University of Twente Student Theses


Application and evaluation of the 3Di Groundwater Model in the Waalenburg Polder, Texel, the Netherlands

Kling, D.J. (2019) Application and evaluation of the 3Di Groundwater Model in the Waalenburg Polder, Texel, the Netherlands.

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Abstract:Hydrological models are developed in order to support the decisions and strategic plans of operational water management by governments. These models can be used to analyse, understand and explore solutions for water management. The models used by water authorities have a wide range in size and complexity. This includes, but is not limited to, hydrodynamic models and groundwater models. One of the models used is the 3Di Hydrodynamic model, a process-based, hydrodynamic model for ooding, drainage and other water management studies such as regional water distribution. The 3Di Hydrodynamic model was recently expanded with the addition of a groundwater domain, the 3Di groundwater model. This research focuses on the evaluation of the 3Di groundwater model for a polder area on its accuracy and its sensitivity for changes in time-independent model parameters and model design choices. This is done by the creation of a model for the Waalenburg polder on the island of Texel, the Netherlands. This model is based on a highly detailed elevation model and information on from data models of the water system including, locations and depths of channels and heights of weirs for the surface water domain. By the use of the REGIS II model, a schematisation of the phreatic aquifer is included for the groundwater domain. A sensitivity analysis was done for the time-independent model parameters, hydraulic conductivity and storativity. This analysis showed that the mean of the simulated groundwater levels is most sensitive for changes in its hydraulic conductivity, increasing values of hydraulic conductivity cause lower mean groundwater levels. The standard deviation in simulated groundwater levels was shown to be sensitive for the storativity of the ground. The same volume of water can create a bigger change in groundwater levels for grounds with lower storativity. This sensitivity analysis was used to calibrate the model for its hydraulic conductivity and storativity. The calibrated model is further evaluated on its accuracy. The simulated model results correlate well compared to the measured groundwater levels, little deviation is shown in the mean results of the model and measurements, and the variability of the model results is in accordance with the measurements. The model performance for computing groundwater levels provides confidence in the ability of the model to simulate the groundwater ows, especially so for the winter period. The effects of design choices in temporal resolution of precipitation time series input, surface water level boundary conditions and the model grid have been investigated. The calibrated model gives good results using daily time series for precipitation and evapotranspiration. It was shown that refining the resolution of the precipitation time series to 5 minutes did not affect the results in a significant way. Boundary conditions along the model edges that are not in direct connection with ditches along modelled areas do not have a significant impact on groundwater levels within the area. They do however have an impact on the discharges through ditches in the surface water domain. It was shown that a well-performing model could be created using a grid of 20 m by 20 m for the majority of the area of interest. The grid size is mostly dictated by the surface water system as a calculation cell cannot include multiple surface water levels. It was shown that grid size does affect the groundwater levels. A finer grid may lead to an increase in groundwater levels of up to 30 cm. Due to this fact, changes in grid size may lead to the need for re-calibration of the model. It can be concluded that with the 3Di groundwater model it is possible to simulate groundwater levels within a polder with good accuracy, especially for winter periods. The modielled mean groundwater level is sensitive for the hydraulic conductivity and the modelled variability in groundwater levels is sensitive to the storativity. These sensitivities can be used to calibrate a model of a particular area. The model design is adequate for the simulation of groundwater levels during wet periods. The current state of the 3Di groundwater model may lack the ability to simulate the groundwater recharge of high precipitation events after a dry period as depicted by the overestimation of in the period July 2017 through November 2017. The two-dimensional approach of the 3Di Hydrodynamic model makes it so spatial variation in parameters for both surface and groundwater can better be taken into account. Interaction between the surface and phreatic groundwater domain is resolved simultaneously relieving the need for iterative runs of multiple models, which often result in high computation times.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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