Search inside publication
Global economic analysis in the 21st century - challenges and opportunities : 20th Annual conference on global economic analysis (June 7-9, 2017, Purdue University, West Lafayette, USA)
Improving nitrate load estimates in an agricultural catchment using Event Response Reconstruction
Low-frequency grab sampling cannot capture fine dynamics of stream solute concentrations, which results in large uncertainties in load estimates. The recent development of high-frequency sensors has enabled monitoring solute concentrations at sub-hourly time scales. This study aimed to improve nitrate (NO3) load estimates using high-resolution records (15-min time interval) from optical sensors to capture the typical concentration response to storm events. An empirical model was developed to reconstruct NO3 concentrations during stormevents in a 100-km2 agricultural catchment in Germany. Two years (Jan 2002 to Dec 2002 and Oct 2005 to Sep 2006) of high-frequency measurements of NO3 concentrations, discharge and precipitation were used. An Event Response Reconstruction (ERR) model was developed using NO3 concentration descriptor variables and predictor variables calculated from discharge and precipitation records. Fourteen events were used for calibration, and 27 events from four periods of continuous records of high-frequency measurement were used for validation. During all selected storm events, NO3 concentration decreased during flow rise and increased during the recession phase of the hydrograph. Three storm descriptor variables were used to describe these dynamics: relative change in concentration between initial and minimum NO3 concentrations (rdN), time to maximum change in NO3 concentration (TdN) and time to 50% recovery of NO3 concentration (TNrec). The ERR consisted of building linear models of discharge and precipitation to predict these three descriptors. The ERR approach greatly improved NO3 load estimates compared to linear interpolation of grab sampling data (error decreased from 10 to 1%) or flow-weighted estimation of load (error is 7%). This study demonstrated that ERR based on a few months of high-resolution data enables accurate load estimates from low-frequency NO3 data.
NCR-days 2018 (Delft, February 8-9, 2018) - The future river : book of abstracts
The impact of climate change on the morphology of a tidal freshwater wetland affected by tides, discharge, and wind
Tidal freshwater wetlands are threatened by climate change, especially by rising sea levels. Until now, research in these wetlands has focused mostly on determining historical and present‐day accretion rates without analysing the influence of climate change on future developments. We study a recently constructed freshwater wetland under influence of tides, wind, and riverine discharges and carry out a scenario analysis to evaluate the impact of climate change on morphodynamics. We use a numerical model that describes the hydrodynamics and morphology in the study area and includes the impact of vegetation and carry out transient scenario runs for the period 2015–2050 with gradually changing boundary conditions. We conclude that the simulated accretion rates are significantly lower than the rate of sea level rise, meaning that the wetland will gradually convert to open water. We also find that the morphological changes can largely be attributed to morphological stabilization of the constructed wetland and not to climate change. Wind plays an important role through resuspension and redistribution of fine sediment, and neglecting it would lead to a significant overestimation of accretion rates on the flats.
Collaborative Risk Informed Decision Analysis : a water security case study in the Philippines
More frequent and intense hydrologic events under climate change are expected to enhance challenges for water security and flood risk management worldwide. Traditional planning approaches must be adapted to address climate change and develop solutions with an appropriate level of robustness and flexibility. The Collaborative Risk Informed Decision Analysis (CRIDA) method is a novel planning approach embodying a suite of complementary methods, including decision scaling and adaptation pathways, in a stakeholder driven process which guides decision makers through the planning and decision process, taking into account how the confidence in the available science, the consequences in the system, and the capacity of institutions should influence strategy selection. The purpose of this study is to apply the CRIDA approach to a water supply case study in Central Cebu, the Philippines in order to evaluate the added benefits of the method for planning and design under climate change uncertainty. This work will equip practitioners and decision makers with an example of a structured process for decision making under climate uncertainty that can be scaled as needed to the problem at hand.
