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The integration of forecasting and decision-making in real-time Decision-Support Systems (DSS) provides a powerful tool to operators of water resources systems for evaluating the future control of hydraulic structures. Decisions may be supported by presenting information about predicted disturbances, e.g. inflows into the water system, enabling the operator to try out future trajectories of structure control, or suggesting an optimum control based on predictive controllers. Ongoing work is undertaken under the programme Flood Control 2015 (FC2015) with respect to the management of flood events. This MSc thesis research was supervised jointly by the Operational Water Management research group of Delft University of Technology and the research institute Deltares. The aim of the MSc project is the transfer and extension of real-time DSS knowledge and techniques to a typical Dutch canal system such as Twentekanalen using simulation tools in development at Deltares. The main research objective is to assess the potential of DSS in this context and to investigate and verify a robust concept for applying Model Predictive Control on canal systems, taking into account missing or wrong data by applying Data Assimilation techniques. The main system characteristics and relevant processes of the Twentekanalen system are the following: • 3 Canals connected by locks in which the water level needs to be controlled. • The water level is chiefly governed by the operation of locks, which need to turn in order for ships to pass, discharging a large quantity of water each time in comparison to other water flows in the system. Measurements of water level and flows at the locks are relatively complete. • The water level is regulated by pumps and discharge structures at the locks • Other water flows that occur in the system are lateral inflow and outflow. The measurements of these flows are relatively incomplete. At the start of the research a set of tools was available at Deltares. FEWS, a data management system, and RTC Tools, a reservoir routing model in development which was later extended with Data Assimilation capabilities. Near the end of the research a detailed model of the system in Sobek, a 1D and 2D water flow model, became available. A model framework has been designed to assess the potential of applying MPC and DA in a DSS for such a system. The incremental design and verification of this model framework has been the core of this research. The novel research is the addition of Data Assimilation techniques to Model Predictive Control. In order to show the added value of DA and verify its implementation a verification approach is needed to address the other components in the framework as well. The first method taken to achieve this was to set-up the MPC for Twentekanalen and integrate it into Delft-FEWS in hindcast mode assuming a perfect forecast. When the data set was made available it became clear that it contained large water balance errors. Adding DA showed improvements in the forecast, but while using realistic values for the DA, the forecasts were still far from accurate. By creating a workaround in the DA module it was shown that especially the Eefde-Delden reach had a large balance error that did not have a high correlation with the known lateral flows. Considering the low quality of the data set it was decided to expand the scope of the research and replace the data set by an accurate hydraulic model that became available near the end of this research. This model still uses measurements from the Twentekanalen system as input, but with internal controllers to regulate the pump and spill structures the water balance is maintained. With an extra expansion to inject known errors in the system, a thorough investigation of the effects of Data Assimilation and Model Predictive Control can be executed. First results from this expanded approach show promising results, but because of practical implementation issues of conflicting software modules, the full results will not be available within this research. Conclusions: From a theoretical point of view DA has a lot of potential. State updating solves an important issue of real time control; keeping the model state as close as possible to the real system state. Model training by parameter updating can be a good way to increase model forecasting performance. Online Parameter Updating can be very effective in systems were a high correlation occurs between measurements and unmeasured processes. These elements will make the model more robust, it can adapt to changing conditions. This also provides the model developer with interesting feedback on the workings of the modeled water system. From a practical point of view DA has shown improvements in the performance of the DSS as designed within this thesis project. But because of the large errors in the measurements it is difficult to translate these improvements to the effects in other systems. Implementation of the designed model framework gives a more satisfactory answer to that question. Recommendations have been made for improvements of the RTC Tools module, the development of prediction modules for the Twentekanalen system and further research using the developed framework with the models, scripts and programs written for this research. Most importantly getting predictions and real-time measurements on lock turning in the Twentekanalen system, and increasing the flexibility of model design in RTC Tools.

Introduction and problem definition The IJsselmeer is located in the center of the Netherlands. For its relevance for the Dutch economy and society, it is often addressed as the Wet Hearth of the country. When looking into the future, the IJsselmeer is under climate threats. Wetter winters will bring more water into the system, in combination with sea level rise, and lower gravity discharge to the Waddenzee. This will generate safety issues. On the other hand summers will be drier, putting the satisfaction of water demand in danger. Research approach and research question The goal of the research is to define for the IJsselmeer a dynamic target water level which is variable through the whole year by means of an optimization approach. The optimization uses a single objective function considering dikes safety and water demand. Such approach has been chosen because follows a different path than the ones mainly used so far to tackle the issue. When management measures alone are not enough to define a climate-proof IJsselmeer, extra measures are taken into consideration: a pumping station at the Afsluitdijk and early storage in March. The main research question asks for an evaluation of the optimization methodology used to define efficient alternatives for the IJsselmeer. The sub-question requires the assessment of the flexibility of the IJsselmeer towards a climate-proof system, and the definition of extra measures, when needed. Methodology The definition of the optimum measures is achieved in several steps. Firstly the objective of the problem owner is defined. The Dienst IJsselmeergebied is the only problem owner. Its interests are safety and water demand satisfaction. Then indicators are derived from the objectives, and merged into the objective function. Classes of measures are selected, and a model of the system designed for their evaluation. Finally the optimization problems are defined in order to design the optimum alternatives. Results A different planning of the target water level alone is not able to satisfy the needs of safety and water demand on the long term. As it is now, the IJsselmeer is flexible on the short term, but not enough to accommodate the impacts of longer horizons: extra measures are needed in order to define a climate proof system in 2050 and 2100. Pumping station at the Afsluitijk is an effective measure to guarantee safety for all the scenarios. Early storage in March is effective in the medium horizon (2050) but need high target water levels along the summer for the long term (2100). This might generate safety issues. Even if applied on a simplified case, the use of an optimization methodology manages to define a realistic picture of the flexibility of the IJsselmeer, and retrieves efficient options for possible future strategies. For this reasons, the present research can be considered a successful implementation of an optimization approach for the IJsselmeer. Conclusions and recommendations For the short term it is recommended to use the flexibility of the system, implementing the changes in summer target water levels which would allow deeper satisfaction of water demand. For the medium/long term, options for early storage need to be investigated together with the summer target water levels needed. This would probably require reinforcement of the dikes. Options for safety can be then defined for the new reinforced system, considering combinations of pumping station and raise of the dikes. A more extensive and detailed optimization tool should be realized for the IJsselmeer, and applied for the definition of the measures above. In particular it is recommended to use a multi-objective analysis and include costs in the definition of the indicators.

