Organisation

Lunchtalks

Department of Water Resources

This lunchtalk series aims to increase the interactions and awareness of WRS and colleagues from WEM Twente University in each others' ongoing research activities and projects. PhD candidates are especially encouraged to present their research findings. Lunchtalks are held roughly twice a month on Thursday's at 12:30 and consist of one or two presentations of about 20 minutes each followed by discussion. The location is alternately at ITC and UT.

Lunchtalks 2010    Lunchtalks 2009     Lunchtalks 2008     Lunchtalks 2007     Lunchtalks 2006

Lunchtalks 2010

Lunchtalk 21 January 2010
"A comparison of new practical wave-dominated cross-shore sand transport models"
Wing Hong Wong, UT

Most of the existing cross-shore sand transport models for coastal areas are based on data measured in experiments conducted in oscillatory flow tunnels. In these experiments boundary layer streaming, which is a steady current induced by surface waves, does not occur. The presence of boundary layer streaming can result into additional sand transport.

Recently practical wave-dominated cross-shore sand transport models have been developed. They use different methods to include the effects of boundary layer streaming. The objective of this study is to identify how well these practical models perform under surface wave conditions. For this, newly obtained data from wave flume experiments is used. Comparisons are made between the transports calculated by the models and the transports measured in the wave flume experiments. These comparisons show that the methods to include the boundary layer streaming enhance the performances of two of the three models.

Lunchtalk 21 January 2010
"Effect of discharge sampling errors on the parameter estimation and performance of the HBV model applied on sub basins of the Meuse river"
Sander van den Tillaart, UT

In many researches about hydrological modelling an assumption is made that there is no uncertainty in the used discharge data, which are used for model calibration. The objective of this study is to investigate the influence of uncertainties in discharge measurement on the estimation of the model parameters and the performance of a lumped version of the HBV model. This investigation is applied on two sub basins of the Meuse river, namely the Ourthe river and the Chiers river. First, an analysis of possible errors in discharge determination is made. After that, the effects of these errors are implemented into existing measurement data series of the Ourthe and Chiers over the period 1968 - 1998. These adapted discharge measurement series are used as a reference in the calibration. For the calibration the automatic global SCEM calibration method is used (Vrugt, 2003). The calibration gives an indication of the influence of uncertainties in discharge determination of model performance and parameter estimation.

 

Lunchtalks 2009

Lunchtalk 12 November 2009
"Vegetation resistance: Evaluation of vegetation resistance descriptors for flood management"
Ali Galema, UT

Abstract: 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 predicting water levels for flood management purposes. Seven vegetation resistance methods for submerged vegetation are selected from literature and compared with data for rigid and flexible vegetation. Six methods perform well in predicting water levels and velocities for rigid vegetation, and four of that methods perform also well for flexible vegetation.

Lunchtalk 12 November 2009
"Simulation of present and future discharges at the Nile River upstream Lake Nasser"
Daniël Tollenaar, Deltares & UT

Abstract: The objective of this study is to simulate present and future discharges at the Nile River upstream Lake Nasser. For this purpose, the existing water distribution model (RIBASIM-NILE) is integrated with the HBV rainfall-runoff model. The integrated model (referred to as NHSM) is calibrated and validated over the observed climate. To simulate future discharges, the NHSM is forced by meteorological variables derived from simulations with three Global Circulation Models (GCMs). First, an assessment is made how well NHSM-GCM combinations are able to represent the current hydro-climatology. Thereafter NHSM-GCM simulations are used to derive future trends in climate and discharges.

Lunchtalk 12 November 2009
"Modeling the three-dimensional tidal flow structure in semi-enclosed basins"
Olav van Duin, UT

Abstract:To improve modeling and gain new knowledge a new analytical 3D-model that describes tidal flow in a semi-enclosed basin using Kelvin and Poincaré modes with partial slip was created. To see how 3D dissipation / vertical structure properties (slip, viscosity) translate to 2DH dissipation properties (friction) certain wave mode properties are investigated. The 2DH model is run with the friction values derived from this investigated properties and is compared to the 3D results. A estimation is made of the ability of the 2DH model to represent the 3D situation regarding wave mode properties and shear stress predictions.

Lunchtalk 5 November 2009
"Developing a spatial decision support system for identifying suitable rainwater harvesting sites for upgrading rain-fed agriculture in sub-saharan Africa"
Ms. Jeniffer Kinoti Mutiga
 
Abstract: Food security in most of water scarce areas of Sub Saharan Africa (SSA) is not only threatened by increased water shortages particularly for crop production purposes but also by climate change which is likely to make matters even worse with increases in rainfall variability being predicted. Generally, water-related problems in rainfed agriculture in these areas are often related to high intensity short duration of rainfall with large spatial and temporal variability, rather than to low cumulative amount of rainfall. Such rainfall patterns result in high risk for meteorological droughts and intra-seasonal dry spells that lead to low crop yields and sometimes total crop failures. Although the situation appears to be desperate, adaptation of rainwater harvesting (RWH) could serve as a remedy since they have proven to be a promising potential technology for upgrading rainfed agriculture by improving water availability for crop production and increase groundwater levels.

This paper presents results obtained from a weighted overlay analysis of a spatial Multi-Criteria Evaluation (MCE), a decision support tool used in identifying suitable areas for adoption of appropriate RWH technologies in the Upper Ewaso Ng’iro North in Kenya and Pangani River basin in Tanzania. During the evaluation process, weighted linear combination (WLC) procedure that allows for full tradeoff among all the factors (rainfall, topography, soils, land use and socio-economic) considered was applied in a data rich Ewaso Ng’iro basin and the results transferred to the data scarce Pangani basin. Suitability maps showing suitable areas for RWH in both basins were produced with attributes that serve as indicators for targeted RWH interventions. It is evident that the information generated from this study can be used to raise awareness and guide policy decisions on the contribution of RWH towards meeting the Millennium Development Goals (MDGs) in SSA.

Lunchtalk 22 October 2009
"Assessment of vegetation dynamics and their response to variations in precipitation and temperature in the Tibetan Plateau"
Lei Zhong
 
Abstract: The Tibetan Plateau is a region sensitive to climate change, due to its high altitude and large terrain. This sensitivity can be measured through the response of vegetation patterns to climate variability in this region. Time series analysis of Normalized Difference Vegetation Index (NDVI) imagery and correlation analyses are effective tools to study land cover changes and their response to climatic variations. This is especially important for regions like the Tibetan Plateau, which has a complex ecosystem but lacks a lot of detailed in-situ observation data due to its remoteness, vastness and the severity of its climatic conditions. In this research a time series of 315 SPOT VEGETATION scenes, covering the period between 1998 and 2006, has been processed with the Harmonic ANalysis of Time Series (HANTS) algorithm in order to reveal the governing spatiotemporal pattern of variability. Results show that the spatial distribution of NDVI values is in agreement with the general climate pattern over the Tibetan Plateau. The seasonal variation is greatly influenced by the Asian monsoon. Interannual analysis shows that vegetation density (recorded here by the NDVI values) over the entire Tibetan Plateau has generally increased. Using a 1 km resolution land cover map from GLC2000, seven meteorological stations, presenting monthly data on near surface air temperature and precipitation, were selected for correlation analysis between NDVI and climate conditions in this research. A time lag response has also been found between NDVI and climate variables. Except in desert grassland (Shiquanhe station), the NDVI of all selected sites showed strong correlation with air temperature and precipitation, with variations in correlation according to the different land cover types at different locations. The strongest relationship was found in alpine and subalpine plain grass, the weakest in desert grassland.

Lunchtalk 15 October 2009
"Virtual water trade of the SADC region"
Bert Kort, UT

In this study the water footprint of crops, livestock and industry is computed for the SADC region in Africa over the period 1996-2005. The computation of the water footprint of crops is based on a grid-based vertical hydrological model. This study provides more reliable estimates on the size of the water footprint (split out in the green, blue and grey components), because the spatial distribution of actual evapotranspiration and growing circumstances are taken into account. The water footprint of livestock and industry are determined as well.

