3 Functional Design 



This chapter describes study procedures and results for a shore-protection 

 functional design aimed to reduce the rate of loss of beach fill at Monmouth 

 Beach. An analysis was performed on the geometrical configuration of the 

 structures at the project site to obtain an empirical criterion relating groin length 

 and spacing between groins. Any design-involving placement of a groin field 

 should be consistent with successful groin performance at the site. Then, the 

 GENESIS numerical model (Hanson and Kraus 1989) was evaluated for 

 describing shoreline change of a beach protected by multiple groins and T-head 

 groins. This evaluation was accomplished by comparing calculated shoreline 

 positions with those measured in a movable-bed physical model. 



Two means of specifying boundary conditions at the project for GENESIS 

 were considered, and a regional sediment-budget approach was taken after 

 evaluation of results. Design alternatives were developed based on experience at 

 the site and objective of the study. The alternatives were then examined with the 

 calibrated GENESIS model and refinements made to arrive at two recommended 

 designs for consideration by the New York District. The evaluation was based 

 on a criterion of minimum landward encroachments by the shoreline on the 75-ft 

 (23-iTi) protective bemi width over a 6-year simulation interval. Time series of 

 measurements of the locally incident waves were supplied as forcing conditions 

 for the model. 



Empirical Evaluation of Groin Performance 



For developing alternatives for the functional design of a groin field at the 

 Monmouth Beach hot spot, aerial photographs taken south of Monmouth Beach 

 were examined to evaluate performance of the existing groin field. The primary 

 objective of the proposed groin field at Monmouth Beach is to maintain a 75-ft 

 storm berni width along the 2,600-ft-long (800-m) hot spot. 



The reach of shoreline evaluated ranges between Groins 51 and 104 (Long 

 Branch to Asbury Park city limits) as referenced in the GDM. This reach of 

 shoreline was selected for its close proximity to the hot spot and isolation of the 

 structures within this region from the influence of the beach-fill project con- 

 structed to the north. The set of aerial photographs taken 1 1 October 1997 was 

 analyzed in the evaluation because it represents the most recent aerial 

 photography available for this study. The October 1997 shoreline between 



12 Chapters Functional Design 



