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A coupled chemical-mechanical approach to model biogenic sulfide corrosion in concrete sewer pipes
This contribution focuses on the biochemical degradation of concrete sewer pipes, particularly on the influence of the chemical attack by sulfates on the load bearing capacity and durability of the system. The process under consideration is generally known as biogenic sulfide corrosion; this process is caused by bacteria of the genus ”Thio-oxidans”, which can grow on the concrete surface above the wastewater level in relative acidic environments.
CFRAC 2019 - proceedings of the VI International Conference on Computational Modeling of Fracture and Failure of Materials and Structures (Braunschweig, Germany, 12-14 June 2019)
Large scale model test on sand-filled geosystems for coastal protection (GEOS)
Large scale model tests have been performed on a scale 1:5 in the ICTS-CIEM to test the stability of sand-filled geosystems, both tube and bags, and their effect on the morphological evolution of a beach profile. Tube and bags were buried in sand at the upper part of a beach profile with a slope 1:15 in the area where it was transitioning to a beach berm (horizontal flat section). Erosion of the beach during the experiment exposes the tube and bags to direct wave attack. Tests were done under the action of irregular waves with a significant wave height of 2.5 m in prototype, also the effect of two different water levels was considered. Under these conditions the erosion at the seaward side of the tube and bags was limited. Remarkable there was more erosion around the bags. As a consequence of the limited erosion the stability of the structure was never a problem.
Groundwater representation in continental to global hydrologic models : a call for open and holistic evaluation, conceptualization and classification
Continental- to global-scale hydrologic models increasingly include representations of the Earth’s groundwater system. A key question is how to evaluate the realism and performance quality of such large-scale groundwater models given limitations in data availability. We argue for a transparent approach to system conceptualization, which would enable distinguishing differences in model behavior that are caused by system conceptualization from those that are caused by differences in the implementation of physical processes in models. In addition, we argue for systematic model classification to distinguish the impacts of choices in model implementation. Evaluation options include comparing model outputs with available observations of groundwater levels or other state or flux variables (data-driven evaluation); comparing several models with each other with or without reference to actual observations (model-driven evaluation); or relying on experts to propose hydrologic behaviors that we expect to see in particular regions or at particular times (expert-driven evaluation). We discuss the strengths and weaknesses of these three evaluation strategies as well as how they might be integrated to achieve a more holistic approach. We call on various scientific communities to join us in our effort to improve the representation of groundwater in continental to global models using the recommendations discussed here.
Overtopped wave loads on walls (WALOWA) : numerical and physical modelling of large-scale experiments in the Delta Flume
Large-scale experiments on overtopping wave impact loads on dike mounted walls were conducted in the Deltares Delta Flume for mildly sloping foreshore and shallow water conditions. The experiments were accompanied by a set of numerical model tools in order to help design the experimental set-up, extend the measured data by the high resolution output of the numerical models and to numerically remodel a change in geometry. The methods used for the hybrid modelling approach and first results are herein discussed.
Large-scale iceberg - tsunami experiments
Iceberg calving at outlet glaciers contributes to global sea-level rise in the context of climate change. This study investigates tsunamis generated by iceberg calving, so-called iceberg-tsunamis. Such tsunamis reached amplitudes of 50 m in the recent past and endanger human beings and coastal infrastructure. 73 unique large-scale experiments have been conducted in the 50 m × 50 m Delta Basin at Deltares. These experiments involved the five iceberg calving mechanisms: A: capsizing, B: gravity-dominated fall, C: buoyancy-dominated fall, D: gravity-dominated overturning and E: buoyancy-dominated overturning. Gravity-dominated icebergs essentially fall into the water body whereas buoyancy-dominated icebergs essentially rise to the water surface. The iceberg-tsunamis from gravity-dominated mechanisms (B and D) are roughly an order of magnitude larger than from mechanisms A, C and E. The maximum wave heights and amplitudes and their decay with distance from the calving locations are correlated with six dimensionless parameters, with the Froude number, the relative iceberg width and the relative released energy identified as the most important ones. Empirical equations for initial iceberg-tsunami hazard assessment were derived predicting the wave features reasonably well, considering the variety of the underlying physics involved in the iceberg calving mechanisms. Ongoing and future work aims to analyse the wave parameters in more detail, investigate the wave features with a novel wave component decomposition method, compare iceberg- with landslide-tsunamis and investigate iceberg-tsunamis numerically.