Based on this water footprint data and gridded data on domestic and industrial water use, total water use is determined in each grid cell. Water use is compared with water availability estimates from different sources to indicate areas with water shortage. Also the impact of virtual water trade on the areas with water shortage is analyzed.

Lunchtalk 15 October 2009
"The influence of lateral depth variations on tidal dynamics in semi-enclosed basins"
Wiebe Boer, UT

Understanding tidal dynamics is important for coastal safety, navigation and ecology. This study investigates the influence of basin-scale, lateral depth variations on tidal dynamics in rectangular, rotating (due to the Earth’s rotation) semi-enclosed basins by means of Taylor’s (1921) idealized approach. A semi-analytical, hydrodynamic model is used to find fundamental wave solutions, i.e. modified Kelvin and Poincaré waves. The solution to the Taylor problem is written as a truncated sum of these modified wave modes. It is found that lateral depth variations can lead to shifts in the locations of the elevation and current amphidromic points, both in lateral and longitudinal direction, compared to a uniform depth assumption. In addition, the practical case of large-scale sand extraction in the Southern North Sea is studied. It is concluded that large-scale sand extraction may considerably impact on the tidal system.

Lunchtalk 11 June 2009
"Energy scenarios in a water perspective; changes in water footprints related to energy transitions"
Sander van Lienden

Energy scenarios all project an absolute increase in bio-energy consumption in 2030. This means that more biomass will be produced for energy purposes. The objective of this research is 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.

To achieve this, the research includes an investigation of the types of bio-energy that contribute to the total bio-energy consumption and what kinds of biomass are (likely to be) used in each country to produce them. Using the virtual water content of energy crops, a translation is then made from bio-energy consumption to water demand (i.e. the water footprint). Comparing this to water availability data, allows a statement to be made about the water stress.

Lunchtalk 11 June 2009
"Operationele hoogwaterbeheer (in Dutch)"
Dr. Joop Gerretsen

Ten vervolge van zijn lunchtalk gehouden op 19 maart j.l. over het strategisch hoogwaterbeheer, zal Joop Gerretsen op donderdag 11 juni 2009 een lunchlezing houden over het operationele hoogwaterbeheer , handelend over het voorspellen van topwaterstanden op de Maas voorafgaand aan een dreigend hoogwater. Het doel daarvan is om rivierbeheerders en andere publieke diensten te ondersteunen bij het tijdig treffen van eventuele beschermende maatregelen. De lezing wordt besloten met de beantwoording van de in zijn proefschrift gestelde onderzoeksvragen voor zowel het strategische als het operationele deel en met de aanbevelingen voor nader onderzoek.

Lunchtalk 10 June 2009
"Two-dimensional sediment graph theory"
Dr. Veysel Guldal

The erosive behavior of the catchment and fundamentals of the black-box analysis of a catchment are briefly discussed. A physically realizable nonlinear model, called two-dimensional unit sediment graph is developed for predicting the sediment concentration of rivers. The comparative application is made of the two-dimensional unit sediment graph model and convolution integral and second order functional series.

Lunchtalk 10 June 2009
"Saltwater intrusion along the Mediterranean coast of Turkey"
Dr. Amet Dogan

Along the Mediterranean coast of Turkey, irrigation achieved by means of both surface water where/when it is available and groundwater obtained from the coastal aquifers (alluvium or Karstic) as supplement to the use of surface water. In this investigation, simulation and optimization models were developed to evaluate groundwater pumping subject to saltwater intrusion in the Silifke Plain (also known as the Goksu Delta) along the Mediterranean coast of Turkey. A numerical model was developed and calibrated along a cross-section of the study area, using the variable-density groundwater flow and transport code SEAWAT, which is a generic MODFLOW/MT3DMS-based computer program designed to simulate three-dimensional variable-density ground-water flow coupled with multi-species solute and heat transport developed by U.S. Geological Survey. An optimization model was formulated with an objective function subject to water demands and water-quality constraints, and pumping rates at two wells in a selected cross-section were optimized as a function of allowable chloride concentrations using the General Algebraic Modeling System (GAMS) to execute the optimization model. The resulting models provide water managers with a tool that can be used to optimize groundwater pumping in the Silifke Plain.

Lunchtalk 28 May 2009
"Comparison of soil moisture products obtained from active and passive microwave data"
Laura Dente
 
Abstract: Forty years of research on passive and active microwave observations have led so far to a better understanding of the sensitivity of satellite microwave observations to soil moisture and to a higher confidence in the possibility to retrieve reliable soil moisture from these sensors at small as well as large scale. The research has been recently focussed more on the development of soil moisture retrieval methods which can be applied at global scale and on their application over the existing scatterometer (ERS scatterometer and Metop ASCAT) and radiometer (SMMR and AMSR-E) data to obtain long time series of global products.

In this work, two global soil moisture products, one obtained from radiometer data and the other from scatterometer data, have been compared. The main objective of this comparison is to better understand the potential and limitations for soil moisture retrieval of both the data and the applied method and to investigate the possible complementarity of the different datasets. The two surface soil moisture datasets employed in this study are: the product obtained from AQUA AMSR-E data by the Department of Hydrology and Geo-Environmental Sciences of the Vrije Universiteit of Amsterdam and the product retrieved from ERS-2 scatterometer data by the Institute of Photogrammetry and Remote Sensing of the Vienna University of Technology. The temporal variability from 2003 to 2007, the seasonal trends, the anomalies, the autocorrelations and the correlation between the two global datasets have been analysed. Two in-situ datasets collected by large soil moisture monitoring networks in Oklahoma (Oklahoma Mesonet) and in Australia (OzNet) have been also included in this comparison. The results of this work will be presented during the lunch talk.

 Lunchtalk 28 May 2009
"Integrating Remote Sensing Information into a distributed hydrological model for improving water budget predictions in large-scale basins through data assimilation"
Changbo Qin
 
Abstract: This paper investigates whether remote sensing evapotranspiration estimates can be integrated by means of data assimilation into a distributed hydrological model for improving the predictions of spatial water distribution over a large river basin with an area of 317,800 km2. A series of available MODIS satellite images over the Haihe River basin in China are used for the year 2005. Evapotranspiration is retrieved from these 1×1 km resolution images using the SEBS (Surface Energy Balance System) algorithm. The physically-based distributed model WEP-L (Water and Energy transfer Process in Large river basins) is used to compute the water balance of the Haihe River basin in the same year. Comparison between model-derived and remote sensing retrieval basin-averaged evapotranspiration estimates shows a good piecewise linear relationship, but their spatial distribution within the Haihe basin is different. The remote sensing derived evapotranspiration shows variability at finer scales. An extended Kalman filter (EKF) data assimilation algorithm, suitable for non-linear problems, is used. Assimilation results indicate that remote sensing observations have a potentially important role in providing spatial information to the assimilation system for the spatially optical hydrological parameterization of the model. This is especially important for large basins, such as the Haihe River basin in this study. Combining and integrating the capabilities of and information from model simulation and remote sensing techniques may provide the best spatial and temporal characteristics for hydrological states/fluxes, and would be both appealing and necessary for improving our knowledge of fundamental hydrological processes and for addressing important water resource management problems.

Lunchtalk 14 May 2009
"Water scarcity and availability in the semiarid north-eastern Brazil"
José Carlos de Araújo

Abstract: The HIDROSED research group investigates water scarcity and availability in the northeast of Brazil, a one-million km2 semiarid area, home to 25 million inhabitants, which covers nine Federal States. The region is extremely vulnerable to droughts, which occur statistically once every decade. Its annual average rainfall is 700 mm with potential evaporation three times higher, and the rivers are intermittent due to shallow soils on top of crystalline bedrock. The main HIDROSED research themes are focused on water availability: hydrology (runoff generation, interception, river-aquifer interaction, yield-reliability assessment), sedimentology (sediment yield and related connectivity, impact of reservoir silting on water availability), water quality (WQ in dry rivers, agro toxic contamination of groundwater, eutrophication and tap water contamination) and water management (water pollution licensing, water tariff modelling). The methodological approach is based on three steps: (1) understanding and modelling hydrological processes in semiarid environments; (2) monitoring of three nested basins in different scales: Aiuaba experimental basin (12 km2), Bengue representative basin (960 km2) and Upper Jaguaribe planning basin (25,000 km2); and (3) co-design of a large-scale hydrological model in cooperation with German, Spanish and Dutch institutions. The group's focus research area is the Upper Jaguaribe River basin (25,000 km2), one of the driest regions in the Country, home of about 600,000 inhabitants in 37 municipalities. The basin, which is controlled by the Orós reservoir -the second largest in the State-, has the largest Caatinga preservation area in Brazil. Some of the main investigation results are: the hydrological data-base (since Jan 2003); the WASA-SED model; a comparative-hydrology investigation of two tropical small watersheds: a Cuban humid and a Brazilian semiarid; a water quality program for the Salgado River; the assessment of agro toxic contamination of the Serra Grande aquifer; the quantification of the reduction of water availability due to reservoir silting; the spatially-distributed modelling of runoff and sediment yield / connectivity in meso-scale basin; and a water tariff model, which has been applied to the States of Ceará and Rio Grande do Norte.

