Abstract
Compound floods are an active area of research where the complex interaction between pluvial, fluvial, coastal or groundwater flooding are analyzed. A number of studies have simulated the compound flooding impacts of precipitation, river discharge and storm surge variables with different numerical models and linking techniques. However, groundwater flooding is often neglected in flood risk assessments due to its sporadic frequency - as most regions have water tables sufficiently low that do not exacerbate flooding conditions -, isolated impacts and considerably less severity in respect to other types of flooding. This paper presents a physically-based, loosely-coupled modelling framework using FLO-2D and MODFLOW-2005 that is capable to simulate surface-subsurface water interactions to represent compound flooding events in North Miami. FLO-2D, responsible of the surface hydrology and infiltration processes, transfers the infiltration volume as recharge to MODFLOW-2005 until the soil absorption capacity is exceeded, while MODFLOW-2005 return exchange flow to the surface when groundwater heads are higher than the surface depth. The model calibration is based on three short-lived storm events that as individual processes represent minimum flooding conditions but in combination with pre-existing high-water table levels results in widespread flooding across the study area. Understanding groundwater flood risk is of particular interest to low-elevation coastal karst environments as the sudden emergence of the water table at ground surface can result in social disruption, adverse effects to essential services and damage infrastructure. Results are validated using FEMA’s severe repetitive loss (SRL) property records and crowdsourced data. Further research should assess the exacerbated impacts of high tides and sea level rise on water tables under current and future climate projections.
Highlights
Flood inundation modelling is of critical importance for better planning, forecasting and decision-making practices (Teng et al, 2017)
While the joint impact of rainfall and tide levels per se do not pose significant threats to infrastructure as the surface runoff rapidly infiltrates into the 430 porous permeable soil (Fig. 9a, 9c, 9e), the shallow water table of the Biscayne Aquifer quickly responds to high-intensity short-duration storms which results in the sudden increase of groundwater levels, leading to extensive urban flooding in parts of the Arch Creek Basin (Fig. 9b, 9d, 9f)
Rainfall-runoff is the primary source of flooding in the urbanized Arch Creek Basin, abnormally high groundwater levels triggered groundwaterinduced flooding resulting in the amplification of chronic flooding near historic waterways or zones below the County’s land elevation flood criteria within North Miami and Unincorporated Miami-Dade County (MDC), with flood depths ≈ 1 meter (Fig. 10a, 10b)
Summary
Flood inundation modelling is of critical importance for better planning, forecasting and decision-making practices (Teng et al, 2017). Most flood inundation models are designed to simulate specific flood hazards (i.e., pluvial, fluvial, coastal, groundwater) independently and are unable to assess complex flood dynamics per se due to code limitations and burdensome compatibility. To address these numerical constraints, some models have the ability to operate as linked units or groups by using coupling schemes (i.e. one-way, loosely, tightly, fully) to build compound models capable of simulating multiple flood drivers (Santiago-Collazo et 40 al., 2019). The transition from traditional univariate approaches to a multivariate perspective is necessary to improve flood hazard understanding and predictions (Bates et al, 2021)
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