One method of evaluating different transition plans is to compare total 

 life cycle costs for the beach restoration and periodic nourishment projects 

 with alternate combinations of transition angle and length and select the plan 

 that provides optimum improvement (e.g., the plan with the lowest life cycle 

 costs to accomplish the project objectives). Chapter 4, Section V,3 provides 

 equations and procedures for determining longshore transport rates along beach 

 segments with varied transition angles. As the transition angle decreases, 



(1) The expected rate of erosion per unit length of the transition zone 

 decreases. 



(2) The length of the transition fill increases and hence the volume of 

 required fill increases. 



(3) The volume of fill required for periodic nourishment increases in 

 order to maintain the longer length of project shoreline. 



These varying relationships make possible an optimization procedure to 

 minimize the cost of a transition plan. 



An example situation could be to minimize transition costs for a beach 

 fill on a beach which 



(1) Is widened 56 meters (184 feet). 



(2) Requires 7.5 cubic meters of fill per square meter (0.9 cubic yard 

 per square foot) of beach. 



(3) Is eroding at a rate of 22 cubic meters per linear meter (8.8 cubic 

 yards per foot). 



(4) Has a left-to-right yearly littoral transport rate of 425,000 cubic 

 meters (555,900 cubic yards) generated by waves with a breaker angle of 

 23°. 



(5) Has a right-to-left yearly littoral transport rate of 85,000 cubic 

 meters (111,200 cubic yards) generated by waves with a breaker angle of 

 15.5°. 



A comparison of alternate transition plans for this example indicates that 

 minimal costs would be achieved with a long transition segment (1070 meters or 

 3510 feet) oriented at about 3° to the existing shoreline. This example is 

 intended to illustrate that optimal transition zones are generally quite long 

 and oriented at gentle angles to the existing shore. It may sometimes be more 

 practical, however, to either compartment the beach-fill material with groins 

 or construct fairly sharp transition angles and deal with high rates of fill 

 loss at project boundaries if land ownership constraints or other factors 

 preclude the construction of the optimum transition. 



g. Feeder Beach Location . Dimensions of a stockpile or feeder beach are 

 generally governed primarily by economic considerations involving comparisons 

 of costs for different nourishment intervals. Therefore, planning a stockpile 

 location must be considered in conjunction with stockpile dimensions. If the 

 problem area is part of a continuous and unobstructed beach, the stockpile is 



5-23 



