Flood Risk Management

A correction for balancing discontinuous bed slopes in two-dimensional smoothed particle hydrodynamics shallow water modeling

by renato vacondio

R. Vacondio, B.D. Rogers, P.K. Stansby, P. Mignosa

In this paper, a smoothed particle hydrodynamics (SPH) numerical model for the shallow water equations (SWEs) with bed... more In this paper, a smoothed particle hydrodynamics (SPH) numerical model for the shallow water equations (SWEs) with bed slope source term balancing is presented. The solution of the SWEs using SPH is attractive being a conservative, mesh-free, automatically adaptive method without special treatment for wet-dry interfaces. Recently, the capability of the SPH–SWEs numerical scheme with shock capturing and general boundary conditions has been used for predicting practical flooding problems. The balance between the bed slope source term and fluxes in shallow water models is desirable for reliable simulations of flooding over bathymetries where discontinuities are present and has received some attention in the framework of Finite Volume Eulerian models. The imbalance because of the source term resulting from the calculation of the the water depth is eradicated by means of a corrected mass, which is able to remove the error introduced by a bottom discontinuity. Two different discretizations of the momentum equation are presented herein: the first one is based on the variational formulation of the SWEs in order to obtain a fully conservative formulation, whereas the second one is obtained using a non-conservative form of the free-surface elevation gradient. In both formulations, a variable smoothing length is considered. Results are presented demonstrating the corrections preserve still water in the vicinity of either 1D or 2D bed discontinuities and provide close agreement with 1D analytical solutions for rapidly varying flows over step changes in the bed. The method is finally applied to 2D dam break flow over a square obstacle where the balanced formulation improves the agreement with experimental measurements of the free surface

KONYA HAVZASI AKARSULARI YILLIK PİK AKIM SERİLERİNİN TAŞKIN FREKANS ANALİZİ

by Ercan Kahya

Sustainable Solutions for Global Crisis of Flooding, Pollution and Water Scarcity

by Aminuddin Ab Ghani

Lau, T.L. & Ab. Ghani, A. (2012). Sustainable Solutions for Global Crisis of Flooding, Pollution and Water Scarcity, International Journal of River Basin Management, IAHR., Vol. 10, No. 2, pp. 137-138, ISSN 1571-5124

A Cloud-based Virtual Observatory for Environmental Science

by Yehia El-khatib

Analysis of flash flood regimes in the North-Western and South-Eastern Mediterranean regions

by Paolo Tarolli

Published in Natural Hazards and Earth System Sciences, 2012. Co-authored with Marco Borga, Efrat Morin, Guy Delrieu.

This work analyses the prominent characteristics of flash flood regimes in two Mediterranean areas: the North-Western... more This work analyses the prominent characteristics of flash flood regimes in two Mediterranean areas: the North-Western Mediterranean region, which includes Catalonia, France and Northern Italy, and the South-Eastern Mediterranean region, which includes Israel. The two regions are characterized by similarities in the hydro-meteorological monitoring infrastructure, which permits us to ensure homogeneity in the data collection procedures. The analysis is articulated into two parts. The first part is based on use of flood peak data, catchment area and occurrence date for 99 events (69 from the North-Western region and 30 from the South-Eastern region). Analysis is carried out in terms of relationship of flood peaks with catchment area and seasonality. Results show that the envelope curve for the South-Eastern region exhibits a more pronounced decreasing with catchment size with respect to the curve of the North-Western region. The differences between the two relationships reflect changes in the effects of storm coverage and hydrological characteristics between the two regions. Seasonality analysis shows that the events in the North-Western region tend to occur between August and November, whereas those in the South-Eastern area tend to occur in the period between October and May, reflecting the relevant patterns in the synoptic conditions leading to the intense precipitation events. In the second part, the focus is on the rainfall-runoff relationships for 13 selected major flash flood events (8 from the North-Western area and 5 from the South-Eastern area) for which rainfall and runoff properties are available. These flash floods are characterised in terms of climatic features of the impacted catchments, duration and amount of the generating rainfall, and runoff ratio. Results show that the rainfall duration is shorter and the rainfall depth lower in the South-Eastern region. The runoff ratios are rather low in both regions, whereas they are more variable in the South-Eastern area. No clear relationship between runoff ratio and rainfall depth is observed in the sample of floods, showing the major influence of rainfall intensity and the initial wetness condition in the runoff generation for these events.

