et al. 2009; Jilali et al. 2015; Denner et al. 2015). This commentary illustrates the differences between vulnerability, probability and risk. Margat (1968) was the first to introduce the term vulnerability (Witkowski et al. 2007), which is based on the assumption that the physical environment of a groundwater system may provide some protection against contamination. Vulnerability indicates the weakness of a system based on hydrogeological settings and classifies an aquifer system into different zones of variable degrees. One of the most widely used methods of intrinsic vulnerability assessment is the DRASTIC approach, which uses seven parameters to create a vulnerability map (Aller et al. 1987). Many other methods exist in the literature such as EPIK (Dörfliger and Zwahlen 1998) for karstic aquifers and many others. Vulnerability is neither a risk nor a probability of contamination, as some studies confuse these terms. Many studies mix vulnerability and risk or incorrectly calculate risk as a combination between vulnerability and contamination load (for example, Al-Adamat et al. 2003; Varol and Davraz 2010). While vulnerability indicates the likelihood of susceptibility to contamination or weakness of a system, by no means does it indicate the actual degree of contamination. A high vulnerability area within an aquifer may not become contaminated if it was not exposed to a contamination source (Baalousha 2016). In contrast, a low vulnerability zone may become contaminated (albeit to a lesser extent than a high vulnerability area) if it was exposed to a strong contamination source. In conclusion, although vulnerability indicates the degree of weakness of a system, it does not necessarily mean a total protection or exposure to contamination. Specific vulnerability maps can be transformed into risk maps by the inclusion of hazards, the probability of contaminant spills and the value of groundwater resources (Zwahlen 2003). As explained above, vulnerability is not necessarily directly proportional to contamination risk. Hence, probability of contamination cannot be measured by vulnerability alone. By definition, probability of an event varies between 0 and 100%, whereas vulnerability may take any number. A high probability of contamination can be achieved only when a highly vulnerable area has a high probability of exposure to contamination. Unlike vulnerability, risk by its nature always has a negative impact. Risk is not a probability, but it is used to evaluate the probability of contamination (Bogardi and Kundzewicz 2004). It indicates the possibility of damage, with a certain degree of probability. As such, risk assessment requires probability of occurrence of an event (in this case contamination) and the degree of damage occurred, whether it is health, environmental damage or both. Ostrom and Wilhelmsen (2012) defined risk as ‘‘the probability of an unwanted event that results in negative consequences’’. They further explained that risk assessment requires answering three questions: (1) what can go wrong? (2) how likely is it? and (3) what are the consequences? Rausand (2011) explained how these questions can be answered. The first question requires identification of hazards that may lead to harm. Probability or frequencies are required to obtain a qualitative assessment to answer the second & Husam Musa Baalousha Baalousha@web.de

An Efficient ELLAM Implementation for Modeling Solute Transport in Fractured Porous Media

The goal of this study is to introduce an adaptation of the Eulerian-Lagrangian localized adjoint method (ELLAM) for the simulation of mass transport in fractured porous media, and to evaluate the performance of ELLAM in such a case. The fractures are represented explicitly using the discrete fracture model. The velocity field was calculated using the mixed hybrid finite element method. A sound ELLAM implementation is developed to address numerical artifacts (spurious oscillations and numerical dispersion) arising from the presence of fractures. The efficiency of the developed ELLAM implementation was further improved by taking advantage of the parallel computing on shared memory architecture for the tasks related to particles tracking and linear system resolving. The performance of ELLAM was tested by comparing its results with the Eulerian discontinuous Galerkin method based on several benchmark problems dealing with different fracture configurations. The results highlight the robustness and accuracy of ELLAM, as it allows the use of large time steps, and overcomes the Courant-Friedrichs-Lewy (CFL) restriction. The outcome also shows that ELLAM is more efficient when fracture density is increased.

Groundwater pumping versus surface-water take

Surface-water bodies and aquifers are normally connected and it is widely recognised they should be treated as one entity. Numerous studies were done to analyse the effect of groundwater pumping on nearby streams, however, little is known on the differences of effects between surface-water take and a pumping well of equal rate. The question, which often arises by water resources managers and allocation authorities, is whether to allocate or consent-transfer from a surface-water body or from an aquifer. This study explores the different effects of each case and makes a comparison using analytical analysis and numerical models. A hypothetical model is presented where two cases are considered: (1) a stream water take through a diversion and (2) a pumping well. In both cases, the drawdown and water budget of surface and groundwater are presented. Results show the pumping well produces high drawdown in the aquifer, and induces stream leakage. The stream leakage results in stream level drop. It takes a long time for such a system to stabilise or to reach a steady state. In contrary, the direct stream water take produces much lower drawdown in the aquifer, albeit higher drop in stream water level. The latter case stabilises and reaches steady state conditions considerably faster than the first one. These results reveal it is recommended to allocate from surface-water bodies than aquifers as the impact is less and for a shorter time, given the same allocated volume of water.