Search inside publication
Including sediment in European river basin management plans : twenty years of work by SedNet
This paper describes the efforts made by SedNet (the European Sediment Network) to generate attention for the inclusion of sediment in River Basin Management Plans (RBMPs) under the European Water Framework Directive (WFD). The SedNet response to key WFD implementation events is described using the “three-streams and windows-of-opportunities model” published by John Kingdon in 1995. SedNet was initially a response to the realization that the WFD -which came into force in 2000- largely neglected sediment. For SedNet, it was clear from the beginning that the WFD objectives can be achieved only if sediment is included in RBMPs. The SedNet efforts inspired the establishment of a sediment management concept for the Elbe river basin. That concept was used as a basis for the full inclusion of sediment in the second Elbe RBMP (2015–2021). SedNet experts are currently involved in the drafting of the WFD Common Implementation Strategy (CIS) sediment document which will be completed in 2021 and that will provide guidance about how to include sediment in RBMPs. Since 2000, SedNet has persistently drawn attention to the need to include sediment in RBMPs. However, it was not until 2015 that the Elbe became the first European river basin to include sediment management fully in their RBMP. The 2021 WFD CIS sediment document and the focus on sediment in the Water Fitness Check in 2019 make it significantly more likely that the sediment will be included in the updates of WFD RBMPs in the near future.
Bank protectionstructures along the Brahmaputra-Jamuna River, a study of flow slides
The planform of the Brahmaputra-Jamuna River followed its natural path in Bangladesh until the construction of bank protection works started to save Sirajganj from bank erosion since the 1930s. Several so-called hardpoints such as groynes and revetments were constructed in the period 1980–2015 and the Jamuna Multipurpose Bridge was opened in 1998. The Brahmaputra Right Embankment and other projects had saved the western flood plain from inundation during monsoon floods. These river training works experienced severe damage by geotechnical failures, mostly flow slides. A flow slide is an underwater slope failure because of liquefaction or a breaching process in the subsoil or a combination of both. The design of most of these training works did not consider the risk of damage by flow slides. All descriptions of the observed damages show that scour phenomena in the channel close to a river training work are a cause of flow slides, besides pore water outflow. The research question was: how can the design of river training works be improved to reduce the risk of damage by flow slides? The main part of the investigation was focussed on reducing local scour holes near river training works. The most promising results are river training works with gentle bank slopes, permeable groynes, bed protections in dredged trenches with gentle side slopes, and methods to increase locally the bearing capacity of the subsoil. It is recommended to increase the knowledge of the failure mechanisms in the Brahmaputra-Jamuna River by improved monitoring in the field, the setup of a database with descriptions of all observed flow slides and the circumstances in which they occur. In addition to these recommendations, a field test facility is proposed to verify the knowledge of the failure mechanisms in that river. These activities will optimise the design of new river training structures with a very low risk of damages by flow slides and geotechnical instabilities and they will contribute to an improvement of the current design guidelines for river training structures.
Physics-based basin-scale modelling of water quantity and sediment dynamics using wflow
The wflow_sediment model was developed to address basin-scale geomorphological processes and problems. It is a distributed physics-based model that uses the results of the wflow_sbm hydrological model in order to estimate soil erosion, delivery to the river, transport and deposition. Both the hydrologic and sediment dynamics wflow models are open-source and use openly available global datasets and parameter estimation in order to limit calibration and be applicable even in data scarce environments. Terrestrial processes include splash and overland flow erosion, as well as transport over the grid using either a total flow transport capacity or a transport capacity with particle differentiation. In-stream routing and erosion/deposition processes are adapted from the semi-distributed SWAT model. The wflow_sediment model was first tested in the Rhine basin (Western Europe) at a daily resolution and on a 1 km (0.008333°) grid. Both the inland and instream parts of the model gave promising results, showing the potential of this new tool for a very diverse range of applications.
Carboxymethylcellulose as a Newtonian viscous fluid for centrifuge modelling
In geotechnical centrifuge modelling, the unification of time-scaling factors is particularly important for studies regarding coupling consolidation and dynamic phenomena, for example pile installation problems and earthquake loading. A common method to achieve this unification is the use of a substitute pore fluid, which has a viscosity which is larger than that of the prototype pore fluid (generally water). Aqueous methyl celluloses have proven very valuable for this purpose, mainly because the viscosity can be increased while the density remains relatively unaffected and the solution can be characterised as near-Newtonian. In this paper we describe the use of a low molecular weight sodium carboxymethylcellulose (designated lCMC) in 1% to 4% solutions as an alternative to methyl celluloses through physical chemical, (density, temperature dependence) and geotechnical (permeability in sand and friction angle) analyses and describe the experience with this pore fluid at the Delft Geotechnics centrifuge over the past 20 years.
