INVESTIGATING THE IMPORTANCE OF BED ROUGHNESS ON TURBULENCE IN THE INNER SURF AND SWASH ZONES

Abstract

This senior thesis investigates the effect of bed roughness on turbulence in the swash- and inner surf-zones under controlled laboratory conditions. These experiments collected velocity data using acoustic Doppler profiling velocimeters (ADPVs) at three cross-shore locations during wave flume experiments conducted at Queen’s University. Test conditions varied by wave height, incident wave angle, and surface roughness (SMOOTH vs. ROUGH). The analysis used ensemble decomposition to isolate wave-resolving and turbulent components of velocity, enabling the calculation of turbulent kinetic energy (TKE). Each test yielded depthand time-averaged TKE (𝐾̂) values to compare turbulence across conditions. Roughness effects on turbulence intensity varied across cross-shore positions and wave conditions. Rough surfaces produced higher 𝐾̂values in only 5 of 27 comparisons, with smooth surfaces often generating higher turbulence levels, particularly at more oblique wave angles. Roughness effects were strongest at more onshore sensors under low-angle wave conditions, while turbulence generally increased with wave height at all positions. These results highlight the complex relationship between bed roughness, wave forcing, and turbulence generation in nearshore environments, contributing to a better understanding of hydrodynamics relevant to sediment transport and coastal protection.