Trans-national Access in Hydralab+ : proceedings of the Joint User Meeting (Bucharest, May 23, 2019)
HYDRALAB is an Integrated Infrastructure Initiative, financially supported by the EC, to optimise the use of unique facilities for laboratory experiments in the field of Hydraulics, Geophysical Hydrodynamics, Environmental Fluid Dynamics and Ice Engineering. One of the three main activities of Hydralab was enabling international groups of researchers to conduct hydraulic research in selected large and unique facilities, which is called ‘transnational access’. The contract period of Hydralab+ is from September 2015 to August 2019. Hydralab+ is financially supported by the European Union’s Horizon 2020 Research and Innovation programme (grant agreement 654110). The Joint User Meeting is the final event of four years of Transnational Access in the framework of Hydralab. It is a mini conference in which the results of 31 research projects are presented. These projects have been carried out by international groups of researchers in a large and unique facility of Hydralab, to which they normally do not have access to. About each project a paper is available, describing the main results of the research.
Using MODIS estimates of fractional snow cover area to improve streamflow forecasts in interior Alaska
Remotely sensed snow cover observations provide an opportunity to improve operational snowmelt and streamflow forecasting in remote regions. This is particularly true in Alaska, where remote basins and a spatially and temporally sparse gaging network plague efforts to understand and forecast the hydrology of subarctic boreal basins and where climate change is leading to rapid shifts in basin function. In this study, the operational framework employed by the United States (US) National Weather Service, including the Alaska Pacific River Forecast Center, is adapted to integrate Moderate Resolution Imaging Spectroradiometer (MODIS) remotely sensed observations of fractional snow cover area (fSCA) to determine if these data improve streamflow forecasts in interior Alaska river basins. Two versions of MODIS fSCA are tested against a base case extent of snow cover derived by aerial depletion curves: the MODIS 10A1 (MOD10A1) and the MODIS Snow Cover Area and Grain size (MODSCAG) product over the period 2000–2010. Observed runoff is compared to simulated runoff to calibrate both iterations of the model. MODIS-forced simulations have improved snow depletion timing compared with snow telemetry sites in the basins, with discernable increases in skill for the streamflow simulations. The MODSCAG fSCA version provides moderate increases in skill but is similar to the MOD10A1 results. The basins with the largest improvement in streamflow simulations have the sparsest streamflow observations. Considering the numerous low-quality gages (discontinuous, short, or unreliable) and ungauged systems throughout the high-latitude regions of the globe, this result is valuable and indicates the utility of the MODIS fSCA data in these regions. Additionally, while improvements in predicted discharge values are subtle, the snow model better represents the physical conditions of the snowpack and therefore provides more robust simulations, which are consistent with the US NationalWeather Service’s move toward a physically based National Water Model. Physically based models may also be more capable of adapting to changing climates than statistical models corrected to past regimes. This work provides direction for both the Alaska Pacific River Forecast Center and other forecast centers across the US to implement remote-sensing observations within their operational framework, to refine the representation of snow, and to improve streamflow forecasting skill in basins with few or poor-quality observations.
A greedy algorithm for optimal sensor placement to estimate salinity in polder networks
We present a systematic approach for salinity sensor placement in a polder network, where the objective is to estimate the unmeasured salinity levels in the main polder channels. We formulate this problem as optimization of the estimated salinity levels using root mean square error (RMSE) as the “goodness of fit” measure. Starting from a hydrodynamic and salt transport model of the Lissertocht catchment (a low-lying polder in the Netherlands), we use principal component analysis (PCA) to produce a low-order PCA model of the salinity distribution in the catchment. This model captures most of the relevant salinity dynamics and is capable of reconstructing the spatial and temporal salinity variation of the catchment. Just using three principal components (explaining 93% of the variance of the dataset) for the low-order PCA model, three optimally placed sensors with a greedy algorithm make the placement robust for modeling and measurement errors. The performance of the sensor placement for salinity reconstruction is evaluated against the detailed hydrodynamic and salt transport model and is shown to be close to the global optimum found by an exhaustive search with a RMSE of 82.2 mg/L.
Experimental and numerical studies of saturation overshoot during infiltration into a dry soil
Downward infiltration of water into almost dry soil, when there is no ponding at the soil surface, often occurs in the form of fingers, with saturation overshoot at the finger tips. While this is well known, there is still uncertainty about the exact saturation pattern within fingers. We performed a series of one-dimensional water infiltration experiments into a dry soil to study the non-monotonicity of the saturation. We observed that saturation showed a non-monotonic behavior as a function of time. The overshoot was somewhat plateau shaped at relatively low flow rates but was quite sharp at higher flow rates. Two mathematical models, referred to as the extended standard (ESD) model and the interfacial area (IFA) model, were used to simulate the experimental results. Both models were based on extended forms of the Richards equation by including a dynamic capillary term. In the ESD model, standard equations for hysteresis were used. In the IFA model, the specific interfacial area was introduced to simulate hysteresis. Parameter values for both models were obtained from preliminary experiments or using empirical formulas. Only one parameter, the dynamic capillarity coefficient t, was optimized to model saturation overshoot. While the ESD model did not reproduce the form of saturation overshoot for any combination of parameter values, the IFA model could provide good agreement with the data. To our knowledge, this is the first time where a combination of the IFA model and the dynamic capillarity equation has been used to simulate a set of experiments.