Lunchtalk 14 May 2009
"GEO, GEOSS and GEONETCast"
Chris Mannaerts and Ben Maathuis

Abstract: The Group on Earth Observations or GEO is coordinating international efforts to build a Global Earth Observation System of Systems (GEOSS). This emerging public infrastructure is interconnecting a diverse and growing array of instruments and systems for monitoring and forecasting changes in the global environment. This "system of systems" supports policymakers, resource managers, science researchers and many other experts and decision-makers. The GEONETCast real-time and on-line data dissemination system represents the technical backbone of the system. It is used by ITC and its partners worldwide for education, outreach and research. It permits direct use of near real time reception of Earth Observation and in situ data around the globe for a variety of applications and societal benefit areas of GEO. In this presentation, GEOSS and GEONETCast and ITC's involvement will be shown and discussed.

Lunchtalk 9 April 2009
"Shallow groundwater effect on surface soil temperature"
Fouad Alkhaier

Abstract: Whether or not shallow groundwater affects skin temperature is important to detect depth and extent of shallow groundwater by dint of remote sensing and important for land surface modelling studies. Although few studies have been conducted to investigate that effect, they have yielded contradicting conclusions and they stopped in 1982. To determine that shallow groundwater affects skin temperature, we measured soil temperature at two different depths (5 and 10 cm) in seven places with variable water table depths every ten minutes and for six days. After that, we correlated the minimum, maximum and average daily temperatures to average groundwater depth. We also built a simple numerical model using a differential equations solver, Flex PDE, to simulate heat transfer into soil profile and used it to simulate groundwater effect on skin temperature. We found quite high negative correlation between the maximum and average daily soil temperature and groundwater depth. Contrarily, we could hardly find any correlation between the daily minimum temperature and groundwater depth. Numerical simulations, though simple, were useful in showing that groundwater shifted skin temperature curve up in the winter and down in the summer without affecting the shape of the curve. We conclude that shallow groundwater affects skin temperature directly by its distinctive thermal properties in the soil profile and indirectly by affecting soil moisture which in turn has many different and contradictory effects on skin temperature. This study recommends building comprehensive numerical model that simulate the effect of shallow groundwater on skin temperature and on the different energy fluxes at land surface.

Lunchtalk 9 April 2009
"Lakes in desert; an exploration to the Badain Jaran desert"
Yijian Zeng

Abstract: Located in western Inner Mongolia, Badain Jaran Desert is the second largest desert in China and consists of a regular series of stable megadunes. Among these dunes, numerous groundwater-fed perennial lakes are found primarily in the south-eastern section of the desert, and shallow groundwater can be found in interdune areas throughout. This somewhat unexpected feature, i.e. the occurrence of 'permanent' freshwater lakes despite arid climatic conditions, appears to be in contrast to the general trend of increasing water scarcity in surrounding locations. As a result, the Badain Jaran Desert has attracted substantial research interests on exploring water sources for unexpected lakes. In 2004, Chen and his colleagues claimed that a huge "underground river" existed between Qilian Mountain and Badain Jaran Desert and recharged these desert lakes; while Wang (1990) argued that the precipitation was the main source to support these lakes. In this talk, the explanations from above viewpoints were introduced. At last, a specific issue related to the determination of effective rainfall was put forward on the basis of field experiment in the Badain Jaran Desert.

Lunchtalk 19 March 2009
"Flood level prediction for regulated rain-fed rivers"
Joop Gerretsen

Abstract: The thesis consists of two parts, viz. (1) the strategic part dealing with the problem of the safety against inundation and (2) the operational part dealing with a timely first order forecasting of the flood level, to enhance local decision making.
Although, so far, many investigations have been made into this matter, other methods have been used in this thesis concerning the height of dikes and levees. That asks for comparison of the predicted water levels with those of the current view (Design Water Levels 2001).
Concerning the operational matters, an easy-to-use warning algorithm is urgently needed to predict timely water levels for rivers which respond quickly to heavy rainfall and for which the hinterland is less protected.
Answers to the research questions in connection with the differences between the current results (DWL 2001) and those of the present study (thesis) are given. To what extent the water levels at Borgharen can be estimated with a warning algorithm in the event of an imminent flood will be considered, especially for the public awareness.

Lunchtalk 19 March 2009
"Stream restoration hydraulic and morphologic effects of possible measures in order to create natural streams"
Ronald Duijvestijn

Abstract: Two streams in Twente, the Saasvelderbeken, are straight streams, filled with weirs and sunken away in the surrounding vicinity. The streams are not of any ecological value and the water level is (far) too low for either natural as well as agricultural reasons. These streams are about to be restored. Goal is to make these streams natural and maintain them at a certain water level. The responsible water board wants to remove the weirs and heighten the bed level in order to restore the water level. Lowering of the bed level afterwards is expected due to high velocities in combination with fine sediment. Complementary measures are probably needed. The water board does not want to put too much effort in maintaining these streams and therefore the complementary measures taken need to be able to maintain the water and bed level at the new, higher level for the next decennia. These measures need to look natural as well. In this study two measures have been investigated, meandering of the streams and implementation of stone dams.

Lunchtalk 19 February 2009
"Plaquemines Spillways; the impact of the lower Mississippi river levees on storm surge during hurricanes"
Marcel van de Waart

Abstract: 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 Mississippi 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.

Lunchtalk 22 January 2009
"Sustainability of sand mining along the Yangtze River, China"
Jan de Leeuw

The Chinese construction industry generates a high demand for sand. In 2001 dredging began in Poyang Lake following a ban on sand mining on the Yangtze. Concern over the impact on the biodiversity of Poyang Lake recently led to a ban on sand mining in Poyang Lake until further plans would be developed. Planning would require consideration of the sustainability of the sand extraction in relation to available sediment resources, future demand and environmental impacts. In this paper we apply Aster satellite imagery to estimate the number of vessels leaving the lake and based on this we calculate a rate of sand extraction in 2005 – 2006 of 2.36x108 m3.yr1. This corresponds to 9% of the Chinese demand for sand, and implies that sand extraction currently dominates the sediment balance of the lower Yangtze River. We question whether it will be possible to preserve the rich biodiversity of the lake, while continuing at the same time satisfying the Chinese demand for sand, which will further increase to 2030, and review alternative options for sand mining in order to release the pressure from the Poyang Lake ecosystem.

Lunchtalks 2008

Lunchtalk 20 October 2008
"Meassurements and modeling of evapotranspiration to assess agricultural water productivity in basins with changing land use patterns: a case study in the Sao River Francisco basin, Brazil"
Dhr. A.H. (Heriberto) de Castro Teixeira

The São Francisco River basin in Brazil is marked by socio-eco¬nomic disparities and environmental vulnerabilities. Water managers in the semi-arid region of the basin are faced with several challenges. Because of the importance of agricultural water management on basin hydrology, daily and seasonal actual evapotranspiration were measured in irrigated orchards, along with experimental data collection over natural savannah ecosystems. Advanced radiation and energy balance measurements were conducted using the Bowen ratio and eddy correlation energy balance methods. The field results have been further used to calibrate and validate an existing remote sensing algorithm for the estimation of spatially distributed energy balance fluxes: the Surface Energy Balance Algorithm for Land (SEBAL). After calibration, the SEBAL algorithm has been applied to determine regional scale evapotranspiration and biomass production. The economic water productivities indicated that irrigated fruit crops have around 20 times more value per unit water consumed than other irrigated arable crops.

