Michael Nones

Implications of cascading effects for the EU Floods Directive

ABSTRACT The adoption of the European Floods Directive (2007/60/EC) represented a crucial improvement in the management of watercourses and coastlines. However, the beginning of a new phase of implementation requires the assessment of which emerging topics may be included in the review process. The aim of our research is to understand the existence of any legislative gaps that could limit the preparedness to cascading events and critical infrastructures breakdowns. First, we provide a review of the Floods Directive, the cascading phenomena and the vulnerability of critical infrastructures in the European legislation. Secondly, we analyse some case studies to test the present approach and to improve the work of decision makers. Our results suggest that the Floods Directive tends to focus on localized flood impacts at smaller time scale and it could be ineffective to address the cross-scale impact of cascading events. Although some of the corrective actions may not be of competence of the Directive, we argue that their inclusion could limit uncertainties in the attribution of responsibilities and the coordination among different institutional levels.

Parana River morphodynamics in the context of climate change

ABSTRACT This paper presents an analysis of the sediment dynamics that takes place at different scales within the Middle and the Lower Parana River in the La Plata Basin. The aim of this study is to provide a multi-disciplinary and multi-scale approach for the prediction of river future morphology in the context of climate change, the intended use of which is the prognosis of river morphodynamics’ long-term impact on manmade structures and activities over or near the river. The study is based on three levels of mathematical modelling, with the output of wider-scale models providing the input conditions for more specific ones. Climate models give the input ensemble, i.e. future precipitation and temperature over La Plata Basin. The semi-distributed macroscale variable infiltration capacity hydrological model simulates the flow discharge time series that are applied to an own-developed 1D morphodynamic model. The 1D model simulates future rate of sediment transport and corresponding bed-level changes at watershed scale and provides the boundary conditions for a 2D model. Therefore, streamflow divagations at channel scale are simulated by means of the MIKE21C code developed by the Danish Hydraulic Institute. The analysis indicates a rather low sensitivity of the Parana River bed profile, i.e. 1D morphology, to the increase predicted in flow discharge, whereas the streamflow appreciably divagates. In particular, surpassing an upper bound in the most frequent discharge appears effective in driving the actual bifurcated morphology into a meandering-multithread configuration.

Modelling the impact of large impoundments on the Lower Zambezi River

The Lower Zambezi River is influenced by the presence of two very large hydropower impoundments which have modified the natural seasonal flows, the sediment balance, the morphology of the river and the pattern of the riparian vegetation. Downstream of these large impoundments, appreciable local effects are reported to take place, such as scour, bank collapse and shoreline degradation. In order to quantify the sediment transport along the Lower Zambezi River and to predict the effects of the dams on morphology we have developed a simplified 1-D hydro-morphodynamic model capable to deal with the scarcity of available data. Besides the systematic flow records at the dam gauging station and few occasional measurements of turbidity and grain size of the river bed, only the Digital Elevation Model (DEM) and some recent satellite images of the river have been used as the input data of the model. The results confirm the expected qualitative response of the river to the constructions of dams: the reduction of water flow has an immediate effect downstream of the reservoirs by initially fostering the sediment deposition; afterwards, the total interception of sediment by the dams slowly takes over and inverts this tendency; a smaller aggradation rate with respect to the natural conditions without dams, seems to represent the dominant effect of damming in the long-term evolution of the river. The morphological effects of damming over the transversal cross-section of the river have been studied by a simplified transversal quasi 2-D sub-model, coupled to a 1-D longitudinal model. Besides the evolution of the bottom longitudinal profile and grain size composition, the model simulates also the evolution of the cross-section shape and the growth of the riparian vegetation. A first application confirms the qualitative observations reported in the literature on the recent planimetric evolution of the Lower Zambezi.

Modeling of River Width Variations Based on Hydrological, Morphological, and Biological Dynamics

AbstractOne-dimensional (1D) models can be applied, for engineering purposes, to long-term and large-scale morphodynamic simulations of entire river systems only if appropriate simplifications are introduced. This paper proposes an improvement of an existing simplified 1D model based on the local uniform flow hypothesis, coupled with a synthetic description of the transverse profile, which provides the active river width by analyzing the total and the vegetated widths of a watercourse, with assumed variables of the water flow. The overall density of the riparian vegetation, expressed in terms of biological carrying capacity, is predicted as a function of the local climate and some stresses due to interaction between hydrology, morphology, and biology. The constitutive equations have been deduced and the relevant parameters have been calibrated and validated against various hydrological and geometrical data, taken by satellite imagery covering two large watercourses located in tropical and subtropical area...

Po River Morphodynamics Modelled with the Open-source Code iRIC

The paper presents the numerical modelling of the hydro-morphological evolution of a 10 km reach of the Po River in Italy. The simulation is performed with the freeware code iRIC, recently developed by an international community of scientists and practitioners. Starting from a non-detailed description of the studied area and using synthetic data, the reach has been modelled adopting a 2-D solver. Based on a Digital Elevation Model of the area, the domain is discretized by an unstructured grid with triangular meshes. First results show a promising capability of the model in reproducing the behaviour of the reach, both in terms of liquid flow and morphodynamics, if compared with historical data measured along the watercourse and reported in literature. In the future, additional simulations will be performed, enlarging the studied area and using detailed input data measured with traditional and innovative techniques.

Is Equilibrium Modelling Outdated for Recent Challenges in River Management

To date, several different approaches are available to study sediment dynamics at reach 10 or watershed scale, based on very different hypothesis. One of such assumptions, the so-called 11 “morphodynamic equilibrium hypothesis” is becoming little unpopular for its embedded 12 simplifications. The aim of this work is to demonstrate how this approach proves yet effective in 13 modelling landscape morphodynamics at the watershed scale, for what concerns the longitudinal 14 profile of a river and the sedimentary aspects. The application of a 1-D model based on the 15 equilibrium hypothesis has been implemented for several large rivers worldwide. 16 Geomorphological parameters have been analysed, which describe the evolution of longitudinal 17 profile (concavity) and sediments characteristics (aggrading and fining), and the results show a 18 reasonably good correspondence with qualitative estimation of the same parameters. At the scale of 19 analysis and for the chosen systems, which show high inertia to geomorphological changes likely 20 owing to their longitudinal extension, the model can detect where the present conditions reflect a 21 big disturbance to the “natural equilibrium” thus allowing water managers to identify present 22 issues to be addressed. 23

Vulnerability, impacts and assessment of climate change on Jakarta and Venice

ABSTRACT In the next future, cities located in coastal areas are likely to suffer for climatic changes more than all other human systems. The demographic growth, combined with sea-level rise and global warming related to natural causes and anthropogenic activities, endanger those systems. Thence, to effectually cope with new climate forcing, coastal cities need improvements to be sustainable, resilient and liveable, applying flexible design approaches rather than a traditional one. The paper highlights such concepts presenting two case studies of important coastal cities: Venice, in Northern Italy, and Jakarta, the capital city of Indonesia. Although characterized by completely different climatic conditions and living habits, these two metropolises are highly impacted by humans and threatened by similar factors like subsidence and sea-level rise, which increase their exposure to future calamities principally driven by climate change but strictly related to anthropic pressures. The present situation shows that, for the future, the resilience of coastal megalopolis can be increased only using a mix of approaches at various levels, spanning from technical measures to adaptable planning instruments that consider future uncertainties.