PORTER and DEMERITT (2012) Flood risk management mapping and planning - the institutional politics of decision-support in England

by James Porter

Impact of relief accuracy on flood simulations and road network vulnerability analysis

by Frederic Rousseaux

Jean-François Gleyze Institut Géographique National Service de la Recherche, laboratoire COGIT, Frédéric Rousseaux, UMR LIENSS, Institut du littoral et de l'environnement

The increased availability and accuracy of multi-sources data enhance the simulation quality of natural disasters... more The increased availability and accuracy of multi-sources data enhance the simulation quality of natural disasters (hazard). Moreover, it enables a better prediction of their impact on the territory (vulnerability). Numerical representation of relief (DTM) is a prime necessity in risk simulation, in particular in flood study. Integrating 2D objects into a DTM significantly improves the relief representation around each object. The aim of this paper is first to enrich the relief accuracy with the altimetric attributes of 2D vector objects, and then to assess the impact of these modifications within the context of a rise in the water level and its consequences on the road network vulnerability.
The first part focuses on the integration of 2D vector data (e.g. roads) on a 2.5D digital terrain model. The integration of 2D vector data on a DTM usually raises data consistance issues. These data often stem from different acquisition modes ; moreover, their scale and their dimension (2D, 2.5D, 3D) vary according to their nature and the data capture. In order to overcome these problems, our approach consists in converting 2D vector data in 2.5D vector data by assigning them a width and computing their elevation. Then, these latter are integrated into the DTM and make it sharper, especially on the former interpolated areas.
In a second part, we analyze the floods effects on the running of the road network in Orléans (France). In addition to the direct damages caused by the physical action of the water, the flood also leads to functional disruptions on the road network by forcing users to take detours. In a risk preventive viewpoint, the network administrator has first to consider a given flood scenario and consequently to identify the network components to be protected as a priority, in order to reduce to the minimum the costs induced by the detours. On account of both levels of precision considered in the original DTM and in the enriched DTM, we have to compare two damaging scenarios of the road network for a given flood hazard. To that end, we quantify the functionality of the network components with centrality measures and we compare the efficiency of the different configurations of damaged network with accessibility measures. The results of this study prove how much the flood of the road network, the induced functional disruptions and the associated preventive actions depend on the adopted precision in the representation of the terrain.

Porter (2009) Lost in Translation - managing the 'risk' of flooding - the story of consistency and flood risk mapping

by James Porter

Porter (2010) The Extreme Flood Outline - Co-Producing Flood Risk Mapping and Spatial Planning in England (PhD Thesis)

by James Porter

River Engineering Assignment

by Nuttavikhom Phanthuwongpakdee

Floods in Greece, a statistical and spatial approach

by Michalis Diakakis

A method for flood hazard mapping based on basin morphometry: application in two catchments in Greece A method for flood hazard mapping based on …

by Michalis Diakakis

A method for flood hazard mapping based on basin morphometry: application in two catchments in Greece A method for flood hazard mapping based on …

by Michalis Diakakis

Effects on flood hazard in Marathon plain from the 2009 wildfire in Attica, Greece

by Michalis Diakakis

Flash flood event of Potamoula, Greece: Hydrology, geomorphic effects and damage characteristics

by Michalis Diakakis

A GIS method for rapid flood hazard assessment in ungauded basins using the ArcHydro model and the Time-Area method

by Michalis Diakakis

Mathematical modelling of tidal currents in mangrove forests

by Roger Falconer - Cardiff University

Paper 56:  Wu, Y., Falconer, R. A. and Struve, J. 2001. Mathematical modelling of tidal currents in mangrove forests. Environmental Modelling and Software. 16(1), 19-29.

Abstract
The effects of mangrove forests on the flow structure in estuaries have been studied in this paper. An... more Abstract
The effects of mangrove forests on the flow structure in estuaries have been studied in this paper. An existing two-dimensional depth-integrated mathematical model has been refined to include both the effects of drag force induced by mangrove trees and the blockage effects on the mass fluxes through mangrove forests. To investigate the influence of mangrove trees on the flow structure two idealised cases have been considered. These include: (i) steady channel flow, with mangrove trees distributed within the middle reach of the channel along both sides, and (ii) tidal flow in a straight creek, fringed by mangrove swamps. Comparisons of velocity profiles at a cross-section for the case of steady channel flow, and of the time series of velocities in both the creek and its floodplain for the case of tidal flow in the straight creek–mangrove swamp system, have been undertaken. Six cases of different diameters and densities of mangrove trees have been studied to examine the significance of the drag force and blockage on the flow structure in the mangrove swamp system. It was found that mangrove trees have a significant impact on the flow structure in a mangrove system. The drag force induced by the mangrove trees plays a key role, and the blockage from the mangrove trees also plays an important role when the porosity of the mangrove trees is less than 0.8. The model has also been applied to simulate tidal flows in the Merbok Estuary, Malaysia. Simulations have been undertaken, both with and without mangrove tree effects, as well as for an extreme case of complete removal of mangrove areas from flooding, termed ‘complete bunding’, to study the effects of the mangrove trees on the hydrodynamic processes in the basin. The results show that the model provides an ideal management tool for mangrove systems.