 Lunchtalk 2 October 2008
“The hydrogeological role of trees in water limited environments”
Maciek W. Lubczynski, Dept. of Water Resources

Abstract: Field experiments have already proven that many tree species in water limited environments (WLE) depend on groundwater. Typically, such trees survive dry seasons and droughts by uptake of water, directly from the groundwater body or from the capillary fringe, by rooting systems that may extend to several tens of meters depth. Such trees are also very efficient in finding soil moisture in the unsaturated zone, reducing groundwater recharge. Considering that WLE are typically characterized by low recharge, and that trees may use a significant amount of groundwater, this groundwater “consumption” should not be neglected in groundwater balancing, modeling and resources management. In practice groundwater uptake by trees in WLE is either underestimated or disregarded because of limited knowledge about that phenomenon. This presentation discusses the current understanding of the hydrogeological role of trees in water limited environments, the partitioning of tree transpiration into groundwater and unsaturated zone contributions and the integration of that partitioning in numerical groundwater models. Problems involved in this research will be highlighted and possible future research directions will be discussed.

Lunchtalk 18 September 2008
“Laboratory study on the development of a pavement layer beneath river dunes”
Matthieu Spekkers, Twente University

Abstract: Insights in the development of a pavement layer - an immobile layer of the coarsest bed sediment - beneath dunes in riverbeds is of great importance to correctly predict the bed surface composition, the sediment transport rates, the bed roughness, the related water levels and so forth. A pavement layer may develop as a result of partial transport conditions - a condition in which the coarsest grain size fraction is immobile and the finest grain size fraction is mobile. A model which properly represents the pavement layer in partial transport conditions is not yet available. In addition, laboratory studies with detailed analysis of the vertical structure of the pavement layer are scarce.

We simulated the development of a pavement layer beneath dunes in a laboratory flume using a bimodel sand-gravel mixture. We made detailed measurements of the vertical sorting - the organisation of grain size fractions within the layers of the bed. We systematically varied the volume of the gravel within the initial bed to study the effect on the structure of the pavement layer, as well as the dimensions of dunes above the pavement layer in equilibrium conditions. During the lunchtalk I will present the results of the flume experiments. The results can be used to develop and verify a new model concept which represents the presence of the pavement layer.

Lunchtalk 18 September 2008
“Spatial quality as a criterion for river management”
Wout Bremer, Twente University

Abstract: The improvement of the spatial quality of the river basin is the second objective of the PKB Room for the river, a policy of the Dutch government. A few of the questions I try to answer in the presentation are the following: How do different stakeholder groups fill in the spatial quality of the river basin? And which values of spatial quality are emphasized in the case studies?

In the presentation spatial quality will be presented by using the following three case studies of my master thesis, bypass Kampen, flood diversion channel Veessen-Wapenveld and the dike relocation at Lent.

Lunchtalk 12 June 2008
“Automated collection of intertidal beach bathymetries from Argus video images”
Laura Uunk (Witteveen en Bos/UT)

Abstract: Knowledge of the beach behaviour is required from both a coastal management and a scientific point of view. An easy and relatively cheap way of collecting bathymetry data is offered by the use of Argus video images. Daily bathymetries of the intertidal beach can be derived from Argus video images by detecting the shoreline on (half) hourly images and combining its location to the calculated shoreline elevation. In this MSc thesis, the automated shoreline detection routine, Auto Shoreline Mapper (ASM), was improved for application on low sloping beaches. Tests have shown that the bathymetries obtained by ASM show a good agreement with manually obtained bathymetries. The ASM is able to map shorelines over very long periods of time without the need of human support. Long time series of bathymetry data, with a high resolution in time, can thus be obtained. These time series show a direct response of the beach to changes is wave height and to storm events. ASM time series may help us translate short-term beach changes into long-term beach behaviour.

Lunchtalk 12 June 2008
“Water footprint of bioenergy”
Bouke van Meekeren, MSc student at the UT

Abstract: Impending shortage of fossil energy and climate change cause an increased interest for bioenergy. One of the issues of bioenergy is the use of agricultural resources and the corresponding impact on the water system. This research quantifies the volume of water which is required to produce various kinds of bioenergy.

Lunchtalk 8 May 2008
“Water issues in Hawaii”
Ali Farel, Associate Professor of Hydrology at the Natural Resources & Environmental Management Dept. of the University of Hawaii in Manoa

The talk comprised a GIS based irrigation requirement calculation project and a brief overview of the Makaha project where Robert Verger conducted this infiltration work.

Lunchtalk 17 April 2008
“Measurements and modeling of cross-shore morphodynamics”
Joris Eekhout, MSc student, WEM dept. of the Twente University

Abstract: In 2007 flume experiments have been performed in the Grosse WellenKanal (GWK) in Hannover. The GWK is a full-scale wave flume with a length of 300 m, a width of 5 m and a depth of 7 m. The bottom of the flume consisted of a horizontal sand bed, with a beach profile (slope of 1:20). During the experiments water elevation and bed level changes were measured along the whole length of the flume. Locally, flow velocities and sediment concetrations were measured by instruments on a measurement frame and on the flume wall. The data from these experiments are used to validate a cross-shore profile model, UNIBEST-TC. The model computes the sediment transprots and the resulting bed level changes along any coastal profile under the combined action of waves, longshore tidal currents and wind. The validation of the model is focused on wave height and total sediment transport along the whole length of the flume, and locally on the time-averaged velocity profile, the time-averaged concentration profile and the near-bed orbital velocity.

Lunchtalk 17 April 2008
“Spatially eco-hydrological modeling in riparian zone – A case study in Beijing, China”
Xuelei Wang, PhD student, State Key Laboratory of Remote Sensing Science, Beijing Normal University

Abstract: Riparian ecosystem is known to be important in controlling the non point source pollution and maintaining aquatic ecosystems healthy. In this study, we couple a soil nitrigon movement process-based model with remote sensing data and techniques to analyze the spatial and temporal dynamics of soil denitrification, nitrification and ammonia voatilization in the riparian area of the Guanting reservoir, an important water supply of Beijing, China. SPOT-5 and Landsat TM5 satellite data were used to interpret the spatial land surface information and derive model parameters. The model is based on chemical and physical relationships that govern soil heat, moisture, and nitrogen movement. Processes considered include diffusion, denitrification, nitrification, and ammonia (NH3) volatilization. A laboratory-scale anaerobic incubation experiment was used to estimate the soil denitrification model parameters for the different soil types. A field-scale simulated riparian in-situ experiment was used to test soil moisture and temperature modules. According to the field experiment, an indirect method was used to test soil nitrificaton and ammonia (NH3) volatilization modules. Soil denitrification simulation results were compared and validated with a dataset from a nearby experimental N2O emission research site. Results showed that the process-based model performed good and had sound simulation results on the riparian reservoir basin.

Lunchtalk 20 March 2008
“Application of DSS’s for risk assessment in operational (day-to-day) water management”
Arnejan van Loenen from the consultancy office Hydrologic in Amersfoort

Abstract:  Every year extreme precipitation events occur. Water managers then face an important task: prevention of flooding and inconvenience caused by high water levels. More and more water boards choose to be supported in this task by DSS-s. These DSS-s are able to calculate whether problems will arise in an area, based on predictions of precipitation. During the lunchtalk Arnejan van Loenen will address the operation and application of such DSS-s.

