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Detection of Flood Prone Areas using Digital                 Elevation Models                                        Salva...
Flooding                                         21%Universidad Politecnica de Valencia,6-10 June 2010                    ...
Firenze, November 1966Universidad Politecnica de Valencia,6-10 June 2010                         3
Flood and Landslides occurences in Italy           - AVI project                                                       (pr...
Motivation       There are essentially two scientific questions posed here:       i) Are there geomorphological signatures...
Digital Elevation Models        The increasing availability of digital terrain models has given a      strong impulse to t...
Description of the study area and         morphological characteristics of the basin       A)flood inundation exposure map...
The Geomorphological Characteristics of the        Areas Exposed and Non-Exposed to Flood        Inundation        The con...
The Topographic Index        The topographic index was                                                     The concept of ...
Relationships among topographic index and       flood prone areas Po River and Arno River                                 ...
Arno River basin       Slope                                                                           Risk map PAI       ...
Error functions       The error ER1 defines the percentage of error in       relation to the correct identification of flo...
Testing the New Approach on the Arno River       A) the areas exposed to flood inundation;       B) the map of areas with ...
Arno River sub-catchments                Sub -catchments                                   6                         4    ...
Results 1/2Universidad Politecnica de Valencia,6-10 June 2010                         15
Results 2/2Universidad Politecnica de Valencia,6-10 June 2010                         16
Universidad Politecnica de Valencia,6-10 June 2010                         17
DEM Resolution affects morphological indexes                                          (Wood, 1996)Universidad Politecnica ...
Scale Dependence of the       Modified Topographic Index       The spatial distribution of the topographic       index is ...
Scale Dependence and Associated ErrorsUniversidad Politecnica de Valencia,6-10 June 2010                                  ...
Patameter n vs spatial scale              nUniversidad Politecnica de Valencia,6-10 June 2010                          21
Patameter t vs nUniversidad Politecnica de Valencia,6-10 June 2010                         22
VALIDATIONUniversidad Politecnica de Valencia,6-10 June 2010                         23
CONCLUSIONS            The methodology proposed for the delineation of areas exposed to         flooding offers an estimat...
Publication related to this research line           Manfreda, S., M. Di Leo, A. Sole, Detection of Flood Prone Areas using...
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Detection of Flood Prone Areas using Digital Elevation Models

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Seminar given at the Polytechnic University of Valencia, June 2010

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Transcript of "Detection of Flood Prone Areas using Digital Elevation Models"

