| dc.description.abstract | The summer of 2018 has been noted as one of the driest in the current history of the Netherlands. Its effects were widespread, impacting several sectors and water management infrastructure. Despite the above average rainfall in most of the country during the autumn of 2019, areas in the Pleistocene uplands (the sandy elevated regions in the Netherlands) did not reach the required amounts to supply sufficient groundwater recharge in the region and compensate for the 2018 hydrological drought. The scopes of this thesis were to study the effects of managed aquifer recharge (MAR) for hydrological drought prevention in the context of the Pleistocene uplands and determine how much effect it has in alleviating drought stress of agricultural and natural areas. The research question guiding the thesis was What are the regional effects of locally applied managed aquifer recharge as a measure to prevent hydrological drought and its impacts on natural and agricultural ecosystems in the Pleistocene uplands of the Netherlands?
After the general characteristics of the Pleistocene uplands were sketched, a theoretical conceptual model was made based on the Achterhoek region of the Netherlands, an area which represents these characteristics well. Next, a combined groundwater (MODFLOW) and a soil-vegetation-atmosphere (MetaSWAP) model was built in iMOD version 5.0. The hypothetical model spanned a region of 15 km long and 15 km wide, where a steady-state model was run and three transient scenarios were applied in a modeling experiment. The 13 scenarios represented different strategies in dealing with hydrological droughts, where the first was a baseline (do nothing) scenario. Two batches of six scenarios applied MAR through the use of injection wells. For one batch (AG MAR) the wells were located at the higher elevation area of the model, and for the second (N MAR) the wells were located at the lower elevation area, about 2 km from the river. Each batch consisted of treatments with different recharge amounts per well (500 m3/d, 5000 m3/d and 10000 m3/d) and each treatment consisted of MAR application in either the summer or winter. Calibration of the model was done based on its steady state simulation, while the validation was done by comparing the normalized groundwater level time series of the baseline scenario and actual groundwater data in the region taken from the DINOloket database. The groundwater level and relative transpiration of each scenario were observed at 12 different locations.
The results show that MAR did have regional effects in preventing hydrological drought and, to a lesser degree in increasing relative transpiration. In general, N MAR scenarios had more widespread effects than AG MAR scenarios, except for the 500 m3/d treatments, the which effects were too small to be noticed. On the other hand, AG MAR scenarios provided greater groundwater level increase except for where the influence of the river was strongest. In addition, because of the higher groundwater levels, AG MAR also resulted in higher transpiration increase in the area closer to the injection wells than N MAR, as well as a greater overall regional effect in transpiration increase.
Assumptions were made in the model design and in the analysis methods. However the results are conclusive and comparable to literature on MAR measures for hydrological drought prevention and transpiration increase. Recommendations for future research include studying the effects of MAR in a model with the presence of groundwater drainage and to study the combined effects of MAR with the increase of drainage levels in the Pleistocene uplands. Coupled to this combination is the need for restoration of nature areas near rivers and at seepage zones, where often agriculture is practiced and intense drainage occurs. Therefore, the policy recommendation given by this thesis is to apply MAR not only as a stand-alone technical solution, but within a process of land use planning in order to maximize the retention of groundwater and better prevent the impacts of drought. | |
