16 
The hot spot at Monmouth Beach is approximately 0.7 miles south of 
Shrewsbury Rocks. Impacts of the rocks on the beach-fill project are expected 
directly inshore from the rocks or to the north, not to the south. The expected 
impact could include increased wave height and a local reversal in wave 
direction, producing gradients in longshore sand transport. A previous study of 
coastal processes in the region (Kraus et al. 1988) showed one example of wave 
height and angle variation along the shore from the wave transformation model 
RCPWAVE (Figure 14 reproduces Figure |] from Kraus et al.). Figure 14 
shows, for an incident wave angle of 101.5 deg (-7.5 deg in wave model), the 
wave amplification at Cell 142 is 1.7. Cell 142 is approximately directly west of 
Shrewsbury Rocks, near sta 218. More southerly wave directions would move 
the location of the wave focusing further north of the rocks. 
The bathymetry contours just south of Shrewsbury Rocks angle offshore 
toward the rocks. This bathymetry feature could increase the breaking wave 
angles on the northern portion of the hot spot and contribute to a local increase 
in northerly sand transport. It is interesting to note that the indentation in the 
shoreline to the north of the hot-spot region is located in the lee of Shrewsbury 
Rocks. Accelerated erosion of the recently completed beach fill in the lee of 
Shrewsbury Rocks (centered around sta 218) may be a future concern. 
Storms 
Nineteen storms with maximum wave heights exceeding 6.6 ft (2 m) were 
measured at the Long Branch directional wave gauge during the 27 months of 
data collection (approximately 19 months, excluding gauge downtime). Storm 
peaks are denoted as the time when the maximum wave height occurred. Table | 
summarizes peak wave conditions for each storm. The peak period and direction 
are the period and direction associated with the maximum wave height. Storm 
duration is the approximate length of time when the wave height exceeded 6.6 ft 
(2m). Wave conditions exceeding 6.6 ft (2 m), sorted by storm magnitude, are 
listed in Appendix A3. The period of record at the Long Branch gauge is not 
sufficient to characterize the storm climatology, but does give examples of 
typical, short-return-period storm conditions. The range of peak directions for 
wave heights exceeding 6.6 ft (2 m) is 86 to 140 deg, with a mean direction of 
109 deg. The storm wave conditions imply predominant storm transport to the 
north in Contract 1A. Focusing of wave energy by Shrewsbury Rocks would be 
manifested as a hot spot in the middle or northern half of Contract 1A (near 
sta 218), not the southern end. Storm wave directions are approximately shore 
normal (100 deg) or well south of shore normal (130 deg). Waves in the 
northeast quadrant are fetch limited, because of the presence of Long Island, and 
wave heights are limited to approximately 1.6 ft (0.5 m). 
Chapter 2 Waves Focusing by Shrewsbury Rocks 
