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Comparative Assessment of Drought Hazard and Risk Modeling Tools
The main purpose of this report is an evaluation of available drought hazard and risk modeling tools and other resources that are available at the global scale for their suitability to be applied for drought hazard mapping and hotspot identification, drought risk assessments and drought detection and forecasting. This report describes a quantitative and qualitative comparative assessment of a selection of drought hazard and risk modeling tools and resources that are available from the global drought inventory as developed by the GFDRR (Deltares, 2018). Not all modeling tools and resources collected in the global drought inventory were taken up in these analyses. Only modeling tools and resources that are available online, free of cost, and have global coverage were assessed. The reason for these selection criteria is that the results of this study should be applicable for all users in all countries of the world. However, for the review and qualitative comparison of drought monitoring and forecasting systems, regional and national systems were also assessed.
Redressing the balance : quantifying net intercatchment groundwater flows
Intercatchment groundwater flows (IGFs), defined as groundwater flows across topographic divides, can occur as regional groundwater flows that bypass headwater streams and only drain into the channel further downstream or directly to the sea. However, groundwater flows can also be diverted to adjacent river basins due to geological features (e.g., faults, dipping beds and highly permeable conduits). Even though intercatchment groundwater flows can be a significant part of the water balance, they are often not considered in hydrological studies. Yet, assuming this process to be negligible may introduce misrepresentation of the natural system in hydrological models, for example in regions with complex geological features. The presence of limestone formations in France and Belgium potentially further exacerbates the importance of intercatchment groundwater flows, and thus brings into question the validity of neglecting intercatchment groundwater flows in the Meuse basin. To isolate and quantify the potential relevance of net intercatchment groundwater flows in this study, we propose a three-step approach that relies on the comparison and analysis of (1) observed water balance data within the Budyko framework, (2) results from a suite of different conceptual hydrological models and (3) remote-sensing-based estimates of actual evaporation. The data of 58 catchments in the Meuse basin provide evidence of the likely presence of significant net intercatchment groundwater flows occurring mainly in small headwater catchments underlain by fractured aquifers. The data suggest that the relative importance of net intercatchment groundwater flows is reduced at the scale of the Meuse basin, as regional groundwater flows are mostly expected to be self-contained in large basins. The analysis further suggests that net intercatchment groundwater flow processes vary over the year and that at the scale of the headwaters, net intercatchment groundwater flows can make up a relatively large proportion of the water balance (on average 10% of mean annual precipitation) and should be accounted for to prevent overestimating actual evaporation rates.
The design guideline basal reinforced piled embankments ; The Dutch CUR226:2016 and the German EBGEO:2010 ; A comparison of design models and safety approaches
The Dutch Design for geosynthetic-reinforced pile-supported embankments had a major revise before publishing its second version in 2016 (CUR226, Van Eekelen and Brugman, 2016). This paper compares this new design guideline and the German design guideline EBGEO 2010. The following is compared: (1) the design models that calculate the tensile force in the geosynthetic reinforcement (GR), without using partial factors, and (2) the safety approaches, while using the same GR design model. CUR226 uses the Concentric Arches model for the design the geosynthetic reinforcement, which is a modification and extension of EBGEO’s model. It is concluded that the EBGEO model calculates on average 2.5 times the GR strain measured in many projects, while the CUR226 model calculates on average 1.1 times that measured strain: a nearly perfect fit. CUR226 uses partial safety factors for load and material parameters that were determined using a probabilistic study. EBGEO uses partial factors on load effect and GR resistance. It is concluded that the most strict reliability class of EBGEO, Lastfall 1, equals or exceeds the least strict reliability class of CUR226 (RC1, applied for roads) for most geometries that are applied frequently, as long as the subgrade reaction is less than 100 kN/m3, for the considered cases. However, Lastfall 1 is in most cases less safe than the most strict reliability class of CUR226: RC3, which is applied for railways.
Effects of water level variations on the stability of rock armoured slopes
Physical model tests on the stability of rock armoured slopes have been performed to demonstrate the importance of water level variations during a storm, due to a tide or a storm surge. For the stability of rock armoured slopes also the importance of the sequence of storms at various water levels has been studied. The test results indicate that a smooth sinusoidal water level variation leads to an increase in damage compared to the same wave conditions at a constant water level. Furthermore, a stepwise approach of the sinusoidal water level elevation leads to other results than the approach with a continuous water level variation, whereas the continuous water level variation resembles the peak of a storm or the tidal water level variation better than a stepwise approach. If storms with different water levels attack the armour layer, the damage is generally smaller than if all storms attack the armour layer at the same water level. Furthermore, the results have been discussed based on earlier analyses where the statistics of rock armoured slopes have been addressed and the importance of the length effect has been illustrated using a method to apply results from physical model tests to real structures.