Lunchtalk 20 March 2008
“Study of the Water footprint of bio-energy”
Bouke van Meekeren, WEM dept. of the Twente University

Abstract: Limited fossil energy and climate changes drive the interest for bio-energy. Bio-energy is energy derived from biomass. Biomass is derived from plants and plants can be grown for energy purposes. Because plants need water to grow, the demand for bio-energy results in a demand for water. Other sources of energy, such as fossil energy, require an amount of water which is at least multiple times lower than the demand of bio-energy. While the use of bio-energy creates benefits in several areas, it puts an increased demand on water resources. The research quantfies this increased demand with the water footprint

Lunchtalk 6 March 2008
“Remote sensing of carbon dioxide, water and energy exchange in the biosphere”
Joris Timmermans and Christiaan ven der Tol

Regional estimates of carbon dioxide, water and energy fluxes between land and atmosphere are important for many fields. The large scale estimation of fluxes is relevant for applications like precision agriculture, weather prediction, drought monitoring and climate change studies.  Remote sensing can be used to provide large spatial coverage of observations of the land surface. However, remote sensing can only measure the spectrum of reflected radiation from the surface (the ‘spectral signature’). A biophysical model is needed to retrieve information about the fluxes from the spectral signatures.  Current biophysical models developed so far use only parts of the spectral signature. We now developed a model that uses the whole spectrum of optical and thermal radiation to calculate the fluxes. The model is able to calculate scattering and absorption of radiation, photosynthesis and the aerodynamic heat exchange between land and atmosphere.  In the presentation, we will give examples of the use of the model, and discuss possible future applications.

Lunchtalk 21 February 2008
“Turbulent boundary layer under finite amplitude sea waves”
Paolo Blondeaux, Dept. of Civil, Environmental and Architectural Engineering, University of Genova

Abstract: The objective of the seminar is to present the results of a detailed analysis of the streaming velocity in a fully developed turbulent wave boundary layer produced by a uniform train of progressive finite-amplitude surface waves. Turbulence characteristics are determined by means of a two-equation closure model of turbulence proposed by Saffman (1970). The model can describe both smooth and rough walls as well as trasitional regimes such that turbulence characteristics depend both on the Reynolds number and the relative roughness size.

Lunchtalk 21 February 2008
“Study on the effect of froundwater extraction on urban groundwater resources in Kuala Lumpur, Malaysia”
Pieter Stek, WEM dept. of the Twente University

Abstract: A groundwater flow model is constructed to study the likely effects of groundwater extraction. This is challenging given the limited availability of data and the fractured limestone geology of the main aquifer. The simple quantitative flow model, together with qualitative knowledge about pollution, geohazards and local institutions provides a picture of Kuala Lumpur’s groundwater resources and relevant management options.

Lunchtalk 7 February 2008
“Geometry and dynamics from full-field sandy river bed evolution”
Brandon McElroy, Dept. of geological science of the University of Texas

Lunchtalk 17 January 2008
“Exploring scientific challenges in Dutch water management”
Pieter Lems, PhD student and project leader at Waterschap Groot Salland

Abstract: A short analysis will be given of the current everyday practice of water management, the ambitious policies that play a role, and the scientific research that contributes to it. The aim of this talk is to initiate a discussion about these topics placed in the context of the research of our group and Pieter’s PhD research.

Lunchtalks 2007

Lunchtalk 18 January 2007
“Long waves generated by wave groups propagating over bathymetry”
Gert Klopman, Applied Analysis and Mathematical Physics, University of Twente

Abstract: Sea waves vary in height continuously. Generally, the sea waves propagate in wave groups: if an individual wave is high, its neighbours will probably also be high, and vice versa.
Due to the non-linearity of the waves, a so-called bound long wave is associated with each wave group: under the higher waves in the group there is a slight depression and near the lower waves there is a slightly higher mean water level. These long waves travel with the wave group, that is why they are called bound to the wave group.
When the waves groups travel over a sea bed of varying depth, resonant interactions between the wave groups, the associated bound long waves and the bed undulations result in the generation of free long waves.
These long waves, both free and bound, may be important in several
circumstances:

• low-frequency resonance of harbours and moored ships
• morphological changes due to the correlation of sediment stirring and the long waves

In this presentation the modelling of long-wave generation by propagating wave groups over a variable sea bed will be discussed.

Lunchtalk 18 January 2007
“Sand motion induced by oscillatory flows: sheet flow and vortex ripples”
Jan S. Ribberink, Jebbe J. van der Werf and Tom O’Donoghue (Euromech 477, Particle Laden Flows, 21-23 June 2006)

Abstract:Shoaling short gravity waves at sea approaching the shore become asymmetric and are able to generate a net resulting sand transport in cross-shore direction (onshore-offshore transport). The wave-related sand transport is still very difficult to predict due to the complexity of its underlying processes, which mainly take place in a thin layer near the sea bed in the wave boundary layer (thickness of order centimeters). The development of models for cross-shore sand transport heavily relies on experimental lab research, especially in large oscillating water tunnels and large wave flumes. In oscillating water tunnels the near-bed horizontal orbital velocity, as induced by short gravity waves, can be simulated above fixed or mobile sandy beds. The presentation is focused at the sediment motion as occurring under the influence of horizontal oscillatory flows and measuring results will be presented of the Large Oscillating Water Tunnel (LOWT) of WL | Delft Hydraulics and the Aberdeen Oscillating Flow Tunnel (AOFT). Due to their large size (length of test sections: 10-15 m) they belong to the few available facilities in which the near-bed flows of full-scale waves can be generated and scale effects can be avoided. The mathematical modeling of the sand transport processes is carried out at different levels of detail, varying from 2-phase flow boundary layer models to semi-empirical sand transport formulas. Some insights as obtained during a series of Ph.D. studies in the preceding years (Dohmen-Janssen, 1999; Clubb, 2001; Wright, 2002; Hassan, 2003; Van der Werf, 2006) are presented and different types of sand transport models are reviewed.

Lunchtalk 22 March 2007
“Technologies for distributed data access”
Valentijn Venus and Marcel van Helvoirt, ITC

Abstract: New technologies for data acquisition and analysis may well change our perception of geo-information. Currently, “data” consumes a significant portion of our time and energy, whereas advances in Geo Data Infrastructures (GDI’s) try to sell us the concept that data and not our time is a ‘consumable’. In the past, spatial data was hard to come by, and our desktop solutions (software/hardware) reflect this: they are often single-purpose, privatized, and secured. Even when data should be accessible, the nature of the infrastructure caused problems such as data format incompatibility, data duplication, redundancy, versioning, and data identity. This in turn limits its use in natural resources management. In this meeting some technologies developed by Unidata and ITC are presented that help ease the transition from desktop GIS/RIS to distributed data access, processing, visualization and analysis.
Partnerships in GDI development:                                                                                   

• 52 north – an open source initiative that explores the horizon of geospatial technolgies (http://52north.org/).

52°North is an open initiative that advances the development of cutting edge open source geospatial software. Leading research organizations in the field of geo-informatics participate in 52°North’s innovative development for establishing open spatial data infrastructures (SDI) and transformation of these into practical technological solutions.

• Unidata - community that provides data, tools, and leadership for enhanced Earth-system education and research (http://www.unidata.ucar.edu/).

Unidata, funded primarily by the National Science Foundation of the U.S., is one of eight programs in the University Corporation for Atmospheric Research (UCAR) Office of Programs (UOP). UOP units create, conduct, and coordinate projects that strengthen education and research in the atmospheric, oceanic and earth sciences.
Unidata is a diverse community of over 160 institutions vested in the common goal of sharing data, and tools to access and visualizes that data. For 20 years Unidata has been providing data, tools, and support to enhance Earth-system education and research. In an era of increasing data complexity, accessibility, and multidisciplinary integration, Unidata provides a rich set of services and tools.

Lunchtalk 19 April 2007
“No models, no differential equations, no statistical analysis, but just policy and societal issues”
Ralph Schielenn(RWS & UT)

Abstract: Innovation at a public institute like the Ministry of Transport, Public Works and Water Management turns out to be different than for instance the innovation policy in the private sector. Different mechanisms play a role. Nevertheless, there IS a (water) innovation platform within the ministry, and interesting things happen over there. In this talk, I will go into the differences between innovation in the public and the private sector, and position the Water INNovation (WINN) platform of the ministry. Recent developments enable the ministry to focus on long term developments, especially related to climate change. In climate change, the challenge to prepare the Netherlands for the coming centuries is found, and innovation is needed. I will also address some projects which have been carried out in the (recent) past of WINN to get a flavour of the program.

