Influence of wind and current on wave-run up and wave overtopping

Influence of wind and current on wave-run up and wave overtopping

Lorke, S.
Bornschein, A.
Schüttrumpf, H.
Pohl, R.

TU Delft

Flowdike

2012-04-01

The investigations of FlowDike 1 and FlowDike 2 on the effects of onshore wind and longshore current on wave run-up and wave overtopping for perpendicular and oblique wave attack. These variables were two of the missing effects in freeboard design and therefore a main interest for design purposes. Model tests were carried out in the shallow water wave basin at DHI (Hersholm, Demnark) and included the configuration of a 1:3 sloped dike (FlowDike 1) and a 1:6 sloped dike (FlowDike 2). The data analysis on wave run-up was based on an advanced data extraction from video films considering 10 separate strip es of the run-up board which provided additional measurement results. In a first step the measured wave run-up was analyzed with respect to the influence of single parameter oblique wave attack. onshore wind and a longshore current. Results considering oblique wave attack confirm former empirical investigations. The increasing effect of onshore wind on wave run-up as described regarding former model tests with monochromatic waves could not be validated by the FlowDike test results. The investigated onshore wind speed of < 10 m/s had no significant effect on the wave run-up in the model tests with the 1:3 sloped dike and a very slightly decreasing effect in the model tests with the 1:6 sloped dike. Furthermore no significant effect on wave run-up in case of a longshore cm-rent velocity < 0.4 m/s and a perpendicular wave attack was obtained. In a second step the combined effect of oblique wave attack and a longshore cm-rent was investigated. The results show non obvious dependencies but it has to be considered that the relative wave run-up height is a very sensitive parameter. The third step within data analysis was the comparison between measured and calculated relative wave nun-up. Calculation was done using the formula of EUROTOP-MANUAL (2007) together with the estimated influence factors. The comparison shows a good agreement between the measured and the calculated values. All pairs of values are in a range of± 20 %. The tests on perpendicular wave attack without influencing parameter validated the extreme wave overtopping formulae from the EUROTOP-MANUAL (2007). For both model tests the data points of the reference tests fit well within the 95 % confidence range of the formula. All wind tests confumed the stated assmnptions by Gonzlez-Escirva (2006) aud De Waal et al. (1996) concerning the significant wind impact on small overtopping discharges. For high overtopping discharges practic.ally no influence is noticeable as the data points for wind match those of the reference test, thi.s validales the stated theory of Ward et al. (1996). The influence of oblique waves on overtopping was analyzed as a last resort. In a first attempt the results found for both investigations validate the trend for obliqueness to reduce wave overtopping. The influence factors found for FlowDike 1 validate we 11 the regression trend found for former investigations. For wave overtopping the combination of oblique wave attack and longshore current was analyzed by determining an influence factor. Using therefore the relative wave period instead of the absolute wave period lead to rather high values and does not account the current influence on wave overtopping. Instead of that the influence-factor can be detenniued by using the angle of wave energy instead of the angle of wave attack. The influence factors for the angle of wave attack, the longshore current and wind on wave set-up correspond well to the influence factors on wave overtopping. For both analysis on wave run-up and wave overtopping the absolute wave parameters and the angle of wave attack should be used. According to the modification of empirical coefficients used in formulae by Schüttrumpf and Van Gent (2003) it is possible to determine the flow depths and flow velocities on the seaward side of the crest. Additionally the dimensionless flow depths for different dimensionless freeboard height and different angles of wave attack have been analyzed. The higher the angle of wave attack the smaller is the dimensionless flow depth for unchanged dimensionless freeboard heights. This behavior corresponds well with the characteristics of the wave overtopping rate. Further investigations on very oblique wave attack with slopes > 45 degrees are planned within the HYDRALAB IV project CornerDike.

overtopping
overflow
run-up

TLJ700600

http://resolver.tudelft.nl/uuid:73cb6cbe-8931-4499-b4d6-aa31548f5dda

RWTH Aachen, Institute of Hydraulic Engineering

Hydralab IV report for KfKI

Hydraulic Engineering Reports

report

© 2012 Authors