Testing Urban Flood Mapping Approaches from Satellite and In-Situ Data Collected during 2017 and 2019 Events in Eastern Canada

Ian Olthof,Nicolas Svacina

doi:10.3390/rs12193141

Abstract

The increasing frequency of flooding worldwide has driven research to improve near real-time flood mapping from remote-sensing data. Improved automation and processing speed to map both open water and vegetated area flooding have resulted from these research efforts. Despite these achievements, flood mapping in urban areas where a significant number of overall impacts are felt remains a challenge. Near real-time data availability, shadowing caused by manmade infrastructure, spatial resolution, and cloud cover inhibiting optical transmission, are all factors that complicate detailed urban flood mapping needed to inform response efforts. This paper uses numerous data sources collected during two major flood events that impacted the same region of Eastern Canada in 2017 and 2019 to test different urban flood mapping approaches presented as case studies in three separate urban boroughs. Cloud-free high-resolution 3 m PlanetLab optical data acquired near peak-flood in 2019 were used to generate a maximum flood extent product for that year. Approaches using new Lidar Digital Elevation Models (DEM)s and water height estimated from nineteen RADARSAT-2 flood maps, point-based flood perimeter observations from citizen geographic information, and simulated traffic camera or other urban sensor network data were tested and verified using independent data. Coherent change detection (CCD) using multi-temporal Interferometric Wide (IW) Sentinel-1 data was also tested. Results indicate that while clear-sky high-resolution optical imagery represents the current gold standard, its availability is not guaranteed due to timely coverage and cloud cover. Water height estimated from 8 to 12.5 m resolution RADARSAT-2 flood perimeters were not sufficiently accurate to flood adjacent urban areas using a Lidar DEM in near real-time, but all nineteen scenes combined captured boroughs that flooded at least once in both flood years. CCD identified flooded boroughs and roughly captured their flood extents, but lacked timeliness and sufficient detail to inform street-level decision-making in near real-time. Point-based flood perimeter observation, whether from in-situ sensors or high-resolution optical satellites combined with Lidar DEMs, can generate accurate full flood extents under certain conditions. Observed point-based flood perimeters on manmade features with low topographic variation produced the most accurate flood extents due to reliable water height estimation from these points.

Highlights

In the spring of 2017, large regions in Canada’s provinces of Quebec and Ontario experienced severe flooding caused by consecutive record-setting rain events during snowmelt from early April to mid-May
Approaches using new Lidar Digital Elevation Models (DEM)s and water height estimated from nineteen RADARSAT-2 flood maps, point-based flood perimeter observations from citizen geographic information, and simulated traffic camera or other urban sensor network data were tested and verified using independent data
Points observed along the flood perimeter are overlain on the DEM first to determine floodwater height by sampling the DEM at the shoreline location

Summary

Introduction

In the spring of 2017, large regions in Canada’s provinces of Quebec and Ontario experienced severe flooding caused by consecutive record-setting rain events during snowmelt from early April to mid-May. 2020, 12, 3141; doi:10.3390/rs12193141 www.mdpi.com/journal/remotesensing across the river in Ottawa, people in approximately 350 residences were displaced [1,2]. Two years later in the spring of 2019, flooding affected the region once again, including many of the same communities along the Ottawa and St-Lawrence Rivers. Unlike in 2017, a breach ofwere the flooded dike in the town of Sainte-Marthe-sur-le-Lac flooded significant portion of the 2400 residences in 146 communities in Quebec, forcing massa evacuations and declaration municipality, forcing more than 6500 people to leave [5]. First responders in Gatineau, Quebec evacuated more than 500 people while communities westward were impacted by the flood. Insured damages from the 2019 across the river in Ottawa, people in approximately 350 residences were displaced [1,2]

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