Het onderzoek Het gebied ‘polder Westzaan’ is een uniek brakwatergebied in Europa en dankt zijn bijzondere flora en fauna aan het brak oppervlaktewater. Sinds de Zuiderzee in 1932 werd afgesloten en het IJsselmeer ontstond, wordt nog hoofdzakelijk zoet water in het gebied ingelaten. Het gaat om een gebied van circa 900 ha in de natuurgebieden Guisveld en De Reef. Door het inlaten van het zoetwater vanuit de Zaan, menging van het water met meststoffen en de afbraak van laagveenvegetaties is het water in polder Westzaan onnatuurlijk voedselrijk en troebel geworden. Dit heeft gevolgen voor zeer zeldzaam brakwater vegetatie en bijbehorende aquatische fauna. De oorspronkelijke natuurwaarden van het gebied staan onder druk door de verzoeting van het gebied. De doelstelling van dit onderzoek is het ontwikkelen van maatregelen in het waterbeheer voor het verbrakken van de noordelijke deel van polder Westzaan. Onderzocht wordt, hoe het chloridegehalte van het openwater van polder Westzaan kan worden gehandhaafd op het voor de ecologische systeem gewenste niveau van 2000 mg/l, zonder dat dit leidt tot problemen voor de waterkwantiteit zoals hogere peilen en wateroverlast. Om de bovengenoemde doestelling te behalen is er een model ontwikkeld waarbij het water ingelaten wordt vanuit het Noordzeekanaal. Onderdeel van het onderzoek is daarom in eerste instantie het bepalen van een tracé van het Noordzeekanaal naar het noordelijke gedeelte van de polder. Hierbij wordt water uit diepere lagen van het Noordzeekanaal als brakke bronstroom gebruikt. Methodologie Voor het verkrijgen van inzicht in het waterhuishoudkundig functioneren van het watersysteem van polder Westzaan en van de te ontwerpen maatregelen, is gebruik gemaakt van het Sobek instrumentarium met de modules Channel Flow (CF), Rainfall Runoff (RR), Water Quality (WQ) en Real Time Control (RTC). In eerste instantie is het huidige watersysteem geanalyseerd. De huidige dimensies van de watergangen en kunstwerken zijn bepaald op basis van de gegevens van het Hoogheemraadschap. Het nieuwe tracé met benodigde kunstwerken zijn in een veldbezoek bepaald. Dit tracé is in overleg met het Hoogheemraadschap van Hollands Noorderkwartier en de Dienst Landelijk Gebied definitief gemaakt. Op basis van de randvoorwaarden en de uitgangspunten zijn de benodigde afmetingen van nieuwe watergangen en kunstwerken zoals stuwen, duikers en sifons doorgerekend. In het hoofdstuk Methodologie is verder ingegaan op deze randvoorwaarden en de uitgangspunten. Voor de berekening van de benodigde dimensies van watergangen en water kunstwerken is gebruik gemaakt van het door de DLG ontwikkelde berekeningsmodel Water SF. Deze ontwerpgegevens van watergangen en kunstwerken zijn, samen met de bestaande watergangen en kunstwerken, vervolgens in het SOBEK model ingevoerd. De maatvoering van het nieuwe tracé is verder verfijnd in SOBEK door steeds de resultaten met gewenste resultaten te vergelijken. De gebiedsregeling voor zowel waterkwantiteit als waterkwaliteit is geprogrammeerd in het programma Matlab. Door de afstemming tussen SOBEK en MATLAB is het eindresultaat van het model bereikt. Resultaten Voor de modelberekeningen is uitgegaan van 3 scenario’s. De scenario’s zijn zodanig gekozen dat er voor een korte droge periode (15 dagen), een lange periode(een jaar) en nat, en een lange periode(een jaar) en droge situatie berekeningen worden uitgevoerd. Als scenario 1 is gekozen voor een korte droge periode (eerste helft van april 2009), als scenario 2 voor een nat jaar (1998) en als scenario 3 voor een droog jaar (2003). De gewenste waterpeilen worden niet overschreden bij enkele gevallen na tijdens een natte periode in 1998. Het gewenste chloride gehalte van minimaal2000 mg/l wordt bereikt met uitzondering van enkele dagen in 1998 in verband met zeer natte omstandigheden. De gemalen functioneren goed voor alle scenario’s. Na een week inlaten van water zijn de effecten van de verbrakking te zien in het gebied. In een nat jaar als1998 wordt een chloridegehalte van 2000 mg/l na een maand bereikt. Door het ontwikkelde meet en regelsysteem kan dit in stand worden gehouden.

