Effects of Storm Surge Barrier Closures on Estuary Saltwater Intrusion and Stratification

Gated storm surge barriers have been constructed or proposed in many estuaries worldwide for coastal flood risk reduction. Past studies have shown that, even when open, a barrier system's fixed infrastructure can increase estuary stratification and salt intrusion, potentially affecting water quality and ecological processes. However, surge barrier closures could have a much stronger influence on estuary conditions by temporarily blocking the tidal exchange. In this project, we use an existing regional three-dimensional hydrodynamic model, with modifications to simulate surge barrier closure and reopening, to study the effects on estuarine salt intrusion and stratification of the Hudson River. Across a range of modeled scenarios of gate closure frequencies, durations and river streamflows, we evaluate the changes caused by gate closures, as well as the recovery time to normal conditions. Our results for the Hudson show long-duration gate closures (three or more days) with low streamflows temporarily lead to salt intrusion and stratification beyond recent historical extremes. Moreover, monthly frequency closures, which could occur as soon as 2070 under realistic scenarios of sea-level rise and barrier management, do not allow for recovery under low streamflow conditions and could lead to durable changes to estuary physical conditions. As a result, long duration closures and high-frequency closures both constitute a threat to municipal water supplies. This study demonstrates a framework for understanding the potential impacts of any proposed surge barrier system and can help improve our understanding of corresponding ecological impacts.