The Use of DEM-Based Approaches to Derive a Priori Information on Flood-Prone Areas

Knowing the location and the extent of areas exposed to floods is the most basic information needed for planning flood management strategies. Unfortunately, a complete identification of these areas is still lacking in many countries. Recent studies have highlighted that a significant amount of information regarding the inundation process is already contained in the structure and morphology of a river basin. Therefore, several geomorphic approaches have been proposed for the delineation of areas exposed to flood inundation using DEMs. Such DEM-based approaches represent a useful tool, characterized by low cost and simple data requirements, for a preliminary identification of the flood-prone areas or to extend flood hazard mapping over large areas. Moreover, geomorphic information may be used as external constraint in remote-sensing algorithms for the identification of inundated areas during or after a flood event.

How to cite: Salvatore Manfreda, Caterina Samela and Tara J. Troy, The Use of DEM-Based Approaches to Derive a Priori Information on Flood-Prone Areas, Springer International Publishing AG 2018, Pages 61 – 79, (doi: https://doi.org/10.1007/978-3-319-63959-8_3), 2018. [pdf]

A GIS tool for cost-effective delineation of flood-prone areas

Delineation of flood hazard and flood risk areas is a critical issue, but practical difficulties regularly make complete achievement of the task a challenge. In data-scarce environments (e.g. ungauged basins, large-scale analyses), useful information about flood hazard exposure can be obtained using geomorphic methods. In order to advance this field of research, we implemented in the QGIS environment an automated DEM-based procedure that exhibited high accuracy and reliability in identifying the flood-prone areas in several test sites located in Europe, the United States and Africa. This tool, named Geomorphic Flood Area tool (GFA tool), enables rapid and cost-effective flood mapping by performing a linear binary classification based on the recently proposed Geomorphic Flood Index (GFI). The GFA tool provides a user-friendly strategy to map flood exposure over large
areas. A demonstrative application of the GFA tool is presented in which a detailed flood map was derived for Romania.

How to cite: Caterina Samela, Raffaele Albano, Aurelia Sole, Salvatore Manfreda, A GIS tool for cost-effective delineation of flood-prone areas, Computers, Environment and Urban Systems (doi: https://doi.org/10.1016/j.compenvurbsys.2018.01.013), 2018. [pdf]

Geomorphic classifiers for flood-prone areas delineation for data-scarce environments

Knowing the location and the extent of the areas exposed to flood hazards is essential to any strategy for minimizing the risk. Unfortunately, in ungauged basins the use of traditional floodplain mapping techniques is prevented by the lack of the extensive data required. The present work aims to overcome this limitation by defining an alternative simplified procedure for a preliminary floodplain delineation based on the use of geomorphic classifiers. To validate the method in a data-rich environment, eleven flood-related morphological descriptors derived from remotely sensed elevation data have been used as linear binary classifiers over the Ohio River basin and its sub-catchments. Their performances have been measured at the change of the topography and the size of the calibration area, allowing to explore the transferability of the calibrated parameters, and to define the minimum extent of the calibration area. The best performing classifiers among those analysed have been applied and validated across the continental U.S. The results suggest that the classifier based on the Geomorphic Flood Index (GFI), is the most suitable to detect the flood-prone areas in data-scarce regions and for large-scale applications, providing good accuracies with low requirements in terms of data and computational costs. This index is defined as the logarithm of the ratio between the water depth in the element of the river network closest to the point under exam (estimated using a hydraulic scaling function based on contributing area) and the elevation difference between these two points.

How to cite: Caterina Samela, Tara J. Troy, Salvatore Manfreda, Geomorphic   classifiers   for   flood-prone   areas   delineation   for data-scarce   environmentsAdvances   in   Water   Resources (doi: 10.1016/ j.advwatres.2017.01.007) 2017. [pdf]

Flood-prone areas assessment using linear binary classifiers based on flood maps obtained from 1D and 2D hydraulic models

The identification of flood-prone areas is a critical issue becoming everyday more pressing for our society. A preliminary delineation can be carried out by DEM-based procedures that rely on basin geomorphologic features. In the present paper, we investigated the dominant topographic controls for the flood exposure using techniques of pattern classification through linear binary classifiers based on DEM-derived morphologic features. Our findings may help the definition of new strategies for the delineation of flood – prone areas with DEM-based procedures. With this aim, local features—which are generally used to describe the hydrological characteristics of a basin—and composite morphological indices are taken into account in order to identify the most significant one.
Analyses are carried out on two different datasets: one based on flood simulations obtained with a 1D hydraulic model, and the second one obtained with a 2D hydraulic model. The analyses highlight the potential of each morphological descriptor for the identification of the extent of flood-prone areas and, in particular, the ability of one geomorphologic index to represent flood-inundated areas at different scales of application.

How to cite: Manfreda, S., C. Samela, A. Gioia, G. Consoli, V. Iacobellis, L. Giuzio, A. Cantisani, A. Sole, Flood-Prone Areas Assessment Using Linear Binary Classifiers based on flood maps obtained from 1D and 2D hydraulic modelsNatural Hazards, 79 (2), 735-754, (doi: 10.1007/s11069-015-1869-5), 2015. [pdf]

Investigation on the use of geomorphic approaches for the delineation of flood prone areas

Three different geomorphic approaches to the identification of flood prone areas are investigated by means of a comparative analysis of the input parameters, the performances and the range of applicability. The selected algorithms are: the method proposed by Manfreda et al. (2011) based on a modified version of the Topographic Index (TIm); the linear binary classifier proposed by Degiorgis et al. (2012), which uses different geomorphic features related to the location of the site under exam with respect to the nearest hazard source; the hydro-geomorphic method by Nardi et al. (2006) simulating inundation flow depths along the river valley with the associated extent of surrounding inundated areas. Comparison has been carried out on two sub-catchments of the Tiber River in Central Italy. The simulated flooded areas, obtained using the selected three methods, are evaluated using as a reference the Tiber River Basin Authority standard flood maps. The aim of the research is to deepen our understanding on the potential of geomorphic algorithms and to define new strategies for prompt hydraulic risk mapping and preliminary flood hazard graduation. This is of foremost importance when detailed hydrologic and hydraulic studies are not available, e.g., over large regions and for ungauged basins.


