Environmental Engineering Reference
In-Depth Information
Important parameters in evaluating the performance of a renourishment often
include the dry beach width, the volume of sand remaining after a storm, and the
remaining subaqueous sand volume (NRC
1995
). Coastline location is also used
as a key performance indicator, as in Holland where maintaining the 1990 coast-
line is one objective, while in the UK beach renourishment performance is often
measured against the standard of protection offered against flooding.
Controlling factors of nourishment performance vary from one project to
another, as well as spatially and temporally. For example, in three phases of ren-
ourishment at Sand Key Beach in west central Florida, controlling factors on per-
formance included location in the regional sediment transport regime, magnitude
of wave energy, sediment characteristics of the renourishment beach material,
local reversals in longshore transport, presence of hard structures, adjacent beach
nourishment, variation in coastline orientation, and beach fill technique (Davis
et al.
2000
).
Nevertheless, there are still doubts about the durability of beach renourishment
projects. Walton and Purpura (
1977
) found that several renourished beaches on the
Atlantic coast had performed poorly, and this they attributed to the widespread use
of undersized material, renourishment too close to tidal inlets, and unexpectedly
frequent storm activity. The proximity of beach renourishments to tidal inlets was
also considered a key factor in renourishment performance by Roberts and Wang
(
2012
). They used post-renourishment monitoring of a number of barrier island
beaches renourished in 2006, including Sand Key, Treasure Island and Long Key
in west-central Florida to demonstrate the importance of tidal inlet processes on
renourishment performance.
Pilkey and Clayton (
1987
,
1989
) critically reviewed more than 90 beach ren-
ourishment projects on the Atlantic coast and found that few had persisted as long
as originally predicted while most of them had proved far more costly than antici-
pated. South of Cape Kennedy engineers had been more successful in predict-
ing the fate of replenished beaches, with Miami Beach a notable success, but on
most of the beaches on the Atlantic coast the sand deposited had been completely
washed away in less than 5 years (26 % in less than a year), usually because of
erosion during storms; only 12 % had persisted for more than 5 years (Leonard
et al.
1990a
,
b
). Moreover, the renourished beaches had not recovered from hur-
ricanes as quickly as natural beaches.
In an editorial in the
Journal of Coastal Research
in 1990 Pilkey noted that
storms seemed to have been the major factor determining renourished beach lon-
gevity on the Atlantic coast, unpredicted erosion often being attributed to unusual
storm activity. The public were told that a replenished beach would recover during
fair weather, that loss rates would diminish over time, and that the lost sand had
moved offshore and would diminish wave energy on the depleted beach, so that
the next beach renourishment would last longer.
Questioning the success of Atlantic coast beach renourishment projects led
to a spirited discussion in the
Journal of Coastal Research
by Houston (
1990
),
Pilkey and Leonard (
1990
) and Houston (
1991
). This indicated that documenta-
tion of beach changes, both before and after renourishment, had been inadequate,
