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In het Beleidsplan Drink- en Industriewatervoorziening is voor de waterleidingbedrijven in Nederland een toekomstbeeld geformuleerd waarin de inpassing van oppervlaktewater als bron voor de (drink-)watervoorziening in Nederland centraal staat. Hierbij wordt gesproken over een 'stabilisatie en optimalisatie' van de inzet van grondwater, hetgeen gemotiveerd wordt op basis van de verdrogingsproblematiek. Enkele waterleidingbedrijven in Nederland zijn derhalve al enige tijd bezig grootschalige projecten te realiseren waarbij de grootste zorg uitgaat naar het bereiden van goed drinkwater uit veelal verontreinigd oppervlaktewater. De grootschaligheid van deze projecten is noodzakelijk vanwege de hoge kosten die gemoeid zijn bij de geavanceerde zuiveringstechnieken die hierbij nodig zijn. Deze technieken kunnen pas rendabel gemaakt worden bij grote te behandelen volumestromen. Hoe moeten echter deze grootschalige oppervlaktewaterprojecten ingepast worden in de distributiestructuur van de veelal van oudsher uit grondwater leverende drinkwaterbedrijven? Gescheiden of gemengde levering van drinkwater uit de twee bronnen, oppervlaktewater en grondwater, is een hierbij een belangrijke optredende vraag. In het kader van deze studie is deze problematiek voor de inpassing van het Project Infiltratie Maaskant in Oost-Brabant nader onderzocht. Op basis van een aantal alternatieven die ieder getypeerd worden door kenmerken van een bepaald 'distributieprincipe' (gescheiden of gemengd), is getracht een uitspraak te doen over de gewenste structuur voor de distributie van het oppervlaktewater. Naast kosten spelen hierin kwaliteit van het (meng)produkt, leveringszekerheid, inpasbaarheid in de bestaande infrastructuur en flexibiliteit ten aanzien van de fasering een belangrijke rol. Het blijkt dat een gemengde levering verschillende voordelen heeft. Hierin speelt de optimalisatie van de grondwateronttrekkingen (zoals gesteld in het BDIV) een belangrijke rol. Deze kunnen namelijk zonder concessies te doen aan de totale jaarlijkse onttrekking een grote rol vervullen in het optimaliseren van de in te passen oppervlaktewaterzuivering. Hierbij is een sleutelrol weggelegd voor het reduceren van de piekfactoren van de levering uit het oppervlaktewater. De pieken die slechts een aantal dagen per jaar voorkomen kunnen tegen lagere kosten door het grondwatersysteem opgevangen worden. Bij de inpassing van PIM blijkt een piekfactorreductie voor de levering vanuit het oppervlaktewater van 1,72 naar gemiddeld 1,32 mogelijk te zijn. Dit heeft zowel lagere investeringskosten voor de zuivering als voor het transportsysteem tot gevolg. Globaal berekend kan hierdoor op het Project Infiltratie Maaskant 80 miljoen gulden aan investeringskosten worden bespaard. Verder blijkt het gemengd inpassen van het PIM-water gunstige gevolgen te hebben op de leveringszekerheid, op de kwaliteit, op de aansluiting bij de bestaande infrastructuur en op de flexibiliteit ten aanzien van de gefaseerde inpassing.

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.

