Experimental investigation of tidal bore-like unsteady flow interaction with solitary spur dike

Abstract

In a river and estuarine region dominated by strong tidal bores, spur dikes play a crucial role in influencing both hydrodynamics and morphodynamics. The present study experimentally quantifies the hydrodynamics around a solitary spur dike during tidal bore-like unsteady flow interaction by varying the flow Froude number (Fr) and relative dike height (h_d/h). During the tidal bore interaction with the spur dike, splashing occurred during bore impact, followed by continuous overflow, resulting in a significant difference in flow characteristics in the spur dike vicinity during the quasi-steady flow phase. Fr and h_d/h positively correlated with the upstream water elevation (backwater rise) and negatively correlated at the downstream region. At the head region, the backwater upstream and the overtopped flow together dictated the flow characteristics. Empirical equations for predicting the flow characteristics (bore depth and velocity) around the spur dike during tidal bore interaction are obtained through the non-linear multivariate regression analysis. At high Fr and high h_d/h conditions, the spur dike was found to effectively reduce the tidal bore energy at the downstream region by nearly 25% due to high turbulence intensity. Overall, the paper provides quantitative and qualitative discussion on tidal bore hydrodynamics and the variation in the tidal bore energy around a solitary spur dike for engineering design and operational appraisal.