Flood risk analysis for the river Scheldt estuary

This report gives an overview of the history of flood risk management along the Scheldt estuary. Thepurpose of this overview is twofold. It documents the results obtained in the first activity of the Task25 Pilot, being focused on flood risk analysis, both in historical perspective and with regard to currentpolicies. Secondly, it provides an introduction to the Scheldt estuary for other partners in theFLOODsite project which will use the Scheldt Pilot for their own tasks and activities.The Scheldt estuary is a clear example where integrated water management is required. Integratedmeans in this case: meeting the objectives for 3 major basic functions and values of the estuary: safety,accessibility (navigation) and ecology. Recently finalised and ongoing projects, such as Proses and theSIGMA plan show a highly multidisciplinary approach in order to fulfil these objectives.From the perspective of flood risk management we see a significant difference in approach betweenBelgium and the Netherlands. The Belgian New Sigma Plan has used an approach that is strikinglysimilar to the FLOODsite methodology, i.e. going through the three phases Risk Analysis, RiskAssessment and Flood Management Strategy formulation. In contrast, the Dutch flood riskmanagement was developed over a long historical period, with the Delta Plan as the final apotheosis.In the time the Delta Plan was formulated, there was hardly any attention and technology available todetermine flood probability and flood damage

Adaptation of river channels to a wetter or drier climate: Insights from the Lower Pilcomayo River, South America

Climate change has a direct influence on both hydrology and floodplain vegetation of water courses, which are key players in river morphodynamics. The river system response to climate change is complex and the effects of non-linear interactions between alterations in water, sediment and vegetation remain incompletely understood. Which of these components becomes dominant in shaping the river channel when climate becomes drier or wetter? To answer this question, we investigate the cross-sectional response of sand-bed rivers to climate change focusing on channel width and depth, which respond directly to changes in boundary stresses. Thanks to the exceptional availability of long time-series of daily discharge and cross-sectional profiles, the Pilcomayo River is an ideal living lab for this investigation. We constructed a two-dimensional model of the river using the open-source state-of-the-art, structured Delft3D code. The highly dynamic behaviour and quick morphological adaptation of the Pilcomayo allowed reducing the period of time covered by the simulations because the river cross-section adapts its morphology to a new value of the water discharge within hours or days, which is crucial for modelling investigations. Calibration and validation were successfully performed by comparison with historical data. We considered several scenarios representing current, dryer and wetter climates. The results show that a dryer climate reduces the river channel depth and enlarges the width. A wetter climate increases the channel depth but produces negligible widening. Vegetation, sparser with a drier climate and denser with a wetter climate, is found to control the channel width. This analysis is unique and shows which alterations can be expected in alluvial sand-bed rivers with natural vegetated banks due to climate change

Bank erosion processes measured with UAV-SfM along complex banklines of a straight mid-sized river reach

We apply structure from motion (SfM) photogrammetry with imagery from an unmanned aerial vehicle (UAV) to measure bank erosion processes along a mid-sized river reach. This technique offers a unique set of characteristics compared to previously used methods to monitor banks, such as high resolution and relatively fast deployment in the field. We analyse the retreat of a 1.2&thinsp;km restored bank of the Meuse River which has complex vertical scarps laying on a straight reach, features that present specific challenges to the UAV-SfM application. We surveyed eight times within a year with a simple approach, combining different photograph perspectives and overlaps to identify an effective UAV flight. The accuracy of the digital surface models (DSMs) was evaluated with real-time kinematic (RTK) GPS points and airborne laser scanning of the whole reach. An oblique perspective with eight photo overlaps and 20&thinsp;m of cross-sectional ground-control point distribution was sufficient to achieve the relative precision to observation distance of  ∼ 1&thinsp;:&thinsp;1400 and 3&thinsp;cm root mean square error (RMSE), complying with the required accuracy. A complementary nadiral view increased coverage behind bank toe vegetation. Sequential DSMs captured signatures of the erosion cycle such as mass failures, slump-block deposition, and bank undermining. Although UAV-SfM requires low water levels and banks without dense vegetation as many other techniques, it is a fast-in-the-field alternative to survey reach-scale riverbanks in sufficient resolution and accuracy to quantify bank retreat and identify morphological features of the bank failure and erosion processes. Improvements to the adopted approach are recommended to achieve higher accuracies.</p

Long-duration laboratory experiment of slow development of steady alternate bars

River morphodynamics and sediment transportRiver morphology and morphodynamic

Effects of sediment flushing operations versus natural floods on Chinook salmon survival

Flushing is a common measure to manage and reduce the amount of sediment stored in reservoirs. However, the sudden release of large volumes of sediment abruptly increases the suspended solids concentration and alters the riverbed composition. Similar effects can be produced also by natural flood events. Do flushing operations have more detrimental impacts than natural floods? To answer this question, we investigated the impact of flushing on the survival of the Chinook salmon ($\textit{Oncorhynchus tshawytscha}$) in the Sandy River (OR, USA), assuming that sediment is flushed from hypothetical bottom gates of the, now decommissioned, Marmot Dam. The effects of several flushing scenarios are analyzed with a 2D morphodynamic model, together with habitat suitability curves and stress indicators. The results show that attention has to be paid to duration: the shorter the flushing operation, the lesser the stresses on fish survival and spawning habitats. Flushing causes high stress to salmon eggs and larvae, due to unbearable levels of suspended sediment concentrations. It also decreases the areas usable for spawning due to fine-sediment deposition, with up to 95% loss at peak flow. Without the dam, the corresponding natural flood event would produce similar effects, with up to 93% loss. The study shows that well-planned flushing operations could mimic a natural impact, but only partly. In the long-term, larger losses of spawning grounds can be expected, since the removal of fine sediment with the release of clear water from the reservoir is a lengthy process that may be undesirable due to water storage reduction

Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

Large‐scale morphology, in particular meander bend depth, bar dimensions, and bifurcation dynamics, are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows. Overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology, while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream. However, existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes, and in practice models are calibrated on measured morphology. The objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near‐bed flow conditions with varying secondary flow intensity, sediment sizes (0.17–4 mm), sediment transport mode, and bed state to test existing predictors. We conducted over 200 experiments in a rotating annular flume with counterrotating floor, which allows control of the secondary flow intensity separate from the streamwise flow velocity. Flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions. We isolated separate effects of all important parameters on the transverse slope. Resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on Shields number, and strongly depend on bed state and sediment transport mode. Fitted functions are provided for application in morphodynamic modelin

Limits to scale invariance in alluvial rivers

Assumptions about fluvial processes and process–form relations are made in general models and in many site‐specific applications. Many standard assumptions about reach‐scale flow resistance, bed‐material entrainment thresholds and transport rates, and downstream hydraulic geometry involve one or other of two types of scale invariance: a parameter (e.g. critical Shields number) has the same value in all rivers, or doubling one variable causes a fixed proportional change in another variable in all circumstances (e.g. power‐law hydraulic geometry). However, rivers vary greatly in size, gradient, and bed material, and many geomorphologists regard particular types of river as distinctive. This review examines the tension between universal scaling assumptions and perceived distinctions between different types of river. It identifies limits to scale invariance and departures from simple scaling, and illustrates them using large data sets spanning a wide range of conditions. Scaling considerations and data analysis support the commonly made distinction between coarse‐bed and fine‐bed reaches, whose different transport regimes can be traced to the different settling‐velocity scalings for coarse and fine grains. They also help identify two end‐member sub‐types: steep shallow coarse‐bed ‘torrents’ with distinctive flow‐resistance scaling and increased entrainment threshold, and very large, low‐gradient ‘mega rivers’ with predominantly suspended load, subdued secondary circulation, and extensive backwater conditions

Social and dental status along the life course and oral health impacts in adolescents: a population-based birth cohort

<p>Abstract</p> <p>Background</p> <p>Harmful social conditions in early life might predispose individuals to dental status which in turn may impact on adolescents' quality of life.</p> <p>Aims</p> <p>To estimate the prevalence of oral health impacts among 12 yr-old Brazilian adolescents (<it>n </it>= 359) and its association with life course socioeconomic variables, dental status and dental services utilization in a population-based birth cohort in Southern Brazil.</p> <p>Methods</p> <p>Exploratory variables were collected at birth, at 6 and 12 yr of age. The Oral Impacts on Daily Performances index (OIDP) was collected in adolescence and it was analyzed as a ranked outcome (OIDP from 0 to 9). Unadjusted and adjusted multivariable Poisson regression with robust variance was performed guided by a theoretical determination model.</p> <p>Results</p> <p>The response rate was of 94.4% (<it>n </it>= 339). The prevalence of OIDP = 1 was 30.1% (CI95%25.2;35.0) and OIDP ≥ 2 was 28.0% (CI95%23.2;32.8). The most common daily activity affected was eating (44.8%), follow by cleaning the mouth and smiling (15.6%, and 15.0%, respectively). In the final model mother schooling and mother employment status in early cohort participant's life were associated with OIDP in adolescence. As higher untreated dental caries at age 6 and 12 years, and the presence of dental pain, gingival bleeding and incisal crowing in adolescence as higher the OIDP score. On the other hand, dental fluorosis was associated with low OIDP score.</p> <p>Conclusion</p> <p>Our findings highlight the importance of adolescent's early life social environmental as mother schooling and mother employment status and the early and later dental status on the adolescent's quality of life regardless family income and use of dental services.</p

The prediction of floods in Venice: methods, models and uncertainty (review article)

This paper reviews the state of the art in storm surge forecasting and its particular application in the northern Adriatic Sea. The city of Venice already depends on operational storm surge forecasting systems to warn the population and economy of imminent flood threats, as well as help to protect the extensive cultural heritage. This will be more important in the future, with the new mobile barriers called MOSE (MOdulo Sperimentale Elettromeccanico, Experimental Electromechanical Module) that will be completed by 2021. The barriers will depend on accurate storm surge forecasting to control their operation. In this paper, the physics behind the flooding of Venice is discussed, and the state of the art of storm surge forecasting in Europe is reviewed. The challenges for the surge forecasting systems are analyzed, especially in view of uncertainty. This includes consideration of selected historic extreme events that were particularly difficult to forecast. Four potential improvements are identified: (1) improve meteorological forecasts, (2) develop ensemble forecasting, (3) assimilation of water level measurements and (4) develop a multimodel approach