Rainfall nowcasting using commercial microwave links
Accurate and timely precipitation forecasts are crucial for early warning. Rainfall nowcasting, the process of statistically extrapolating recent rainfall observations, is increasingly used for short‐term forecasting. Nowcasts are generally constructed with high‐resolution radar observations. As a proof of concept, we construct nowcasts with country‐wide rainfall maps estimated from signal level data of commercial microwave links (CMLs) for twelve summer days in the Netherlands. CML nowcasts compare well to radar rainfall nowcasts. Provided well‐calibrated CML rainfall estimates are employed, CML nowcasts can outperform unadjusted real‐time radar nowcasts for high rainfall rates, which are underestimated as compared to a reference. Care should be taken with the sensitivity of the advection field derivation to areas with low CML coverage, and the inherent measurement scale of CML data, which can be larger than the application scale. We see potential for rainfall nowcasting with CML data, for example in regions where weather radars are absent.
Morphololgical computation of a cascade system of dams using Delft3D-FM coupled with a real-time control tool
This paper presents a detailed hydraulic and morphological study of a cascade system of dams, located in Marsyangdi River in Nepal. Firstly, a severe morphological problem in one of the dams, namely Middle Marsyangdi Hydropower Project (MMHPP), was studied. We revealed one of the key reasons of the problem, which is related to the ignorance of large- and meso-scale morphological feature of the river while selecting the site. Secondly, the sedimentation process at the reservoir was replicated using a two-dimensional morphological model, namely Delft3D-Flexible Mesh (D-FM) coupled with Real-Time Control (RTC) tool to simulate reservoir gate operation. We attempted to incorporate downstream dam in the model, namely Marsyangdi Hydropower Project (MHPP), to simulate synchronized operation and its morphological impact. The effect of synchronized operation of two dams was assessed by simulating different synthetic flushing scenarios. Sensitivity of two different sediment transport formulae (Ashida-Michiue and Engelund-Hansen) on the model results was assessed as well. Given a rapid modelling exercise of such complex system using D-FM, the results can be regarded as satisfactory. They showed consistent model behaviour and observed trend despite the complexity involved in morphological modelling with synchronized operation of two dams. The study can further be improved in case more data and information are available. The model can also be applied to optimize dam operation considering morphological and ecological impacts on downstream reach.
A new geotechnical centrifuge at Deltares, Delft, the Netherlands
A new geotechnical centrifuge has been commissioned by Deltares, Delft, The Netherlands, as a replacement of the previous facility, which has expended its serviceable life. The new centrifuge is an Actidyn C72-31 beam type centrifuge, and has a 260 g-tonne capacity and a platform radius of 5.0 m. The platform can house test set-ups with dimensions up to 1.2 m × 1.2 m × 1.2 m (length × width × height). The data-acquisition system is supplied by HBM and has 40 channels with a sampling rate of up to 100 kHz. Two high speed cameras and four monitoring cameras are available for imaging. A 4-axis robotic system allows in-flight excavation and installation operations. The centrifuge is fully prepared for later installation of an earthquake simulator. Supporting facilities consist of a clay mixer and a consolidation frame. This paper details the choices made leading to this centrifuge, the specifications of the centrifuge and supporting facilities.
Proceedings of the 4th European Conference on Physical Modelling in Geotechnics - ECPMG 2020 (Lulea, Sweden / Zoom, 7-8 September 2020)
Large‑scale stochastic flood hazard analysis applied to the Po River
Reliable hazard analysis is crucial in the flood risk management of river basins. For the floodplains of large, developed rivers, flood hazard analysis often needs to account for the complex hydrology of multiple tributaries and the potential failure of dikes. Estimating this hazard using deterministic methods ignores two major aspects of large-scale risk analysis: the spatial–temporal variability of extreme events caused by tributaries, and the uncertainty of dike breach development. Innovative stochastic methods are here developed to account for these uncertainties and are applied to the Po River in Italy. The effects of using these stochastic methods are compared against deterministic equivalents, and the methods are combined to demonstrate applications for an overall stochastic hazard analysis. The results show these uncertainties can impact extreme event water levels by more than 2 m at certain channel locations, and also affect inundation and breaching patterns. The combined hazard analysis allows for probability distributions of flood hazard and dike failure to be developed, which can be used to assess future flood risk management measures.