Het wereldklimaat verandert en het Nederlandse klimaat verandert mee. Wat staat ons de komende eeuw te wachten? Klimaatwetenschappers schetsen het volgende toekomstbeeld: De invloed van de mens op het klimaat zal toenemen waardoor de wereldtemperatuur verder stijgt met 1 tot 6 graden. Meer en hevigere neerslag is dan het gevolg. In Nederland heeft dat verstrekkende gevolgen voor de waterhuishouding. Rioolstelsels die vaker moeten overstorten ten gevolge van hevigere neerslag. Poldersystemen die die aanhoudende neerslag niet kunnen verwerken met overstromingen en te hoge grondwaterstanden tot gevolg. Onderzoek naar trends in neerslag in Nederland heeft onder meer hetvolgende opgeleverd. Een statistisch significante toename van neerslag: 100 mm per eeuw in het winterhalfjaar (oktober - maart). Meteorologisch gezien het wel meer en vaker kan gaan regenen, maar dit betekent niet automatisch een toename van situaties waarbij wateroverlast optreedt. Pas als de extreme situaties, die al groter zijn dan de capaciteit waar een watersysteem is op ontworpen nog extremer worden is er mogelijk een probleem. Bovendien is het opmerkelijk dat men conclusies trekt op basis van De Bilt of een gemiddelde van meerde stations. De doelstelling van dit rapport is onderzoeken of extreme neerslag inderdaad heviger wordt en vaker voorkomt. Bovendien wordt onderzocht of er verschillen zijn tussen verschillende meetstations. De vraagstelling die hier bij hoort is: Zijn er trends in extreme neerslag in Nederland en zijn er regionale verschillen? In dit rapport zal op wetenschappelijke wijze, door middel van het analyseren van trends, getracht worden te ontdekken of het aannemelijk is dat extreme neerslag in de toekomst vaker en heviger zal voorkomen. Hierna wordt gecontroleerd of er een statistisch significante trend is te vinden in de hoeveelheid neerslag (Gaat het harder regenen?) evenals de intervalduur tussen extreme buien (Gaat het vaker extreem regenen?). Dit wordt getest met behulp van de Spearman’s Rank Test, F-test voor de stabiliteit van de variantie en de T-test voor de stabiliteit van het gemiddelde. De enige statistisch significante trends in het winterhalfjaar zijn gevonden bij de T-test voor 4-, 24- en 36-uursneerslag voor het station Groningen. Hier lijkt het vaker extreem te regenen. Met de Spearman’s Rank Test worden deze trends echter niet statistisch significant bevonden, daaruit kan geconcludeerd worden dat het toch onzeker is of het in de toekomst daadwerkelijk vaker zal gaan regenen. Naarmate er wordt gekeken naar langere duur neerslag (24-240uur) ontstaat er wel een sterkere positieve trend ten aanzien van de neerslagsommen, deze is echter niet statistisch significant. Over trends in intervalduur kan voorgaande uitspraak niet gedaan worden. In het zomerhalfjaar zijn zowel bij de testen op de neerslagsommen als op de intervalduur zijn voor de korte duur neerslagcijfers positieve trends te ontdekken, als er wordt gekeken naar langere duur neerslagcijfers slaat dit om in negatieve trends. Geen van alle neerslagcijfers zijn echter statistisch significant dus mag er niet geconcludeerd worden dat het harder of vaker gaat regenen. Er zijn aanzienlijke regionale verschillen gevonden in trends Het is aan te raden geen uitspraken te doen over heel Nederland op basis van enkel De Bilt of een gemiddelde over meerdere stations. Conclusies mogen alleen verbonden worden aan de regio van het waarnemingsstation.

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.

Introduction Gully pots or roadside catch basins are a common and important part of sewerage drainage networks. Their primary function is to retain larger solids from road runoff. They are used to minimize the problems associated with sediment in downstream drainage structures, pumps, treatment plants and receiving waters. Problem definition Gully pots clogging problems have gradually been recognized over recent years. Blockage of inflow devices (especially gully pots) is the most frequent cause of flooding, for flooding of buildings and of roads. Gully pot blockages cause the highest numbers of flood incidents and are subject to larger uncertainty than other basic events. Research After literature study, it is clear that my research focuses on large particles clogging problem. To achieve my goal, the approach could be divided in several aspects: 1. In the first place, In order to define the large particles which real clogged gully pot, a field work to interview the on-site workers from cleaning company is done. 2. Based on feedback from on-site field work, 4 kind of new alternatives are proposed. 3. Then a laboratory experiment is designed to test these alternatives and also a new re-designed gully pot provided by Wavin Company. Results 1. The new grating alternatives for original gully pot can significantly reduce the incidence of gully pot clogging problem. They can reduce the covering percentage of the grating during the extreme rain fall event and leave more opening space on the grating. 2. The new gully pot from Wavin Company has a better performance than the original gully pot. But considering the big settling tank and large grating of the new gully pot, it is not fair to directly compare with the other alternatives of original gully pot. Conclusions and recommendations The gully pot clogging problems can be improving by new alternatives design. And the results show that big size of gully pot design also will be a good choice in the future. However, the experiment results show that the new alternatives will cause a higher water level on the testing table. Also the bicycle safety on the road should be considered. For the further research, the experiment method should be improved and the maintenance cost for the new design should be a concern.

