Msc wem boekje

faculty of engineering technology Water engineering and ManageMent

Master graduation ProJects 2009 supervIsed by The waTer engIneerIng and managemenT (wem) deparTmenT aT The unIversITy of TwenTe

Faculty of Engineering Technology Water Engineering and Management

2

Preface This document contains the summaries of master graduation projects of 2009 supervised by the Water Engineering and Management (WEM) department at the University of Twente. Water Engineering and Management is one of three specialisations of the master programme in Civil Engineering and Management, the other two are Transport Engineering and Management and Construction Process Management.

The research focus of Water Engineering and Management is on the management of large surface water systems. The aim is to increase the understanding of natural processes in water systems and the socioeconomic processes that affect these systems and to develop tools that can effectively be used to support the management. The research focus is reflected in the educational programme with courses on physical processes, modelling, management aspects and policy processes. More information about the master programme can be found on: www.cem.utwente.nl The two year master programme is concluded with an individual research project. Prior to this project a preparation course is scheduled in which the student performs a literature study and writes a research proposal to prepare for the final research project. This course can also be used to get acquainted with a model or to study a specific topic relevant to the research project. The thesis research is done internal in our department or external, for example at a consultancy or research institute; in all cases we prefer a link to the research of the department. Each project is supervised by at least two employees of the university and often by a third person from outside. The preparation course counts for 7.5 ECTS (European Credit Transfer System, where 1 ECTS stands for 28 hours of work), the final thesis project for 30 ECTS, which is equivalent to 21 weeks.

In this booklet 14 summaries of final master projects finished in 2009 are collected and ordered by graduation date. It gives a nice overview of the different topics that are being researched during the master projects.

We hope it gives you a good impression of the skills of our students and the possibilities for collaboration with external parties. If you are interested in the complete theses or theses from previous years you can find most of them at: http://www.wem.ctw.utwente.nl/onderwijs/afstuderen/afgerond/index.html If you were involved in one of the projects we would like to thank you for your contribution. The contacts with professionals outside the university is of vital importance for our educational programme. Enjoy reading.

Prof. Dr. Suzanne J.M.H. Hulscher Head of the department Water Engineering and Management For more information contact: Secretariat WEM P.O. Box 217 7500 AE Enschede The Netherlands Phone: +31-(0)53-489 3546 Internet: www.wem.ctw.utwente.nl

Faculty of Engineering Technology Water Engineering and Management

table of content Plaquemines Spillways

4

Increasing complexity in hydrologic modelling: An uphill route?

5

Dynamic control of salt intrusion

6

Indicator development to determine the state of the (South-West) delta

7

The water footprint of sugar and sugar-based ethanol

8

Morphological developments in aggrading secondary channels:

9

Energy Scenarios in a Water Perspective Changes in water footprints related to energy transitions

10

The effects of Jonglei Canal operation scenarios on the Sudd swamps in Southern Sudan

11

The consequences of future change for the Wet Heart in the Netherlands in 2050

12

Simulation of present and future discharges at the Nile River upstream Lake Nasser

13

Three dimensional flow structure in semi-enclosed basins

14

The Influence of Lateral Depth Variations on Tidal Dynamics in Semi-enclosed Basins

15

Wave boundary layer streaming

16

Evaluation of vegetation resistance descriptors for flood management

17

Faculty of Engineering Technology Water Engineering and Management

Marcel van de Waart Graduation Date: 6 March 2009 Graduation committee: University of Twente Prof. Dr. Suzanne Hulscher Dr. Jan Mulder Royal Haskoning Dr. Mathijs van Ledden Ir. Wiebe de Jong

4

Plaquemines Spillways The Impact of the lower Mississippi river levees on storm surge during hurricanes The Mississippi river runs through Louisiana towards the Gulf of Mexico where it becomes a bird-foot delta.

Various settlements of often no more than 2 km in width exist along the lower 125 km of this river; this area is known as Plaquemines Parish. Nowadays levees protect the Parish from storm surges and high river discharges. During major hurricane events in the Gulf of Mexico the levees block the storm surge and this leads to a build-up of surge locally but also forces the water to flow upriver towards New Orleans. By creating spillways within the levees of Plaquemines Parish the maximum water levels in and around New Orleans can be reduced during hurricanes. To gain insight into the quantitative effects of the spillways on storm surge the Advanced CIRCulation flow model (ADCIRC) has been used to perform storm surge simulations. The commonly used ADCIRC grid for Louisiana encompasses approximately two million computational nodes and therefore a parallel computing environment is required to run the model. For this study a smaller computational grid has been created with approximately one million nodes and a simplified modeling strategy has been applied in order to improve the balance between computational speed and model accuracy. The model has been validated by performing a hind-cast of hurricane Katrina. The modified grid was then used to simulate different levee alignments during three different storms. Model results show that the spillways are capable of reducing maximum surge levels locally in Plaquemines Parish as well as in regions closer to New Orleans and on the Mississippi River; the length of the spillways in the northern part of Plaquemines Parish was found to be very important for the reduction of the surge in these areas.