  1. 1. Detection of Flood Prone Areas using Digital Elevation Models Salvatore Manfreda Dipartimento di Ingegneria e Fisica dell’Ambiente, Università degli Studi della BasilicataUniversidad Politecnica de Valencia,Universidad Politecnica de Valencia, 6-10 June 20106-10 June 2010 1
  2. 2. Flooding 21%Universidad Politecnica de Valencia,6-10 June 2010 2
  3. 3. Firenze, November 1966Universidad Politecnica de Valencia,6-10 June 2010 3
  4. 4. Flood and Landslides occurences in Italy - AVI project (probability of a flood and a land slide over 50 years)(http://sici.irpi.cnr.it/ ) (e.g., Reichenbach et al., 1998; Guzzetti et al., 2002)Universidad Politecnica de Valencia,6-10 June 2010 4
  5. 5. Motivation There are essentially two scientific questions posed here: i) Are there geomorphological signatures useful for the delineation of flood prone areas? ii) Is possible to define a simplified approach for the delineation of flood prone areas? iii) What is the optimal scale to describe such characteristics?Universidad Politecnica de Valencia,6-10 June 2010 5
  6. 6. Digital Elevation Models The increasing availability of digital terrain models has given a strong impulse to the development of so called distributed and DEM-based models. Digital terrain model obtained through interferometric data gathered by the space shuttle campaign by NASA with a cell-size of 90m. (CGIAR-CSI: http://srtm.csi.cgiar.org/) ASTER GDEM 30m available from June 2009 (http://asterweb.jpl.nasa.gov/gdem.asp )Universidad Politecnica de Valencia,6-10 June 2010 6
  7. 7. Description of the study area and morphological characteristics of the basin A)flood inundation exposure map of (A) (B) the Arno river basin where different codes correspond to different flood exposure levels (1=P1; 2=P2; 3=P3; 4=P4; 5=stagnant water, and 6=water bodies); B)Digital Elevation Model (DEM); (C) (D) C)log(ad) where ad is drained area per unit contour length; D)Surface local slope; E)Surface curvature; F)TOPMODEL Topographic index (E) (F) proposed by Kirkby (1975).Universidad Politecnica de Valencia,6-10 June 2010 7
  8. 8. The Geomorphological Characteristics of the Areas Exposed and Non-Exposed to Flood Inundation The conditioned probability distributions of the different geomorphological measurements at the 4 exposure levels (P1, P2, P3, P4) show very similar shapes and are very different from the one conditioned on P0 (areas non exposed to flood inundation).Universidad Politecnica de Valencia,6-10 June 2010 8
  9. 9. The Topographic Index The topographic index was The concept of contributing area per introduced in the TOPMODEL with unit contour length the aim to mimic soil moisture Stream line patterns based on: • local slope • basin area •Topographic convergence Contour line ln a / tan(  )  D Algorithm (Beven and Kirkby, 1979)Universidad Politecnica de Valencia,6-10 June 2010 9
  10. 10. Relationships among topographic index and flood prone areas Po River and Arno River Po River Topographic index Arno River Flood Exposure Probability distribution of the Topographic index conditional on the flood exposure Topographic indexUniversidad Politecnica de Valencia,6-10 June 2010 10
  11. 11. Arno River basin Slope Risk map PAI   A d n  Cell size 20 m TIm  ln   Tan β    Resize of DTM: 20m – 40m 60m – 80m 100m – 120m 140m – 160m 180m – 260m 360m – 720m Flow Accumulation MFDUniversidad Politecnica de Valencia,6-10 June 2010 11
  12. 12. Error functions The error ER1 defines the percentage of error in relation to the correct identification of flooding areas while ER2 represents the error due to the overestimation of the method. It should be remarked that a reduction in the value ITms generally produces an overestimation of the flood inundation area and (n=0,2; ITms=3.9) an increasing reduction in ER1. The objective was to define a threshold value which minimizes both errors in the delineation of the flood inundation areas. Underestimation Flooding areas with ITm  ITms ER1  100 , Flooding areas from PAI Overestimation Non Flooding areas with ITm  ITms ER2  100. Non Flooding areas from PAIUniversidad Politecnica de Valencia,6-10 June 2010 12
  13. 13. Testing the New Approach on the Arno River A) the areas exposed to flood inundation; B) the map of areas with topographic index superior to the threshold value of 8.40; C) error distribution given by the difference between the map A and B; D) map of areas with modified topographic index superior to the threshold value of 3.90; E) error distribution given by the (Manfreda et al., 2008) difference between the map A and D.Universidad Politecnica de Valencia,6-10 June 2010 13
  14. 14. Arno River sub-catchments Sub -catchments 6 4 1 3 5 8 2 7 11 10 9Universidad Politecnica de Valencia,6-10 June 2010 14
  15. 15. Results 1/2Universidad Politecnica de Valencia,6-10 June 2010 15
  16. 16. Results 2/2Universidad Politecnica de Valencia,6-10 June 2010 16
  17. 17. Universidad Politecnica de Valencia,6-10 June 2010 17
  18. 18. DEM Resolution affects morphological indexes (Wood, 1996)Universidad Politecnica de Valencia,6-10 June 2010 18
  19. 19. Scale Dependence of the Modified Topographic Index The spatial distribution of the topographic index is inevitably linked to the cell-size of the adopted DEM (Zhang and Montgomery, 1994). This dependence is investigated comparing the errors ER1 and ER2 obtained using the topographic index by Kirkby and its modified version (ITm) computed from DEMs with different cell-size. The scale dependence analyses were carried starting from a digital elevation model with cell-size of 20m. From this model, DEMs with different resolution were obtained through aggregations of the first and intermediate hydrological elaborations for the construction of the topographic index and modified topographic indexUniversidad Politecnica de Valencia,6-10 June 2010 19
  20. 20. Scale Dependence and Associated ErrorsUniversidad Politecnica de Valencia,6-10 June 2010 20
  21. 21. Patameter n vs spatial scale nUniversidad Politecnica de Valencia,6-10 June 2010 21
  22. 22. Patameter t vs nUniversidad Politecnica de Valencia,6-10 June 2010 22
  23. 23. VALIDATIONUniversidad Politecnica de Valencia,6-10 June 2010 23
  24. 24. CONCLUSIONS The methodology proposed for the delineation of areas exposed to flooding offers an estimation of the flooded areas with a very low underestimation and a more relevant overestimation. This may be due to terrain characteristics and to protective measures which cover conspicuous portions of the territory otherwise subject to flooding. The geomorphological method described here is a valid preliminary tool in contexts where there is a lack of data for detailed hydrologic and hydraulic simulations. The methodology may benefit from the use of a higher resolution DEM. The errors associated with different scales are deeply influenced by the grid cell resolution and tend to decrease when using a more detailed description of the topography. The threshold values of ITms were found to vary with the reference scale.Universidad Politecnica de Valencia,6-10 June 2010 24
  25. 25. Publication related to this research line Manfreda, S., M. Di Leo, A. Sole, Detection of Flood Prone Areas using Digital Elevation Models Journal of Hydrological Engineeering, Journal of Hydrologic Engineering, Vol. 16, No. 10, September/October 2011, pp. 781-790 (10.1061/(ASCE)HE.1943-5584.0000367), 2011. Fiorentino, M., S. Manfreda, V. Iacobellis, Peak Runoff Contributing Area as Hydrological Signature of the Probability Distribution of Floods, Advances in Water Resources, 30(10), 2123-2144, 2007. Manfreda, S., A. Sole, e M. Fiorentino, Valutazione del pericolo di allagamento sul territorio nazionale mediante un approccio di tipo geomorfologico, LAcqua, n. 4, 43-54, 2007 (In Italian). Manfreda, S., A. Sole, M. Fiorentino, Can the basin morphology alone provide an insight on floodplain delineation?, on Flood Recovery Innovation and Response, WITpress, 47-56, 2008. Thanks for your attention…Universidad Politecnica de Valencia,6-10 June 2010 25
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