Delta areas are attractive areas to live in. They are valuable due to their major economic potential as well as their large environmental values. However, due to ongoing urbanization, demand for space is still increasing and since delta areas are low-lying, they are vulnerable to flooding. Polders provide opportunities for further developing these delta areas, either by improving existing areas, or by establishing a new living environment. At the same time, polders have their limitations. This research aims at finding possibilities to enhance the application of the polder concept, leading to business opportunities for the different sectors in the Netherlands (government, business sector and knowledge institutes). In this research, a polder is defined as a level area which has originally been subject, permanently or seasonally, to a high water level (groundwater or surface water) and is separated from the surrounding hydrological regime to be able to control the water levels in the polder (groundwater and surface water). The research focuses on increasing safety, sustainability and flexibility in future polder settings. Based on an analysis of the Strengths, Weaknesses, Opportunities and Threats (SWOT analysis) it is shown that there are definite opportunities for developing polders in the future. An important strength of the polder concept is the economic aspect. The concept allows applying a flexible design; the construction may be carried out in different phases leading to financial advantages. Moreover, the construction costs of a polder are in most cases (depending on the size and availability of fill material) much less compared with a traditional land reclamation. Weaknesses of the polder concept relate to the operation and maintenance requirements and costs. Polders require a long-term operation and maintenance (O&M) commitment in order to sustain. Due to subsidence and sea level rise, a decrease in safety levels will occur. An opportunity for applying the concept abroad relates to the ongoing urbanization of delta areas and the development in flood prone areas. A threat for applying the concept abroad relates to local governance and administrative weakness. Another threat is the vulnerability of the concept to climate change leading to a discussion on safety. It may be concluded that in the future, the focus should be on urban polders since most development potential can be found in urban delta areas. Urban areas that have an elevation at approximately sea level are getting more prone to flooding due to ongoing subsidence and sea level rise. The most important boundary condition for successful polder development is the presence of the right institutional setting. A qualified and preferably non-political entity (public, private) should be present in order to guarantee the long-term commitment for operation and maintenance. Another important boundary condition, related to the construction and operation and maintenance, is that sufficient financial resources should be available in order to sustain the polder. Possibilities for future business development for knowledge institutes relate to the application and further development of Dutch innovations such as the “Building with Nature” concept, application of smart dikes and prevention of subsidence. Governmental institutions, such as water boards, drinking water companies and municipalities, can be involved in the polder development process by assisting in the set up of an administrative body. The Dutch governmental institutions can also demonstrate their excellent experience with organizing the operation and maintenance in polder settings.

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.

In the entrance of the estuary of the Western Scheldt (defined as the area between Vlissingen and Terneuzen), wave conditions are dominated by local wind conditions rather than by wave conditions at the North Sea. This is caused by the presence of the ebb tidal delta in front of the entrance. Waves influence the simulated morphology by eroding shoals edges, depositing sediment in the adjacent channels and by partly shifting patterns of erosion and sedimentation. Waves have the most influence at relative shallow areas where also tidal currents are present. These areas are in particular the shoals of Spijkerplaat and the shoals south of the Everingen flood channel. The way the wave climate is schematised influences the simulated local morphological development up to 20% to 25% (on the spatial scale of the channels and shoals and a time scale of one year). The amount of wind and wave classes within the climate schematisation has the most influence on the simulated morphology (up 20% to 25%). Other influences within the schematisation are subordinate to the influence of the amount of classes (in the order of 5%). Including a storm event within the wave climate schematisation, has limited influence on the considered time and spatial scale (order of 5%). On the time scale of one year, the influence of the storm is to a large extent redone by more occurring, moderate conditions. For the simulation of the morphological development in the entrance of the Western Scheldt it is recommended to apply a wave climate schematisation of five wind and wave classes at most. The schematisation should be based on the reproduction of the bottom changes in the estuary, seasonality and storm event don’t need to be taken into account.

