Validity of the equilibrium beach profiles: Nile Delta Coastal Zone, Egypt M.F.M. Kaiser a, ⁎, O.E. Frihy b a Geology Department, Faculty of Sciences, Suez Canal University, Ismailia, Egypt b Coastal Research Institute,15 El pharaana Street, 21514, El Shallalat, Alexandria, Egypt abstract article info Article history: Received 12 December 2005 Received in revised form 27 July 2006 Accepted 5 September 2006 Available online 18 November 2008 Keywords: Cross-shore Morphodynamics Beach fill Sand transport Cross-shore sediment transport Longshore sediment transport Beach nourishment Beach profile equilibrium is the principal concept assumed by most numerical modelling. The response of beach profile configuration to natural and anthropogenic changes could be predicted to help in selecting the most appropriate engineering design required to mitigate coastal erosion and accretion alongshore. Thus, in order to apply coastal engineering projects, the predicted profile of equilibrium should be close enough to the measured profile. Therefore, before application of numerical modelling techniques, equilibrium expressions have to be validated at the study site. This research aims to assess the validity of the equilibrium profile concept on the Nile Delta coast based on beach profiles surveyed in 1990 from the main promontories; Abu-Quir Bay, the Rosetta promontory and the El-Burullus promontory. The results indicate that the equilibrium beach profile is consistent with the measured profiles at the study sites beyond 200 m distance offshore at -4 m depth. In contrast, the equilibrium status is not valid along the beach face at -1 m depth. Accreted beaches at Abu-Quir bay and Burullus promontory are characterized by wide berms and gentle beach face whereas eroded stretches at Rosetta promontory have a narrow berm and steep beach faces. The measured profiles are also compared with the exponential beach profile concept. An exponential hypothesis is not valid along the Nile Delta coast. Profiles measured at Abu-Quir, Rosetta and El-Burullus depart significantly from the exponential equation. Despite the fact that equilibrium expression can describe beach profiles along the Nile Delta, one equilibrium profile equation is not sufficient to assess all beach profiles. This can be explained as the morphology of beach profiles is subjected to some factors including; sediment characteristics, wave parameters and closure depth, which vary alongshore. Analysis of the validity of the equilibrium beach profile is recommended to get accurate results in modelling simulations and design the most appropriate engineering projects required for shore protection. © 2008 Published by Elsevier B.V. 1. Introduction A beach profile represents the cross-shore morphology of the beach along the coast; it may extend out through the breaker zone and into deep water offshore (Komar, 1998) and the landward limit tends to end at the berm or backshore. An equilibrium beach profile represents a profile morphology which has adjusted its shape to the characteristics of the incoming waves (Bruun, 1954; Komar, 1998). Larson (1991) described the equilibrium beach profile for a beach of a specific grain size, its shape displays no net change in time when it is subjected to constant short-period breaking waves. The equilibrium can be achieved experimentally because wave parameters approach- ing the shore are constant, but in reality the beach may not achieve a full stability. It has been documented in many field studies that coarser beaches are characterized by steeper slopes (Bascom, 1951; Dubois, 1972; Wright and Short,1984). In contrast, finer beaches show gentle slope profiles. This result was confirmed by the results obtained by Bagnold (1940), Rector (1954) and Van Hijum (1974) from laboratory wave-tank experiments. Therefore, the morphological features and steepness of the equilibrium profile, predicted at a specific coastal zone, depend mainly on the grain size characteristics of beach sand at the concerned site. Prediction of beach profile change based on field experience is not recommended, it should be supported by numerical models. Most models such as GENESIS (Hanson and Kraus, 1989) are based mainly on the concept of beach profile equilibrium. The final answer to the validity of the equation should come from extensive field measurement of beach profiles (Pilkey et al., 1993). Modelling is required to determine the grain size of fill material, the volume of fill material and position of filling which applied to beach sand nourish- ment projects. Studying the relationship between grain size, equili- brium profile and wave conditions shows that the use of materials equally coarse or coarser than the native sediment is recommended in beach nourishment (Komar, 1998). Otherwise, the nourished sand will immediately be moved offshore and thus a new flatter equilibrium profile corresponding finer sand will be generated. The equilibrium hypothesis is also used to predict cross-shore beach profiles required in the design of coastal engineering projects (Bruun, 1954; Dean, 1977, Geomorphology 107 (2009) 25–31 ⁎ Corresponding author. Tel.: +20643230368. E-mail addresses: mona_kaiser66@hotmail.com (M.F.M. Kaiser), frihyomr@link.net (O.E. Frihy). 0169-555X/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.geomorph.2006.09.025 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph