Sedimentation Position Prediction in the Swash Zone of Sandy Beaches using Response Surface Method

Authors
M. motalebizadeh 1
M. Shafieefar 2
M. ghodsian 3
1 PhD student of Hydraulic, Faculty of Civil and Environmental Eng., Tarbiat Modares University
2 Prof., Coastal Engineering. Faculty of Civil and Environmental Eng., Tarbiat Modares University
3 Prof., Hydraulic Structures. Faculty of Civil and Environmental Eng., Tarbiat Modares University
Abstract
Reflective beaches requires a combination of lower waves, longer periods and particularly coarser sands. They are typically steep in beach profile with a narrow shoaling and surf zone, composed of coarse sediment. Coarser sediment allows percolation during the swash part of the wave cycle, thus reducing the strength of backwash and allowing material be deposited in the swash zone
The Swash zone, as extreme area of inner surf zone, influences coastal area and coastal structures. It defined as the part of the beach between the minimum wave run-down and maximum wave run-up. It constitutes a beach area where waves dissipate or reflect their remaining energy after traveling towards the shore. The role of Swash zone is influenced by incoming waves from surf zone, the geometry of beach face and the interaction between beach groundwater and surf zone.
The review of Laboratory researches indicated that wave height and period, beach slope, grain size distribution of beach material, still water level (SWL), beach groundwater level, the hydraulic conductivity of beach influence on the evolution of sand beaches. In a few laboratory researches, experiments is designed with One Factor At a Time method (OFAT) and the qualitative effect of parameters of regular wave height and period, SWL and beach groundwater level, and beach slope are investigated on nearshore evolution.
In this research, experiments are designed using Central Composite Design (CCD) of Response Surface Method (RSM). CCD is a type of response surface design that present very good predictions in the middle of the design space. Important properties and features of CCD are orthogonality, rotatability and uniformity. The quantitative effects and interactions of irregular wave height and period, beach groundwater level and SWL, and beach slope on beach profile evolution is examined in a sandy beach by 50 experiments designed with CCD. The experiments are carried out in laboratory flume in Faculty of Civil and Environmental Engineering, Tarbiat Modares University with high accuracy. The experimental setup is designed to simulate varying beach groundwater level and SWL and course sand (d50=0.8mm) is selected for beach material. Analysis of hydrodynamic data of the experiments indicated that the type of breaking waves is plunging wave and the hydrodynamic status of the swash zone is intermediate condition. The starting position of swash sedimentation (SWS) is extracted from mean of the beach profiles evolution.
By analyzing of experiments' SWS using CCD, a cubic model is suggested with %95 confidence level and predicted R-squared of 0.86. The results of model revealed that groundwater level has no significant effect on SWS. Wave height is the most influential factor affecting SWS and increasing wave height result to this position moves to upper beach rapidly. In addition, increasing beach slope causes the movement of SWS toward the beach. Increasing sea level lead to the displacement of SWS toward the sea.
This model indicated that the effect of wave height on SWS depends on wave period strongly and there is significant interaction between them. In addition, there is slightly interaction between the SWL and wave height and these variables influence on the role of each other in SWS.