In deze studie is gekeken naar de invloed van het tijdstip van neerslagpieken op inboedel- en opstalclaims. Deze invloed zou verklaard kunnen worden door de variaties in neerslag over de dag, maar ook de mogelijkheid van mensen om schadebeperkende maatregelen te treffen. Als mensen slapen of niet thuis zijn kan het zijn dat er vaker of meer schade optreed. Hiertoe zijn neerslaggegevens van 26 KNMI-weerstations over een periode van 1992 tot 2010 bekeken, waaruit onafhankelijke buien zijn ge¨extraheerd. Per bui is het uurvak waarin de hoogste intensiteit werd waargenomen aangemerkt als het referentietijdstip van de bui, met een bijbehorende datum en locatie van het weerstation. Per referentietijdstip zijn de verzekeringsgegevens, binnen een straal van 10 km rond het weerstation en van de desbetreffende datum, samengevoegd voor verdere analyse. De gebruikte verzekeringsgegevens zijn het relatieve aantal claims (aantal claims / aantal polissen), gemiddelde claimhoogte (totale claimhoogte / aantal claims) en relatieve claimhoogte (totale claimhoogte / aantal polissen). Uit de analyse van de neerslaggegevens blijkt dat in de zomer ’s ochtends minder neerslagpieken voorkomen. Uurvak 8 (07:00-08:00 UT) bevat met 21% minder dan het daggemiddelde het minste aantal pieken. Deze pieken hebben ook een lagere intensiteit, tijdens uurvak 9 is de gemiddelde intensiteit 16% lager dan het daggemiddelde. In de namiddag komen vaker neerslagpieken voor en deze hebben ook een hogere intensiteit dan het daggemiddelde, respectievelijk 30% en 20%. Voor de winterperiode is ook gevonden dat het aantal pieken ’s ochtends lager (10%, uurvak 9) is en in de namiddag hoger (25%, uurvak 18), maar de intensiteit van deze pieken wijken niet significant af van het gemiddelde. Uit de analyse van de verzekeringsgegevens komt naar voren dat tijdens de zomerperiode het aantal inboedel- en opstalclaims, behorende bij neerslagpieken in de ochtend, lager uitvalt dan het daggemiddelde. Het relatieve aantal inboedelclaims is 38% lager tijdens uurvak 8, voor opstalclaims is dit 33% tijdens uurvak 10. Voor de relatieve claimhoogte is dit respectievelijk 52% tijdens uurvak 7 en 40% tijdens uurvak 8. Dit lag in lijn der verwachting aangezien het gemiddeld gezien minder hard regent in deze periode. Hoewel het in de namiddag gemiddeld harder regent, is dit niet terug te zien in een verhoging in het aantal claims. Voor de winterperiode zijn deze afwijkingen niet gevonden. Voor zowel de zomer- als winterperiode is geen variatie in de tijd gevonden voor de gemiddelde claimhoogte. Op basis van deze studie is niet te zeggen of de mogelijkheid tot het nemen van maatregelen bijdraagd aan het verband, of dat dit alleen op neerslagvariaties berust. Door middel van een andere aanpak in het indentificeren van buien, een betere ruimtelijke resolutie van neerslag, en nauwkeurigere verzekeringsgegevens zou dit in een vervolgonderzoek verder onderzocht kunnen worden.

