CP51B-08 - The Influence of Human Induced Landscape and Bathymetry Changes on Tides, Surge and Extreme Water Levels

Recent hurricanes have produced high water marks in cities such as New York, Jacksonville, and Wilmington (NC). Are human-mediated changes to landscape and bathymetry playing a role in these events? Time-lapse snapshots of the typical estuary over the last 150 years would show continual change from dredging, land reclamation, and infrastructure development. Research over the last decade has established that depth, width, and length affect tidal amplitudes, sometimes by several meters. Here we show that the dynamical processes and the response to human interventions are spatially variable, and affect storm surge and other long-waves as well. We highlight two types of dynamical processes that influence extreme water levels. First, changes in wave reflection and constructive interference—caused, for example, by channel deepening—produce amplification (or sometimes attenuation) near the reflection point. Hence, tidal range in the upstream portions of multiple US and European estuaries have increased by a factor of 2x to 10x. Second, within strongly frictional and non-reflective estuaries, the maximal change due to bathmetric changes typically occurs with-in the middle reaches (~20 & 60km in the St Johns River (FL) and Columbia River Estuary). Interestingly, the maximum change in storm surge occurs in a similar location as maximal tide change. Nonetheless, bathymetric alterations usually reduce the mean river slope. Therefore, flood risk in some locations has reduced over time (Albany, NY) due to falling mean river levels, despite a doubling of tidal range. By contrast, more coastal locations such as Wilmington (NC) are subject to greater marine flood risk that outweighs the reduction in fluvial risk. Such human-induced factors potentially exacerbate sea-level rise to produce spatially varying flood risk on both estuary and regional scales, producing “winners” and “losers”