Analysis of contribution of the shallow groundwater system to climate adaptations using groundwater modeling. A case study of Stadioneiland in Amsterdam, The Netherlands
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Climate change models predict an increase in precipitation intensities as well as longer periods of drought during summer for the Netherlands (IPCC, 2014). In urban environments, it is essential to adapt water systems to these changes in climate in order to prevent water nuisance and protect wooden foundation poles. For the Stadionbuurt in Amsterdam, a groundwater model is built in finite element modeling program MicroFEM. Time series analysis is used to pre-process observation data from 2007-2016 on trends, measuring errors and outliers. The transient model is run from 2014 until 2016. The groundwater model is extensively calibrated using both MicroFEM and the automated parameter estimation program PEST for parameter optimization. The maximum average residual is reduced to 0.26 m from 0.46 m initially, with the gross amount of residuals falling below 0.10 m. In KNMI climate change scenario Wh for the year 2050 (scenario I), the model shows an decrease in lowest calculated groundwater levels up to 0.10 m. Consequently, 64% of wooden foundations would lack water coverage at a certain point during the calculated two years, compared to 49% currently. To prevent these low groundwater levels and the potentially harmful effects on foundations, scenarios are created to analyze the effects of a climate adaptive design. For scenario II, an infiltration experiment is performed and the infiltration capacity of the Drainvoeg permeable paving is determined to be 40mm hour-1 after a lifespan of five years. If constructing this type of permeable paving instead of the current semi-permeable paving, groundwater levels increase to an extend that can be damaging to trees and cellars while not raising the groundwater significantly during drought. In scenario III, DIT-sewage is constructed where currently drainage is located. The sewage has a variable drainage depth of NAP -0.20 m at the end of winter until beginning of summer and NAP -0.40 m during the rest of the year. At locations where foundations is threatened in a scenario of changed climate, this renewed DIT-sewage design can ensure a sufficient water coverage (for example, figure 4.6). Finally, interpretation of the previously described scenarios leads to answering the main research question of how the shallow groundwater system of the Stadionbuurt can contribute to climate adaptations. The capacity between surface level and groundwater levels indicate possibilities for infiltrating surface water or precipitation. Scenario III shows the shallow groundwater system can contribute to climate adaptations, at least sufficiently for minimizing negative effects of drought. The balance between too high and too low groundwater levels remains delicate and caution has to be taken to the disadvantages of climate adaptations, as shown in scenario II. The calibrated shallow groundwater model developed in this research for the Stadionbuurt has proved to be useful for climate exploration as well as analyzing the effects, both positive and negative, of possible adaptations. Many more scenarios can be explored by Waternet, for example scenarios of increase in cellars or the expansion of surface waters in the area. In addition, the model can be used to dimension the adaptations. Increase in drought and extreme precipitation will face challenges not only for Stadioneiland, but for the entire city of Amsterdam. Soil properties and wooden pole foundations are rather specific to Dutch cities, but climate adaptations need to be designed in all urban areas. The technique of calibrating a transient groundwater model for highly urbanized neighbourhoods could be used as a template to design other local models. Furthermore, half of the world’s population live in delta regions like the Dutch delta and face similar challenges (VHL, 2018). Water management as modeled in this research might be a source of inspiration for other delta regions.