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1. Nel R., et al., 2014 The status of sandy beach science: Past trends, progress, and possible futures. Estuarine, Coastal and Shelf Science, 150(0): p. 1-10.
2. Steele J. H., Thorpe S. A.& Turekian K. K., 2008, Encyclopedia of ocean sciences-volume 1: A - c. Elsevier ScienceDirect: Amsterdam.
3. Larson M., Kubota S.& Erikson L., 2004 Swash-zone sediment transport and foreshore evolution: Field experiments and mathematical modeling. Marine Geology, 212(1-4): p. 61-79.
4. Bakhtyar R., et al., 2009 Modeling sediment transport in the swash zone: A review. Ocean Engineering, 36(9–10): p. 767-783.
5. Elfrink B.& Baldock T., 2002 Hydrodynamics and sediment transport in the swash zone: a review and perspectives. Coastal Engineering, 45: p. 149-167.
6. Longo S., Petti M.& Losada I. J., 2002 Turbulence in the swash and surf zones: A review. Coastal Engineering, 45(3-4): p. 129-147.
7. Butt T., Russell P.& Turner I., 2001 The influence of swash infiltration–exfiltration on beach face sediment transport: onshore or offshore? Coastal Engineering, 42: p. 35-52.
8. van der Zanden J., et al., 2015 Bed level motions and sheet flow processes in the swash zone: Observations with a new conductivity-based concentration measuring technique (CCM+). Coastal Engineering, 105: p. 47-65.
9. Masselink G.& Turner I. L., 2012 Large-scale laboratory investigation into the effect of varying back-barrier lagoon water levels on gravel beach morphology and swash zone sediment transport. Coastal Engineering, 63(0): p. 23-38.
10. Steenhauer K., Pokrajac D., O'Donoghue T.& Kikkert G. A., 2011 Subsurface processes generated by bore‐driven swash on coarse‐grained beaches. Journal of Geophysical Research: Oceans, 116(C4).
11. Heiss J. W., Ullman W. J.& Michael H. A., 2014 Swash zone moisture dynamics and unsaturated infiltration in two sandy beach aquifers. Estuarine, Coastal and Shelf Science, 143(0): p. 20-31.
12. Erikson L., Larson M.& Hanson H., 2005 Prediction of swash motion and run-up including the effects of swash interaction. Coastal Engineering, 52: p. 285-302.
13. Masselink G.& Russell P., 2006 Flow velocities, sediment transport and morphological change in the swash zone of two contrasting beaches. Marine Geology, 227: p. 227-240.
14. Guza R. T.& Thornton E. B., 1982 Swash oscillations on a natural beach. Journal Of Geophysical Research, 87(C1): p. 483-491.
15. Miles J., Butt T.& Russell P., 2006 Swash zone sediment dynamics: A comparison of a dissipative and an intermediate beach. Marine Geology, 231(1-4): p. 181-200.
16. Baldock T. E., et al., 2011 Large-scale experiments on beach profile evolution and surf and swash zone sediment transport induced by long waves, wave groups and random waves. Coastal Engineering, 58: p. 214-227.
17. Alsina J. M., Cáceres I., Brocchini M.& Baldock T. E., 2012 An experimental study on sediment transport and bed evolution under different swash zone morphological conditions. Coastal Engineering, 68: p. 31-43.
18. Vicinanza D., et al., 2011 Swash zone response under various wave regimes. Journal of Hydraulic Research, 49(SUPPL.1): p. 55-63.
19. Ang L., et al., 2004, Measurement and modelling of controlled beach groundwater levels under wave action, in 15th Australasian Fluid Mechanics Conference. Sydney, Australia.: The University of Sydney. p. 17.
20. Horn D. P., Baldock T. E.& Li L. 2007. The influence of groundwater on profile evolution of fine and coarse sand beaches. in Proceedings of Coastal Sediments. New Orleans, LA.
21. Cartwright N., et al., 2006 Swash-aquifer interaction in the vicinity of the water table exit point on a sandy beach. Journal Of Geophysical Research, 111(C9): p. n/a-n/a.
22. Bezerra M. A., et al., 2008 Response surface methodology (RSM) as a tool for optimization in analytical chemistry. Talanta, 76(5): p. 965-977.
23. Montgomery D. C., 2012, Design and Analysis of Experiments, 8th Edition. John Wiley & Sons, Incorporated.
24. Mansard E. P. D.& Funke E. R., 1980 The measurement of incident and reflected spectra using a least squares method. Coastal Engineering Proceedings, 1(17).
 
Modares Civil Engineering journal
Volume 17, Issue 3
September and October 2017
Pages 183-184