Exploring the application of topographic indices in urban areas as indicators of pluvial flooding locations

Abstract

In urban areas, the presence of impervious surfaces limits natural drainage and routes water to stormwater infrastructure with finite capacity, making these areas especially prone to flooding. Though large floods are responsible for endangering lives and causing extensive damage, there is growing evidence that more frequent floods with shallow water depths, termed nuisance flooding, can have a high cumulative cost and many direct and indirect damages. To determine whether locations of nuisance flooding may be linked to topography, we took a parsimonious, spatially distributed approach to explore whether high topographic index values co-occur with citizenreported nuisance flooding. We obtained nuisance flood reports from the municipal data service 311 for several watersheds in New York City and Baltimore, USA. Our analysis tested two topographic indices (TI)-topographic wetness index (TWI) and sink depth-both calculated from high-resolution (~1 m) digital elevation models.Generally, our findings suggest that not all but many locations of reported flooding tend to coincide with deep sinks or large TWI. However, nuisance flooding reports most commonly coincided with deep sinks and high TWI when using a maximum, instead of coincident, TI value extracted around each reported location of flooding, an approach we used due to the uncertainty in location accuracy of flooding reports.Overall, our results show promise for application of topographic indices, typically applied in more natural settings, as indicators of nuisance flooding areas in urbanized environments. Although limitations to this approach exist, the application of TIs and crowd-sourced reporting in tandem could provide a useful starting point for mapping flood-prone areas in many cities with technologically adept community members and ample geospatial data. K E Y W O R D Scrowd-sourced data, nuisance flooding, pluvial flooding, spatial indicators, topographic indices, urban hydrology

Suitable Dem Assessment Study for Data Scarce Cities Towards Urban Extreme and Nuisance Flood Mapping

“…The higher TWI indicates the higher chances of getting nuisance to extreme floods in urban areas (Kelleher and McPhillips, 2020). SLR and ALOS AW3D showed the same higher value, while NED 10m and NED 30m showed strip lines in TWI maps, indicating its smoothness and small valley streams.…”

“…New York is one of the most urbanized, populated and near to coastal belt, it is prone to pluvial and low-lying (Nuisance) floods. More details of the study area can be found in other literature (Kelleher and McPhillips, 2020).…”

“…The locations of nuisance floods in cities are linked to topography, which can be predicted with TWI and Sink depths. The locations where high TWI value and large sink depths are having more chances to experience the nuisance floods (Kelleher and McPhillips, 2020). In this study, the TWI based comparison was performed to identify the alternative medium resolution DEM.…”

“…In this study, the TWI based comparison was performed to identify the alternative medium resolution DEM. The procedure for estimating TWI was adopted from literature (Kelleher and McPhillips, 2020) at each cell according to below-given equation ( 1)…”

“…To get exact stream lines the datasets has to be preprocessed which is complex and time expensive. Although many researchers are carried out to assess the accuracy of DEMs towards fluvial floods, river modeling etc., (Zhang et al, 2019, Fereshtehpour andKaramouz, 2018, Li * Corresponding author and Wong, 2010, Sanders, 2007 but very few studies are attempted for urban flood mapping and modeling (Kelleher and McPhillips, 2020). It is very important to study and identify the suitable freely available medium resolution DEM for urban flood modeling and mapping in data scare urban areas.…”