How to cite: Salvatore Manfreda, Fernando Nardi, Caterina Samela, Salvatore Grimaldi, Angela Celeste Taramasso, Giorgio Roth, Aurelia Sole, Investigation on the use of geomorphic approaches for the delineation of flood prone areas, Journal of Hydrology, Pages 863 – 876 (doi: 10.1016/j.jhydrol.2014.06.009), 2014. [pdf]

Utilizzo di tecniche GIS per la delineazione di aree di inondazione nei tronchi incisi, alluvionati e incassati di un corso d’acqua: sviluppo di un metodo geomorfologico applicato al bacino del fiume Basento

L’espressione “rischio idraulico” indica il pericolo di inondazione da parte di corsi d’acqua naturali o artificiali e definisce il manifestarsi di eventi di inondazione che producono danni misurabili a persone o cose (Frescura, 2007). Il progressivo aumento di vittime e danni, causato tanto dal manifestarsi di eventi di inondazione quanto da un’antropizzazione spesso incompatibile con le dinamiche naturali del territorio, ha fatto sì che negli ultimi anni si registrasse un aumento dell’interesse, in ambito scientifico, tecnico e legislativo, attorno al problema della previsione e gestione del rischio idraulico (Plate, 2002). Le cause naturali che possono generare un’inondazione sono molteplici: un evento di pioggia con intensità tale da determinare portate in eccesso rispetto alle normali capacità di convogliamento di un fiume o di un canale di drenaggio; un accumulo di acqua su zone che hanno scarsa capacità di drenaggio e che normalmente non sono sommerse; un deflusso proveniente da aree urbane e suburbane poste a monte; le maree ed il moto ondoso. A queste cause naturali c’è da aggiungere l’effetto legato all’interferenza umana. La costruzione di strutture di controllo quali argini, traverse, dighe e sbarramenti ha cambiato le dinamiche proprie dei corsi d’acqua provocando modifiche sostanziali all’esposizione al rischio di inondazione del territorio. Eventuali collassi delle citate strutture antropiche possono provocare fenomeni di inondazione da un lato ed un ritorno dei corsi d’acqua nei propri percorsi naturali dall’altro.

How to cite: Manfreda, S., L. Giuzio, L. Giosa, B. Onorati, A. Sole, V.A. Copertino, Utilizzo di tecniche GIS per la delineazione di aree di inondazione nei tronchi incisi, alluvionati e incassati di un corso d’acqua: sviluppo di un metodo geomorfologico applicato al bacino del fiume Basento, in Catalogo di morfologie fluviali ed instabilità idrodinamiche nei corsi d’acqua di V.A. Copertino, G. Scavone, V. Telesca, Editoriale Bios, pp. 679-694, (ISBN: 978-88-6093-061-3), 2009. 

Can the basin morphology alone provide an insight into floodplain delineation?

The present research was aimed to evaluate flooding exposure by exploiting the potential of morphological indices (e.g., drainage area, local slope, curvature, etc.). It was found that the areas exposed to flood inundation may be delineated quite well by adopting a modified topographic index computed from DEMs (Digital Elevation Models). Since the modified topographic index is sensitive to the spatial resolution of the digital elevation model, the scale dependence is investigated showing an increase in the performances of the method with the resolution of the DEMs. The procedure proposed is tested over the Arno river basin using the existing documentation on flooding exposure produced by the local River Basin Authorities. The use of the proposed modified topographic index may represent a useful and rapid tool in delineating the flood prone areas in ungauged basins and in areas where expensive and time consuming hydrological-hydraulic simulations are not possible.

How to cite: Manfreda, S., A. Sole, M. Fiorentino, Can the basin morphology alone provide an insight on floodplain delineation?, on Flood Recovery Innovation and Response (edited by C.A. Brebbia), WITpress, 47-58, 2008. [Link]

THE FLOOD EXPOSURE OF THE ITALIAN TERRITORY THROUGH A GEOMORPHOLOGIC APPROACH

The objetive of the present research was the evaluation of the flood exposure of the Italian territory. For this reason, the national territory has been subdivided in national, interregional and regional catchments according to the actual legislation regarding the soil defence (Law 183 of 1989). Such approach has been used in order to organize, within a Geographical Information System, the existing cartographic and technical documentation on flood exposure and risk produced by the local Agencies recently instituted. Using this documentation, we obtained a partical coverage of the Italian territory that has been extremely useful to explore new methods to define areas where the flood exposure is relatively high. A new method is presented for the definition of the areas exposed to floods that is based on the geomorphological characteristics of the territory. In particular, it was found that the flooding areas can be delineated fairly well trough a modified topographic index ITm = ln(an / tan(b)), where a is the drainage area per unit contour length, tan (b) is the local slope in the steepest descent direction and n is an exponent that was found to be close to 0.15-0.20. Such analyses have been carried out using a digital elevation model at 230 m and one at 90 m of resolution produced by NASA.

How to cite: Manfreda, S., A. Sole, e M. Fiorentino, Valutazione del pericolo di allagamento sul territorio nazionale mediante un approccio di tipo geomorfologicoL’Acqua, N.4, 43-54, 2007. [pdf]