Maximum water level differences near New Orleans between four levee alignments and the current levee alignment for a combination of three hurricanes (in m).

New Orleans (River) St.Bernard Parish Plaquemines Parish Jefferson Parish

Removal of all levees

Only protect important settlements

Minimum Spillway Length

Medium Spillway Length

–1.20 –0.50 –2.70/ –0.20 –0.20

–1.10 –0.50 –1.80 / +2.10 –0.20

–0.50 –0.20 –0.60 / +2.20 –0.10

–0.80 –0.20 –1.70 / + 1.40 –0.30

(Left) Aerial view of southern Plaquemines Parish (Right) ADCIRC computation of water levels and flow velocities near Plaquemines Parish during a hurricane.

Faculty of Engineering Technology Water Engineering and Management

Han Vermue Graduation Date: 25 March 2009 Graduation committee: University of Twente Dr.ir. Denie Augustijn Dr.ir. Martijn Booij Waterschap Aa en Maas Ing. Jos Moorman Royal Haskoning Ir. Roel Velner

5

Increasing complexity in hydrologic modelling: An uphill route?

To understand the exchange of water between domains spatially distributed, physically based and first order coupled models are useful. The MODular Hydrological Modeling System (MODHMS) is such a concept. When modelling in these kinds of models a number of problems can arise such as the problems of uncertainty, nonlinearity, equifinality and scale. The result of these problems is that a more complex model might not necessarily generate better results. Therefore it is interesting to know which complexity gives the best result.

In this study several compositions of the catchment of the Astense Aa in the province of Noord Brabant are modelled in MODHMS. Starting from a very simple model, more complexity is added to assess the influence of the complexity on model performance and hydrological behaviour. Model performance is defined as the capacity to reproduce observed spatially distributed groundwater levels and surface water discharge with the model. The influence of complexity on model performance and hydrological behaviour is assessed in two ways.

The first method includes a comparison between steps using equal parameter values. This gives insight in the actual influence of the introduced complexity. In the second method selected parameter values were optimized using a global optimization algorithm (SCEM-UA). The optimized model was then run for a validation period on which the model performance is based.

Results indicated that a certain minimum amount and composition of complexity is needed to be able to describe hydrological behaviour in a reliable manner. The chosen methodology made it possible to determine the influence of complexity but was also influenced by unexpected results due to the coarse discretization.

Furthermore, the optimization results were distorted due to a water balance error caused by an insufficient description of the evapotranspiration process. The optimized parameters were chosen in such a way that, given the mathematical definition of the model performance, the excess of water is distributed optimally. The water balance error occured at every complexity step. The model performance is thus more a representation if the introduced complexity improves the possibility to better distribute the excess of water instead of describing the hydrological behaviour. The mathematical definition of the model performance proved to cause a biased result.

The groundwater levels have relatively more influence on model performance than the discharge has, while an equal influence was intended.

(Left) Schematic overview of two different complexities (Right) Results of step 1, plus, and step 2, circle, for a selected observation point.

Faculty of Engineering Technology Water Engineering and Management

Marcel van den Berg Graduation Date: 9 April 2009 Graduation committee: University of Twente Prof. Ir. Eelco van Beek Dr. Ir. Denie Augustijn Witteveen + Bos Ir. Ebbing van Tuinen Ir. Erik de Bruine

6

Dynamic control of salt intrusion Originally the Volkerak-Zoommeer (figure 1) was part of the delta in the South-East of the Netherlands.

It contained saltwater until it became a freshwater lake in 1987 because of the construction of the Delta Works. Nowadays, the Volkerak-Zoommeer experiences water quality problems in the form of blue-green algae. To solve this problem, two different strategies can be distinguished: freshwater and saltwater alternatives. The saltwater alternatives seem the most promising.

The Mark-Vliet system (figure 2) lies in the west of Noord-Brabant, a province in the Netherlands.

The Mark-Vliet system has two important functions: water supply for agriculture and shipping.

The Volkerak-Zoommeer is connected to the Mark-Vliet system at two different locations. At each location a sluice and a lock are present. When the lake becomes salt in the future, saltwater can enter the system through the locks. The agricultural areas next to the Mark-Vliet system will experience problems due to this salt-intrusion.

