Figure 25. Cumulative volume change at Vero Beach P.E.P. Reef installation (Stauble, 2002).

Submerged Narrow-Crested Breakwaters

711

slightly larger gain of 15.31 cu m/m (6.10 cu yd/ft). The north

m/m (7.54 cu yd/ft) length of beach and in the south control

control area showed the largest gain in sand volume of 31.88

zone gain an average 30.1 cu m/m (12.01 cu yd/ft).

cu m/m (12.70 cu yd/ft). The majority of the volumetric gain

The majority of the volumetric changes in the P.E.P. Reef

in all three zones occurred on the berm area of the profile.

zone occurred landward of the breakwater axis and in both

This gain in sand on the berm in December 1999 reflects the

control zones landward of the natural hardbottom. Little

rapid recovery of sand to the beach by a period of fair weather

change was detected in all of the profile volumes seaward of

waves in November and December after the storms, which

the P.E.P. Reef axis and over the natural hardbottom.

ended in October.

A similar trend in sediment volume was observed over the

Settlement

winter months between December 1999 and June 2000 with

a slight gain averaging 7.3 cu m/m (2.9 cu yd/ft) in the P.E.P.

Detailed survey measurements of reef settlement were lim-

Reef zone, mostly on the upper beach adjacent to the sea-

ited to the first two years of the study. The tops of each unit

walls. A larger gain of 14.8 cu m/m (5.91 cu yd/ft) was mea-

were surveyed immediately after placement and during sub-

sured on the beaches in the south control zone, again mostly

sequent survey periods. Biofouling occurred very rapidly, and

on the foreshore and berm (Figure 26). The north control zone

the growth of marine organisms had to be scraped off the tops

experienced a slight loss in volume averaging 3.3 cu m/m

of the units to measure the top of the concrete on each survey.

( 1.31 cu ft/yd), which was mostly confined to the nearshore

The inner P.E.P. Reef segments settled approximately 1 m

area of the profile between 0 NGVD and the first hardbottom

(3.4 ft) and the outer segments settled 0.9 m (2.8 ft) during

outcrop. The berm and foreshore also gained sand volume in

the first four months (Figure 27). The units over hardbottom

this zone. The long-term project monitoring measured during

settled until the units rested on the hardbottom, which

the August 1996 to June 2000 period, showed that the area

caused some shifting over the uneven bottom. The units over

to the north of the P.E.P. Reef experienced an average accre-

sand also settled during this adjustment period. After initial

tional volume of 28.6 cu m/m (11.39 cu yd/ft). Volume change

settlement, the units remained more-or-less stable over the

in the vicinity of the P.E.P. Reef averaged a gain of 18.9 cu

rest of the monitoring period. During the final extended year

Journal of Coastal Research, Vol. 19, No. 3, 2003