Proposed methodology for risk analysis of interdependent critical infrastructures to extreme weather events
Growing scientific evidence suggests that risks due to failure of critical infrastructures (CIs) will increase worldwide, as the frequency and intensity of extreme weather events (EWEs) induced by climate change increases. Such risks are difficult to estimate due to the increasing complexity and interconnectedness of CIs and because information sharing regarding the vulnerabilities of the different CIs is limited. This paper proposes a methodology for risk analysis of systems of interdependent CIs to EWEs. The methodology is developed and carried out for the Port of Rotterdam area in the Netherlands, which is used as a case study. The case study includes multiple CIs that belong to different sectors and can be affected at the same time by an initiating EWE. The proposed methodology supports the assessment of common cause failures that cascade across CIs and sectors. It is based on a simple, user-friendly approach that can be used by CIs owners and operators. The implementation of the methodology has shown that the severity of cascading effects is strongly influenced by the recovery time of the different CIs due to the initiating EWE and that cascading effects that result from a disruption in a single CI develop differently from cascading effects that result from common cause failures. For most CIs, vulnerabilities from EWEs on the CI level will be higher than the cascading risks of common cause failures on the system of CIs; moreover, cascading risks for a CI will increase after its recovery from the event.
Rheological characterisation of concentrated domestic slurry
The much over-looked element in new sanitation, the transport systems which bridge the source and treatment facilities, is the focus of this study. The knowledge of rheological properties of concentrated domestic slurry is essential for the design of the waste collection and transport systems. To investigate these properties, samples were collected from a pilot sanitation system in the Netherlands. Two types of slurries were examined: black water (consisting of human faecal waste, urine, and flushed water from vacuum toilets) and black water with ground kitchen waste. Rheograms of these slurries were obtained using a narrow gap rotating rheometer and modelled using a Herschel-Bulkley model. The effect of concentration on the slurry are described through the changes in the parameters of the Herschel-Bulkley model. A detailed method is proposed on estimating the parameters for the rheological models. For the black water, yield stress and consistency index follow an increasing power law with the concentration and the behaviour index follows a decreasing power law. The influence of temperature on the viscosity of the slurry is described using an Arrhenius type relation. The viscosity of black water decreases with temperature. As for the black water mixed with ground kitchen waste, it is found that the viscosity increases with concentration and decreases with temperature. The viscosity of black-water with ground kitchen waste is found to be higher than that of black water, which can be attributed to the presence of larger particles in the slurry.
A continuation approach to the optimization of hydropower operations
The instantaneous power generation from a hydroelectric turbine is proportional to the product of head difference and turbine flow. The equation relating power to hydraulic variables is therefore nonlinear. Hence, optimization problems subject to this relation, such as release schedule optimization, are nonconvex and may admit multiple local isolated minima. This renders such problems problematic for use in operational model predictive control. This paper shows that release schedule optimization problems subject to the nonlinear turbine generation equation may be set up using a continuation approach to be both zero-convex and path stable. In this way such optimization problems become suitable for decision support systems based on model predictive control. An example problem is studied, and it is shown that significant productivity gains may be realized using the presented methodology.
A continuation approach to nonlinear model predictive control of open channel systems
The equations governing open channel flow are strongly nonlinear when considering the full range of possible flows. Hence, optimization problems that aim to select optimal flow regimes for hydraulic structures such as weirs and pumps are subject to nonlinear relations between optimization variables. Such optimization problems are nonconvex, and may admit multiple isolated local minima, rendering them problematic for use in operational model predictive control. This paper introduces the notions of zero-convexity and path stability, i.e., the property of a parametric optimization problem that I) is convex at the starting parameter value and II) that when computing a path of solutions as a function of the parameter, such a path exists and no bifurcations arise. Path stability ensures that the parametric optimization problem can be solved in a deterministic and numerically stable fashion. It is shown that a class of numerical optimal control problems subject to simplified 1D shallow water hydraulics is zero-convex and path stable, and hence suitable for deployment in decision support systems based on model predictive control.
The state of the world’s beaches
Coastal zones constitute one of the most heavily populated and developed land zones in the world. Despite the utility and economic benefits that coasts provide, there is no reliable global-scale assessment of historical shoreline change trends. Here, via the use of freely available optical satellite images captured since 1984, in conjunction with sophisticated image interrogation and analysis methods, we present a global-scale assessment of the occurrence of sandy beaches and rates of shoreline change therein. Applying pixel-based supervised classification, we found that 31% of the world’s ice-free shorelines are sandy. The application of an automated shoreline detection method to the sandy shorelines thus identified resulted in a global dataset of shoreline change rates for the 33 year period 1984–2016. Analysis of the satellite derived shoreline data indicates that 24% of the world’s sandy beaches are eroding at rates exceeding 0.5 m/yr, while 28% are accreting and 48% are stable. The majority of the sandy shorelines in marine protected areas are eroding, raising cause for serious concern.