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 City of Solana Beach
Section 3
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Environmental Impact Analyses
Seawalls
Effects of Seawalls on Shoreline Erosion
The importance of understanding the influence of seawalls and other engineered protective
structures on the dynamics of the shoreline is well recognized. The active urbanization along
the southern California coastline brought about concern on the part of the coastal property
developers and owners with the rates of cliff erosion and retreat, overall cliff stability, and
possible mitigation options. The short-term rate of erosion accelerated following the severe
El Nino storms of 1982-83 and 1997-98. As increased coastal erosion and cliff collapse
jeopardized the existence of the upper bluff properties, a number of protective seawalls were
constructed at the base of the coastal cliff. These seawalls prevented an immediate property
loss, but were thought by some as having an adverse effect on the public beach. There was no
documented evidence that seawalls caused beach or coastal bluff erosion.
The southern part of Solana Beach, especially areas underlain by the weakly consolidated
material such as old alluvial channel deposits, faced the problems first, and several seawalls
were constructed in the early 1970s and 1980s. The northern part, underlain by the more
resistant sandstone bedrock exhibited extensive formation of seacaves primarily along joints
and other planes of weakness. The infilling of seacaves and notches with erodible concrete
constituted the major protective measure. The three seawalls constructed in the northern part
of Solana Beach are Tide Park (1972), Mullen Wood (1992), and Colton (2000). Most of the
seawalls south of Fletcher Cove were built prior to 1980.
Effects of Seawalls on Beaches
Although understanding the effects of seawalls on beaches is important, it should be kept in
mind that the majority of seawalls were designed for the purpose of protecting landward
structures from erosion, and not for protecting the beaches.
Interactions of the beaches and seawalls remain the subject of debate in the scientific
community, and there are very few long-term quantitative field studies available that document
these interactions. The majority of these types of studies include field observations over a
relatively short period of time and lack sufficient data on long-term effects of waves, beach
profiles, and shore configuration (Kraus, 1987; Wiegel, 2000). Dr. Wiegel (2000) reports only
two well-documented and complete field studies (Griggs and others, 1994; Basco and others,
1994). A third study began in 1993 on Duck Lake, Michigan. This study has not been
completed and is not specifically relevant to the subject case (due to unsimilar conditions).
The better-documented field studies conclude that seawalls, in general, do not cause long-term
beach erosion, except for special circumstances, such as the prevention of the erosion of dunes
or sandy bluffs that supply downdrift beaches, or acting as a groin with resulting shoreline
updrift and recession downdrift (Dean, 1987; Wiegel, 2000). Dr. Wiegel (2000) pointed out that
comparisons of beaches with structures and beaches without structures often led to a
Project No. 323530000
Page 3-14
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