Lunchtalk 19 April 2007
“The stochastic characteristics of geometric properties of sand waves in the North Sea”
Michiel de Koning, MSc student, UT

Abstract: The variability in geometric properties of sand waves is investigated by analysing field data from the North Sea. Sometimes information is needed, not only on mean sand wave heights or sand wave lengths, but also on the more extreme values. For instance, for dredging purposes, the highest possible crest elevation in an area may be more relevant than the mean crest elevation. The geometric properties of sand waves (sand wave height, sand wave length, crest elevation, trough elevation, asymmetry of the sand wave) are determined from bed elevation profiles. Each geometric property is plotted in histograms and the best fit probability density functions are determined. A relationship is found between the standard deviation and the mean value for each geometric property. Also a relationship is found between the standard deviation and the distance between the mean value and the value for the largest 5% of the geometric properties. These relationships make it possible to predict the stochastics of a geometric property based on the mean value, which may be useful to users in the North Sea area.

Lunchtalk 3 May 2007
“Beach morphology at Banda Aceh, Indonesia in response to the tsunami on 26 December 2004”
Ella Meilianda, UT/ITC MSc student

Ella Meilianda1, C. Marjolein Dohmen-Janssen2, Ben H.P. Maathuis3, Suzanne J.M.H. Hulscher4, Jan P.M. Mulder5
1,2,4&5. Water Engineering & Management (WEM), University of Twente, Enschede
3. Water Resources, International Institute for Geo-Information Science and Earth Observation (ITC), Enschede
Abstract: A study of morphological response and development of beaches which were affected by the earthquake and the tsunami on 26th December 2004 has been conducted at two selected coastal sections of Banda Aceh, Indonesia. A simplified principle adopted from one-line shoreline theory in a geospatial analysis utilizing identified shoreline features across the foreshore zone is applied. The analysis yields a rough estimation of the shoreline and sediment volume changes since the tsunami. After the severe impact as revealed by a significant chaotic shoreline retreat, the morphological development in the following 6 months has shown that about 15% of the total sediment loss due to the tsunami on the northwest coast has further been eroded, while 60% of that on the west coast has been compensated by accretion. This leads to a conclusion that different coastal characteristics show different responses to, and developments after the tsunami.

Lunchtalk 24 May 2007
“Monitoring of wetlands with the examples from Sistan, Iran/Afghanistan, Lake Cuitzeo, Mexico and more”
Zoltán Vekerdy, ITC

Abstract: The vulnerability of wetlands is manifested in their sensitivity to the changes in the balance of their water budget and water quality. These environments are loosing ground due to human pressure and climatic changes since they were looked at as harmful (e.g. diseases spread by
mosquitoes) and unusable (marshes), so they were targets of environmental pogroms. Gradually, their values are recognized, but this does not lead directly to their survival: mismanagement and overexploitation also pose a threat to their sustainability.

In ITC WRS we are involved in research and projects related to wetlands.
The focus is on documenting the hydrological and ecological processes in the wetlands (monitoring). Mapping the state variables, like water and vegetation cover or water quality, identifying the processes (change detection, trends in vegetation cover, water budget and fluxes, etc.) lead to a more comprehensive understanding of wetland processes.

During the presentation, we take a tour from Sistan (Iran, Afghanistan), to the Lake Cuitzeo in Mexico, with short stops over Shadegan in Iran, Lake Velence in Hungary and the Nile Delta in Egypt; looking at different aspects of wetland monitoring. The intention is not only to inform the audience about ITC's activities, but to trigger ideas and to 'provoke' thinking together.

Lunchtalk 7 June 2007
“Linking long-term coastal evolution and super storm dune erosion forecasts”
Lisette M. Bochev-van der Burgh, UT

Abstract: To assess the long-term safety of a dune-protected coastal area, models are needed for forecasting both long-term coastal evolution and dune erosion due to the occurrence of a super storm. In long-term model forecasts, however, information on dune shape is lost. Explorative calculations show that the output of the event-scale dune erosion model is quite sensitive to the dune height. For a given super storm, a higher dune leads to a larger forecasted erosion volume, but to a less land inward position of the erosion line (the line that indicates how far erosion is expected to reach land inward). Clearly, a solution should be found for adding information on realistic dune shapes to the long-term coastal evolution forecast. EOF decomposition of observed dune profiles provides simple but realistic dune shape functions that could be used to redistribute forecasted dune volumes into realistic dune shapes.

Lunchtalk 7 June 2007
“Using remote sensing for the calculation of energy, water and carbon fluxes”
Christiaan van der Tol, ITC

Abstract: Many researchers from different disciplines have tried to measure or to calculate the exchange of energy, water and carbon dioxide between the land surface and the atmosphere. This interest has many reasons: understanding the exchange fluxes is important for optimizing crop production, calculating climate scenarios, weather models, and drought and flood prediction. This talk focuses on the question: how can remote sensing help to improve the calculation of these fluxes? With remote sensing we can measure the spectrum of radiation reflected by the surface, and from this spectrum we can derive, for example, the temperature of the surface, biomass, and chlorophyll content. How can this information be used to calculate the fluxes in a consistent way, and what is the accuracy of the result?

An approach will be presented in which Soil-Vegetation-Atmosphere modeling and Radiative-Transfer-Models are integrated. This enables us to combine a-priori knowledge from ecology and meteorology with remote sensing information. An example for a forest in the Netherlands shows that the approach is promising.

Lunchtalk 12 June 2007
“Modelling river dune splitting”
Joost Lansink, UT MSc student

Lunchtalk 12 June 2007
“Global water governance; Conceptual design of global institutional arrangements”
Maarten Verkerk, UT MSc student

Lunchtalk 21 June 2007
“New physically based method called MRS, in quantification of water in subsurface”
Maciek Lubczynski

Lunchtalk 13 September 2007
“A discrete particle model for sheet flow simulation”
Renske Gelderloos

Abstract: Under high waves in shallow water sufficiently high flow velocities can be observed to wash out ripples and set a whole layer of sediment in motion. This regime is commonly referred to as sheet flow. Because of the large quantities of sand transported in this regime, accurate predictions of the sediment fluxes is very important. Current sheet flow models encounter some difficulty in successfully predicting the sediment fluxes, especially when time dependent effects play an important role.
In an attempt to improve the currently used models for sheet flow, a very detailed model is used in this study to describe the motion of individual sand particles under the influence of water flow, and their influence on the flow in return. We started from a Discrete Particle Model that is normally used for chemical engineering purposes, and adapted this model is such a way that it could describe the motion of sediment in water. During the presentation examples will be given of what the model is currently capable of, in order to show that a successful first step has been taken into detailed simulations of sheet flow processes.

Lunchtalk 13 September 2007
“Evaluation of statistical properties of dune profiles”
Andries Paarlberg

Abstract: A set experiments for dunes developing from a flattened sand bed was obtained in a narrow 0.44-m-wide and 12-m-long glass-sided open channel. The sand in use was a coarse uniform sand of D50=0.85-mm and was exposed to a series of steady and uniform flow conditions. The chosen flow depths generated practically 2D dunes in flow direction over the length of the channel. Spatial sand-bed-elevation profiles were recorded on the centreline of the flume over a distance of 6-m, roughly every 23-sec over the time of development. The recorded dune geometries were evaluated with both the discrete and the continuous approach. For the discrete approach, discrete height and length values are obtained for dunes. For the continuous approach, the second-order distribution moments, standard deviations, were used to obtain characteristic height and length values of the dune field. It is shown that a lack of clear definitions for the discrete approach results in a wide range of averaged dune geometries, depending on how thresholds were set during the analysis process. The continuous approach provides more objective results, but interpreting the results of the analysis requires careful consideration. For this paper, the analytical results of applying both approaches are compared. A preliminary correlation between both approaches is discussed.

