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Title : WL Rapporten. Waterbouwkundig Laboratorium: Antwerpen. Volume : 21_087_1 Issue : Pagination : VII, 27

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Title : WL Rapporten. Waterbouwkundig Laboratorium: Antwerpen. Volume : 22_034_1 Issue : Pagination : XIII, 67 + 68 p. bijl.

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The innovative flexible hydrological modelling concept proposed by Tran et al. (2014) was further developed in this inventory. A generalized model structure which consists of the most basic and/or popular hydrological components was constructed. It includes the meteorological components, the storage components, the splitting components, the routing components and a component for closing water balance. Equations from the NAM, PDM and VHM models were used as demonstrations for each components. The additional components can be added by users depending on applications and on the available data.Since the concept allows flexibility in spatial resolution, the Grid-to-Grid approach for explicitly representation of the hydrological connectivity between gird cells with the catchment is needed. Next to that, the Source-to-Sink approach was also implemented but it was not discussed in details in this report due to its simplicity in implementation. Two schemes of Grid-to-Grid approach were developed: i) the normal routing scheme, in which the interaction between different subflow components are omitted and ii) the detailed routing scheme, which allows to describe more detail the infiltration and percolation processes.The step-wise methodology for calibration was developed for both lumped and spatial distributed models. For the distributed models, the calibration process starts from the well-calibrated model parameters for lumped case and then uses the catchment characteristics (i.e. the topography map, the land use map and the soil type map) and other additional data (e.g. the groundwater observation, the internal gauging station…) to disaggregate into spatial distributed parameters. Those spatial parameters can be fine-tuned to capture the distribution of the runoff in the whole catchment. The efficiency of the identified model structure is assessed using both traditional statistical indices and the graphical evaluation.Three conceptual model codes (NAM, PDM and VHM) spatially implemented in the proposed framework were applied for a case study of Grote Nete catchment in Belgium. They were calibrated using the predefined parameters from the lumped models. The comparison of the distributed outputs versus the lumped results and versus the observations at gauging stations indicated good matches, which show that the proposed framework has successfully implemented. Nevertheless, further research is still in need in order to complete the concept., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_130_8 Issue : Pagination : VIII, 94

The water balance model of the Scheldt and Meuse basins will be used in order to perform low flow forecasts and calculate climate change scenarios. Within the current subtask is investigated which is the most appropriate hydrological model for the sub catchments of the water balance model of the Scheldt basin in order to meet this prerequisite. This sub report describes the calibration and evaluation of the VHM model, a lumped conceptual model for continuous rainfall-runoff simulation (Willems P., 2014) developed by the Hydraulics Division in KU Leuven in Belgium.The optimization during calibration is performed based on an automatic procedure, followed by a visual control. During the optimization routine the parameter sets are selected based on 2 criteria: (1) absolute error on cumulated total flow at each time step, and (2) logarithmic Nash-Sutcliff efficiency. The first criterion aims to model the global flow pattern, the latter focuses mainly on the low flows.Overall, the performance of the calibrated VHM models is similar compared to the other lumped rainfall-runoff models already calibrated: PDM, NAM and WETSPA. The summarized results for each of the gauged sub catchments within the study area, allow the user to get insight in the performance of the VHM model for each of the involved sub catchments. Based on this information and the evaluation of the NAM, PDM and WETSPA models, the user can make a well-grounded decision on which model to use for the considered objective., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_162_4-4 Issue : Pagination : XII, 85 + 326 p. app.