In order to reduce the salt-intrusion, the Mark-Vliet system can be flushed with freshwater. The water inlet near Oosterhout can be used for this. The goal is to achieve a desired water quality near the water inlets for agriculture. In an earlier study by Witteveen+Bos the flushing of the Mark-Vliet system has been examined.

One of the recommendations of this study was to examine whether the flushing of the system can be optimized using Real Time Control. With Real Time Control the structures in the Mark-Vliet system can be controlled automatically by a computer. The adjustments in the settings of the structures – like the opening height of the drainage sluice gates – are based on actual measurements of salt concentrations and discharges. To evaluate the Real Time Control strategies the Sobek computer model was used.

The results show that by using Real Time Control the desired water quality near the agricultural water inlets can be achieved with a significantly smaller flushing volume than determined in the previous study. The use of water quality parameters in Real Time Control of surface water systems, as applied in this study, is an innovative and effective approach.

Figure 1: Location of the Volkerak-Zoommeer.

Figure 2: The Mark-Vliet system and the most important locations for this study.

Faculty of Engineering Technology Water Engineering and Management

Wilco van Bodegraven Graduation Date: 22 April 2009 Graduation committee: University of Twente Dr. Ir. Maarten Krol Ir. Rianne Bijlsma Deltares Dr. Jurjen van Deen

7

Indicator development to determine the state of the (South-West) delta This research describes the development of a set of indicators to reflect the state of the Dutch delta.

Based on a literature study, an indicator development method is designed to compose the intended indicator set. The main process steps are formulating the scope, defining quality criteria, analyzing the system and formulating the indicators. An important aspect is the usage of participative approaches in the process.

This method was applied in a case study about the Dutch South-West Delta (figure 1) with the purpose to give a picture of the urgent societal issues that are affected by the water and soil system. Experts and a number of intended users – decision-makers and citizens – were involved in the development process.

They gave input to identify urgent societal issues, to analyse the water and soil system and to formulate potential indicators. The potential indicators are assessed by quality criteria, based on literature, and a final indicator set is selected. Furthermore, differences in mental mapping, interests and perceptions of reality between experts and intended users are assessed and mapped.

The final step was the evaluation of the application of the method during the case study. This was done by using four process criteria: applicability, coherence, satisfaction of the final product and enthusiasm of persons involved. On account of this evaluation, recommendations are made to adapt the indicator development method. The most important changes are a stronger emphasis on clear objectives and on sharp quality criteria, more participation – up to the level of coproduction - and explicit attention for the representativeness of the participation groups.

Figure 1: The area of the case study: the South-West Delta

Figure 2: The structuring method used to analyse the system.

Faculty of Engineering Technology Water Engineering and Management

Wolter Scholten Graduation Date: 24 April 2009 Graduation committee: University of Twente Prof. dr. ir. Arjen Hoekstra Dr. Winnie Gerbens-Leenes

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The water footprint of sugar and sugar-based ethanol The two most cultivated sugar crops are sugar cane and sugar beet. For centuries both crops have been used for the production of sucrose, generally known as table sugar. During the past decades, bio-ethanol production from sugar crops has become competitive with sugar production. In the USA, High Fructose Maize Syrups (HFMS) and maize-based ethanol are two substitutes for sugar and sugar crop-based ethanol. Crop production in general, and sugar cane production in particular, requires a lot of water. The aim of this study is to calculate the water footprint of sugar, HFMS and bio-ethanol in the main producing countries, to identify favourable production areas and to assess the impact on the water system in certain production areas.

The water footprint is used here as indicator of water consumption in the full production chain of sugar or ethanol production. There is a large variation in the water footprint of sweeteners and ethanol produced from sugar beet, sugar cane and maize between the twenty main producing countries. Tables 1 and 2 present the water footprint of sweeteners and ethanol.

Table 1. The water footprint of cane sugar, beet sugar and HFMS 55 (m3/ton).

Cane sugar Weighted global avg.

Low

Beet sugar

1500 Peru

HFMS 55

935 870

1125

Belgium

425

Argentina

565

High

Cuba

3340

Iran

1970

India

3325

Main prod. country

Brazil

1285

France

545

USA

740

Table 2. The water footprint of cane-beet- and maize-based ethanol (l/l).

Cane-based ethanol Weighted global avg.

Low

Beet-based ethanol

2855 Peru

Maize-based ethanol

1355 1670

1910

Belgium

490

Argentina

955

High

Cuba

6365

Iran

2570

India

5630

Main prod. country

Brazil

2450

France

615

USA

1220

For the calculation of the grey water footprint international drinking water standards for nitrogen are applied. The contribution of the grey water footprint to the total water footprint is limited. The impact of stricter, ecological standards for nutrients and agrochemicals, on the grey and total water footprint is enormous. No international accepted standards for ecology however are available at present.

