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COPYRIGHT 2006 Coastal Education & Research Foundation, Inc.
ABSTRACT
GUNAYDIN, K. and KABDASLI, M.S., 2006. Protection of shoreline by using partial revetment structure under regular and irregular waves. Journal of Coastal Research, 22(6), 1349-1359. West Palm Beach (Florida), ISSN 0749-0208.
In this paper, results obtained from an experimental investigation conducted to determine wave-induced geometric characteristics of shorelines protected by partial revetment structure are presented. The experiments were performed with both regular and irregular waves. The beach sand used in this study had a mean diameter of 0.35 millimeter and a specific gravity of 2.63. The beach had an initial slope of 1:5 and was protected by the partial revetment structure. For this purpose, the armor units, mean diameters and specific gravities of which were varied in the range 8.5-67.95 millimeters and 1.81-2.77, respectively, were placed on the wave-breaking area. Different wave groups were generated over an initially flat, partially protected beach, and a number of geometric characteristics of equilibrium beach profiles was determined. Moreover, the static damage of the armor layer was obtained for all test groups. The results of this experimental study were evaluated, and empirical expressions based on the results were formulated to define geometric parameters of equilibrium profile under pure regular waves, pure irregular waves, and regular-irregular waves. The findings showed that the partial revetment structure decreases shore erosion on average 65-70%. Because the sand of the unprotected area spreads over the armor layer, this revetment type does not disturb the beauty of the area and its aesthetics. Moreover, it is a low-cost structure, because the armor layer was placed only within the wave-breaking area, not across the entire slope.
ADDITIONAL INDEX WORDS: Partial revetment, static stability, dynamic stability, static damage, beach profile, coastal erosion, armor layer, wave channel.
INTRODUCTION
Classical shoreline protection structures are large in size because of their design criteria. As a result, environmental consciousness has grown, with expectations that coastal areas will be protected by structures that are in aesthetic harmony with the environment. Also, low-cost shore protection structures are preferred. In this study, a partial revetment structure that is low in cost, is in harmony with the environment, does not disturb the beauty of the area, and has aesthetic value has been investigated for the protection of shoreline. The behavior of the structures and the geometric characteristics of unprotected parts of the wave-induced equilibrium beach profile are described under both regular and irregular waves.
Because waves apply more energy to the wave-breaking area, protection of this area is more important. As shown in Figure 1, the armor layer is placed below the still water level, and only the wave-breaking area of the sand beach is protected. Therefore, this revetment structure is called a partial revetment. The unprotected part of the beach exposed to waves is highly dynamic. On this part of the beach, the sand transports downward and spreads over the armor layer. As a result of this phenomenon, wave-induced coastal erosion takes place and an offshore bar is formed. To describe the geometric characteristics of an equilibrium beach profile for which the partial revetment structure is applied, the parameters Xe, he, Xp, hp, Xu, hu, Xc, hc, Xb, and hb are used. Xe and he are the distance and depth from the maximum erosion point to the maximum upper erosion point, respectively; Xp and hp are the distance and depth from the low point of the erosional area to the maximum upper erosion point, respectively; Xu and hu are the distance and depth from the top point of the offshore bar and the maximum erosion point, respectively; Xc and hc are the distance and depth from the bar crest to the maximum upper erosion point, respectively; and Xb and hb are the distance and depth from the low point of the bar to the maximum upper erosion point, respectively. Various factors play vital roles on the values of these parameters, including wave characteristics, sediment properties, characteristics of armor units, and armor layer types.
[FIGURE 1 OMITTED]
As mentioned previously, a partial revetment structure contains an armor layer, which is a static structure, and an unprotected part of the beach, which is a dynamic structure. Therefore, the partial revetment structure includes both dynamic and static stability concepts.
To describe the static stability of armor layers of breakwaters and revetments under wave impact, considerable research has been performed in recent years. To determine the weight of an armor unit, empirical formulas were proposed by HUDSON (1959), IRIBARREN (1938, 1965), SVEE, TRAETEBERG, AND TRUM (1965), RAICHLEN (1974), and BRUUN (1985). The Coastal Engineering Research Center Shore Protection Manual (CERC 1984) recommended a table of stability numbers ([K.sub.D]). The importance of the surf similarity parameter and of breaking types on the stability of armor units were investigated by AHRENS (1975), AHRENS AND MC-CORTNEY (1976), and BRUUN AND GUNBAK (1976, 1977). This parameter was introduced by IRIBARREN (1950) and elaborated by BATTJES (1974). The permeability effect was studied by HADER (1986) and VAN DER MEER (1988). VAN DER MEER (1988) also investigated the angle of wave attack and proposed some empirical formulas that included the wave height, wave period, properties of the armor unit, wave-breaking type, permeability, and angle of wave attack. The degree of armor damage was studied by LOSADA, DESIRE, AND ALEJO (1986), VIDAL, LOSADA, AND MEDINA (1991), and VIDAL, LOSADA, AND MANSARD (1995a). BRUUN (1985) analyzed wave reflection, calculated from the envelope of wave records of maximum and minimum wave heights. MELITO AND MELBY (2002) proposed a new empirical model to predict run-up levels for rock revetments and analyzed reflection coefficients. The...
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