The assessment of climate change impact on the hydrological system is becoming more and more a key issue for establishing best management practices for the limited water resources. Climate change impact analysis requires state of the art hydrological models to perform simulations of different climate scenarios. The study of these scenarios is however not sufficient to compensate for the high uncertainty of future forecasting. With the purpose of including model structure uncertainty, the iFramework was developed (Pannemans et al., 2014). This Python-based framework is a powerful platform for managing and creating flexible hydrological models. Within the iFramework, three well known lumped hydrological models can be used: NAM, PDM and VHM. The available tools have however a lumped model structure which can be a limiting factor for complex hydrological applications. To overcome this limitation, we extended the library of hydrological tools by including the spatially-distributed model WetSpa in the iFramework toolbox. This report describes the development of a iFramework-compatible WetSpa model, and its implementation and testing by means of theoretical and real case study.The WetSpa model (Water and energy transfer between Soil plant and atmosphere) is a well established GIS-based, spatially-distributed rainfall-runoff model for hydrological simulations at the catchment scale. Recently a process-based Python version of the model has been developed (Salvadore, E. et al., 2012, 2014), this new version is based on a different Python framework (Schmitz, et al. 2013a, 2013b) but facilitates the integration with the iFramework. To perform the integration, we carried out an in-depth comparison of the two framework paradigms to identify the appropriate strategy to bridge the gaps between the two frameworks. Afterwards, we developed new Python codes for the WetSpa model in the iFramework and we modified some parts of the iFramework to allow the integration of the WetSpa model in the toolbox. In this phase, we decided to develop two versions of the WetSpa model: a spatially-distributed and a lumped version. Distributed and lumped WetSpa models share the same Python codes, the main difference is the flow routing approach. Finally, these two versions were verified by means of a theoretical and a real case study. We compared the results generated by the two model versions with the original WetSpa-Python model. In both validation tests, the spatially-distributed model produced nearly identical results to the original model, with only negligible rounding errors. In the lumped model, all the inputs and parameters were averaged over the all catchment. The validation of the lumped model is less straightforward as model parameters partially lose their physical meaning and cannot be directly compared with the distributed ones. However, by modifying a number of parameters we were able to achieve a good match between the lumped model and the original spatially-distributed model, which ensure the correct implementation of the model code. Further tests on the lumped model are however required for a better understanding of the behavior of the model parameters., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_130_9 Issue : Pagination : VII, 17 + 9 app.

To be able to perform up to date simulations with the water allocation model of the Flemish navigable waterways, it is necessary to update its input regularly. Besides updating the network and possible new structures like new canal reaches, new locks, new pumping regimes, … also the water demand of the different water users should be updated. In contrary to the update of the network – which needs to be done manually – the update of the water demand can be done automatically by means of a new developed tool. This sub report describes the development of this tool., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_162_2 Issue : Pagination : VIII, 35

The recent studies by Vansteenkiste et al. (2011, 2012a and 2012b) have shown that the potential hydrological impacts caused by climate change scenarios for Belgium have high uncertainty. For a given climate scenario, the quantitative impact results on the hydrological extremes and overall water balance strongly depend on the selected hydrological model. However, there is a wide variety of existing hydrological models which are now available with different levels of complexity. Therefore, it is necessary to analyze the model structure uncertainty affecting the impact results. An ensemble approach is recommended, where different plausible model structures are tested and inter-compared.To make such approach feasible in an operational context, an innovative flexible framework is developed and proposed in this study. The framework starts from the multi-model / multi-process ensemble concept, which provides the ability to pinpoint the uncertainties related to hydrological modelling, including the selected model structure, in impact investigations such as climate change or land use change or other types of scenario investigations. This framework, moreover, contains some advantageous aspects, namely the data based approach, the flexibility in model components (hydrological processes) and equations, the spatial implementation, the flexibility in spatial resolution, the model calibration approach for various spatial scales and the flexibility for future extension.Several well-known lumped and distributed prevailing hydrological models and modelling systems (platforms) were reviewed and presented in order to define the most basic or common hydrological processes that should be implemented in the proposed concept. The popular approaches for presenting hydrological connectivity inside catchments are as well listed. Moreover, PCRaster in Python programming language with its great functionality for spatio-temporal environmental modelling was selected as the platform for the proposed framework.Three lumped models (i.e. NAM, PDM and VHM) were translated into Python language within the PCRaster environment. The converted scripts were then applied to the case study of the Grote Nete catchment, using the same inputs and model parameters as in the report of Vansteenkiste et al. (2012a). The performance of the translated scripts was evaluated by comparing the simulation results to those from the existing Matlab scripts. The comparisons done for the NAM, PDM and VHM lumped conceptual models have shown a perfect match, which indicates the potential for further implementation of the proposed concept in PCRaster. A distributed version of the NAM model was built and recalibrated for the same catchment to show the possibility for spatial implementation in PCRaster. A concrete work phase is made where the flexible modelling framework, including the flexible approaches for spatial calibration or disaggregation and hydrological spatial linking (explicit versus non-explicit), is implemented and applied for (climate change) impact analysis for a number of catchments., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_130_7 Issue : Pagination : VIII, 47