In this thesis, the concept of water budgeting is discussed. This concept is based on a comparison between water resources and financial resources. It aims to approach water resources management problems more like a treasurer would. Water resources can be distributed in such a way as to optimise the chance of achieving a desired goal. Depending on what the most important goal of the water manager is, different ‘water budgets’ are possible. The concept of water budgeting is: to distribute the available water resources in such a way as to optimally achieve a certain objective. Model Predictive Control is considered a potential tool for water budgeting. This tool can translate the desired objectives into operational water management. The objective for the water system, in the form of penalties and constraints, are used as input for the Model Predictive Controller. The controller then determines the operational water management, which is most successful at achieving the desired goals. The concept of water budgeting is applied to the South-Western Delta in order to test its usefulness. Different goals are set for the area, and these different goals result in different operational water management strategies. During the application of the water budgeting concept several shortcomings became apparent. These shortcomings follow from the fact that: the comparison between water resources and financial resources is complicated by the physical properties of water. Two very important properties of water in this respect are: water is bulky and water is fugitive. These properties result in: water being difficult to store and transport, in comparison to financial resources. Because water is difficult to handle, it is not straightforward to budget water. The water budgets become very variable in time and space. Due to this variability in time and space the sum of the water distribution does not tell the whole story. The moment at which the water resources are used is equally, or might be even more, important. The application of Model Predictive Control, as a tool for water budgeting, has also proven to be limited. The most important limitation of using Model Predictive Control is: the reduced transparency of the decision making process. It is difficult to trace back why the controller ‘chooses’ certain control actions. This reduces the predictability of the operational water management. Reduced predictability of the operational water management, results in a less predictable water system. This will make it harder for stakeholders to be dependant on the water system. The application of Model Predictive Control to a water system of this size and without a very clear (single) objective is relatively new. During the research it became clear that: it is very important to be able to control all the (large) in and outflow structures, and that it is important to included the parameter that needs to be controlled in the internal model. In the case used, it was not possible to control the Maeslantkering. This resulted in limited control over the water bodies connected to the Nieuwe Waterweg. In the internal model water salinity was not included. This made it very hard to control salinity. Penalties for the controller were developed that were assumed to influence salinity. These penalties were however not sufficient to prevent salinities to become too high in certain areas. This shows that the controller needs to be able to directly predict what the salinities will be.

This research focuses on polder-belt canal systems. More is demanded from these systems every day. Man induced changes, like increasing population density and increasing land value on one hand and climate change in the form of longer dry spells and more extreme precipitation events on the other hand are the main sources. The operation of the structures in these systems plays a critical role in successfully dealing with these challenges. To get the most out of the current system and its structures, operation by humans alone is not enough, they need to be aided by computers. A promising technique is Model Predictive Control (MPC). A control algorithm that uses a model of the system and forecasts of the future disturbances to determine the control actions for the structures, whilst adhering to the constraints of the system. Forecasts are uncertain and are therefore provided in the form of ensemble forecasts that consist of multiple scenarios. MPC uses only one scenario and is thus vulnerable to these uncertainties. Treebased Model Predictive Control (TBMPC) considers the complete ensemble to determine control actions. TBMPC has, however, only been tested in theory. Only open loop simulations have been carried out, no continuous closed loop simulations have been done. TBMPC uses the complete ensemble, but to save calculation time reduces it to a tree-shaped representative ensemble with fewer nodes. This means aggregating nodes and scenarios on various points in the ensemble. There are multiple rules that determine which nodes and scenarios are aggregated, however, their optimal setting is not known. Also if TBMPC has more added benefit over MPC on certain system configurations (e.g. configurations with higher discharge or storage capacity) is not known either. A model is developed to simulate the performance of MPC and TBMPC. It can deal with different precipitation series, forecasts, system configurations and control algorithm parameters. All simulations have a duration of one year and a one hour time step. The rules that determine which nodes and scenarios are aggregated are investigated first. Transforming the inflow forecast scenarios to cumulative inflow scenarios before determining which nodes and scenarios to aggregate yields better results. The threshold value is also important as it determines whether or not two scenarios are close enough to each other to be aggregated. Nothing was known about the right value for this parameter. One of the objectives was to be able to fine tune this value to the system con guration. Setting this value as a percentage of the maximum pump capacity of the system works well across di erent system configurations. The optimal value is 100% of the maximum pump capacity. The scenario reduction algorithm (i.e. the algorithm that creates the tree from the original ensemble) has two parts. First it reduces the number of scenarios in the ensemble to a predefined number and secondly it creates a tree out of the reduced ensemble. No information was available about the right amount of scenarios for the first part. The simulations show that using more than eight to 10 scenarios does not yield any better performance, but only increases calculation time. To determine if TBMPC is more beneficial on certain system configurations 81 configurations are examined. The performance of MPC with a perfect forecast (i.e. equal to the inflow), MPC and TBMPC is simulated for these configurations. For all configurations TBMPC shows a considerable added benefit, however, there are different reasons for different configurations. For configurations with a high storage and pump capacity the increased performance can be attributed to a more stable water level and a slight improvement in the deviation from set point. For configurations with a low storage and pump capacity the added benefit of TBMPC is seen in a better peak event anticipation. Overall significant improvements to TBMPC have been realized. It is shown that TBMPC not only works in theory, but provides benefits over MPC in practice for a multitude of configurations as well. TBMPC can now be tuned to the water system configuration it is used on and it can be set to reduce calculation time as much as possible without decreasing the performance.

