See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/305115228 National Scale Landslide Susceptibility Assessment for Dominica Technical Report · May 2016 DOI: 10.13140/RG.2.1.4313.2400 CITATIONS READS 0 832 1 author: C.J. Van Westen University of Twente, Faculty of Geo-Information Science and Earth Observation (ITC) 309 PUBLICATIONS 8,901 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Monitoring landslide risk dynamics after a major earthquake in a mountainous environment View project Seismic amplification modelling and resulting effects View project All content following this page was uploaded by C.J. Van Westen on 10 July 2016. The user has requested enhancement of the downloaded file. The World Bank CHARIM Caribbean Handbook on Risk Information Management National Scale Landslide Susceptibility Assessment for Dominica May 2016 C.J. Van Westen Faculty of Geo‐information Science and Earth Observation (ITC), University of Twente. E‐mail: [email protected] Table of Contents Summary ............................................................................................................................................... 5 Acknowledgements .............................................................................................................................. 6 1. Introduction .................................................................................................................................... 7 1.1. About CHARIM ......................................................................................................................... 7 1.2. Definitions and requirements ................................................................................................. 8 1.3. Previous work on landslide susceptibility assessment ............................................................ 9 2. Method used for the national‐scale landslide susceptibility assessment .................................. 10 2.1. Presentation of the method used ......................................................................................... 10 2.2. Considerations for selecting this method ............................................................................. 13 3. Evaluating landslide triggering characteristics ............................................................................ 15 3.1 Collection of existing data ..................................................................................................... 15 3.2 Results ................................................................................................................................... 16 3.2.1 Disaster impact ................................................................................................................ 16 3.2.2 Analysing main triggering events .................................................................................... 17 3.3 Rainfall analysis ..................................................................................................................... 23 3.3.1 Analysing the distribution of rainfall over the island ...................................................... 24 3.3.2 Evaluation of rainfall thresholds ..................................................................................... 26 3.3.3 Rainfall frequency analysis .............................................................................................. 27 4. Landslide inventory mapping ....................................................................................................... 29 4.1 Available landslide inventories .................................................................................................... 29 4.2 Landslide inventory mapping in 2014 ......................................................................................... 33 4.3 Landslide inventory mapping in 2015 ......................................................................................... 39 4.4 Some examples of landslide characteristics in Dominica ............................................................ 41 4.4.1 The Good Hope Landslide. .............................................................................................. 41 4.4.2 Layou Valley landslides: domino effects of landslides .................................................... 41 4.4.3 San Saveur slide in 2010 .................................................................................................. 42 4.4.4 Large landslides related to volcanic activity. ................................................................... 43 4.4.5 Landslides along the road network ................................................................................. 43 4.4.6 Landslide during tropical storm Erika in the south‐eastern part of Dominica ................ 44 5. Landslide conditioning factors ..................................................................................................... 46 5.1 Digital Elevation data ................................................................................................................... 46 3 | Page 5.2 Geology and soils ......................................................................................................................... 47 5.3 Land‐cover ................................................................................................................................... 51 6. Landslide susceptibility assessment ............................................................................................ 53 6.1. Evaluation of landslide factors using bi‐variate statistical analysis ............................................ 53 6.2 Results of the statistical analysis for Dominica ........................................................................... 55 6.3 Summary...................................................................................................................................... 62 6.4 Landslide initiation assessment using SMCE ............................................................................... 63 6.5 Generation of the susceptibility maps for Dominica ................................................................... 64 6.6 Validation of the final susceptibility maps .................................................................................. 65 6.7 Combining and classifying the susceptibility maps ..................................................................... 67 6.8 Evaluating the quality of the susceptibility map ......................................................................... 69 7 Landslide susceptibility assessment along the road network ..................................................... 74 7.6 Segmentation of the road network into homogeneous sections. .............................................. 74 7.7 Generation of landslide inventories for specific events .............................................................. 75 7.8 Landslide susceptibility assessment along the road network ..................................................... 77 8 Characterizing the susceptibility classes ...................................................................................... 79 8.1 Density and frequency information ............................................................................................ 79 8.2 Buildings located in the susceptibility classes ............................................................................. 80 9 Conclusions and recommendations ............................................................................................. 82 9.1 Conclusions ............................................................................................................................ 82 9.2 Recommendations................................................................................................................. 85 10 References..................................................................................................................................... 88 Author: Dr. Cees J. van Westen Associate Professor University Twente, Faculty of Geo‐Information Science and Earth Observation (ITC) PO Box 217, 7500 AA Enschede, The Netherlands T: +31534874263 E: [email protected] I: http://www.itc.nl/about_itc/resumes/westen.aspx This report should be cited as: Van Westen, C.J. (2016) National Scale Landslide Susceptibility Assessment for Dominica. CHARIM Caribbean Handbook on Risk Information Management, World Bank GFDRR, ACP‐EU Natural Disaster Risk Reduction Program. 4 | Page Summary The aim of this study was to generate a national‐scale landslide susceptibility map for Dominica. As the available data turned out to be insufficient to generate reliable results, we decided to generate several new data layers, and significantly improved some of the existing data. We generated a new database of disaster events for Dominica, making use of many different sources. This is the most complete inventory to our knowledge. It is quite clear from this database that the landslide reporting became more frequent in recent years, and less information on landslides is available when going back in time, whereas the data on tropical storms and hurricanes seems to be much more constant over time. The underreporting of landslides is a big problem in trying to evaluate landslide frequency/magnitude relations. We also compiled all available landslide occurrence data from different sources. We had to digitize some