Table 4 



Monmouth Beach Groins (modified from New York District 1989) 



structure 

 Number 



Material' 



Length 

 ft 



Average 

 Crest 

 Elevation 

 ftNGVD 



Crest 

 Width 

 ft 



Stone 



Size 



ft/ton^ 



Condition 



Year 

 Built 



41 



1.2,3 



350 



10.8 



10-15 



4-6/10.3 



Fair 





42 



1,2 



110 



11.1 



12-14 



4-5/7.5 



Poor 



1923 



43 



1,2 



80 



5.4 



10 



3-4/3 5 



Poor 





44 



1,3,4 



710 



10.9 



10-15 



4-6/10.3 



Fair 



1924 



45 



1,2,3,4 



360 



6.5 



15 



3-5/5.3 



Fair 



1966 



46 



1,2,4 



490 



8.0 



12 



4-6/10.3 



Fair 



1927 



M -stone, 2-timber, 3-steel, 4-concrete. 

 ^1/1/ = dV where y = 165 Ib/cu ft- 



Structure Design 



The 100-ft extension of Groin 44 (Alternative 3) will be added to the seaward 

 end of the existing structure, directed perpendicular to the updrift shoreline. The 

 present crest elevation of the seaward end (+1 1 .0 ft NGVD) will be extended for 

 the groin extension for 33 ft, connecting to a sloping section (approximately 

 1 :6.6) for 33 ft. and terminated by the seaward horizontal section at +6.0 ft 

 NGVD. Side slopes will be 1:2. 



Design wave 



Wave conditions for specification of structure stone size are depth-limited 

 breaking waves determined from the nearshore slope adjacent to Groin 44 and 

 from three storm-surge water levels ( 1 0-. 50- and 1 00-year recurrence intervals) 

 (New York District 1989). The June 1994 (prefill) Profile 255 (Smith, Gravens, 

 and Smith, in preparation) was selected as the design condition because it 

 represents a reasonable eroded condition that maximizes the water depth and 

 breaking wave height at the structure. Figure 37 shows the June 1994 profile, the 

 equilibrium nearshore profile, the center-line cross section of Groin 44. the 

 proposed Groin 44 extension, and the three water-level elevations. From this 

 figure, the depth at the exposed part of the structure relative to each water level is 

 identified for calculating the depth-limited breaking wave. Table 5 lists the 

 water-level elevation, profile elevation, and water depth for each condition. 



The maximum, depth-limited wave height for each water level was deter- 

 mined from the water depth of each design water level and wave data from the 

 Long Branch gauge. Ten periods (midvalue in each of the 1-sec period bands 

 ranging from 3 to 13 sec) from the Long Branch wave gauge (see Appendix A) 

 were selected for calculating the depth-limited breaking wave height. The 



Chapter 4 Structure Design 



41 