Areas outside the primary flood defenses, here called unembanked areas have a special status in the Dutch water safety policy. Whereas, primary flood defenses have to fulfill to legal standards and a functional manager is appointed for construction, maintenance and management. For unembanked areas this situation is different; some provinces have water safety policy and according to the national water plan residents and users are responsible for taking consequence reducing measures of floods. For the development of new areas decisions have to be made about the desired level of safety and how this is achieved. This leads to the issue of optimal adaptation strategies. What is the best level of safety so that unnecessary high risk levels and overinvestment in safety related infrastructure can be circumvented? This study presents a framework for municipalities and property developers how to deal with flood risk in unembanked areas. 952 developments are planned in unembanked areas of which 183 comprise urban dwelling projects. This thesis especially focuses on these urban dwelling projects where flood events can be regarded as a local, regional and direct tangible risk. The following research question is answered: How can we deal with the uncertainties of flood risk in investment decisions in the development of unembanked areas? 1. What is the current policy of building in unembanked areas and what are the responsibilities of the government? 2. Which strategies can be formulated to create the desired level of safety and how should they be compared? 3. How can a multi-layer safety approach contribute to the safety of the project area? 4. How do area specific characteristics influence the cost effectiveness of the measure? 5. How to deal with the residual risk? A multi-layer safety approach assumes three layers in flood control: 1. Prevention: characterized by structural measures which influence the boundary conditions of the project area. Surface level heightening and the construction of an embankment are discussed 2. Spatial planning, characterized by structural measures which influence the exposure and vulnerability. Wet proofing, dry proofing and an elevated configuration are discussed. 3. Disaster control, characterized by non-structural measures which influence the exposure and vulnerability. Organizational aspects and financial compensation are discussed. It was founded that the urban dwelling density of a project area determines the profitability between individual consequence reducing measures (layer 2 of the MLS approach) and collective probability reducing measures (layer 1). The profitability of collective measures grow linear and transcend individual measures at 24 dwellings/ha. An elevated configuration is preferred above wet and dry proofing. Considering the construction of an embankment it was founded that the profitability grows according to a power function and transcends surface level heightening at 35 ha. All proposed urban dwelling plans in unembanked areas are analyzed on these criteria and it was founded that for 23% of the plans individual measures are preferred above collective measures. 62% of these plans are located in areas where the province has no flood probability standards and therefore consequence reducing measures have a good chance. The other 38% of the plans are located in provinces with flood profitability standards and the profitability of extra consequence reducing measures is dependent on this standard. For the remaining 77% of the areas a probability reducing approach is preferred; of which for 6% the construction of an embankment is preferred and for the other a surface level heightening strategy is preferred. All criteria of insurability (grouped in actuarial, market-determined and societal) are analyzed for a flood damage insurance for unembanked areas. Due to the physical aspects and policy of unembanked areas the formulated criteria of insurability score better for unembanked areas. The actual realization will depend on the market determined criteria. This approach has been tested for a redevelopment project in Rotterdam, Heijplaat, where it was founded that surface level heightening is the only profitable measure.

Introduction Low Impact Development (LID) is an alternative approach in managing stormwater runoff. Its main philosophy is to replicate the pre-development hydrological properties of water catchment. It seeks to first infiltrate, filter, store and retaining the surface runoff near to its source before draining it to downstream. Some of the common LIDs include green roofs, permeable pavement, vegetated swales, infiltration drains, bioretention cells (also known as rain gardens). While LID seems to be a viable solution to reduce the flooding problem, we would like to investigate its performance after the LID (in particular infiltration drain system) has been put into operation for some time. A case study in Prinsejagt, Eindhoven will be used as data from previous studies is available to allow for comparison on the performance of infiltration drains after ~10 years of installation. Problem definition Infiltration drain has been used in Netherlands quite extensive, it is important to find out its current performance after years of operation. Existing researches or studies of infiltration drain system concentrate on its performance when it is newly installed. Studies that look into performance of an existing system which has been put into operation for quite some time are still quite rare. Research My research focused on determining the percentage reduction in exfiltration rate at the measurement site as compared to initial readings derived from previous research. It involves the monitoring of water levels at the same locations of the infiltration (IT) drain system in Prinsejagt (as carried out the previous monitoring scheme in 2003) and to carry out IT drain model simulations. In addition, we also conducted closed-loop test at four selected stretches of infiltration pipes to ascertain the exfiltration properties of the particular stretch of pipe. First, we seek to explain the phenomenon observed at our monitoring site qualitatively before applying quantitative approaches (like graphical, curve-fitting and simulation methods) to assess the percentage reduction in exfiltration rates at the monitoring locations. Based on the projected clogging rate, simulations were carried out to predict the future system exfiltration rate. Results 1. System behaviour (of the IT drains network) coupled with the influence of groundwater level determine the overall performance of the IT drain system. 2. Individual IT pipes exhibit more varied rates of exfiltration (due to different localized conditions) 3. Verified that linear mathematical function can adequately describe the water level trends to an accuracy of 0.01m RMSE for all monitoring locations 4. Observed a 9.4% drop in exfiltration rate [L3/T] in the IT drain model. By 2021, the exfiltration rate is expected to drop by 20% from its starting value. Conclusions and recommendations Regular maintenanceto clear the accumulated sediment inside IT drains and thereafter monitoring of performanceshould be carried out so as to determine its effectivenessin increasing the overall permeability.Moreover, water quality monitoring in IT drain system could be implemented to prevent any contamination to groundwater resources. In lowering the pipe invert level of the entire IT system, the IT system performance can be enhanced during low groundwater period.