Phosphorus depletion is an emerging and serious global environmental issue. At this moment, research and policy discussion on phosphorus scarcity is still limited. This research investigates the possibilities of phosphorus recovery by controlled precipitation of struvite from digested sludge. At Waternet’s wastewater treatment plant Amsterdam West, plans for a struvite reactor are scheduled. The advantage of phosphorous recovery through struvite precipitation from digested sludge is three-fold. First, struvite can be directly used as fertilizer. Second, undesirable struvite precipitation in the wastewater treatment plant is prevented by reducing the phosphorus concentration in the dewatering reject stream which is fed back to the inlet of the treatment plant. Third, sludge dewaterability improves due to the addition of MgCl2. This thesis investigates the influence of mixing speed, aeration rate, magnesium dosing method and crystal recycle method on struvite growth and phosphorus removal, as well as separation of struvite from sludge. For that purpose, experiments have been performed in a crystallization reactor and a counter-current washing column at lab scale at wastewater treatment plant Amsterdam West. MgCl2 was added under varying reactor conditions, struvite constituent concentrations were measured and struvite growth was assessed. First, it is demonstrated that struvite recovery is well possible in a stirred sludge environment at neutral pH commonly applied in sludge digesters (7.0 - 7.1). Phosphorous removal under these circumstances is at least 85%. More complete mixing by stirring at a higher speed further improves struvite recovery by keeping supersaturation low. Secondly, a significant difference in struvite recovery was observed between experiments in which MgCl2 is dosed instantly versus experiments in which MgCl2 is dosed gradually. Gradual MgCl2 dosage, and therefore rapid mixing, improves recovery compared to instant dosage. Mixing at a higher stirring speed further improves recovery. Thirdly, it is found that struvite recovery under given circumstances is poor in a combined aerated and stirred sludge environment. In such environment higher aeration rates deteriorate struvite recovery further, while struvite recovery improves with decreasing aeration rates at a higher stirring speed. Fourthly, struvite separation experiments have verified that separation is well possible in a counter-current washing set-up, separating 86% of detectable struvite within 15 minutes at an upflow velocity of 1.3 mm/s.

gReverse Osmosis systems are wildly used for sea water desalination and water reclamation but they meet problems regarding bio-fouling. Bio-fouling increases their work pressure and operational costs and decreases their removal efficiencies. Phosphorus limitation is one strategy to control bio-fouling. This report focuses on phosphorus removal by ceramic tight ultra-filtration (CTUF) membranes (1kD and 3kD MWCO) as a pretreatment before RO. In this research we investigated different factors affecting phosphorus rejection by CTUF such as flux, cross flow velocity, ion strength, zeta potential and pH. The results show that increasing the flux, the cross flow velocity and the zeta potential increased the removal rate of phosphate. Increasing ion strength decreased the double layer thickness and decreased the removal rate of phosphate. All these results are in agreement with the theory of membrane filtration. The pH affected both the zeta potential of the membrane and the charge of the phosphate ion. Increasing pH increased the removal rate of phosphate but after pH 8.3, the removal rate of phosphate began to decrease. There is no explanation for this decrease in rejection at higher pH at this moment.

Desalinated or demineralised water or even soft water is characteristically low in hardness, alkalinity and pH. Thus, these kinds of water need to be re-conditioned (re-mineralized) before distributing for usage as drinking water. The produced water is expected to satisfy the following requirements: safe quality for human health, no quality change during distribution and no demolishing of the distribution infrastructure (no corrosion or excessive scaling). In order to achieve both targets, the water alkalinity, pH and calcium saturation level must be considered as the three main parameters in re-mineralization process. In general, limestone contactors are frequently used for increasing these three parameters before the water can be distributed. This technology should be considered as one of the most popular conditioning techniques used in drinking water treatment field nowadays. Typical examples are limestone contactors of Ashkelon Desalination plant in Israel, Larnaka sea water reversed osmosis (SWRO) plant in Cyprus and Barcelona SWRO plant in Spain. In fact, the determining factor for remineralized water quality is the kinetics of limestone dissolution. There are several theoretical models (PWP, Chou) as well as practical models (Dreybrodt) to describe the calcite dissolution kinetics. However, the theoretical models tend to idealize the real kinetics in practice while the empirical models are not systematic and constituent to be widely applied. Consequently, this study would mainly focus on developing the two popular theoretical kinetics models (PWP and Chou) to a practical model with theoretical basis that could fully capture the practical calcite dissolution kinetics. On top of that, a layer model concept would be introduced as the base for further developing the downflow and upflow limestone contactor model. Subsequently, simulated results indicate that upflow model is technically more superior to downflow hence providing more economical benefits as well. Vosbeck, Anderlohr’s experiments as well as the marble filtration recorded data at Hoenderloo pumping station of Vitens (Netherlands) would be utilized for building and verifying models throughout this research. In the end, an optimal design would be introduced for the remineralizing process at Hoenderloo marble filtration with the aim to increase the filtering capacity, effluent quality and reducing the operational costs at the same time. In addition to the technical research, a computer based program was built in Excel application with PHREEQC embedded, which includes all of the developed kinetics models for calcite dissolution. The program is developed in order to assist the users as an accurate yet handy tool for quickly predicting or simulating certain calcite dissolution kinetics.

