Performance Assessment of Coastal Hydraulic Structures Influence of Sea Level and Tidal Variations

Abstract

Efficient and reliable operation of coastal hydraulic structures for discharging the excess inland water to the oceans is essential for addressing regional flooding and seawater intrusion. Often, the sea level variations combined with tidal conditions establish the downstream water levels of these structures, thus influencing the discharge capacity and level of service (LOS) provided by these entities. This study focuses on assessing the influence of sea-level rise and tidal variations on the operational capacity of a coastal hydraulic structure in South Florida, USA. Historical daily and hourly tailwater levels are analyzed to assess different stage hydrographs and their shapes. The tailwater stages are evaluated to derive the stage hydrograph through a moving window overlapping temporal block (MWOTB) approach using several nonparametric (such as bootstrapping and kernel density estimation), parametric and cluster-based techniques. Harmonic analysis of tailwater stage data is carried out to obtain the tidal constituents such as storm surge, tidal residuals, and mean sea level variations. The storm surge hydrographs associated with hurricane (cyclone) and nonhurricane events are developed using nonparametric, cluster- and frequency-based approaches to assess their shapes. Results from the comprehensive analysis of stages indicate that stage extremes are confined to specific months of the year. A persistent increase in the stage was observed for all the months during the past decade, which plausibly hints towards the sea level rise in the region. An increasing trend in the consecutive days with tailwater stages equaling or exceeding the 90th and 95th percentile stage value is noted. High tailwater stages are observed during the periods that coincide with occurrences of King tides in the region based on the analysis using the MWOTB approach. The storm surge hydrographs have shown different distribution characteristics for the hurricane and the non-hurricane events. The work reported in this study proposes several approaches for the performance assessment of coastal hydraulic structures. © 2022 IAHR.