The impact of the water footprint of sugar crops is assessed for the Indo-Gangetic basin in India, where sugar cane is an extensively cultivated crop as well as for the area north of the Black and Caspian Sea, where many sugar beets are cultivated. Water consumption by sugar cane contributes for a considerable part to the water stress in the Indus and Ganges basins. Future developments in demography and industry, as well as climate change, will stress the basins even more. Agriculture, and especially the cultivation of thirsty crops, will put even more pressure on water resources. Although water stress is increasing in the Black and Caspian Sea area, the main problem with the rivers feeding both seas, Dnieper, Don and Volga, is pollution. Many tributaries and reservoirs, as well as the Black Sea ecosystem, are heavily polluted by contaminants from industry and excessive fertilizer application. Sugar beet, as one of the major crops in the area, shows a relatively big grey water footprint and is one of the contributors of pollution.

Faculty of Engineering Technology Water Engineering and Management

Ward Klop Graduation date 19 June 2009 Graduation committee Universiteit Twente (UT) Dr. ir. J.S Ribberink UT and Waterdienst Dr. R.M.J. Schielen Royal Haskoning Ir. G.J. Akkerman Rijkswaterstaat ON Ir. H. Havinga

9

Morphological developments in aggrading secondary channels: design parameters & sediment control measures Within the framework of the program ‘Room for the River’ the number of secondary channels, which will be excavated in the floodplains of the river Rhine, is increasing. The secondary channels that are morphological active can result in major river management problems (for example strong aggradative channels). The prediction of morphological developments of secondary channels is still difficult, because the processes that determine the sediment division at river bifurcations are not yet fully understood. The first objective of this research is therefore to gain more insight into the morphological development of secondary channels with analytical equilibrium analyses combined with numerical simulations in a 1D SOBEK-RE model. The model is using a predefined artificial secondary channel that resembles the secondary channels in the river Waal near Gameren. The second objective is to explore the effects of (temporary) measures, which can be implemented in the water system, to solve these river management problems. These analyses showed that, dependent on the actual sediment division, the morphological developments in the secondary channel can be divided in three regimes: A) instable situations wherein the secondary channel will always be closed, B) stable situations wherein sedimentation can be expected or C) stable situations wherein erosion can be expected, till a certain equilibrium depth. For instable situations it is recommended to apply measures at the intake that will decrease the supply of sediment to the secondary channel. In other cases it is recommended to design the channel in such a way, that the in- and outflow of sediment is equal which will lead to ‘neutral’ morphological activity in the secondary channel. At the moment this can only be achieved by redesigning the secondary channel after a certain trial/monitoring period with newly developed guidelines.

Geometry and location of the predefined secondary channel in the SOBEK-RE model

Secondary channel

Upstream location [River kilometer]

Upstream excavation depth [m+NAP]

Length [m]

Average width [m]

Roughness height [m]

Bottom slope [-]

937

0.4

2,500

55

0.18

6:100,000

Time scale 0,6 m (1 m+NAP) and 1,1 m (1,5 m+NAP) aggradation in the secondary channel 10

70

9

60

8 7

50

6

40

5

30

4

Time scale [years] 20

3 2

10

1 0

0 0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

Sediment supply to the seco [% of total sedimenttrans

Parameter Y [-] Time scale 0,5 m aggradation

Interim regimes of the morphological development

Time schale 1,1 m aggradation

Sediment supply to the secondary channel

Left) Aerial view of a secondary channel at Gameren in the River Waal. (Right) Time scale for 0.6 m and 1.1 m aggradation in the secondary channel (blue lines) as a function of the sediment division at the river bifurcation (parameter ‘Y’ ). An increase in the value of parameter ‘Y’ results in a decrease of the sediment supply to the secondary channel (light orange line). Hereby the sediment supply is given in percentage of the total sediment that will be transported (0.043 m3/s) in the Waal in a situation with a constant discharge of 2,000 m3/s.

Faculty of Engineering Technology Water Engineering and Management

Sander van Lienden Graduation Date: 1 July 2009 Graduation committee: University of Twente Prof. dr. ir. Arjen Hoekstra Prof. dr. ir. Theo van der Meer Dr. Winnie Gerbens-Leenes

10

Energy Scenarios in a Water Perspective Changes in water footprints related to energy transitions Transitions in the energy sector are occurring continuously. They are driven by the need to find more efficient, cleaner and sustainable fuels. The use of bio-energy is currently seen as an alternative that has many of these characteristics. Renewable energy from plants and trees seems very promising. In general, it is expected that in 2030 biomass will have the largest share of all renewables. However, the large-scale production of energy from biomass also has its complications. Issues about competition between food and energy crops and the carbon dioxide neutrality of bio-energy are already discussed plentiful. In addition, many studies have been done to examine the extent bio-energy can be used in the light of land availability, agricultural technology, biodiversity and economical development. But there are very few studies that look at the impact of bio-energy on the water system. Plants and trees need water to grow and the production of biomass is indisputably one of the largest water consumers in the world. This research aims to map the consequences of the transition to a larger share of bio-energy in total energy consumption on the water footprint of energy sectors across the globe, and subsequently assess the water stress caused by existing energy scenarios for 2030. The water footprint is a measure of how much fresh water is used to produce goods and services, in this case bio-energy. This research uses water footprint analysis to investigate the change in water demand related to a transition to bio-energy. Information about these transitions is based on specific energy scenarios. A clear distinction is made between three different bio-energy carriers. The analysis includes the consumption of first generation bio-ethanol, bio-diesel and bio-electricity and heat in nearly all countries of the world. Each of these bio-energy types uses different biomass feedstocks (i.e. energy crops) and this research examines the probable feedstock choice per type in each country.

Using blue and green virtual water content data of each crop per country, a translation is then made from bio-energy consumption to water consumption. It is found that existing energy scenarios all project an absolute increase in bio-energy consumption in the future. In the global bio-energy mix, it is expected that about 91 percent is bio-electricity and heat, 6 percent is bio-ethanol and 3 percent is bio-diesel. Overall, this means that more biomass will be grown for energy purposes and, since biomass needs water to grow, the transition to bio-energy will lead to a larger water footprint of the global energy sector. Together with the blue and green water demands from other sectors, the bio-energy water footprint is compared to the blue and green water availability. For each country, a balance is made of fresh water resources and uses, enabling the determination of the water volume available for bio-energy. The comparison allows a measure of water stress to be established corresponding to the (projected) bio-energy consumption. The competition for available runoff between blue water users will likely cause blue water stress in many countries, especially in Europe, Developing Asia and the Middle East. In about half of the countries that are likely to suffer blue water stress in 2030, bio-energy consumption contributes to, or is fully responsible for, the water stress. It is expected that the green bio-energy water footprint, will cause green water stress in even more countries all over the world. The primary reason is the enormous projected increase in consumption of bio-electricity from rain fed plantation wood. This is expected to take up much of the productive green water supply in many countries. On a global level, the green bio-energy water footprint will comprise almost 40 percent of the total green water supply, whilst the blue bio-energy water footprint is expected to be about 4 percent of total available runoff for humans in 2030. Hence, energy scenarios should not only be analyzed in the context of land availability, food production, biodiversity and the carbon dioxide balance, they also need to be looked at in a water perspective. This study shows the repercussion of extensive bio-energy consumption on the fresh water resources. It advocates that countries should consider the water factor thoroughly when investigating the extent to which bio-energy can satisfy their future energy demand.

Faculty of Engineering Technology Water Engineering and Management

Erwin Lamberts Graduation Date: 27 August 2009 Graduation committee: Prof. ir. Eelco van Beek Dr. Maarten Krol

11

The effects of Jonglei Canal operation scenarios on the Sudd swamps in Southern Sudan The Sudd, one of the largest wetland areas in the world, is faced by huge evapotranspiration rates. More than 50% of the Sudd inflow is evaporated out of the Sudd swamps, resulting in a lower water availability downstream. To enhance water availability, planners have proposed to dig a canal (Jonglei Canal) around the Sudd area, to save 4.8 Gm3 of water per year. What the effects on the swamp area in the Sudd will be is still relatively unknown. The goal of this research is to study the effects of different Jonglei canal scenarios on the Sudd swamps.

The first phase of the research consisted of simulating the monthly historic water balance for the period 1961 – 2000. The model that is used describes the Sudd as a reservoir, where the input comes from the precipitation and the inflow, and the outflow from the evapotranspiration and the outflow.

The results from the water balance show that the swamp size in the period 1961 – 1964 increased by almost 300 % from 15 Gm2 to around 60 Gm2. In the period 1965 – 1978 the swamp size recovered to around 42 Gm2 where it slightly decreased to 35 Gm2 by 1978. In the period 1979 – 1981 the swamp shows a sudden increase in size. This is caused by a high precipitation in that period. In the last period until 2000 the Sudd swamp size fluctuated around 30 Gm2.

In the second phase of the study three types operation scenarios for the Jonglei canal were tested: fixed canal flows, seasonally dependent canal flows, and canal flows where the extra water volume, available downstream of the Sudd, would be 4.8 Gm3/year.