Powdered Activated Carbon (PAC) has been successfully used in conjunction with membrane microfiltration (MF) to reduce taste, odour, colour and other concerns caused by organic material present in raw drinking water sources. PAC addition also significantly reduces the extent of fouling in membranes. And the operation of continuously dosed PAC before membrane filtration is widely applied in drinking water treatment while the operation of PAC precoated on the membrane is a new approach. This research, therefore, aims at evaluating the membrane fouling on these two different PAC operations. Water from the Schie canal in Delft was coagulated with Iron (Ⅲ) Chloride and enhanced with PAC, then filtered through a ceramic membrane. The trans-membrane pressure was monitored during filtration. Samples of the raw water and the permeate water were collected and analysed for DOC and UV254, while LC-OCD tests were carried out on the collected samples as well. In addition, the the backwash water and chemical cleaning solutions after soaking membrane were analysed. The PAC in the continuous dosing channel was dosed before flocculation and the membrane was frequently backwashed every 19 minutes for 1minute. However, the PAC in the precoating channel was precoated on the membrane before the experiment and operated without frequent backwashes. The results show that the membrane fouling in the continuous channel was more severe than that in the precoating channel which was mainly concluded from the recovery of TMP. That is because the different PAC addition modes lead to a different cake structure on the membrane surface. The cake layer in the continuous channel was mostly non-backwashable while it was easy to be backwashed in precoating channel. Recovery in the precoating channel was quite good with a recovery of 99.2% while the continuous channel presented a normal recovery of 85.5%. The DOC and UV254 removal for these two operations was similar. Also, the LC-OCD results of the backwash water and the chemical cleaning solution reveal that, if ignoring the cake fouling, the total fouling for the two operations were not too much different while big difference existed in compositions of NOM. Specially, about 40% of the neutrals fraction and 35% of humic substances fraction were found in sodium hydroxide solution after the membrane had been soaked 24 hours in continuous channel. Whereas, the first two important foulants in precoating channel were humic substances and bio-polymers, with approximate 33% and 19% fraction, respectively.

