Quantification of Hydrodynamic Forcing on Spherical Objects in the Swash Zone

Hydrodynamic forcing and mobility of spherical objects in the swash zone are quantified through laboratory experiments over mobile beds. Similar studies have been conducted over fixed beds. However since swash zone bed levels are highly dynamic, applicability of these results to natural conditions are limited. The experiments were conducted in a two-dimensional wave flume with a planar slope (1:7) sand beach installed at one end of the flume. The slope was reshaped and replicated for each test using a weighted screed pushed along a fixed track located on the flume walls. On the opposing end, a swash event was simulated by a ‘dam-break’ mechanism. Experiments were modeled to analyze a single swash event impinging on a spherical object. Repeatable swash-zone hydrodynamics with no object in the flume were sampled at five cross-shore locations using profiling velocimeters to quantify the velocity in the boundary layer, electromagnetic current meters to measure the near-bed horizontal velocity, ultrasonic distance meters to measure the water level, and a laser system to evaluate bed level change. Identical tests were conducted with spherical objects to observe mobility. Scenarios were tested with different sphere weights, cross shore positions, and initial burial depths. Geo-referenced imagery from two overhead cameras was used to quantify the time history of object position and swash run up distance. Test cases were repeated to provide ensemble averages of the measurements. The results of the swash hydrodynamics and object kinematics are coupled to estimate a force balance on the object under different scenarios. This research will assist in future studies of object transport such as cobblestones or unexploded ordinance in the natural swash zone. Preliminary results will be presented and discussed.