Lunchtalk 27 September 2007
“Bed roughness under partial transport conditions”
Mathieu Spekkers

Abstract: Reliable hydraulic roughness models are of great importance, for example when predicting water levels in rivers. This study has validated existing hydraulic roughness models for fully mobile sand-bed rivers to predict flow resistance in cases where only part of the bed is mobile. This is called 'partial transport condition' and is observed in sand-gravel bed rivers, for example, with an immobile coarse layer limiting the supply of mobile sand. The validation is based on experimental data from recently conducted flume experiments in which the sand supply in a bimodal sand-gravel bed is limited. Furthermore, an existing theoretical relationship between supply-limitation and bed roughness is compared with the measurements (this is called the partial mobility roughness model). Bed surface images, sediment transport rate measurements and laser bed profiles have demonstrated that bed roughness is strongly related to the quantity of available mobile sand. In cases with small quantities of mobile sand, the roughness was dominated by plane-bed skin friction, and roughness decreased proportionally as the quantity of sand covering the surface increased. Bedforms only significantly contributed to the bed roughness for stages with large quantities of mobile sand.Full mobility roughness models - based on basic flow parameters (e.g. mean flow velocity), sediment characteristics and bedform dimensions - do not show this tendency. These models have been applied to the flume data using the grain size characteristics of the mobile sand (e.g. D50, D90). In stages with supply-limited bedforms, the full mobility roughness models overestimate the actual roughness and the prediction error increases for decreasing sand quantity. The trends predicted by the partial mobility roughness model are in line with the measurements. This study suggests that the mobility of the sand is better described using a hiding-exposure corrector.

Lunchtalk 27 September 2007
“Hydrological modelling of the Liuxihe River basin in South-China to contribute to the development of flood management”
Ric Huting

Abstract: Hydrological models can contribute to the development of flood management by simulating river discharge. A HBV hydrological model was set up for the Liuxihe River basin in South–China within the framework of this study.
The HBV model is a conceptual model, which uses simplifications of fundamental physical laws containing non-measurable parameters whose values have to be determined by means of calibration. The model input consists of precipitation, potential evapotranspiration, temperature and discharge data series. Although the input data series were poor in both a qualitative and quantitative way an attempt was made to calibrate the HBV-model with the limited available data for the most upstream sub-basin of the Liuxihe River basin: Huanglong Dai Reservoir (HDR) sub-basin. Model validation was not possible due to the too short temporal extent of the data series.
Unreliable values of discharge data were a major problem concerning the model input data. Four methods were applied to the discharge data series in order to obtain reasonable series for the HDR sub-basin. Two of these methods improved the water balance of the HDR sub-basin, i.e. the residual term in the balance decreased.
The HBV model for the Liuxihe River was calibrated eight times with two differently modified discharge data series, two different temporal extents and both hourly and daily temporal resolution. However, the hydrographs obtained with the HBV model show only partial similarity with the observed hydrograph. This was recognized both visually and by the applied assessment criteria. Although little differences between the model performances exist according to the assessment criteria, these differences are too small to rank the adopted methods used for modifying the discharge data series.

Lunchtalk 18 October 2007
“A continuous model for aeolilan sand dunes and its application to barchan dune fields and vegetated parabolic dunes”
Orencio Duran

Abstract: The existence of a minimal size for Aeolian dunes of about 10m long, and thus, the impossibility of generate them in wind tunnel experiments, has led to an enormous emphasis in numerical simulations as the simplest, and sometimes the only, tool to get insight into dune emergence and evolution under controlled conditions. In this talk, I'm going to present a continuous sand transport model developed in successive contributions by the H.J. Herrmann's group, and I'll focus into two main applications: first, the emergence of barchan dune fields from a "beach" as a result of the coupling of a longitudinal and transversal instability. Second, by including the vegetation dynamics into the model, we were able to study the emergence of inactive parabolic dunes from active barchan ones, and hence, to uncover the mechanisms underlying the dune deactivation induced by the vegetation growth.

Lunchtalk 18 October 2007
“Flood shelters”
Wout de Fijter

Abstract: Floods can be a disaster in which many people die. Who doesn't remember hurricane Katrina, in which more than 1100 people lost their lives? Or the tsunami in the Indian Ocean with almost 300.000 casualties? Closer to home we have to go back to the storm tide of 1953 in Zeeland, in which 1836 people died. In the Netherlands we are now better protected against floods than ever before. Our dikes are one of the best in the world, but herein lies also a great danger. Sooner or later there will be another flood in the Netherlands and which actions do we then have to take to save lives? The majority of the Dutch don't know if they are at risk during a flood and if so what this risk is and what they have to do.

One strategy is to further increase the strength of our defenses. We could build larger dikes, construct a coastal zone to decrease the wave energy and create more room for the river. With these measures we are still not prepared for the possible consequences. In this situation a strategy like compartmentalization may help to reduce the amount of damage. But within one compartment damage and casualties could be higher than without. A better way to reduce casualties is to evacuate the inhabitants out of a flood prone area. When there is enough time and manpower this would be a good option, but what to do when this is not the case?

Another option to reduce the amount of casualties is to construct flood shelters. In Bangladesh flood shelters are the best protection against floods. Since about 500 B.C. there are also flood shelters in the Netherlands, better known as "terpen". With the construction of dikes they no longer served as a flood shelter and a lot of these "terpen" are no longer visible. In my research I made a design for flood shelters in the Netherlands. One part of the research consists of a global design, which is applicable to every dike ring. In this global design I made clear what is needed for flood shelters to work. Besides a global design I made a detailed infrastructural design for 6 municipalities within dike ring 6 and 43. During my presentation I will explain my design method and illustrate the designs.

Lunchtalk 1 November 2007
“Multi-parameter flood risk assessment”
Dinand Alkema, department of Earth Systems Analysis, ITC

Abstract: Flood events are complex spatial-dynamic processes and to quantify their impact on elements in the flooded area a multi-parameter approach is required. In this presentation will be shown that 2D flood propagation modelling generates a series of parameter maps that represent the dynamic behaviour of the inundation process. This is valuable information to assess the socio-economic consequences of a flood event. The problem that arises is that each parameter has a different spatial pattern, which complicates the integration of all these maps into a flood hazard risk zonation. A procedure is required to integrate and aggregate all map layers. This has been recognised by several authors who have proposed multi-parameter risk zonation procedures, but most use two or at maximum three parameters. For instance Gendreau (1998) who combines inundation depth, duration and maximum acceptabl;e return period, Témez (1992 and Penning-Rowsell & Tunstall (1996) who combine flow velocity and inundation depth and Borrows (1999) who combines flow velocity, inundation depth and warning time. In this study seven flood parameter maps are generated for each flood event: maximum water depth, maximum flow velocity, maximum impulse, minimum warning time, estimated duration, maximum rising of the water level and relative sedimentation/scouring. No procedure exists yet that includes all these flood parameter maps. The difficulty is, of course, that it is hard or perhaps impossible to develop such a procedure because information on the spatial distribution of the flood impact is often unavailable (or is classified) which inhibits establishing relationships between flood parameters and flood consequences. However, implicitly, each parameter does hold information on its consequences: Deeper water depths create higher flood risk, and so does longer duration and shorter warning times. This implicit information can be used to assess flood risk. This approach differs from previous multi-parameter flood risk procedures because it does not rely on vulnerability relationships between magnitude of the hazard and the impact on the elements exposed, like stage-damage curves or graphs that predict under what circumstances pedestrians and cars are washed away. It is based on expert knowledge from hydrologists, engineers, disaster managers, economists, relief workers, local and regional authorities, farmers, etc. In short: based on the knowledge of the stakeholders and experts involved in a flood disaster. This presentation will show that spatial multi-criteria evaluation (SMCE) offers opportunities to formalise the procedure for multi-parameter risk assessment using this expert knowledge. The vulnerability is implicitly included in the transformation process from multiple flood parameter maps to a potential flood risk map.

