Australian Journal of Basic and Applied Sciences, 3(3): 2717-2827, 2009 ISSN 1991-8178 Corresponding Author: Babak Kamali, Institute of Ocean and Earth Sciences (IOES), University of Malaya, 50603 Kuala Lumpur, M alaysia Tel: 0060379676855 Fax: 0060379676994 E-mail: b_kamali@perdana.um.edu.my E-mail: kamali_babak@hotmail.com 2817 Recent Advances in Stability Formulae and Damage Description of Breakwater Armour Layer Babak Kamali and Roslan Hashim Institute of Ocean and Earth Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia Abstract: The present paper gives a brief overview of the current state-of-the-art for estimating stability of rubble mound breakwater armour layer, identifying a set of relevant aspects, such as definition of damage, type of armour units, and the sea state. Since all the stability formulae are designed to estimate the appropriate weight of armour units corresponding to a certain damage level, different methods of damage assessment are distinguished, and most well-known stability formulae are discussed with the emphasis on definition of damage. Key words: breakwater, armour layer, stability formulae, damage description INTRODUCTION Determination of the armour layer stability is a matter of concern to many coastal engineers. The uncertainties that come from the complex nature of the wave and nearshore currents, diversity of variables, and the stochastic wave-structure interactions dominate the accuracy of stability estimation. Since 1950s, various experimental studies have been carried out to improve analysis and design of armour layer, seeking to decrease the uncertainties and to avoid overestimating or underestimating armour weight. However, predicting the stability of armour layer still rely to a large extent on the designer’s experience. Different failure modes that can cause damage to a rubble mound breakwater are illustrated in Fig. 1. Armour units hydraulic instability is among the most critical failure modes since it can disintegrate armour layer and consequently initiate progressive failure that is likely to make the breakwater unable to function. This paper aims to briefly overview the major advances in the stability formulae of armour layer with the emphasis on definition of damage and the parameters that affect the hydraulic stability of armour layer, discuss some of widely accepted methods, and address key problems and shortcomings. Fig. 1: Breakwater failure modes. Source: Burcharth (1991) Damage Description: Generally, the main functions of the armour layer are to decrease incident wave energy and wave run-up and to protect the inner layers of a rubble mound breakwater or a revetment from eroding and washing away. To fulfil these goals, armour units should have enough structural and hydraulic stability in order to stay on the mound layer during the storm attacks, protecting the slope without major damage.