Since the end of the last century, polders in the Netherlands have suffered from inundation due to heavy rainfall. Inundation occurrences in 1998 have led to large economic losses, especially in polders with a fast rainfall runoff process due to the high percentage of land occupied by greenhouses. This thesis focuses on water system assessments, conducted in greenhouse dominated polders. The water system assessment is divided in a technical analysis (using a hydrodynamic model) and an analysis on the cooperation between the different parties involved in water management. The inundation of 1998 had a large impact in the area managed by the water board of Delfland. As a reaction to the inundation, policies were created containing storage capacity standards for the open water of polders. Based on these standards the project ABCDelfland (Afvoer- en Bergings Capaciteit Delfland, in English: Drainage and Storage Capacity Delfland) was started, in which water systems of main canals and polders were assessed. The polder assessment was aimed at reviewing if the new standards were met. In the assessment the water board focused on the water system under its own control. The focus of that study was not on how to solve the inundation problem, but on how the open water system could comply with the standards. The solutions which were identified to make the water system meet the standards were financially not feasible. It was found that a better representation of the water system was needed to develop new solutions. Cooperation between the parties involved in water management would be needed to make this happen. This study was conducted to improve the assessment methods of rainfall fed inundation in greenhouse dominated polders. It uses the Oranjepolder (located in the management area of the water board of Delfland) as a case study, since inundation has occurred several times in this polder and is well documented and parties are engaged in finding new innovative solutions for the problem. In this assessment a form of participatory modeling was applied. Input for a new hydrodynamic model was given by all parties involved in the management of water in the Oranjepolder. The water board of Delfland is responsible for the management of the open water, the sewer systems are managed by the municipality of Westland and horticulturists influence the runoff to open water by the storage of water in basins. By sharing information and experiences during workshops, this research has been made possible. Through the cooperation of these parties, the important elements of the water system and the key to future solutions are identified. A hydrodynamic model of the Oranjepolder with a high level of detail is achieved. All important hydrologic processes are included. The hydrology of greenhouses is included on an individual level, resulting in a runoff to open water which represents the actual situation. Secondly, the channel flow model contains all channels and water structures located in the polder. This makes it possible to review inundation at every channel. Thirdly, the sewer system of the village Maasdijk is included in the model. Water flowing out of manholes and the interaction between the sewer and open water system are made visible. Finally, the aspect of overland flow is included. By taking all these hydrologic processes into account, predictions with a high level of precision can be made. The high level of detail and the high precision of the model lead to better insight in the factors that influence inundation. Testing the model with real rainfall data resulted in the identification of multiple inundation locations, which were also reported in reality. Due to this high predictive value it was possible to devise precise measures to prevent future inundation. These measures are not confined to the open water system but also concern the sewer system and the hydrology of greenhouses. It is expected that the total cost and amount of land needed, will be substantially lower than in previous assessments and that all stakeholders will support the implementation of measures.

Ongoing urbanisation and the subsequent extensive use of the urban water system can lead to degradation of its surface water quality. In the Netherlands, urban water bodies often suffer from the manifestations of eutrophication due to (historically) high nutrient loadings. This research focused on the enhancement of surface water quality of semi-confined urban water bodies with a case study on a floating treatment system. Urban water bodies often function as amenities of the urban area. Their ornamental and ecological value depends on the state of their aquatic ecosystem. Excessive nutrient loading, leading to the collapse of the system’s biodiversity, turns a water body into a turbid state without submerged macrophytes. Restoration of the clear water state through reduction of nutrient loadings alone is hindered by hysteresis caused by the ecosystem relations and could be supplemented with an approach focused on increasing the system’s nutrient carrying capacity or an internal approach directly targeting the manifestations of eutrophication. The Bright Water Company floating helophyte filter actively drains a filter bed with bog plants growing in it. The influent of this biofilter is provided by free inflow of surrounding surface water. Its water treatment ability depends predominantly on filtration and adsorption by specific nutrient absorbents. Additionally, its inner reservoir serves as a habitat for small aquatic organisms. Insights on the functioning and applicability of the biofilter were gained through in situ measurements. Two biofilter were applied in the Floresvijver in Groningen and measurements were conducted on influent, effluent and surface water. Visual observations and laboratory analyses of the water samples showed effective filtration and daphnia flourishing in the inner reservoir of the biofilter. Accumulation of the residual solids as a sludge layer on top of the filter bed and formation of biogas inside the filter material proved to reduce the hydraulic capacity significantly. Nutrient removal efficiency could not be determined with the monthly measurements of the water board but for optimal functioning of the phosphorous absorbent the current filter bed design should be adjusted while effluent samples indicated leaching of absorbent components. Application of the biofilter can contribute to the enhancement of urban surface water quality by increasing the nutrient carrying capacity of a water body. Especially in urban areas with various diffusive nutrient sources and physical constrains, the application of the biofilter can be efficient. Additionally, the biofilter functions as a habitat for zooplankton which are an important ecosystem element for the prevention of algae blooms. Furthermore, the effluent of the biofilter can provide a local increase in transparency and improve conditions for macrophyte development. The number of biofilters applied in a water body determine the significance of these contributions relative to the existing conditions.

Soil moisture is important for the Volta Basin. However, in-situ measurements of soil moisture in the Volta Basin are scarce, only remote sensing observations are available. Remote sensing observations are also provided with limited temporal and spatial resolutions. Also capabilities of the sensors are limited (e.g measuring soil moisture limited in shallow layer), and observations from different instruments do not totally agree. Hydrological model can predict soil moisture. But model predictions rely on assumptions and suffer from input uncertainties. Therefore, data assimilation is used to combine the information from observation and model to achieve optimal estimation of soil moisture. In this thesis, AMSR-E data of volumetric water content and ERS data of relative saturation for the Votla Basin were compared, and TRMM precipitation data were also used to compare with the two sets of soil moisture data. The dataset of ERS relative saturation was further assimilated into the PCR-GLOBWB model for the period of January 1st 2003 to December 31st 2006 in the Volta Basin. An ensemble size of 100 was applied. A key objective of the thesis is to address spatial correlation of data. Uncertainties of the model parameter (storage capacity) and input forcings (evapotranspiration and precipitation) were represented with spatial correlation. Correlation lengths of the parameter and forcings were thus calculated. The outcome of perturbation managed to maintain the spatial pattern of data. In the next part, four EnKF schemes (EnKF (Ind), EnKF (Blk), EnKF (DistMx) and EnKF (NonObserved)) were applied and compared. Results show that the block size is consistent with the correlation length and that schemes which account for spatial correlation produce better and more realistic results than the one without spatial correlation.

The importance of moisture feedback between continental precipitation and evaporation, referred to as moisture recycling, is still under debate. Most of the research in the past focused on the contribution of recycling to precipitation within a certain region only. This paper clearly distinguishes between different definitions of moisture recycling. This allows us to study the complete process of continental moisture recycling. In addition to identifying how much of the precipitation originates from continental sources, a new definition is used to identify regions which are major moisture suppliers for continental precipitation. An accounting procedure based on ERA‐40 reanalysis data is used to calculate moisture recycling ratios. As such, this paper derives new information from existing data. It is estimated that on average 38 % of the continental precipitation has continental origin and that 52 % of the continental evaporation returns as precipitation over continents. This paper demonstrates the important role of topography in the Andes and the Tibetan Plateau where regional moisture recycling is a key process. The Amazon and the Congo are identified as very important regions for sustaining continental precipitation. It is also demonstrated that moisture recycling from the Eurasian continent is the major supplier of the fresh water resources of China.

Located between the Andes Mountains and the southwestern coastline of Peru, the irrigation district of La Joya Antigua has a typical sub-tropical desert climate with very little annual precipitation. Study on this irrigation district shows sufficient irrigation water on most of the farms in a wet year but a deficit of irrigation water in a dry year. In order to cope with water shortage, strategies such as focusing on irrigating certain crops, reducing the irrigation area, changing crops to less water demand crops, etc are applied by the local farmers. The farmers' strategies have been proved to be a very effective way of reducing the crop water demand in the irrigation district of La Joya Antigua.

Artificial wetlands are used at different locations in the world as a treatment facility for wastewater of different composition. In order of Rijkswaterstaat several artificial wetlands are constructed for road runoff treatment. In all cases the artificial wetland is preceded by a sedimentation basin / storage buffer. One of them is located along the A1 near ‘t Gooi. A research on the purification efficiency of this wetland shows higher metal concentrations in the effluent in wintertime (Tromp, Helofyteninfiltratiesystemen voor zuivering wegwater, 2005). This is probably due to de-icing salts. The given solution is to bypass the artificial wetland in wintertime to avoid metal flush out. This research strives to deepen the insight into metal mobilisation in artificial wetlands under the influence of de-icing salts. The main question of this research is worded: “What is the influence of de-icing salts on the remobilization of heavy metals in an artificial wetland?” For this research six artificial wetlands located at traffic junction Raasdorp, A5 and A9, are available for measurements. Visual inspection reduced this amount to one due to various deficiencies in the other five. This resulted in a sub question: Does the filter function hydraulically as it is designed for? By use of a water balance, visual inspection and gathered data by use of divers an indication of the hydraulic functioning is made. Since high iron concentrations were measured it is concluded that groundwater is leaking into the artificial wetland. The other option, iron is leaching out of the filter substrate, is rejected by the column test results. Here the iron concentrations are decreasing which should not be the case if it is originating from the substrate. Artificial wetlands are characterised by enhancement of treatment performances because of the presence of vegetation. The main processes which are introduced by vegetation are summarized by the term phytoremediation. Vegetation is able to bind heavy metals in the root zone and also storing them into their biomass. To get insight into the heavy metal concentrations in several parts of the treatment facility water samples were took. The question in relation to the water samples is: “Do heavy metals and PAH occur in the influent of the artificial wetland and is there a difference with the effluent of the artificial wetland?”. Elevated levels for heavy metals were observed at the influent of sedimentation basin and artificial wetland. The highest concentrations were measured for copper and zinc. The other four measured heavy metals were: cadmium, chrome, nickel and lead. These metals did not show significant higher concentrations. In most cases here, the concentration was below the detection limits of the laboratory analysis.PAHs were also measured but in most cases the concentrations were below the detection limits of the laboratory analysis. Because of this less attention is paid to the behaviour of PAHs in comparison to heavy metals. The results of the measurements display a pattern where in general the pollutant concentrations are highest in the influent of the sedimentation basin, followed by the influent of the artificial wetland. The lowest concentrations were in general measured in the effluent of the artificial wetland. This proves the expected behaviour of the treatment facility. The goal of measuring the conductivity at location is to get an answer onto the following question: “Can the presence and movement of de-icing salts be quantified and evaluated based on the measured conductivity into the treatment facility?”. An increase of dissolved salt causes an increase of the conductivity. In wintertime rise of the conductivity in the treatment facility was measured and the results are providing insight in the movement of deicing salt through an artificial wetland. As a last step a column test is carried out to investigate the influence of de-icing salt on a possible flush out of heavy metals. The column test is filled with a soil sample what is took out of the original artificial wetland. Four different runs are carried out where for each consecutive run the de-icing salt concentration in the influent is increased. The question on which an answer should be found here is: “Is for the column test effluent an increase of heavy metal concentrations measured by increasing conductivity of the influent per run?”. The results of the column test did not show the expected increase of heavy metal concentrations into the effluent of each run. The first two runs did show elevated concentrations of copper and zinc but for the last two runs concentrations were considerably lower. For the third run an significant elevated concentration of lead is measured where this concentration is for the other three runs near the detection boundary. The effluent of the fourth run should according to the hypothesis contain the largest heavy metal concentrations, but this was not the case. The measured concentrations of the de-icing salt related ions did show the expected behaviour for the four runs. The concentrations in the effluent were increasing for each consecutive run as was also expected based on the conductivity measurements.

Introduction Flood risks can be reduced by either reducing the probability or the consequences of a flooding. These consequences can be quantified with flood damage models. Such models determine flood damage based on the water depth and the land use. This thesis will investigate the need to also use the flood duration as input parameter. Problem definition Besides the water depth, also other factors determine the resulting flood damages. These factors are often not taken into account in flood damage models. One of these influences is the flood duration. The longer a flooding lasts, the larger the material damage, and especially damage due to interruption will be. Flood duration causes interruptions and extra material damages. Taking into account flood duration can, therefore, theoretically make flood damage models more accurate. Flood duration predictions are, however, at the moment rarely done. This thesis aims to get both a qualitative and quantitative understanding of flood duration and the importance of flood duration for damage assessments. Research This thesis aims to explore the possibilities of assessing flood duration for flood risk management. This is approached by the following steps. 1. Development of a better understanding of flood duration. By looking at different areas and flood threats, a flood type categorization was developed and durations were estimated for each flood type 2. Exploration of the influence of flood duration on damage. A modeling method to roughly estimate the duration-dependent damage was developed. The framework of this method may also be useful for future duration dependent flood damage models. 3. Two case studies were carried out to study flood duration and its influence on damage in more detail: First the Betuwe and Tieler & Culemburgerwaard area was studied and secondly the area threatened by a breach at the Parksluizen in Rotterdam was focused on. Different scenarios were used with varying breach locations, measures and use of outlet and drainage structures. Results 1. The most important factors which determine the flood duration are duration necessary to repair the breaches, the possibilities for drainage by gravity, the elevation and elevation variation in the area and the magnitude of the flood event. Flooding durations in the Netherlands vary between hours and about one year. 2. Adding flood duration as input to flood damage models adds a little extra accuracy. This is limited because flood duration is correlated with the water depth. With the current flood damage accuracy, incorporating flood duration is only useful for specific cost benefit analysis related to measures that aim to change the flood duration. Conclusions and recommendations Flood duration can be significant for large floods in low and endyked areas. In these cases flood duration can also have a significant impact on the damage. However, a complex economic model is necessary to quantify this. Therefore, flood duration can only reach its full value as an input, in combination with better economic modeling.

Urban areas are confronted with higher temperatures compared to rural areas during summer. Buildings, roads and paved surfaces store the heat during the day and then release it slowly during the evening keeping urban lands hotter than surrounding areas. This phenomenon is called Urban Heat Island effect and the differences can be up to 8°C. A rise in mortality and decrease of work productivity are only some of the consequences. To see if and how vegetation, and water can mitigate this urban heat island effect, measurements are done in the city of Rotterdam, using temperature sensors, sap flow measurements and DTS by fiber optic cables. Measurement results of the temperature sensors show that temperature differences between an urban area and a small park within this urban area can be 3°C, when air temperatures are 25°C. Under these circumstances, temperature in the park is equal to the temperature measured outside the city, meaning that the urban heat island effect is abolished in the park. The results also shows that the urban heat island intensity for the city of Rotterdam is the largest during the night and can be up to 7°C. Trees can help mitigate the UHI by evaporating sap which is transported through the trunk to the leaves. The measurements show an increase of sap flow going further in the growing season, starting from about 10 liter per day towards over 500 liters a day. When this amount of water is divided by the surface area of the tree crown, the considered trees can evaporate 4.5 mm/day. The cooling effect of surface water is hard to measure, mainly because it is not possible to compare the temperature just above the water surface with temperatures above paved surface at the same time. It can be seen that water is a good mitigation measure, because DTS measurements show that a minimum of 14% of daily incoming solar energy is absorbed by surface water. DTS show also that the cooling effect of trees can be up to 5°C, partly by providing shade and partly by evaporation of water through the leaves. The same measurements show that the cooling effect by shade of trees is larger compared to the cooling effect by shade of buildings. When water evaporates form a paved surface this results in a decrease of air temperature. The measurements show that this decrease can be 2°C close to the ground when 1 mm of water evaporates and up to 6°C close to the ground when an infinite amount of water is available. Towards a height of 2 meter, the cooling effect decreases to 1°C and 2°C respectively. The directly measureable cooling effect of vegetation is larger than the cooling effect of water. This is mainly caused by the fact that a large part of the cooling effect of trees is provided by shade, which is of course absent with water. Nevertheless, water is a good mitigating factor of the UHI. Surface water is very use full to absorb incoming solar energy.

There are plans for the construction of a multi-purpose dam in the White Volta River near Pwalugu in northern Ghana. The reservoir that will be formed should be beneficial for hydropower generation, irrigation and fishery. Up to now there has been no research into the morphological consequences of the creation of this reservoir. In this study the rate and location of sedimentation in the reservoir and the erosion of the riverbed downstream of the dam are investigated. Sedimentation could lead to a loss of storage capacity having less water available for hydropower generation and irrigation purposes. Delta deposition (i.e. sedimentation of coarse sediment in the upstream part of the reservoir) could lead to higher water levels in the river upstream, causing an increased risk of flooding. Erosion of the riverbed downstream of the dam could lead to decreased water levels in the downstream reach. This could provoke riverbank collapse and have negative effects on agriculture due to lowering of groundwater levels. Possibly bridges downstream could be damaged by scouring of the foundations. The aim of this research is to understand the large-scale morphological processes and to give first order estimations of the morphological changes. Additionally, the sediment balance of the White Volta catchment is investigated to estimate landscape erosion. The method consists of a literature study, a field study and a morphological model (SOBEK) of the White Volta River. The total sedimentation in the intended reservoir has been analysed by determining the yearly sediment transport of the White Volta River. The estimation is based on field measurements, conducted in September 2011 at a location close to the proposed dam site, supplemented with a literature study and theoretical transport formulas. The yearly average sediment inflow appeared to be ± 1 million ton/year. The theoretical trap efficiency of the reservoir is nearly 100%, so it is assumed that all sediment will be deposited. If all sediment settles in the active storage of the reservoir, this would mean a storage loss of 3% per 100 years. The impact of this storage loss on the functions of the reservoir is considered negligible. The delta deposition (i.e. sedimentation of coarse material) and the erosion downstream of the dam have been estimated using SOBEK RE, a 1D software package capable of solving the hydrodynamic, sediment transport and morphological equations. The model parameters followed from the field research. The delta deposition depends on the water level variation in the reservoir. If the water level varies between maximum and minimum operative level, the reservoir will vary in length over 40 km and most of the delta deposition will occur in this region. The delta deposition is propagating in both upstream and downstream direction. Due to upstream propagation the riverbed level upstream of the reservoir will also increase. After 50 years, the effect is restricted to ± 30 cm just upstream of the lake and has damped out at the border of Burkina Faso. The water levels will slightly increase during high flows. More research is needed to analyse the increased risk of flooding. Erosion of the riverbed downstream of the dam will occur. The released flow through the dam is expected to be sediment-free. As the sediment concentration is lower than the sediment carrying capacity, the river will take up sediment and the bed will experience erosion. The riverbed level could decrease by 20-30 m in 50 years just downstream of the dam. The erosion rate is reducing in downstream direction, but propagating in time. After ± 30 years a bridge near Pwalugu could be affected. The erosion could be limited locally if any coarse layers are present beneath the riverbed. The erosion rate depends on the released flow through the dam, which is determined by the operational strategy. Spillage could occur when the reservoir gets completely filled. These high flows will have a substantial negative effect on the erosion. Spillage cannot be completely prevented, but the risk could be reduced by ensuring that the lake is at minimum level at the start of the rain season. The drawback of this solution is a decreased energy generation, as the lake will not fill up completely during dry years. The sediment balance of the White Volta catchment is based on sediment deposition and erosion rates. During the dry season there is a supply of Saharan dust into the catchment by so-called Harmattan winds. During the rain season eroded material is flowing out of the catchment as suspended sediment in the White Volta River. The Harmattan dust deposition rate has been derived from literature. The sediment deposition and erosion rate are equal (± 15 mm/1000 years), therefore there is no net landscape erosion in the White Volta catchment. Some parts might be eroding and some parts accumulating, but on average there is equilibrium. To analyse if there are areas more prone to erosion, the origin of deposited sediment on the riverbanks was analysed. This sediment has been collected during the field research in September 2011 and subsequently the texture and mineralogy have been analysed. This has been compared to the composition of the soil in the catchment and the composition of Harmattan dust. Both compositions were derived from literature. The texture of the deposited sediment on the riverbanks appeared to be mainly silt and clay. The mineralogy of the sediment is quartz, feldspar and kaolinite. As these minerals are abundant in the soil as well as in Harmattan dust, no definite conclusions can be drawn on the origin of the sediment. The general conclusion is that the creation of a reservoir will have morphological effects in the reservoir and downstream of the dam. In the intended reservoir sedimentation will occur, but the effect on the functions of the reservoir is negligible. Delta deposition will mainly occur within the reservoir and partly in the upstream riverbed. As the sand will be spread out over a large distance the riverbed increase will be limited. The effect on the water levels in the river should be further investigated. There will be significant erosion of the riverbed close to the dam. In the future the riverbed erosion could damage Pwalugu bridge. Other negative consequences such as bank collapse and the draw down of groundwater levels could occur locally. Applying sediment management strategies could reduce the impact on the river morphology. Possible measures to reduce the erosion and sedimentation rates include dredging or sluicing of high-turbidity currents. The factors that are most determining the results of this study are the riverbed composition and the suspended sediment load. In order to obtain more accurate results, model refinement should start with collecting more data in the field.