The Floodwater Depth Estimation Tool (FwDET v2.0) for Improved Remote Sensing Analysis of Coastal Flooding

Abstract

Abstract. Remote sensing analysis is routinely used to map flooding extent either retrospectively or in near-real-time. For flood emergency response, remote sensing-based flood mapping is highly valuable as it can offer continued observational information about the flood extent over large geographical domains. Information about the floodwater depth across the inundated domain is important for damage assessment, rescue, and to prioritize relief resource allocation, but cannot be readily estimated from remote sensing analysis. The Floodwater Depth Estimation Tool (FwDET) was developed to augment remote sensing analysis by calculating water depth based solely on an inundation map with an associated Digital Elevation Model (DEM). The tool was shown to be accurate and was used in flood response activations by the Global Flood Partnership. Here we present a new version of the tool, FwDET v2.0, which enables water depth estimation for coastal flooding. FwDET v2.0 features a new flood boundary identification scheme which accounts for the lack of confinement of coastal flood domains at the shoreline. A new algorithm is used to calculate the local floodwater elevation for each cell, which improves the tool's runtime by a factor 15 and alleviates inaccurate local boundary assignment across permanent water bodies. FwDET v2.0 is evaluated against physically-based hydrodynamic simulations in both riverine and coastal case studies. The results show good correspondence, with an average difference of 0.18 m and 0.31 m for the coastal (using a 1-m DEM) and riverine (using a 10-m DEM) case studies respectively. A FwDET v2.0 application of using remote sensing derived flood maps is presented for three case studies. These case studies showcase FwDET v2.0 ability to efficiently provide a synoptic assessment of floodwater. Limitations include challenges in obtaining high-resolution DEMs and increases in uncertainty when applied for highly fragmented flood inundation domains.

The Floodwater Depth Estimation Tool (FwDET v2.0) for improved remote sensing analysis of coastal flooding

“…Code and data availability. FwDET v1.0 and 2.0 ArcGIS and QGIS script code (Python) and demo data are accessible via Surface Dynamics Modeling Lab (SDML, https://sdml.ua.edu/models/, Cohen and Raney, 2019a), the Community Surface Dynamics Modeling System (CSDMS, https://csdms.colorado.edu/wiki/Model_ download_portal, Cohen and Raney, 2019b), and GitHub (https: //github.com/csdms-contrib/fwdet, Cohen and Raney, 2019c).…”

Responses to Interactive comments by Anonymous Referee #2

“…Code and data availability. FwDET v1.0 and 2.0 ArcGIS and QGIS script code (Python) and demo data are accessible via Surface Dynamics Modeling Lab (SDML, https://sdml.ua.edu/models/, Cohen and Raney, 2019a), the Community Surface Dynamics Modeling System (CSDMS, https://csdms.colorado.edu/wiki/Model_ download_portal, Cohen and Raney, 2019b), and GitHub (https: //github.com/csdms-contrib/fwdet, Cohen and Raney, 2019c).…”

Gridded Flood Depth Estimates from Satellite Derived Inundations

“…Using a fully automated open source algorithm, Cohen et al (2018) developed the Flood Water Depth Estimation Tool (FwDET) version 1.0 for the proprietary ArcGIS platform using a raster-based shoreline agonistic 'nearest boundary cell elevation' routine to interpolate shoreline elevations onto the interior inundated region. Version 2.0 replaced the interpolation routine with a more efficient 'cost allocation' routine better suited for inundations with incomplete boundaries (e.g., coastal flooding) (Cohen et al, 2019). Cohen et al (2019) tested this tool against hydrodynamic results for two flood-prone regions in the U.S. using the hydrodynamic inundation for the tool input (rather than satellite derived inundations) and found errors exceeding 1.5 m. Version 2.0 was later ported to Google Earth Engine (Peter et al, 2020).…”

“…Version 2.0 replaced the interpolation routine with a more efficient 'cost allocation' routine better suited for inundations with incomplete boundaries (e.g., coastal flooding) (Cohen et al, 2019). Cohen et al (2019) tested this tool against hydrodynamic results for two flood-prone regions in the U.S. using the hydrodynamic inundation for the tool input (rather than satellite derived inundations) and found errors exceeding 1.5 m. Version 2.0 was later ported to Google Earth Engine (Peter et al, 2020). Cohen et al (2019) reports on a second tool 'FwDET-QGIS', similar to Version 1.0 but for the QGIS open source platform, with the GRASS 'r.grow.distance' function providing the nearest boundary cell elevation routine (Raney and Cohen, 2019).…”

“…Cohen et al (2019) tested this tool against hydrodynamic results for two flood-prone regions in the U.S. using the hydrodynamic inundation for the tool input (rather than satellite derived inundations) and found errors exceeding 1.5 m. Version 2.0 was later ported to Google Earth Engine (Peter et al, 2020). Cohen et al (2019) reports on a second tool 'FwDET-QGIS', similar to Version 1.0 but for the QGIS open source platform, with the GRASS 'r.grow.distance' function providing the nearest boundary cell elevation routine (Raney and Cohen, 2019). With the exception of a two-fold decrease in run-time (compared to Version 2.0), no comparison was reported for FwDET-QGIS https://doi.org/10.5194/nhess-2021-275 Preprint.…”