Introduction In order to improve people’s health worldwide, many efforts have been made in order to meet Millennium Development Goal 7c: reducing by half the proportion of people without sustainable access to safe drinking water and sanitation. Kenya is in the top ten of countries with the largest population without access to safe drinking water (UNICEF and WHO, 2012). Because most of these people live in rural areas, large investments are done in the Kenyan rural water supply. But recent studies show that many of the new water supplies stop functioning within a few years after implementation (MWI, 2007 and RWSN, 2007). Causes for this low ‘post-construction sustainability’ can be technical, institutional, financial, social or environmental. One of the most critical factors which is mentioned in literature is an adequate financing of operation and maintenance. This Master Thesis is about the post-construction sustainability of rural water supplies in Western Kenya, with a specific focus on the financial part of it (or financial sustainability). In the rural water supply practice in Western Kenya, several water supply technologies exist. Some of these technologies require hardly any operation and maintenance (O&M), like springs, surface water catchment, rain water catchment and a well without a pump. These technologies are not included in the current research. Remaining technologies are a handpump and a motorized pump, both used for groundwater pumping. Apart from the differences in technologies, several management models for rural water supply exist within Western Kenya: community management, government management, private management and institutional management. The latter one is not included in the current research because at these locations serving the community is in general not the main purpose. As the access to clean and safe water in adequate quantities is recognised as a human rights issue in Kenya (Constitution of Kenya, 2010), mechanisms for finding sustainable service delivery is a key national priority. As different management models are likely to result into different levels of sustainability, government of Kenya is in search of a most sustainable model for Kenyan context. Objective The objective of this study is to compare the financial sustainability of rural water supplies in Western Kenya. Within this comparison the aim is to compare different technology types, different management models and different combinations of these two. The final goal is that this comparison can be used by the Government of Kenya and other supporting entities in the development of policies and projects for the rural water supplies. Methodology Data for this study is collected during interviews with the responsible persons for the water supplies. Data is collected about service level, O&M, financial management, cost recovery and finances. Service level includes system functioning, water quantity, walking distances and water quality. O&M includes who is responsible for the daily operation and pump check and for the maintenance arrangements and the days it takes between a breakdown and a repair. Financial management includes: responsibility for the finances, water tariff, tariff structure, bank account, bookkeeping and service cut-off for non- payment. Cost recovery includes the practice of the payments, the extent in which the income covers the O&M costs and whether replacement is expected to be a problem on the long term. The finances include the yearly income, costs and costs per user. To all above mentioned factors scores are assigned depending on the output per criteria. The scores are also given a weighing factor. In this way, for every water supply a weighted score can be determined for all the four sustainability categories. In total 27 handpumps and 25 motorized pumps were evaluated. Conclusions and recommendations Out of all handpumps, the locations with community management and the locations with combined community and government management scored low. The communities were not able to collect enough money to keep the system functioning on the long term. The private managed handpumps scored good, especially in terms of cost recovery and quick response to breakdowns. The motorized pumps scored low at the locations with combined community and government management and at the locations with government management. At the combined managed motorized pumps the responsibilities for O&M and financial management were not clear. At the government managed motorized pumps the payments were not good enough to cover the costs. At the community managed motorized pumps, the committees were well organized but they did not manage to make all users pay. At the privately managed motorized pumps, the responsibilities for O&M and financial management were not clearly defined but the financial situation was good. There was enough money for the O&M and for replacement on the long term. Comparing the two technologies, the handpumps score higher on cost recovery and the motorized pumps score higher on O&M and financial management. At the handpumps it happens more often that the regular money collection is neglected. The responsible entities at the motorized pumps have more need to be organized because of the daily need for staff and money for e.g. fuel refilling. A negative side of the motorized pumps are the high costs per user per year, about nine times higher than at the handpumps. Comparing the four management models, the differences were not big. The community managed locations have difficulties with making people pay. At the combined managed systems the responsibilities for O&M and financial management are not clear. At the government systems the costs (including high salaries of government staff) are too high for the amount of users. The privately managed systems score slightly higher, especially in terms of cost recovery. Because of the fact that the water quantity is not sufficient at many locations and the walking distances are large, more water supplies are needed in the research area. It is recommended to focus more on handpumps than on motorized pumps for new water supplies. The reason for that are the high yearly costs at the motorized pumps. These costs make the motorized pumps less suitable for the rural areas of Western Kenya, where domestic income is low and people are not open to pay for their water. In some situations, with low water tables or high population density, a handpump is not feasible and than a motorized pump can be a good option for rural water supply. It is also recommended that action is taken in order to improve users’ willingness to pay. Four recommendations are: - Activities for economic development like job creation and microfinance projects. When people get to spend more, they become more open to pay for water. - Training in communities about the importance of clean water, which is not free. This includes basic insight in costs of water supply technologies. - Training for responsible entities about dealing with sanctions against non-payment and about making finances more transparent. In order to improve community management it is recommended that costs and responsibilities are shared within communities, local authorities and the central government. In the current situation, especially the tasks of the local authorities are not fully recognized: financing a part of major repairs of water supplies, monitoring the performance of individual facilities, conflict and problem resolution and retraining of mechanics and communities. For their monitoring task, the current study and other studies are used to constitute a basic half yearly performance monitoring. Since the private management model scores high on financial sustainability, it is recommended that the Government of Kenya and development partners pay more attention to this option. In order to create a situation where private management is a serious option, several aspects need to be considered: - The government need to contribute in investment costs. For e.g. the handpumps, they can contribute in the same way as in the current programmes with the community managed handpumps where the government pays 65% of the investment costs. - Community sensitization is required about the option of a private handpump. People need to know about this option. And they need insight in the costs and possible revenue. - Training is required for private owners of a water supply about water supply technologies, maintenance and dealing with financial management. - Formal recognition and regulation of such private investors is necessary as they will be running water systems as businesses.

