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Een Nederlandsch Waterbouwkundig Laboratorium
Waterloopkundig Laboratorium te Delft (architect ir. H. Kammer)
Mogelijke gevolgen van versnelde zeespiegelstijging voor het Deltaprogramma : een verkenning
De zeespiegel kan mogelijk (veel) sneller gaan stijgen dan tot nog toe is aangenomen in het Deltaprogramma. Deze extra versnelling heeft te maken met recente inzichten over het mogelijk versneld afbreken en smelten van het landijs op Antarctica. In het Deltaprogramma 2018 is opgenomen dat de mogelijke consequenties van de resulterende extra versnelde zeespiegelstijging nader onderzocht gaan worden. Dit rapport beschrijft de resultaten van een eerste verkenning naar de mogelijke gevolgen van deze extra versnelde zeespiegelstijging voor het kustfundament (inclusief de Wadden en zuidwestelijke delta), de waterveiligheid, en de zoetwatervoorziening in Nederland en de implicaties voor de voorkeursstrategieën van het Deltaprogramma.
Modelling tidal-induced sediment transport in a sand-silt mixed environment from days to years : application to the Jiangsu coastal water, China
In the present study a new multi-fractional, depth-averaged sediment transport module was developed and embedded into a morphodynamic model for a sand-silt mixed shallow water environment. Subsequently, the model was applied to the case of the Jiangsu coast, which features a silt enriched sedimentary environment bordered by two large-scale geomorphological units: the Old Yellow River Delta (OYRD) in the north and the Radial Sand Ridge Field (RSRF) in the south. Based on this case, the predictive abilities of the present model are assessed on both the short-term and the long-term. Comparisons with measurements over two successive tidal cycles indicate that the present model produces very good results on short-time scales. The model performance is extended and further validated by comparing the overall annual Suspended Sediment Concentration (SSC) pattern, the annual morphological changes, the annual sediment budget and the evolution trend of the bed composition. Also, these long-term results agree well with existing observations over the past several decades. Hence, an essential feature of the present modelling approach is the ability to simulate sediment transport and morphological changes over a relatively long time span (i.e., time scale of years) in a sand-silt mixed sedimentary environment, based on its validated short-term performance.
Physical model tests to determine the roughness of stair shaped revetments
Stair shaped revetments are considered as an attractive alternative for traditional revetments since the surface roughness reduces wave overtopping resulting in a lower crest height. The specific shape enables easy access from and to the watar surface, enhancing the attractiveness for tourists and residents. To implement stepped revetments in the design of a seawall there is a need to quantify the roughness of a stair shaped reventment to predict wave overtopping rates. This paper describes research in which 2D physical model experiments were conducted in Deltares' Scheldt Flume. Based on the obtained data a method to quantify the roughness coefficient of such structures is suggested.
Impact of hydraulic and storage properties on river leakage estimates : a numerical groundwater flow model case study from southern Benin
River discharge loss is known to occur on the Zou and Ouémé rivers in southern Benin since a couple of decades ago. The reason behind this discharge reduction remained so far unclear. In this study, we focus on creating a 3D-numerical model of the system and on evaluating the sensitivity of leakage between the rivers and aquifers to various parameters. Results show that leakages along the Zou river and Ouémé stream are tiny (about 3% of the discharge losses). This implies that the observed water loss from the Zou and Ouémé rivers is not likely caused by the leakage (infiltration) along these rivers into the subsurface. The streambed conductance is found to be among the factors that impact less the computed leakages in the study area. This study has ranked the different hydraulic and storage properties in their order of importance with respect to the computation of river leakages along the concerned rivers. The determined rank of importance of the hydraulic and storage properties can guide river leakage modelling exercises in similar regions elsewhere.
Predicting bird collisions with wind turbines : comparison of the new empirical Flux Collision Model with the SOSS Band model
Collision of birds with wind turbines is an important negative effect of wind energy generation. Assessments of the potential numbers of bird collisions are required prior to the construction of wind farms. Collision rate models (CRMs) are used as a tool to estimate numbers of collision victims for wind farm initiatives. In the past couple of decades various CRMs have been developed. These models are all based on the theoretical calculation of collision probabilities (theoretical models). In this paper we introduce an empirical model, the Flux Collision Model (FCM), in which actual knowledge of species (group)-specific collision probabilities collected in existing wind farms on land is used to calculate collision rates for planned wind farms. An important quality of the FCM is that it provides a means to use empirical information to assess collision rates in Environmental Impact Assessments (EIAs) for wind farm initiatives. In addition, no detailed information on bird behaviour close to the rotor is needed, as this information is already incorporated in the empirical collision probability. In two case studies, one offshore and one on land, we compare and discuss the use and performance of the empirical FCM and the theoretical SOSS Band model for predicting collision rates of birds at wind farm initiatives. To date, no actual collision rates are known for the offshore situation. Accordingly, in the FCM, collision probabilities derived from wind farms on land were used. Nevertheless, in the offshore case study, the results of the FCM were comparable with those of the SOSS Band model. Basic sensitivity analyses for both the FCM and the SOSS Band model showed that purely theoretically both models are equally sensitive to changes in avoidance rates. However, because lower values for avoidance are applied in the FCM (wind farm avoidance) than in the SOSS Band model (overall avoidance), in practice the effect of realistic variation in avoidance rates on the resulting collision rates is much smaller for the FCM than for the SOSS Band model. Our results show that the FCM provides a valuable addition to the existing suite of (theoretical) CRMs. The predictive value of the theoretical SOSS Band model is constrained by the limited availability of knowledge on species (group)-specific (wind turbine) avoidance rates, which is not the case for the FCM. By contrast, the reliability of the empirical FCM is determined only by variation in the availability and quality of information on species (group)-specific collision probabilities.
Solution near of navigation problems at Willemstad Harbour
In the open-air laboratory "De Voorst", sub-division of the Hydraulic Laboratory at Delft, a study of the navigation problems for the harbour of Willemstad in Curaçao has been completed. In St. Anna Bay especially large ships sometimes meet with hindrance from a strong current along the entrance, which have repeatedly caused damage. Delft engineers and their co-operators are engaged in engineering projects which should clear this nuisance to navigation.
Royal visit to Eastern Flevoland and North-East Polder
Royal guests from Luxembourg visited the partially completed Flevo Polder, the new museum at Lelystad and the Laboratory of Watercourse experts at De Voorst (Waterloopkundig Laboratorium). The Zuyderzee works and the plans in connection with the regulation of the Zealand waterways greatly interested the visitors. In this paper most attention is paid to the set up of scale models in De Voorst.
Radiational tides: their double-counting in storm surge forecasts and contribution to the Highest Astronomical Tide
Tide predictions based on tide-gauge observations are not just the astronomical tides, they also contain radiational tides: periodic sea-level changes due to atmospheric conditions and solar forcing. This poses a problem of double-counting for operational forecasts of total water level during storm surges. In some surge forecasting, a regional model is run in two modes: tide only, with astronomic forcing alone; and tide and surge, forced additionally by surface winds and pressure. The surge residual is defined to be the difference between these configurations and is added to the local harmonic predictions from gauges. Here we use the Global Tide and Surge Model (GTSM) based on Delft-FM to investigate this in the UK and elsewhere, quantifying the weather-related tides that may be double-counted in operational forecasts. We show that the global S2 atmospheric tide is captured by the tide-and-surge model and observe changes in other major constituents, including M2. The Lowest and Highest Astronomical Tide levels, used in navigation datums and design heights, are derived from tide predictions based on observations. We use our findings on radiational tides to quantify the extent to which these levels may contain weather-related components.