The water balance model of the Scheldt basin will be used in order to perform low flow forecasts and calculate climate change scenarios. Within the current subtask is investigated which is the most appropriate hydrological model for the sub catchments of the water balance model of the Scheldt basin in order to meet this prerequisite. This sub report describes the recalibration and evaluation of NAM models, which are part of the MIKE 11 software package (DHI, 2009).The optimization during calibration is performed based on an automatic procedure, followed by a visual control. During the optimization routine the parameter sets are selected based on 2 criteria: (1) absolute error on cumulated total flow at each time step, and (2) logarithmic Nash-Sutcliff efficiency. The first criterion aims to model the global flow pattern, the latter focuses mainly on the low flows.Overall, the performance of the updated NAM models, is substantially improved compared to the original NAM models. The summarized results for each of the gauged sub catchments within the study area, allow the user to get insight in the performance of the NAM model for each of the involved sub catchments. Based on this information and the evaluation of the PDM, VHM and WETSPA models, the user can make a well-grounded decision on which model to use for the considered objective., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_162_4-1 Issue : Pagination : IX, 71 + 244 p. app.

In the framework of the water allocation projects there are four hydrological models (NAM, PDM,VHM and WETSPA) calibrated for the region of Flanders. The aim of the models is to generate the flows needed as input in the basin model in other to analyze water allocation problems and generate strategies. It is also expected to use the hydrological models to analyze possible impacts of climate variability in the context of water allocation. To realize that, the models are forced with projected climate variables that are frequently out of the range of the data used in the calibration process. Thus models are force to extrapolate conditions for which the parameterization is or may not be optimal. This may bring errors in the projection of climate effects. The problem assessing the performance of the models is that there is not data available in the future to compare with.The aim of this document is to present the proposed approach for testing the capacity of the calibrated hydrological models to project the climate change effects in the context of water allocation for Flanders. The proposed testing framework combine the use of historical data through an adapted form of Differential Split Sample test (Refsgaard et al., 2014) with and approach that use the relative change of statistical properties of flows between historical data and the projected data (van Steenbergen and Willems, 2012). To assess the model we use a robustness criteria based on a Log Nash-Sutcliffe, BIAS on cumulative volumes and relative changes based on Q50/Q90 estimated from the duration curve., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_162_4-6 Issue : Pagination : IX, 29 + 63 p. app.

Title : WL Rapporten. Waterbouwkundig Laboratorium: Antwerpen Volume : 00_162_3-2 Issue : Pagination : IX, 53 + 1 p. bijl.

The water balance model of the Scheldt and Meuse basins will be used in order to perform low flow forecasts and calculate climate change scenarios. Within the current subtask is investigated which is the most appropriate hydrological model for the sub catchments of the water balance model of the Scheldt basin in order to meet this prerequisite. This sub report describes the calibration and evaluation of the PDM model, a lumped conceptual model for continuous rainfall-runoff simulation (Moore, 2007) developed by the UK Centre for Ecology and Hydrology.The optimization during calibration is performed based on an automatic procedure, followed by a visual control. During the optimization routine the parameter sets are selected based on 2 criteria: (1) absolute error on cumulated total flow at each time step, and (2) logarithmic Nash-Sutcliff efficiency. The first criterion aims to model the global flow pattern, the latter focuses mainly on the low flows.Overall, the performance of the calibrated PDM models, is as good if not better compared to the other lumped rainfall-runoff models already calibrated: NAM. The summarized results for each of the gauged sub catchments within the study area, allow the user to get insight in the performance of the PDM model for each of the involved sub catchments. Based on this information and the evaluation of the NAM, VHM and WETSPA models, the user can make a well-grounded decision on which model to use for the considered objective., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_162_4-3 Issue : Pagination : XV, 86 + 293 p. app.

Title : WL Rapporten. Waterbouwkundig Laboratorium: Antwerpen Volume : 00_162_3-1 Issue : Pagination : X, 126 + 2 p. bijl.

The water balance model of the Scheldt basin will be used in order to perform low flow forecasts and calculate climate change scenarios. Within the current subtask is investigated which is the most appropriate hydrological model for the sub catchments of the water balance model of the Scheldt basin in order to meet this prerequisite. This sub report describes the evaluation of WETSPA models (Water and energy transfer between Soil plant and atmosphere, Salvadore, E. et al., 2012, 2021).Hydrological models with WETSPA are developed for the sub catchments included in the water balance model (including the Meuse basin). To assess the water availability and the flow behavior, each catchment was calibrated manually to find an optimal parameter set. The optimization during calibration is performed based on an automatic procedure followed by a visual control. During the optimization routine the parameters set is selected based on 2 criteria: (1) absolute error on cumulated total flow at each time step, and (2) logarithmic Nash-Sutcliff efficiency. The first criterion aims to model the global flow pattern, the latter focuses mainly on the low flows.In general the simulation of the hydrology of the Scheldt and the Meuse basin gives from reasonable to fairly good results and by consequence the developed hydrological models could be used to predict the future water availability under climate change., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_162_4-5 Issue : Pagination : X, 93 + 714 p. app.

