Single wave overtopping volumes and their travel distance

Single wave overtopping volumes and their travel distance Coastal Structures 2007, Venice Lykke Andersen, T. , Aalborg University, Denmark Burcharth, H. F. , Aalborg University, Denmark Gironella, X. , UPC, Barcelona, Spain SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 1 of 17

Introduction • The critical overtopping is typically given as an average discharge and not as single wave overtopping volume and velocity, which are expected to be more directly associated to hazards. • The landward distribution of overtopping in combination with the single wave overtopping volume can be used to give an idea of the damage/forces exerted on a structure. • The landward distance the overtopping water travel put restrictions to the use of these areas and their drainage. SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 2 of 17

Methodology for single wave overtopping estimations: 1. Estimate mean overtopping discharge (e. g. CLASH Neural Network or conventional overtopping formulae) 2. Estimate number of overtopping waves 3. Estimate maximum single wave overtopping volume (use results from 1 and 2) 4. Estimate travel distance of maximum single wave overtopping volume The present work deals with step 2, 3 and 4 for rubble mound breakwaters. SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 3 of 17

Experimental set-up (main tests) Lykke Andersen, 2006 (Ph. D thesis - includes both large and small scale data) • Chambers more narrow at the bottom for good accuracy also for small overtopping discharges. • Chambers equipped with surface elevation gauges and pumps configured to start and stop automatically during tests. • Wave steepness s 0 p: 0. 02 – 0. 045 SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 4 of 17

Experimental set-up (additional tests) Burcharth et. al, 2007 (Puerto de la Cruiz, small scale tests) Long waves (s 0 p = 0. 01) SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 5 of 17

Data analysis • Controlling of pumps in overtopping chambers from data acquisition software (e. g. Wave. Lab 2 software package from Aalborg University). • Select water levels for start and stop of each pump. • Measure levels in chambers and state of pumps. SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 6 of 17

Methodology for single wave overtopping estimations: 1. Estimate mean overtopping discharge (e. g. CLASH Neural Network or conventional overtopping formulae) 2. Estimate number of overtopping waves 3. Estimate maximum single wave overtopping volume (use results from 1 and 2) 4. Estimate travel distance of maximum single wave overtopping volume SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 7 of 17

Number of overtopping waves Formula by Van der Meer & Janssen (1995) Non-breaking waves: • • f = 0. 4 used Armour crest freeboard used (Ac) for all four crosssections Burchart et. al, 2007 ( f = 0. 55) Gives in most cases values in the correct order of magnitude. Large difference between the two data sets. SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 8 of 17

Number of overtopping waves Formula by Besley (1999) Number of overtopping waves related to the dimensionless overtopping discharge: Gives a very good estimate for all tested cases! SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 9 of 17

Methodology for single wave overtopping estimations: 1. Estimate mean overtopping discharge (e. g. CLASH Neural Network or conventional overtopping formulae) 2. Estimate number of overtopping waves 3. Estimate maximum single wave overtopping volume (use results from 1 and 2) 4. Estimate travel distance of maximum single wave overtopping volume SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 10 of 17

Single wave overtopping volume Franco et al. (1994), Van der Meer and Janssen (1995): A = 0. 84, B = 0. 75 Weibulls plotting position formula is used: Combining the two equations leads to: i = 1 => Similar to the equation used by Franco et al. (1994) and van der Meer and Janssen (1995) except that they used Now instead of Now +1 in the logarithm. SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 11 of 17

Single wave overtopping volume Upper envelope: A = 1. 63, B = 0. 75 Lower envelope: A = 0. 60, B = 0. 75 Central: A = 1. 12, B = 0. 75 Franco + Vd. M: A = 0. 84, B = 0. 75 Large Now: Franco + Vd. M is close to a central estimate Small Now: Franco + Vd. M is close to a lower limit (unsafe prediction of Vmax) SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 12 of 17

Methodology for single wave overtopping estimations: 1. Estimate mean overtopping discharge (e. g. CLASH Neural Network or conventional overtopping formulae) 2. Estimate number of overtopping waves 3. Estimate maximum single wave overtopping volume (use results from 1 and 2) 4. Estimate travel distance of maximum single wave overtopping volume SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 13 of 17

Landward distribution of mean discharge Formula by Lykke Andersen & Burcharth, 2006 Ratio of overtopping passing travel distance x at splash down level h level: where is the angle of incidence More than 1000 tests SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 14 of 17

Landward distribution of max single wave overtopping volume Application of formula for distribution of mean discharge on max single wave overtopping volume. Distribution of large single wave overtopping volumes seems not to be very different from the distribution of the mean discharge SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 15 of 17

Influence of wind & scale effects • In the EU-CLASH project differences between prototype and small scale overtopping results have been observed. • The differences might be due to model effects (e. g. wind) or scale effects. • Wind and scale effects are expected to be most pronounced for relatively small overtopping discharges (q < 1 l/sm). • The presented formula for landward distribution of overtopping is limited to green water overtopping and cannot predict travel distance of wind carried spray. • The influence of scale effects on the landward distribution is expected to be quite small as indicated by the test results in large and small scale. SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 16 of 17

Conclusions • Experimental results on overtopping of individual waves have been analysed. • A calculation procedure for calculating single wave overtopping volumes and their travel distance has been presented. • The formula by Besley (1999) estimate the number of waves overtopping with great accuracy in all of the tested cases. • The existing formula for single wave overtopping volume has been slightly modified to account for cases with few overtopping waves. Upper and lower envelope curves has been given for single wave overtopping volume. • The travel distance of maximum single wave overtopping volumes is quite similar to that found for the mean discharge. Thank you for your attention! SINGLE WAVE OVERTOPPING VOLUMES AND THEIR TRAVEL DISTANCE Lykke Andersen, Burcharth & Gironella Coastal Structures 2007, Venice, July, 2007 17 of 17