ICCE 2018 : proceedings of the 36th International Conference on Coastal Engineering (Baltimore, Maryland, July 30 - August 3, 2018)
ICG 2018 - Proceedings of the 11th International Conference on Geosynthetics (Seoul, Korea, 16-21 September 2018) : geosynthetics, innovative solutions for sustainable development
Beneficial use of dredged sediment to enhance salt marsh development by applying a ‘Mud Motor’
We test an innovative approach to beneficially re-use dredged sediment to enhance salt marsh development. A Mud Motor is a dredged sediment disposal in the form of a semi-continuous source of mud in a shallow tidal channel allowing natural processes to disperse the sediment to nearby mudflats and salt marshes. We describe the various steps in the design of a Mud Motor pilot: numerical simulations with a sediment transport model to explore suitable disposal locations, a tracer experiment to measure the transport fate of disposed mud, assessment of the legal requirements, and detailing the planning and technical feasibility. An extensive monitoring and research programme was designed to measure sediment transport rates and the response of intertidal mudflats and salt marshes to an increased sediment load. Measurements include the sediment transport in the tidal channel and on the shallow mudflats, the vertical accretion of intertidal mudflats and salt marsh, and the salt marsh vegetation cover and composition. In the Mud Motor pilot a total of 470,516m3 of fine grained sediment (D50 of ∼10 μm) was disposed over two winter seasons, with an average of 22 sediment disposals per week of operation. Ship-based measurements revealed a periodic vertical salinity stratification that is inverted compared to a classical estuary and that is working against the asymmetric flood-dominated transport direction. Field measurements on the intertidal mudflats showed that the functioning of the Mud Motor, i.e. the successful increased mud transport toward the salt marsh, is significantly dependent on wind and wave forcing. Accretion measurements showed relatively large changes in surface elevation due to deposition and erosion of layers of watery mud with a thickness of up to 10 cm on a time scale of days. The measurements indicate notably higher sediment dynamics during periods of Mud Motor disposal. The salt marsh demonstrated significant vertical accretion though this has not yet led to horizontal expansion because there was more hydrodynamic stress than foreseen. In carrying out the pilot we learned that the feasibility of a Mud Motor depends on an assessment of additional travel time for the dredger, the effectiveness on salt marsh growth, reduced dredging volumes in a port, and many other practical issues. Our improved understanding on the transport processes in the channel and on the mudflats and salt marsh yields design lessons and guiding principles for future applications of sediment management in salt marsh development that include a Mud Motor approach.
Protecting and restoring Europe's waters : an analysis of the future development needs of the Water Framework Directive
The Water Framework Directive (WFD) is a pioneering piece of legislation that aims to protect and enhance aquatic ecosystems and promote sustainable water use across Europe. There is growing concern that the objective of good status, or higher, in all EU waters by 2027 is a long way from being achieved in many countries. Through questionnaire analysis of almost 100 experts, we provide recommendations to enhance WFD monitoring and assessment systems, improve programmes of measures and further integratewith other sectoral policies. Our analysis highlights that there is great potential to enhance assessment schemes through strategic design of monitoring networks and innovation, such as earth observation. New diagnostic tools that use existing WFD monitoring data, but incorporate novel statistical and trait-based approaches could be used more widely to diagnose the cause of deterioration under conditions of multiple pressures and deliver a hierarchy of solutions for more evidence-driven decisions in river basin management. There is also a growing recognition that measures undertaken in river basin management should deliver multiple benefits across sectors, such as reduced flood risk, and there needs to be robust demonstration studies that evaluate these. Continued efforts in ‘mainstreaming’ water policy into other policy sectors is clearly needed to deliver wider success with WFD goals, particularly with agricultural policy. Other key policy areas where a need for stronger integration with water policywas recognised included urban planning (wastewater treatment), flooding, climate and energy (hydropower). Having a deadline for attaining the policy objective of good status is important, but even more essential is to have a permanent framework for river basin management that addresses the delays in implementation of measures. This requires a long-term perspective, far beyond the current deadline of 2027.
Recent insights on uncertainties present in integrated catchment water quality modelling
This paper aims to stimulate discussion based on the experiences derived from the QUICS project (Quantifying Uncertainty in Integrated Catchment Studies). First it briefly discusses the current state of knowledge on uncertainties in sub-models of integrated catchment models and the existing frameworks for analysing uncertainty. Furthermore, it compares the relative approaches of both building and calibrating fully integrated models or linking separate sub-models. It also discusses the implications of model linkage on overall uncertainty and how to define an acceptable level of model complexity. This discussion includes, whether we should shift our attention from uncertainties due to linkage, when using linked models, to uncertainties in model structure by necessary simplification or by using more parameters. This discussion attempts to address the question as to whether there is an increase in uncertainty by linking these models or if a compensation effect could take place and that overall uncertainty in key water quality parameters actually decreases. Finally, challenges in the application of uncertainty analysis in integrated catchment water quality modelling, as encountered in this project, are discussed and recommendations for future research areas are highlighted.
Estimating characteristic times of regional groundwater systems along the global coastline with regard to past sea level fluctuations and sediment accumulation patterns
The rising demand for freshwater in highly populated coastal areas combined with sea level rise, extreme weather conditions such as longer drought periods and more frequent storm events could potentially lead to humanitarian crises. To mitigate the risk of the latter while increasing the resilience of coastal communities, it is important to know the current distribution of fresh and saline groundwater in different coastal regions worldwide.