For a better understanding of the water system and the consequences of interventions, modeling is important. Insights into the water system often translate into the need to make predictions about the behavior of the system under specific circumstances. For example, when there is a risk of flooding, to determine the sustainable amount of groundwater extraction, or to determine the bottlenecks of the sewer system. These insights and predictions are gathered through modeling.
Modeling is a central theme in water studies where cause and effect are connected by a well-founded and structured input. Nectaerra is well experienced in various modeling applications and uses a wide range of software and scripts.
Our geological expertise is one of Nectaerra’s cornerstones. During analysis the first application of modeling is the importance of visualizing the available data and quality checks. This gives a direct overview of the situation. This also laid the foundation for using a model as a data management tool of available information during the current study, but also as a basis for future studies. The second application of modeling is as a schematization of the subsurface for geological analyzes and as a basis for hydrological flow models.
Modeling can vary from simple soil-layering-modelling in a small area to a complex geology with lots of data over a large area. With both, Nectaerra has extensive experiences. The software we use runs in this range, from GIS software such as ArcGIS and QGIS in combination with Python, to highly advanced software such as Kingdom and Petrel. The latter are originally petroleum software, but have no equivalent within the typical water software. For seismic interpretation – which we practice in exploration of deep and offshore groundwater – Kingdom is necessary and Petrel is supplementary.
Many hydrological tasks require predictions about the hydrological behavior of the system for which model calculations need to be performed. The geological model forms the basis for this. Dynamic simulations about groundwater flow (saturated zone) are carried out with Modflow, in principle supplemented with Hydrus 2D / 3D for calculations in the unsaturated zone, such as for example recharge or evaporation.
Due to the complexity of programming the use of Graphical user interfaces, such as ModelMuse or PMWiN, is the most common way to manage Modflow. However, this is accompanied by issues such as a loss of possibilities, loss of detail level, an increasing difficulty in locating and resolving convergence problems, and in a general sense therefore often a drastic loss of calculation speed. Whereas the output possibilities for the data and calculations are also more limited. To avoid these disadvantages, Nectaerra uses Modflow by the use of Flopy and our self-developed scripts based on Python code. With this, the model can be completely tailored to the wishes of the user and problem definitions.
Hydro(geo)logical modelling also provides insight into the sensitivity of available data to the results. In combination with parametrization tests, it can be made clear which data are the most important to be collected first and where that data must be spatially won, and what the required accuracy must be.
The modeling of water-carrying systems is an activity that is carried out from the moment that humans started to intervene in these types of systems. This is highly important for urban hydrology, maintenance of systems and predictions of climate change. Nectaerra uses software from Innovyze and Deltares to carry out model studies. For the progress of a model study, an problem analysis is carried out before choices with regard to the input data. Depending on the research questions or sustainable use of the problem, it is decided what quality of data is sufficient for input, to arrive at a response that offers sufficient certainty that the proposed solution will fit the problem.
Validation of a model, based on measurement data, is an important tool to improve models. This also contributes to confidence in the outcomes of the model studies. Finally, there are practical experiences that can be used in model building. We consider all these sources of information in connection with each other. In light of the aforementioned question and available budgets, we will consider which means are best applicable in a situation. Our working method is aimed at providing the client with insight into how the system works and what the consequences are of possible interventions. We try to transfer as much knowledge about the performance as possible to the client. Our efforts are supportive for the client to come to a decision.
Theoretical approaches to estimate the phreatic water level in embankments are used in the assessment and design of flood defenses in the Netherlands. In some cases, measurement setups are used for extra insight. However, the combination of in-situ measurements combined with hydrological modeling is the solution to determine more accurately how the groundwater flows through an embankment or barrier and how it will respond during various normative climatic situations, like drought or flooding.
At the same time, hydrological modeling can predict the estimated effects of (re)construction measures, such as heighten by the use of clay, installation of such called clay screens or sheet piles. Hydrological modelling also can give insight into different systems which can cause a breakdown of an embankment caused by for example piping or seepage.
For this microscale modelling, of the first few meters, it is also important that the data fit the necessary level of detail; modeling can be used to map and analyze wetting and drying process, and so phreatic and moisture variations within embankments.