Uncertainty in floodplain delineation: expression of flood hazard and risk in a Gulf Coast watershed

Abstract

This paper investigates the development of flood hazard and flood risk delineations that account for uncertainty as improvements to standard floodplain maps for coastal watersheds. Current regulatory floodplain maps for the Gulf Coastal United States present 1% flood hazards as polygon features developed using deterministic, steady‐state models that do not consider data uncertainty or natural variability of input parameters. Using the techniques presented here, a standard binary deterministic floodplain delineation is replaced with a flood inundation map showing the underlying flood hazard structure. Additionally, the hazard uncertainty is further transformed to show flood risk as a spatially distributed probable flood depth using concepts familiar to practicing engineers and software tools accepted and understood by regulators. A case study of the proposed hazard and risk assessment methodology is presented for a Gulf Coast watershed, which suggests that storm duration and stage boundary conditions are important variable parameters, whereas rainfall distribution, storm movement, and roughness coefficients contribute less variability. The floodplain with uncertainty for this coastal watershed showed the highest variability in the tidally influenced reaches and showed little variability in the inland riverine reaches. Additionally, comparison of flood hazard maps to flood risk maps shows that they are not directly correlated, as areas of high hazard do not always represent high risk. Copyright © 2012 John Wiley & Sons, Ltd.

A Hydraulic MultiModel Ensemble Framework for Visualizing Flood Inundation Uncertainty

“…; Christian et al. ); therefore, by not incorporating these uncertainties, deterministic flood inundation maps fail to communicate the full risk for potential flooding.…”

“…Forecasted flood inundation maps are typically based on deterministic model output generated using a hydraulic model forced with a single discharge output from a hydrologic model (e.g., Merwade et al 2008;Grimaldi et al 2013). These deterministic flood inundation maps are subject to uncertainty due to imperfect forcing, initial conditions, model parameterizations, and numerical limitations (Merwade et al 2008;Christian et al 2013); therefore, by not incorporating these uncertainties, deterministic flood inundation maps fail to communicate the full risk for potential flooding.…”

Comparative Analysis of Inundation Mapping Approaches for the 2016 Flood in the Brazos River, Texas

“…Although FEMA has produced ~100,000 flood risk maps based on 100‐year return period flows (NFIP ), inundation maps for real events are unavailable or limited by uncertainties in data sources or modeling (Christian et al. ).…”

“…In the U.S., most major river systems 1 have flood risk maps delineated by the Federal Emergency Management Agency (FEMA) through the National Flood Insurance Program (NFIP). Although FEMA has produced~100,000 flood risk maps based on 100-year return period flows (NFIP 2002), inundation maps for real events are unavailable or limited by uncertainties in data sources or modeling (Christian et al 2013).…”

Simulation and comparison of stream power in-channel and on the floodplain in a German lowland area

“…More accurate information about river flow and floodplain flow is important for analyzing the alluvial and hydrological effects of the river systems, including water pollutants diffusion, hydraulic construction, water quality distribution and prediction, river resource management, flood estimation and flood damage prevention, etc. (Brocca et al, 2011;Christian et al, 2013;Lau and Ghani, 2012;Posey, 2009). The driving force of these flow behaviors is commonly expressed as stream power (Jain et al, 2006).…”