In order to correctly simulate the water availability in the Albert Canal and the Campine Canals, it is important to correctly simulate the flow in the Meuse river. The river is the source for this vast canal system. If it is possible to simulate the hydrology of the Meuse basin, it will be possible to model the water balance of the canal system for a period of over 40 years. The modelling has been done using the NAM software (©DHI).The Meuse catchment is split up in 11 sub catchments. One big catchment of the Meuse itself upstream from Profondeville, 7 catchments of different scale of the tributaries downstream of Profondeville and 3 smaller catchments representing the ungauged area downstream Profondeville. Except for the catchment upstream from Profondeville, the catchments are calibrated separately to find an optimal parameter set. To assess the parameters for modelling the upstream catchment, the latter was split in 5 sub catchments which were calibrated separately. However, for the purpose of the water availability modelling of the Albert Canal and Campine canals, the area upstream from Profondeville is simulated by using the parameters of the biggest sub catchment (i.e. the French part of the Meuse catchment).The optimization during calibration is performed based on an automatic procedure, followed by a visual control. During the optimization routine the parameter sets are selected based on 2 criteria: (1) absolute error on cumulated total flow at each time step, and (2) logarithmic Nash-Sutcliff efficiency. The first criterion aims to model the global flow pattern, the latter focuses mainly on the low flows. In general the simulation of the hydrology of the Meuse catchment gives fairly good results bearing in mind that it is used for simulations on a regional scale., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 00_162_4-2 Issue : Pagination : X, 36 + 78 p. app.

Title : WL Rapporten. Waterbouwkundig Laboratorium: Antwerpen Volume : 00_162_5 Issue : Pagination : VII, 30

Among the advances made in analytical and numerical analysis methods to quantify groundwater/surface-water interaction, one methodology that stands out is the use of heat as an environmental tracer. A large data set of river and riverbed temperature profiles from the Aa River in Belgium has been used to examine the spatial-temporal variations of groundwater/surface-water interaction. Exchange fluxes were calculated with the numerical heat-transport code STRIVE. The code was applied in transient mode to overcome previous limitations of steady-state analysis, and allowed for the calculation of model quality. In autumn and winter the mean exchange fluxes reached −90 mm d−1, while in spring and early summer fluxes were −42 mm d−1. Predominantly gaining conditions occurred along the river reach; however, in a few areas the direction of flow changed in time. The river banks showed elevated fluxes up to a factor of 3 compared to the center of the river. Higher fluxes were detected in the upstream section of the reach. Due to the influence of exchange fluxes along the river banks, larger temporal variations were found in the downstream section. The exchange fluxes at the river banks seemed more driven by variable local exchange flows, while the center of the river was dominated by deep and steady regional groundwater flows. These spatial and temporal differences in groundwater/surface-water exchange show the importance of long-term investigations on the driving forces of hyporheic processes across different scales.

In hydrological modelling, it is often observed that the error on the simulated flow values is heteroscedastic. In order to obtain homoscedastic errors, researchers have been applying transformations of the flow values (e.g. a Box-Cox transformation) within their model calibration procedure or have introduced an error model within a Bayesian framework for parameter estimation and uncertainty analysis. Transient numerical groundwater flow models are also affected by different sources of uncertainty. Nevertheless, the possible heteroscedasticity of the errors on the simulated groundwater levels has been mostly neglected when performing uncertainty analysis for these types of models. Therefore, we introduce a novel heteroscedastic error model for groundwater level predictions within a general and flexible Bayesian framework. In this way, we can consider the heteroscedasticity of the groundwater level error along with the parameter uncertainty. Moreover, we can also analyze these two sources of uncertainty in combination with input uncertainty. The proposed methodology is applied on a fully distributed physically-based groundwater flow model of an overexploited aquifer in Bangladesh. The results of the study confirm that the heteroscedasticity of the groundwater level error should be considered and that it has an effect on the model predictions and parameter distributions. It is also shown that the observation coverage of the parameter uncertainty band increases from 1.5 % to 8.5 % when the heteroscedasticity is explicitly taken into account along with model parameter uncertainty.