Coupled Longshore and Cross-Shore Models for Beach Nourishment Evolution at Laboratory Scale Servet Karasu 1 ; Paul A. Work 2 ; M. Kemal Cambazoğlu 3 ; and Ömer Yüksek 4 Abstract: A series of three-dimensional laboratory experiments on beach nourishment behavior are described and analyzed. The experi- ments were designed to isolate the inﬂuences of berm height, beachﬁll median grain size, wave height, and wave period. The results have not been scaled up to prototype conditions, but many features of the laboratory evolution have also been observed in previous ﬁeld studies. Laboratory results indicate that beachﬁll half-life time required for half of the added volume to leave the nourished footprint is inversely correlated with wave height, and positively correlated with berm height. A weak positive correlation with grain size was found. The inﬂuence of wave period was inconclusive. A coupled model describing the effects of both longshore and cross-shore sediment transport was developed and applied. The model accounts for the rapid loss of nourishment material offshore via cross-shore sediment transport, followed by a more gradual redistribution up- and downcoast of the project via longshore sediment transport. The inﬂuence of cross-shore sediment transport decreases as the beach slope approaches that of the prenourishment beach. The new model has not been calibrated for application at ﬁeld scales, but it does reproduce the salient features of the laboratory dataset, and previous ﬁeld data sets, such as the ﬂattening of the beach proﬁle as the project evolves. By describing the position of three elevation contours berm crest, waterline, and beachﬁll toe, it thus provides a more realistic alternative to the “one-line” models often applied to beach nourishment problems by accounting for cross-shore sediment transport. DOI: 10.1061/ASCE0733-950X2008134:130 CE Database subject headings: Beach nourishment; Numerical models; Sediment transport; Laboratory tests. Introduction Beach nourishment, sometimes referred to as artiﬁcial nourish- ment, beach replenishment, or beachﬁll, involves the placement of large quantities of sand along or near a shoreline, typically in response to long-term shoreline recession. The material is often pumped by dredge from offshore or from an area in need of deepening, or delivered by truck from an upland site e.g., Kerchaert et al. 1986; Wang and Gerritsen 1995; Kana et al. 1997; Muñoz-Perez et al. 2001. Generally it is desired that the new material be slightly coarser than the native sediment, and of simi- lar color and composition Madalon et al. 1991; Schwartz et al. 1991; Kana and Mohan 1998; Creed et al. 2000; Benedet et al. 2004. Sediment quantities exceeding 1 million m 3 per project are not uncommon, and total costs can exceed United States $10 mil- lion per project. In the United States, between 1950 and 1994, a total of 132 shore protection projects were authorized by the United States Congress Committee on Beach Nourishment and Protection, National Research Council 1995, and the U.S. Army Corps of Engineers spent an average of United States $25 million/ year in 2001 dollars on beach nourishment during this period. Hamm et al. 2002 state that 597 sites have been nourished, with 348 million m 3 of sand, throughout Europe since the early 1950s. The annual rate of nourishment is quoted as 28 million m 3 . Nourishment projects are not a permanent solution to beach erosion problems, as they typically do not drastically or perma- nently alter the processes originally responsible for the erosion, but rather delay their consequences. In many locations, hard ero- sion control structures are prohibited and beach nourishment is the only viable option. As a result, many sites have been nour- ished multiple times. Simpliﬁed analytical or numerical models are often used to make predictions of project lifetime. These tools are often acknowledged to represent only some of the processes inﬂuencing project lifetime e.g., Dette et al. 1994. Previous investigations of beach nourishment performance and behavior have been conducted via analytical or numerical model- ing Larson and Kraus 1991; Dean and Yoo 1992; Walton 1994; Groenewoud et al. 1997; Work and Rogers 1997; Walton et al. 2005, laboratory experiments Dean and Yoo 1994; Donohue 1998; Work and Rogers 1998; Dette et al. 2002 and prototype scale measurements Bodge et al. 1993; Work and Dean 1995; Larson et al. 1998; Browder and Dean 2000; Matias et al. 2004; Seymour et al. 2005. A reliable numerical model that provides a detailed description of all of the relevant physical processes— wave transformation, interactions with mean ﬂows in and near the 1 Lecturer, Rize Vocational School, Rize Univ., 53100 Rize, Turkey. E-mail: skarasu@ktu.edu.tr 2 Associate Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Savannah Campus, 210 Technology Circle, Savannah, GA 31407-3039 corresponding author. E-mail: paul.work@gtsav.gatech.edu 3 Graduate Research Assistant, School of Civil and Environmental Engineering, Georgia Institute of Technology, Savannah Campus, 210 Technology Circle, Savannah, GA 31407-3039. E-mail: mkc@gatech.edu 4 Professor, Civil Engineering Dept., Karadeniz Technical Univ., 61080, Trabzon, Turkey. E-mail: yuksek@ktu.edu.tr Note. Discussion open until June 1, 2008. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be ﬁled with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on June 30, 2006; approved on March 27, 2007. This paper is part of the Journal of Waterway, Port, Coastal, and Ocean Engineering, Vol. 134, No. 1, January 1, 2008. ©ASCE, ISSN 0733-950X/2008/1-30– 39/$25.00. 30 / JOURNAL OF WATERWAY, PORT, COASTAL, AND OCEAN ENGINEERING © ASCE / JANUARY/FEBRUARY 2008