Improvement of rice cultivation and water management in the flooded area of the Central Plain of Thailand: a zoning of rice systems by using remote …

by Francois Molle

Modelling flash flood risk in urban areas

by Roger Falconer - Cardiff University

Paper 133: Xia, J., Falconer, R. A., Lin, B. and Tan, G. 2011. Modelling flash flood risk in urban areas. Proceedings of the Institution of Civil Engineers, Water Management. 164(6), 267-282.

Abstract
In urban areas the impacts of flash floods can be very high due to these regions being generally... more Abstract
In urban areas the impacts of flash floods can be very high due to these regions being generally densely populated and containing vital infrastructure. Parts of the UK have been particularly prone to such serious urban flooding in recent years, such as the 2004 Boscastle flood. Due to climate change the occurrence of urban flooding is predicted to increase in the future, which is likely to lead to increasing flood risk to people and property in urban areas. Therefore, it is appropriate to estimate the potential flood risk to people and property for improved flood risk management. In the current study, an integrated numerical model for estimating the flood risk in urban areas is outlined herein, including the module for predicting the 2D hydrodynamic characteristics of urban floods, together with a new module for predicting the flood risk to people (including children and adults) and property (including vehicles and buildings). The hydrodynamic module of this model was then verified against laboratory experimental data and real flood tracks in urban areas. Finally, the integrated model was applied to predict the flood risk to people and property for the Boscastle floods, with different reoccurrence frequencies. The predicted results for different flood scenarios indicated that: (i) people would be swept away in the majority of the flooded area for a flood with P = 1% (a return period of 100 years) , while they would be in danger almost in all the flooded area for a high flood, with P = 0.25% (a return period of 400 years) or 0.1% (a return period of 1000 years); (ii) vehicles would be washed away from the parking area in the centre of a car park during a flood with P = 1%, while they would also be flushed on the main road and main street, and in the car park during a flood with P = 0.25 or 0.1% ; and (iii) there would be no damage to buildings during a flood with P = 1%, but severe damage to buildings would be likely to occur during high floods. Therefore, the developed integrated model can be used to predict the potential flood risk to people and property in urban areas, and these predictions can be used for improved flood risk management.

Sungai Pahang Digital Flood Mapping: 2007 Flood

by Aminuddin Ab Ghani

Ab. Ghani, A., Chang, C.K., Leow, C.S. & Zakaria, N.A. (2012). Sungai Pahang Digital Flood Mapping: 2007 Flood , International Journal of River Basin Management, Vol. 10 No. 2

In this study, visits to areas in the subcatchments of Sungai Pahang, including Mentakab, Temerloh, Maran and Pekan,... more In this study, visits to areas in the subcatchments of Sungai Pahang, including Mentakab, Temerloh, Maran and Pekan, were made throughout the year 2009 to obtain information regarding inundation areas, flood depth, flow discharge and water levels relevant to the 2007 flood. Interviews with local people were also made to ascertain the true picture of the 2007 flood. Analyses of rainfall data, water level, flow discharge and river cross-sectional
changes were carried out from data gathering. The development of a digital elevation model (DEM) was made from a combination of digital topographical maps and satellite images which were purchased from Jabatan Ukur dan Pemetaan Malaysia. This visually enhanced DEM was then used for the development of the actual extent of the 2007 flood in the study area. Several options of flood mitigation works are proposed to reduce the impact of a similar flood in the future based on the developed DEM.

The development of Digital Elevation Model (DEM) was made from a combination of digital topographic maps and satellite images which were purchased from Jabatan Ukur dan Pemetaan Malaysia (JUPEM). This visually enhanced DEM is then used for the development of the actual extend of 2007 flood in the Study Area. Several options of flood mitigation works are proposed to reduce the impact of similar flood in the future based on the developed DEM.