University of Twente Student Theses


Suspended sediment distributions under regular breaking waves.

Til, S.W. van (2014) Suspended sediment distributions under regular breaking waves.

[img] PDF
Abstract:In November and December 2013 experiments were conducted to find out what the effect of breaking waves is on the sediment transport processes. The research was conducted in the CIEM wave flume in Barcelona, where a beach with a slope of 1:10 was created. The beach consisted of medium sized sand ( = 0.246 mm) and the slope was established to create breaking waves. The waves with a height of 0.85 m and a period of 4 s broke at the top of the slope and 13 measurements of 10 minutes were taken. A suction sampling system was used to measure the concentrations. The suction sampling system consists of suction nozzles that are attached to a pump. With this pumps water and sediment are extracted at different elevations in the water column. The used instruments in this report were attached to the mobile frame that could move in the cross-shore and in the vertical direction. This way the position of the instruments could be changed per measurement. The measuring procedure and the changing conditions during the experiments resulted in a random error of 11.3%. The errors are mainly based on findings of Bosman et al. (1987). Because this experiment has different conditions than the experiments where Bosman et al. found the errors, the total error is assumed to be higher. The measured and calculated sediment concentrations show that the highest concentrations are found near the bottom. Sediment concentrations and its distributions were different depending on the measuring position in the wave. Three zones were distinguished: the shoaling zone (zone before breaking), the breaker zone (zone where the waves break) and the surf zone (zone between breaking zone and the shore). In the breaker zone the highest concentrations were found and the turbulence of the breaking wave kept the sediments in suspension. The sediment concentrations in the surf zone were ±2 times lower than in the breaker zone and the concentrations decreased further shoreward. In the shoaling zone the concentrations were comparable to the surf zone, but the concentrations at higher elevations were lower. On the top of the 1:10 slope a sand bulge was formed by wave-induced currents. This bulge is called a breaker bar and as the time passed it increased in size. As it became higher, the waves plunged stronger and the sediment concentrations increased. The breaker bar did not find an equilibrium height like was expected, so the plunging strength increased every measurement. When the data was approached with a trend line, the concave Rouse trend line fitted best for almost all the measurements. This was different from the findings of Aagaard et al. (2013) who found an exponential profile in the breaker zone. For this report a literature study performed with which the results were compared. It was found that the shapes of the concentration profiles are generally in line with other researches. Because not many measurements were taken for this report, the results give only a good estimation of the processes that occur under, and around breaking waves.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
Link to this item:
Export this item as:BibTeX
HTML Citation
Reference Manager


Repository Staff Only: item control page