The results for the fixed canal flows show a highly linear relation between the flow and the change in the permanent (16 – 26 %), seasonal (13 – 22 %) and total swamp size (15 – 25 %).

The effects of seasonally dependent canal flows will be highest on the size of the seasonal swamp.

The change in the size of the permanent swamp depends mainly on the total annual canal flow. The change in the seasonal swamp size depends on the canal flow in the wet period. The change in the total swamp size depends, just like the permanent swamp, on the total annual canal flow.

To achieve an additional 4.8 Gm3/year water downstream of the Sudd, the average canal flow needs to be 18 Mm3/day. In a scenario with a canal flow of 26 Mm3/day in the dry period and 10 Mm3/day in the wet period, negative impacts for various stakeholders will be smallest.

The Sudd area

Faculty of Engineering Technology Water Engineering and Management

Harm-Jan van Donk Graduation Date: 4 September 2009 Graduation committee: University of Twente Prof. ir. Eelco van Beek Dr. ir. Martijn Booij Deltares Drs. Marjolijn Haasnoot

12

The consequences of future change for the Wet Heart in the Netherlands in 2050 The Wet Heart of the Netherlands is the area that contains the IJsselmeer, Markermeer and the Randmeren. It is situated in the middle of the Netherlands and the area is of great importance to the Dutch economy. This is caused by the multifunctional characteristics of the area; the main functions are safety, agriculture, drinking water, shipping, recreation, water storage and industry.

Considering the functioning of the Wet Heart it is expected that both climate change and socio-economic change will have influence. These changes are anchored in scenarios, which give expectations for the year 2040 (socio-economic changes) and 2050 (climate change). The future climate and socio-economic scenarios will have different consequences. In this research the damage for agriculture and shipping in 2050 has been investigated. The damage for agriculture is the consequence of low groundwater levels and a shortage of irrigation water. This will cause drought damage or starvation for the crops. Shipping will suffer consequences because of low water levels in the lakes, which has a negative influence on the transport capacity of the ships.

In order to quantify the consequences of the scenario a model has been developed; which is named the PAWN – Light model. In this model the scenarios for socio-economic changes and climate change have been implemented. The data that varies between the scenarios is evaporation, precipitation and Rhine discharge (for climate scenarios) and area surfaces for the various types of land use. Using the PAWN Light model eight scenario-runs have been carried out which show that significant effects may be expected.

The socio-economic scenarios reduce the amount of damage. This is caused by the decrease of the agricultural areas (-10% for the Regional Communities scenario and -17% for the Global Economy scenario).

The remaining fraction agriculture is equal to the fraction in the reference scenario. The climate scenarios have a larger effect on the Wet Heart. Especially the climate scenario W+ has a large effect on the IJsselmeer system. The increase of damage for agriculture is 31%. This first indication of the PAWN – Light model is that the current policy is not capable of correcting these consequences and adapting measures should be considered to be able to cope with future changes.

Considering the model it is advised to execute further calibration and validation. This way the model can give more realistic values for agricultural damage when implementing scenarios or measures for future analysis. To determine shipping damage it is advised to implement a basic damage module for shipping into the PAWN – Light model.

Faculty of Engineering Technology Water Engineering and Management

DaniĂŤl Tollenaar Graduation Date: 18 September 2009 Graduation committee: University of Twente Prof. ir. Eelco van Beek Dr. ir. Martijn Booij Deltares Dr. Jaap Kwadijk

13

Simulation of present and future discharges at the Nile River upstream Lake Nasser Water managers in the Nile Basin face a challenge, dealing with scarce water resources under changing conditions. Currently downstream countries like Sudan and Egypt use more than 50% and 90% of their long term renewable water resources which are prawn to change under upstream river developments and climate change.

For the upstream developments a River Basin Simulation Model (RIBASIM-NILE) is developed. In this study this model is enhanced to a Nile Hydrological Simulation Model (NHSM) by simulating sub-catchment runoff by the HBV rainfall-runoff model at the locations where RIBASIM-NILE is forced by sub-catchment runoff.

The NHSM is calibrated and validated over the period 1961-2000, for which observed meteorological forcing and discharges are available. Results on the scale of main river tributaries are satisfying. However, on sub-catchment scale improvements can be made. To simulate future river discharges, the NHSM is forced by meteorological variables derived from simulations of three Global Circulation Models (GCMs) under two greenhouse gas emission scenarios. Prior, bias is removed by correcting simulations for the 1961-1990 periods to the observed mean monthly climatology. Performance of NHSM-GCM combinations in representing the current hydro-climate is low, whereby remaining bias in the spatio-temporal variability of simulated rainfall is identified as the main source for improvement.

Simulating 2065 and 2100 hydro-climates with NHSM-GCM reveals a random pattern which is only partly supported by literature. It is presumed that by the current method better results can be obtained by (1) using only GCMs which show a low bias in simulating the local climates, (2) correcting temporal bias in rainfall simulations on more than only observed mean monthly values and (3) increasing spatial representation of simulated rainfall by downscaling GCM simulations to the resolution of the NHSM.

Bar graph showing annual water resources (Bm3∙year-1) at the Nile River based on observations for the 1990 climate and NHSM-GCM simulations for the 2100 climate, including a low, average and high prediction.

Faculty of Engineering Technology Water Engineering and Management

Olav van Duin Graduation Date: 2 October 2009 Graduation committee: University of Twente Prof. Dr. Suzanne J.M.H. Hulscher Dr. Ir. Pieter C. Roos Delft University of Technology Dr. Henk M. Schuttelaars

14

Three dimensional flow structure in semi-enclosed basins Coastal areas are generally intensely used areas with high population density and economic activity.

On a basin scale the tide directly determines water levels and currents in a basin. These flow characteristics furthermore determine the shape of the basin itself, for example the forming and evolution of tidal sandbanks, which in turn influences the flow pattern (this is referred to as the morphodynamic loop).

Because of its importance for various human and natural activities tidal flow has been modelled with various 3D and depth-averaged (2DH) models.

The first analytical 3D-model that describes tidal flow in a semi-enclosed basin using Kelvin and Poincaré modes with partial slip was created for this research. For this the method devised by Mofjeld (1980) for 3D tidal flow along a single coast with viscosity and no-slip was extended, thereby following Taylor’s approach (1921).

As a reference situation the Northern Part of the North Sea was modelled and the properties of the Kelvin and Poincaré modes were described (see figure below for an amphidromic plot of the elevation in m).

Also the flow and shear stress properties were studied. An important conclusion was that a friction parameter for a 2DH model can be reasonably found by fitting the Kelvin dissipation factor of the 3D model with the 2DH model. Eventually this friction leads to an average error in predicting 3D longitudinal bottom shear stress amplitude with a 2DH model of 13% while the theoretically best result would have been 3%.

Amphidromic plot of tidal elevation η [m] (colours signify contours with the same tidal amplitude while black lines signify contours with the same tidal phase) Mofjeld, H.O. (1980). Effect of vertical viscosity on Kelvin waves. Journal of Physical Oceanography (10), pp. 1039-1050.

Taylor, G.I. (1921). Tidal oscillations in gulfs and rectangular basins. Proceedings of the London Mathematical Society (20), pp. 148-181.

Faculty of Engineering Technology Water Engineering and Management

Wiebe de Boer Graduation Date: 9 October 2009 Graduation committee: University of Twente Prof.dr. Suzanne J.M.H. Hulscher Dr.ir. Pieter C. Roos Rijkswaterstaat Drs. Ad Stolk

15

The Influence of Lateral Depth Variations on Tidal Dynamics in Semi-enclosed Basins Understanding tidal dynamics is important for coastal safety, navigation and ecology. Many tidal basins around the world can be classified as semi-enclosed, i.e. bounded at three sides by coasts. In this study Taylor’s (1921) classical problem of tidal wave propagation in a rotating (due to the Earth’s rotation), rectangular semi-enclosed basin of uniform depth is extended to account for basin-scale, lateral depth variations.

A semi-analytical, hydrodynamic model is used to find fundamental wave solutions, i.e. modified Kelvin and Poincaré waves. The properties of the modified wave modes depend on the type of lateral depth profile and have different characteristic length scales compared to the uniform depth solutions.

The solution to the Taylor problem is written as a truncated sum of the modified wave modes, where a collocation technique is applied to satisfy the no-normal flow requirement at the basin’s closed end. In general, it is found that the elevation amphidromic points (EAPs) remain on the centre line of the basin for symmetric lateral depth profiles (as for uniform depth), whereas they are laterally displaced towards the deeper side of the basin for asymmetrical profiles. In addition, the EAPs shift in longitudinal direction, due to altered Kelvin wave lengths. The current amphidromic points (CAPs) show similar shifts.

Finally, a practical case is studied: the Southern North Sea with and without large-scale sand extraction, where sand extraction is represented as a large-scale shore-parallel trench (see Figure 1). It is found that adopting a realistic lateral depth profile instead of a uniform depth considerably alters the tidal amplitudes and currents. Furthermore, it is concluded that large-scale sand extraction may have considerable impact on the tidal system, not only locally, but also farther away from the extraction area. In turn, this may affect the morphodynamics and, consequently, coastal safety and ecology.

