Coastal Flood Modeling Challenges in Defended Urban Backshores

Abstract

Coastal flooding is a significant and increasing hazard. There are multiple drivers including rising coastal water levels, more intense hydrologic inputs, shoaling groundwater and urbanization. Accurate coastal flood event prediction poses numerous challenges: representing boundary conditions, depicting terrain and hydraulic infrastructure, integrating spatially and temporally variable overtopping flows, routing overland flows and incorporating hydrologic signals. Tremendous advances in geospatial data quality, numerical modeling and overtopping estimation have significantly improved flood prediction; however, risk assessments do not typically consider the co-occurrence of multiple flooding pathways. Compound flooding refers to the combined effects of marine and hydrologic processes. Alternatively, multiple flooding source–receptor pathways (e.g., groundwater–surface water, overtopping–overflow, surface–sewer flow) may simultaneously amplify coastal hazard and vulnerability. Currently, there is no integrated framework considering compound and multi-pathway flooding processes in a unified approach. State-of-the-art urban coastal flood modeling methods and research directions critical to developing an integrated framework for explicitly resolving multiple flooding pathways are presented.

Delimitation of flood areas based on a calibrated a DEM and geoprocessing: case study on the Uruguay River, Itaqui, southern Brazil

“…Thus, special attention is required for topographic data because a robust flood model needs high vertical accuracy linked to a geodetic reference system, since in many cases, flood-prone areas are found in marginal regions of low-slope floodplain and may embrace large areas, such as this case study (Uruguay River basin, Itaqui) (Gupta, 2009;Mistry, 2009). The modeling of a flood hazard map is linked to the local geodetic reference system, corroborated with the identification and monitoring of flood situations, and construction of realistic predictive scenarios (operational level) for risk management and adaptation (governmental agencies, such as the local civil defense) (Joshi et al, 2012;Gallien et al, 2018;Jongman, 2018). It is extremely important to do the calibration of the digital elevation model (DEM) using high-accuracy ground control point (GCP) data, aimed at improving the vertical accuracy, and applied to regional or local studies about floods (Araújo et al, 2018).…”

“…To evaluate and calibrate the DEM of the study area, a matrix was constructed with the orthometric height values of control points and the SRTM image. This dataset was subjected to linear regression analysis, with ground control point values as a dependent variable and SRTM data as an independent variable, which is a common procedure found in the literature for DEM calibration (e.g., Gorokhovich and Voustianiouk, 2006;Forkuor and Maathuis, 2012). Then, the DEM obtained from the SRTM image was calibrated using the model proposed by the linear regression.…”

Modelling Coastal Flood Propagation under Sea Level Rise: A Case Study in Maria, Eastern Canada

“…First, the storm event of 6 December 2010 was simulated with XBeach, with boundary conditions extracted from WW3 (same domain and grid as the validation) ( A hypothetical storm scenario for the year of 2100 was simulated based on an increase in sea level only, assuming a stable future wave climate. The observed rate of sea level rise is both the result of eustatic sea level variations and regional glacio-isostatic adjustments (GIA) along Atlantic Canada [5,[42][43][44], varying between −1 and −4 mm/year in the Gulf of St Lawrence [5,45]. The relative sea level has risen at a mean rate of 0.93 ± 1.25 mm/ year over the past ~1500 years in the Chaleur Bay and GIA was a significant contributor to this rate [79].…”

“…Gallien et al [42] further demonstrated that drainage can reduce flood propagation. Multiple flooding pathways can also influence the flood extents [45,46]. Urbanization in coastal areas greatly affects the beach response to, and recovery from, storm events [21].…”

“…Hydrodynamic modelling often uses a cascade of models to simulate hydrodynamic conditions from offshore to shore and to estimate wave runup, overtopping, and flow patterns [39,52,57]. Gallien et al [45] conducted a literature review on coastal flood modelling and underlined the need to integrate the multi-pathway flooding processes (e.g., groundwater and surface dynamics, overtopping and overflow, surface and subsurface sewer flow) into flood mapping. Physics-based processes affecting flow pathways and connectivity, varying water depths, and velocities can be solved with numerous 2D numerical models, such as LISFLOOD-FP [58,59], BreZo [60], and Deflt3D [61], among others.…”