INTRODUCTION: THE CREST ELEVATION OF BREAKWATER AS WELL AS ARMOR WEIGHT IS A FUNCTION OF HYDRAULIC CONDITION I.E WAVE AND WATER LEVEL. IT IS NOTICEABLE THAT WATER LEVEL IS ITSELF RELATED TO THE COMBINATION OF STORM SURGE AND TIDAL VARIATION. EACH OF THESE PARAMETERS (WAVE, STORM SURGE AND TIDAL ELEVATION) CAN BE ANALYZED SEPARATELY. FOR EXAMPLE 100 YEAR WAVE IS A WAVE THAT POSSIBLY OCCURS EVERY 100 YEARS.HOWEVER THE 100 YEAR WAVE AND THE 100 YEAR WATER LEVEL MAY NOT OCCUR SIMULTANEOUSLY EVERY 100 YEARS. IT'S OBVIOUS THAT CONSIDERING THESE EVENTS SIMULTANEOUSLY AS A 100 YEAR HYDRODYNAMIC DESIGN CONDITION WOULD BE UNREALISTIC AND SO CONSERVATIVE. YET, THIS UNREALISTIC COMBINATION HAS BEEN USED NUMEROUSLY AND IT IS ALSO APPLYING NOW BY INTERNAL CONSULTANTS BECAUSE OF THE LACK IN DATA AND KNOWLEDGE. THIS HAS MADE THE PROJECTS CONSERVATIVE AND ALSO EXPENSIVE.TO CALCULATE THE EXACT RETURN PERIOD OF THE ACTUAL SITUATION, JOINT PROBABILITY ANALYSIS SHOULD BE PERFORMED BY MEANS OF THESE VARIABLES AND THEIR SPECIFIC DEPENDENCY. UTILIZING THIS METHOD, COMBINATION OF WATER LEVEL AND WAVE HEIGHT CAN BE CONSIDERED AND DESIGN HYDRAULIC CONDITION CAN BE DEDUCED PROPERLY. HERE, THE ACTUAL DESIGN CONDITION IS CALCULATED FOR SHAHID BEHESHTI DEVELOPMENT PROJECT AS AN ACTUAL CASE STUDY.