Lunchtalk 15 November 2007
“Tree transpiration mapping in the Botswana Kalahari, remote sensing for ecohydrology”
Diana Chavarro, PhD student dept. of Water Resources, ITC

Abstract: Tree transpiration is an important component of water cycle. In arid and semi-arid environments, it can be critical with regard to groundwater balances being often the most unknown component of them. As it has been proved by tracer experiments on Kalahari, groundwater can be subtracted by tree rooting systems from more than 70 m depth, through a process known as hydraulic lift.  Hydraulic descend and reverse sap flow can also take place during the night when transpiration declines and the water stored during the day in the tree trunk is used to moist the upper layers of the soil. Sap flow measurements in tree stems collected in such ecosystems are susceptible to misinterpretations due to the complex soil-water-tree interactions that are the result of adaptation mechanisms.
For the identification of transpiration patterns in Botswana Kalahari savannah vegetation, nine common species were measured with regard to sap velocities using Thermal Dissipation Probes, TDP.  Detailed investigation of the existence of natural thermal gradients which mislead the measurements was carried and corrective measurements implemented. Tree water use thus evaluated was validated by a novel verification experiment that includes real time volumetric measurements of the water consumption.  Analysis of species-dependent sap flow patterns resulted in the identification of transpiration related features as night-time sap flow, tree water storage and hydraulic redistribution which can be related to water availability and tree rooting systems.

Sap flow measurements per species were correlated with biometric characteristics of the trees for the development of upscaling functions. Such correlations were applied to classified high resolution satellite images from which a transpiration map was obtained.  Due to the heterogeneity of the Kalahari savannah vegetation, advanced GIS techniques had to be used for the identification of species. The resulting transpiration map of the region was implemented in the local water balances for the quantification of long term water availability.

Lunchtalk 15 November 2007
Water in the wocioeconomic metabolism; The study of the water metabolism of the fruit and vegetables production and trade in Andalusia, Spain”
Cristina Madrid-Lopez

Abstract: Economy needs to be provided with materials and energy coming from the natural system and is also using the later as a deposit for waste and pollution. That is the so called “Socioeconomic Metabolism” (SM). Material Flow Accounting (MFA) is the tool used to study the material and energy flows coming to and from an Economy. Despite its importance for life, water is usually excluded form this kind of studies due to the volume of its flows and its especial charactristics (mainly related to geographically and temporally variable availability). This work proposes a methodology for the study of water flows in what has been denominated “WaterMetabolism” and an application of it to the Andalusian fruit and vegetable production and trade. The importance of the trade of these products for the economy, their water consumption and the scarcity of the resource of the region justify the selection of it for the study.

Lunchtalk 13 December 2007
“Tsunami erosion and sedimentation”
Dr. Guy Gelfenbaum from the US Geological Survey, USA

Abstract: Evolution of sand bed river topography contains an abundance of information about the dynamic processes of sediment transport. Because of the recent expansion of theability to collect bed topographic data, a set of objective, robust, and intuitive measures of bed geometry and dynamics is needed. A quantification of bed roughness, velocity and deformation will be proposed with examples from the N. Loup River, Nebraska, USA. The associated methods rely heavily on spatial analysis and derived statistics. In addition to description, implications for sediment transport are evident by the variability of topographic change across a single bed. Its impact on the quantification of sediment transport by dune-tracking will be explored.

Lunchtalks 2006

Lunchtalk 22 June 2006
“Effects of LIDAR DEM resolution in flood modelling: A model sensitivity study for the city of Tegucigalpa, Honduras”
Alemseged Tamiru Hailea and T.H.M. Rientjes

• Water Technology Institute (Arba Minch University), P.O.Box 21, Arba Minch, Ethiopia, E-mail: haile07634@itc.nl
• Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O.Box 5048, 2600 GA Delft, The Netherlands.
• Department of Water Resources, ITC, P.O. Box 6, 7500AA Enschede, The Netherlands, E-mail: rientjes@itc.nl

Abstract: An important aspect of hydraulic flood modelling deals with representing topography of river and floodplain. Commonly, flood model applications are reported successful in topographically simple areas where topography only changes gradually and where topography is simulated by DEM’s of relatively low resolution. Such DEM’s are particular useful for flood simulation in rural areas, although important topographic features and properties are not simulated explicitly. In urban areas, however, features like roads, buildings, river banks and dykes have great effect on flow dynamics and flood propagation and as such must be accounted for in the model set-up. This is possible by means of high resolution input data that relates to the systems topography as well as to the identified features. By frequent urban floodings over the past decades, an urgent need is identified to improve and increase our modelling efforts and to address more explicitly the effect model input data has on the simulation results. Society demands accurate and detailed information on magnitude and likeliness of hazardous flood events for design of flood mitigation measures. This also is the case for the city of Tegucigalpa in Honduras that severely has been affected by floodings as caused by extreme rainfall events.

For the study area, a DEM with grid size of 1.5 m. is generated from LIDAR data and served as a base line case for various flood simulations. In this study, this DEM is re-sampled and DEM’s of resolutions up to 15 m. are created and served as input to the flood simulations. By the re-sampling to coarser grid elements, averaging across increasingly larger domains is realized and has resulted in an increased loss of detailed topographic properties that affect flood simulations. The original DEM is also used to extract buildings by using geomorphologic filters and other GIS operations. For the simulation, buildings are represented as solid, partially solid and hollow objects by varying the surface roughness value. The sensitivity analysis to DEM resolution revealed that topographic representation is critical and that model output is significantly affected by the resolution of the DEM.

Lunchtalk 24 August 2006
“Explaining dependencies between irrigational water use and different types of water availability in a GIS-based way”
Anne Leskens and Martijn Huisjes, UT

Abstract: The occasion of this study is the unbalanced relation between agricultural water demand and water availability in a semi-arid region in Brazil and the accompanying problems in allocating the available water.
The goal of this study is to explain  the dynamics of land use and irrigational water use under different water availabilities between 2000 and 2005 and to give recommendations for a better water policy. The availability of water for agricultural land use in the research area has a strong spatial character; for example, farmers downstream from a release point of a reservoir are subjected to another 'type' of water availability than farmers located upstream at the edge of the same reservoir. Both interestgroups are dependent on the same reservoir water, but in another way, determined by spatial properties.

To explain the dynamics of land use and irrigational water use under different water availabilities, a spatial analysis is carried out, using GIS, Remote sensing and methods for calculating the crop water use. During the lunchtalk this methodology will be explained and the first conclusions will be presented.

Lunchtalk 5 October 2006
“Analytical flow description for turbulent river flows”
Fredrik Huthoff, Faculty of Engineering Technology, UT

Abstract: River hydrodynamics can be extremely complex. The interplay between walls or solid objects and the flow field cause vortices and swirling motions at various scales. It is important to understand the characteristics of these motions because they effectively determine the average flow velocity, and hence, (flood) water levels. However, modern computing capabilities are not powerful enough to provide solutions to the fundamental flow equations on temporal and spatial scales relevant in river engineering studies. As a result, many empirical equations or simplifications to the fundamental equations have been proposed in hydraulics.

In the presentation it will be demonstrated that in some cases extremely simplified flow equations can describe overall flow behavior adequately by making scaling assumptions of the dominating mixing motions in the turbulent flow field. Two examples are given where such scaling considerations are applied successfully: compound channel flow (i.e. in a river with floodplains) and flow over (idealized) vegetated areas. In both cases, new analytical descriptions of the depth-averaged flow velocities are put forward. The proposed descriptions can be used for quick evaluation of a river's hydraulic response when (vegetated) floodplains become overflown.

Lunchtalk 23 November 2006
“Separation of scales on a broad, shallow turbulent flow”
Carlos Vionnet, Universidad Nacional del Litoral (Santa Fe, Argentina) and University of Arizona (USA)

Abstract: Two different mechanisms acting on a broad, shallow turbulent flow whose energy spectrum is separated by a gap is investigated experimentally. The study concentrates on the spectral response evolution of the shallow flow approaching an opening induced by a lateral contraction, located halfway in streamwise direction of a large rectangular basin. The geometrical forcing, induced by the lateral contraction that breaks the plan-form symmetry of an otherwise broad and uniform shallow flow, produces an energy concentration in the range of low wavenumbers (large-scale) by an inverse cascade process. The geometrical forcing continues to pile up energy until scales the size of the entire flow geometry are strongly excited. The topographical forcing, induced by the presence of a fixed scour hole located at the contraction end that breaks an otherwise flat bottom, produces an energy concentration in the range of high wavenumbers (small-scale) by trapping some flow modes. The topographical forcing is only local, and has the effect of acting as an eddy viscosity on the large-scale turbulent motion. The problem presented is relevant to determine the fate of suspended sediment downstream of the opening of relief bridges located on flat floodplains in periods of high waters.