Effects of Climate Change and Storm Surge Barriers on Estuary Physical Conditions

Abstract:

Storm surge barriers are being considered by the Corps of Engineers as one of a number of options for coastal storm risk management for the New York City metropolitan area. However, the barriers will also reduce water flow and tidal exchange, which in turn can affect water quality and ecological processes. Past studies have shown enhanced stratification and salt intrusion length simply by constructing the surge barriers (i.e. when they are open), which are similar impacts as those caused by sea level rise and climate warming in some estuaries. Therefore, the combined effects of climate change are also worth evaluating to understand the surge barriers’ potential impact.

In this project we use an existing hydrodynamic model to simulate estuary physical conditions and their evolution with surge barrier closures. We modify the model bathymetry to represent fixed surge barrier components and edit the model code to enable open/close capability for gates. By using a range of modeled scenarios to simulate estuary physical conditions with varying gate closure frequencies, durations and streamflows under present and future conditions, we evaluate the estuary physical changes (including salt intrusion and stratification) caused by gate closures and the recovery time to normal conditions depending on different circumstances. We show that gate closures will have a temporary but aggregate impact on estuary system, increasing stratification, salt intrusion, and temporarily halting water exchange. This impact will increase if the frequency of gate closures increases with sea level rise, and could be significantly aggravated if future river streamflows are reduced during dry periods in this area. This project will improve the understanding of the coupled effects of future climate change and the human flood risk reduction response, and will result in a deeper insight into the potential influences of surge barriers on estuarine physical and ecological conditions.