Nuisance flooding due to groundwater emergence in coastal urban areas

Abstract:

Flooding of coastal areas is generally regarded as a phenomenon arising from wave overtopping during storm events, which leads to devastating sudden effects as well as disruptive changes to the coastal communities in the aftermath. Less is known about nuisance flooding, which is less extreme (water depth between 3 and 10 cm) but may occur more frequently. Nuisance flooding not only poses significant threats to public safety and causes major property damage, but also disrupts routine day-to-day activities, applies added strain on infrastructure systems, and makes significant negative impact on human health. Nuisance flooding can be determined by precipitation, extreme high tides,high river stage, channel and culvert blockages, surcharging sewers, leaks in flood walls, broken water supply pipes, and groundwater emergence.

Here we focus on the emergence of the groundwater due to sea-level rise. Considering future scenarios of the acceleration of sea level rise (SLR), such a phenomenon is recognized to become important in low-lying coastal regions. We investigated the groundwater emergence in a densely populated coastal area along a river estuary (Hoboken, NJ). A three-dimensional (3D) shallow aquifer model was implemented in MODFLOW and calibrated using field measurements. Simulations were run to describe the response of the water table to the sea level and precipitation intensity. Preliminary results show that the aquifer does not response to the tidal behavior of the river but rather it is controlled by its averaged level. In comparison to the river level impact, the precipitation has a negligible effect because of the significant imperviousness of the urban surface, which is up to 80 % of the total ground. The groundwater predictions suggest the possibility of groundwater emergence in any low-lying parts of the study area in case of SLR, which could exacerbate the impact of nuisance flooding if concurrent to large intensity of the precipitation and high-tide.

Overall, this work provides a framework to study critical areas potentially subjected to ground-water flooding and can be applied to refine groundwater maps in urban settings which are oftenobtained from the interpolation of regional aquifers at steady-state.