Figure 1. Differences in tidal currents as a result of a 8*104 Mm3 sand extraction trench (bounded by the dashed lines). The right-hand boundary is open, the other boundaries (indicated by thick black lines) are closed.

Taylor, G.I. (1921). Tidal oscillations in gulfs and rectangular basins. Proc. of Lon. Math. Soc., Vol. 20, pp. 148-181.

Faculty of Engineering Technology Water Engineering and Management

Suleyman Naqshband Graduation Date: 12 October 2009 Graduation committee: University of Twente Dr. ir. Jan Ribberink Ir. Wouter Kranenburg Drs. Jolanthe Schretlen

16

Wave boundary layer streaming Analysis on wave boundary layer streaming and its effect on bed shear stress Cross-shore morphological development of a sea bottom is mainly determined by sediment transport close to the seabed caused by the actions of waves and currents. In addition to pure fluctuations, waves can induce steady currents such as Eulerian boundary layer streaming or boundary layer drift. The presence of such additional near-bed currents can result in additional bottom sediment transport. The aim of this study is to get insight in underlying mechanisms of Eulerian streaming and their effects on bed shear stress that is determinative for sediment transport.

In this study three streaming models are compared under characteristic wave conditions in the North-Sea: a constant viscosity model (Longuet-Higgins, 1953), a time-dependent viscosity model (Davies and Villaret, 1999) and a 1-DV numerical POINT SAND model of Uittenbogaard [1999]. Furthermore, two analytical models for bed shear stress are verified with bed shear stress results from the POINT SAND model: the bed shear stress model of van Rijn [2007], and Nielsen and Callaghan [2003]. Van Rijn [2007] takes account for streaming by adding a positive streaming velocity, where Nielsen and Callaghan [2003] add the wave Reynolds stress to take account for streaming.

In this study it is shown that above flat beds the streaming velocities are onshore-directed near the sea bed as well as away from the bed. This is the result of the dominant, positive contribution of the wave Reynolds stress to streaming compared to the negative contribution of the wave component of mean turbulent Reynolds stress (see Figure 1).

Figure 1: Onshore streaming near the sea bed induced by progressive waves The study also showed that a better representation of the bed shear stress is given by the model of Nielsen and Callaghan [2003] compared to the model of van Rijn [2007].

Davies, A. G., Villaret, C. (1999). Eulerian drift induced by progressive waves above rippled and rough beds.

Journal of Geophysical research, Vol. 104, NO. C1, pages 1465-1488.

Longuet-Higgins, M. S. (1953). Mass transport in water waves. Trans. R.Soc.London Ser. A245, pp. 535-581.

Uittenbogaard, R. E. (1999). Overview of the POINT SAND MODEL. Delft Hydraulics, Z2899.10.

Faculty of Engineering Technology Water Engineering and Management

Alida Galema Graduation Date: 30 October 2009 Graduation committee: University of Twente Dr. ir. D.C.M. Augustijn Dr. F. Huthoff

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Evaluation of vegetation resistance descriptors for flood management For prediction of the behaviour of water levels in rivers, computational river flow models are used.

An important parameter of these models is the (hydraulic) resistance. The presence of vegetation has a major effect on this flow resistance.

Different methods are available to calculate the resistance with a simplified representation of the vegetation. The aim of this research is to identify the practical suitability of different vegetation resistance methods, by compiling a data set of flow experiments and to use this data set to evaluate the ranges of applicability of different (existing) vegetation resistance methods.

For submerged rigid vegetation, seven vegetation resistance methods are selected from literature.

For flexible vegetation such methods are lacking. Methods defined for rigid vegetation are often also used to determine the resistance of more complex flexible vegetation. Therefore, the performance of the descriptors for rigid vegetation are also evaluated using data of flexible vegetation.

An existing dataset was used, supplemented by new data from literature. One of the main uncertainties in the flow experiments is the determination of the drag coefficient (especially for flexible vegetation) and the slope. A scheme is developed which can be used to deal with unknown values for the slope and the drag coefficient. Consistency in determining these parameters makes different data sets easier to compare with each other.

All methods perform well in predicting water levels and velocities for rigid vegetation, except one which shows large deviations for higher water levels (>1 m). The performance of the seven descriptors in predicting the water levels for flexible vegetation is more divers. Three methods perform equally well for flexible vegetation. It is expected that more accurate results could be achieved for flexible vegetation, when the blockage area for natural plants with side-branches and foliage, and the flexibility are taken into account in the drag coefficient.

For further research more laboratory experiments are required especially for larger submergence ratios, and the influence of flexibility, side branches and leaves on the drag coefficient should be investigated.