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Parallel Computing with SEAWAT
Fresh groundwater reserves in coastal aquifers are threatened by sea-level rise, extreme weather conditions, increasing urbanization and associated groundwater extraction rates. To counteract these threats, accurate high-resolution numerical models are required to start optimizing the management of these precious reserves. Major model drawbacks are long run times and large memory requirements, limiting the predictive power of these models. Distributed memory parallel computing is an efficient technique for reducing run times and memory requirements, where the problem is divided over multiple processor cores. A new Parallel Krylov Solver (PKS) for SEAWAT is presented.
3D Paleohydrogeological modelling of the Nile Delta
Several studies found that the area is vulnerable to salt water intrusion due to the shallow topography of the area and the high transmissivity of the aquifer. Furthermore, hydrogeochemical measurement campaigns have shown the strong influence of paleohydrogeologic processes on the current groundwater salinity distribution. In this study, we model the complete Nile Delta Aquifer in 3D over several thousands of years. To tackle the computational burden this model created, we use the new iMOD-SEAWAT code.
Altering hydraulic conductivity for antagonizing seawater intrusion
Modifications of the hydraulic conductivities in an aquifer may result in altered groundwater flow and discharge. This could potentially help to prevent or reverse seawater intrusion in coastal aquifers. In this study we assume a modification of the hydraulic conductivity, e.g. by the blocking of pore spaces. A previously homogeneous porous coastal aquifer may thus be separated into a deeper, more permeable and a shallower, less permeable layer. The analytical solution calculates the length of the saltwater wedge [m], depending on the transmissivities in the upper and lower layer, respectively. A lower conductivity in the upper layer leads to a redistribution of groundwater flow, pushing the saltwater wedge towards the coast. The calculations are supported by physical sand tank experiments and compared to numerical model results. They are in good accordance to each other, suggesting that saltwater intrusion may be reduced by the modification of hydraulic conductivity.
Potential map for large-scale implementation of subsurface water solutions : COASTAR
In coastal areas, increased groundwater extraction rates and climate change stresses (including sea-level rise) are expected to increase the shortage of enough high quality water at the right place and on the right moment. Fresh groundwater resources in the coastal zone are also facing serious salinization issues. The COASTAR approach (COastal Aquifer STorage And Recovery) is to prevent salinization by strategically capturing and using brackish groundwater in the production of fresh water. For now, we focus on the technical and financial-economic feasibility. For the lower areas of The Netherlands, we started to investigate the potential of the subsurface to attain a robust and sustainable fresh water supply and to combat droughts.
Building up 3D salinity models for estimating fresh groundwater resources in major deltas under global and climate stresses
In many delta‘s, hydrogeological data is pretty much limited, so the speed of the depletion of fresh groundwater volumes is very difficult to quantify, although some innovative rapid data collection surveys are very promising (e.g. airborne geophysical surveys). We cannot wait decennia before enough relevant hydrogeological data is available for an accurate quantification of the fresh groundwater resources, and its status under global and climate stresses. A first estimation of the current fresh water reserves in different deltas is warranted, to raise this issue and to see which deltas are the most vulnerable, so that research can be prioritized. Therefore, as a first try-out, we analyzed if it is plausible to utilize free global data for 3D groundwater salinity modelling in data scarce regions: what would be the quality of the models and their ability to predict?.
A quantitative review of 1D airborne electromagnetic inversion methods : a focus on fresh-saline groundwater mapping
An accurate understanding of the fresh-brackish-saline distribution of groundwater is necessary to characterise salt water intrusion in coastal areas. Compared to traditional ground-based techniques, airborne electromagnetic (AEM) surveys offer a rapid and cost-effective method with which to achieve this. To convert observed AEM data into Electrical Conductivity (and ultimately groundwater salinity), an inversion is undertaken. This study quantitatively analyses eight commonly used inversion methods using real data from the Province of Zeeland, the Netherlands.
Impact of coastal forcing and groundwater recharge on the growth of fresh groundwater resources in a mega-scale beach nourishment
For a large beach nourishment called the Sand Engine, constructed in 2011 at the Dutch coast, we have examined the impact of groundwater recharge and coastal forcing (i.e. natural processes that drive coastal hydro- and morphodynamics) on the growth of the fresh groundwater resources between 2011 and 2016.
Large-scale, probabilistic airborne salinity mapping for groundwater management in Zeeland, the Netherlands
Groundwater resources in the Province of Zeeland, the Netherlands, have been largely salinised during marine transgressions, and fresh water is scarce. Climate change and sea-level rise are expected to exacerbate problems with freshwater availability. In FRESHEM Zeeland, we surveyed the entire Province of Zeeland using a frequency-domain helicopter-borne electromagnetic system. Survey results were translated into a 3D salinity distribution using a novel probabilistic approach. This approach aimed to recognize the uncertainty associated with the different steps in the procedure. FRESHEM results were well received by stakeholders and were made available to the public.
The role of evidence-based information in regional operational water management in the Netherlands
The integration of evidence-based information in operational water management is essential for robust decision-making. We investigated the current use of experiential and evidence-based information in Dutch regional operational water management. Interviews with operational water managers at regional water authorities in the Netherlands reveal that they use both evidence-based and experiential information for decision-making. While operational water management is shifting towards an evidence-based approach, experiential information is still important for decision-making. To fulfil the current information need, the operational water managers indicate they would like to have access to high-resolution spatial data, value-added products and tools for communication to stakeholders. We argue that hydrological models are suitable tools to support these needs. However, while several evidence-based information types are used by operational water managers, hydrological models are limitedly applied. Hydrological models are regarded as inaccurate for operational water management at desired spatial scales. Also, operational water managers often struggle to correctly interpret hydrological model output. We propose several means to overcome these problems, including educating operational water managers to interpret hydrological model output and selecting suitable indicators for evidence-based decision-making.
A regional application of Bayesian modeling for coastal erosion and sand nourishment management
This paper presents an application of the Bayesian belief network for coastal erosion management at the regional scale. A “Bayesian ERosion Management Network” (BERM-N) is developed and trained based on yearly cross-shore profile data available along the Holland coast. Profiles collected for over 50 years and at 604 locations were combined with information on different sand nourishment types (i.e., beach, dune, and shoreface) and volumes implemented during the analyzed time period. The network was used to assess the effectiveness of nourishments in mitigating coastal erosion. The effectiveness of nourishments was verified using two coastal state indicators, namely the momentary coastline position and the dune foot position. The network shows how the current nourishment policy is effective in mitigating the past erosive trends. While the effect of beach nourishment was immediately visible after implementation, the effect of shoreface nourishment reached its maximum only 5–10 years after implementation of the nourishments. The network can also be used as a predictive tool to estimate the required nourishment volume in order to achieve a predefined coastal erosion management objective. The network is interactive and flexible and can be trained with any data type derived from measurements as well as numerical models.