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Influence of hydrological model structures on extreme high flow simulations in the Meuse basin

Brink, C.J.R. van den (2018) Influence of hydrological model structures on extreme high flow simulations in the Meuse basin.

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Abstract:Already multiple studies have been performed with the use of synthetic weather data. These studies aim to determine extreme high discharge waves that have not yet been observed. The synthetic weather series are generated over a long period, within these long periods extreme conditions will occur. These synthetic weather series are used as input by hydrological models to simulate long discharge series, during extreme precipitation events the hydrological should simulate extreme high discharge waves. These studies have in common that only a single hydrological model is used for simulating the long discharge series. Therefore, it is unclear how another hydrological model might simulate these discharge waves associated with large return periods. Blazkova & Beven, (2002) already mentions that simulations performed by other models can show completely different results. This thesis is an explorative study, which will analyse the influence of different hydrological model structures on discharges that are simulated with the use of synthetic data series. The synthetic data that will be used for this study is developed by the KNMI and creates daily weather in the Meuse basin for a period of 50000 years. The analysis of the discharge simulations is delimited to daily annual maximum discharge values, which helps with filter the amount of data that is generated. Combining the notions stated above the following research objective can be formulated: Too study the effect of different hydrological model structures on their capability to reproduce statistical characteristics of extreme high flow events of the Meuse river basin using synthetic weather series. In this thesis discharges are simulated for the Meuse basin at Monsin which is located in Liege. The discharges are simulated with the use of 14 sub-basins, which are connected to each other via a routing system. Annual maximum discharge simulations of different hydrological models for individual sub-basins and the whole Meuse basin are compared to each other. However, in order to analyse the influence of the model structure it is important to limit the influence of other factors on the discharge simulations. Therefore, an experiment is designed in which the difference in simulations is only caused by the difference in the model structure. First of all the used hydrological model have similar characteristics. This means that the used hydrological models, which are the GR4J, HyMOD, and HBV model, can use the same data but also have a similar conceptualised model structures. This makes it easier to identify how model structure differences influence the discharge simulations. Secondly, the preparation of the hydrological models in the calibration process is done the same for every hydrological model. The value of an aggregated objective function that combines ........... is optimized using an optimization algorithm. The use of an optimization algorithm reduces the influence of the modeller during the calibration process. As a result the best parameter values are found using a more objective method. The calibration is performed for nine upstream sub-basins (Lorraine Sud, Chiers, Semois, Viroin, Lesse, Ourthe, Ambleve, Vesdre, Mehaigne), four sub-basins that are located downstream (Lorraine Nord, Stenay-Chooz, Chooz-Namur, Namur-Monsin), and one sub-basins is calibrated combined with an upstream basin due to lack of observed discharge data (Sambre). The calibration of downstream sub-basins required input from at least one of the upstream sub-basins. Finally, the routing of the discharge is simulated in the same way for every hydrological model. Upstream sub-basin discharges are added to downstream sub-basin discharges in order to simulate the total discharge of the Meuse. The routing is simulated by applying a lag on the upstream sub-basin discharge. This lag is kept constant and the same for every hydrological model. This ensures that the routing does not influence simulation differences of the hydrological models. The value for the lag is based on previous studies of the Meuse basin. The hydrological models are first used for a simulation of two 15 year historical periods (for most sub-basins, for some sub-basins discharge data within these periods is missing). The first 15 year period (1968-10/1983-10) is used for the calibration of the model. Whereas the second 15 year is used for the validation of the hydrological models (1983-10/1998-10). The results are presented in the form of objective function values for each sub-basin. The GR4J and HBV show the best performance in simulating the historical discharge series. Also these two hydrological models show similar performances for the calibration and validation periods. This indicates that the these two hydrological have robust performances with the optimized parameter values. The HyMOD model performs worse compared to the GR4J and HBV model for upstream sub-basins. The performance improves for the downstream discharge simulations. The results for the simulations using synthetic data are determined with the use of statistical analysis. For the statistical analysis a couple of upstream and downstream are selected from the 14 sub-basins (Chiers, Semous, Lesse, Ourthe, Mehaigne, Stenay-Chooz, Namur-Monsin). First of all the equality of population annual maximum means/variances of the used hydrological models was assessed between: historical data simulations/observations, synthetic data simulations/historical data simulations, and synthetic data simulations/observations. The population means/variances were unequal for synthetic data simulations/observations for the HyMOD model in most upstream basins. Which are in line with the performance results. After this analysis Gumbel plots are presented that show the annual maximum discharges of the observations and synthetic data simulations. In these Gumbel plots the GR4J and HBV synthetic data simulations in upstream sub-basins are almost equal for more common annual maximum discharge values. However, in most upstream sub-basins the GR4J model starts to show higher annual maximum discharge values compared to the HBV model for rare events (associated return periods larger than 10 years). The GR4J and HBV, synthetic data simulations of the annual maximum discharge at Monsin are similar, even for the largest return periods Due to the similarity of the simulations it cannot be determined whether the HBV model or the GR4J model shows a better performance in simulating discharges of the Meuse. Furthermore these similarities continue for synthetic data simulations. However, on a sub-basin level different hydrological model structure have a large influence on synthetic data simulations when looking at discharges associated with large return periods. This means that similar performance does not automatically result in similar synthetic data simulations of the larger more uncommon discharge values. The combination of discharges from multiple sub-basins can lead to an reduction of the effect that was seen for separate sub-basins. This results in similar synthetic data annual maximum discharge simulations of the GR4J and HBV model at Monsin for all return periods. Although the paths might be different the result is encouraging, indicating that these synthetic data simulations are in the right direction.
Item Type:Essay (Master)
Clients:
Deltares
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/74910
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