Introduction Flooding is a natural phenomenon, but human activity has significantly altered the natural drainage processes thereby occasionally causing greater flood risk. Urban flooding has become more frequent due to a number of factors including climate change, urban growth and an increase in paved surfaces. Pluvial flooding results from heavy rainfall when water that does not infiltrate into the ground ponds in hollows or flows over the ground. In flood damage estimation, the concept of damage curves or damage functions is applied. Such functions give the building damage due to inundation. Most damage assessment models have in common that the direct monetary damage is obtained from the type of the element at risk and the inundation depth. Problem definition Flood damage assessment models do not focus solely on pluvial flood damage estimation. In addition, the existing flood damage models and developed depth-damage curves have not been tested for application of pluvial flood events. Research This study is carried out with the main objective to test the flood damage assessment model HOWAD-PREVENT in a case study in Rotterdam and to evaluate the uncertainty and sensitivity of this model. The model applicability and sensitivity was tested by running the model with two building type files together with three water level files.

Sanitation, as described by the World Health Organization (WHO), refers to the provisions of facilities and services for safe disposal of human urine and faeces. On the outset of the 21st century, 40% of the world’s inhabitants do not have access to sanitation facilities and still rely on a bucket, a bush or a backstreet for excretion. Technically, all options that are required to deal with the global sanitation problem seem to have been already developed. However, the challenge remains in selection and implementation of technologies in a way that the desirable outcomes would be resulted. Some decision-making support tools have been developed so far to address this problem by assisting the decision-makers in selecting the appropriate technologies. While decision-making is about considering the likelihood of uncertain events, in most of the existing evaluation approaches the complex task of predicting and evaluating probabilities is reduced to simple judgmental operations. Forinstance, evaluation of sanitation options is often performed based on predicting the outcomes that best represent a sanitation system, with no or little regard to the factors that limit the predictive accuracy. This thesis adopts a new evaluation approach by taking into account the real world examples from executed sanitation facilities and develops a probabilistic evaluation framework in which sanitation options are assessed based on the probabilities that specific outcomes occur in practice. Absolute judgments are replaced by probable assessments, as this approach tries to keep its distance from making the uncertain certain. Although there may be a hidden consensus that quantification of occurrence probabilities for various outcomes of sanitation options is not always possible, some quantification methods are developed and presented in this thesis for all the assessment criteria. Moreover, this thesis does not only focus on making the decisions, but also tries to channel the decisions in a way that the negative outcomes of sanitation facilities would be reduced through the measures that could be taken to improve the performance of sanitation options. By applying the probabilistic evaluation approach for decision-making about sanitation facilities in low-income unplanned slum settlement of Nyalenda in Kisumu, Kenya (based on limited available data about this region in literature) it is indicated that while a sanitation option may be known for fulfilling a certain task by definition, through a probabilistic evaluation it may be revealed that the local conditions are not likely to allow the expected outcome to occur in practice and as a result this option would have no priority among other options. The necessity for monitoring and post-evaluation of implemented sanitation projects in order to have sufficient feedback for improvement of future decisions is also highlighted.

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.

A statistical analysis of water quality data in bathing waters and relations with pollution sources. Main research question is: Why do microbial pollution peaks occur on certain locations and certain periods in time and can we predict these peaks?