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 City of Solana Beach
Section 3
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Environmental Impact Analyses
End scour, or "flanking" is the most often observed seawall effect. It is manifested in
accelerated erosion and lowering of the beach adjacent to the side ends of the protective
structure, especially at the downdrift ends. This effect is reported at the shores backed by
erodible dunes or bluffs. In some cases the end scour effect is primarily due to the seaward
location of the seawall on the beach profiles, e.g., projecting into the surf zone and obstructing
the longshore sediment transport. In the other instances, it may be caused by wave reflection
from the return or end walls (Tait and Griggs, 1991). This is also addressed under long-term
effects.
Scour trough formation was reported both on unprotected beaches and protected beaches, in
front of seawalls, subsequent to hurricanes in South Carolina and Florida. The beach recovery
results were variable, and no clear conclusions on the impact of the seawalls on the beach
recovery process could be drawn. No similar troughs were observed in response to storms in
California (Tait and Griggs 1991).
Deflated (flat) profiles, or lowering of the beach elevations in front of seawalls, were observed by
Griggs and others (1997) during erosive winter season in response to the interaction of waves
with seawalls. This effect is similar to scour trough, except that it is not hurricane induced, but
rather limited to the duration of the winter erosional phase.
Beach cusps were also observed by Griggs and others (1997) in front of seawalls and appeared
to correspond with the formation of deflated profiles.
Sand accretion is sometimes observed when the wall is projected into the surf zone (due to
long-term erosion, seasonal beach width fluctuation, or in response to a storm) and interrupts
the longshore sediment transport, acting as a groin. The wider beach may be formed updrift of
the wall, with the narrowing of the beach downdrift.
It is unlikely that any of the short-term effects would be associated with the seawall constructed
at the base of the relatively resistant cliffs in Solana Beach. Deflated profiles may be observed
adjacent to both unprotected and protected cliffs, as the beach narrows or disappears, and the
gradient of the beach profile may increase. Therefore, short-term effects of shoreline protection
structures such as those allowed under the Shoreline and Coastal Bluff Protection Ordinance
are considered less than significant.
Long-term Effects
Tait and Griggs (1991) and Griggs and others (1994) concluded that whereas the single most
important factor in evaluating the potential effects of seawall construction on beach erosion is
whether or not the shoreline is undergoing a net long-term retreat, geomorphic shore type plays
a role in the impact of stabilizing a shoreline undergoing net retreat (such as the Solana Beach
shoreline) (Tait and Griggs, 1991). It has been long recognized by coastal engineers that the
position of the seawall on the beach profile, and relative to the surf zone, is very important
(Wiegel, 2000). The best location for the seawall is at the back of the beach where it protects
against the largest storms (Tait and Griggs, 1991). Tait and Griggs (1991) conclude that
Project No. 323530000
Page 3-16
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