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 Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 7
gradient of the shore platform ranges from approximately one to two percent. The
boundary between the seacliff (the lower, vertical and near-vertical section of the
bluff) and the shore platform is called the cliff-platform junction, or shoreline angle.
Photo Nos. 9 and 10 (Blackburn collection), taken from just south of Tide Park on
December 12, 1997, during a -1.2 foot MLLW tide, show the gently seaward sloping
bedrock shore platform denuded of sand with minor erosion channeling extending
up to the differentially eroded seacliffs. Photo No. 11 (Folger collection) shows
Tabletop Reef and the shore platform within the northern portion of the study area.
Within the nearshore zone is a subdivision called the inshore zone, beginning where
the waves begin to break (Figure 2). This boundary varies with time because the
point at which waves begin to break is a function of wave height, tidal level, and
sand level. During low tides, large waves will begin to break far out to sea. During
high tide, waves may not break at all, or they may break directly on the lower
seacliff. Closer to shore is the foreshore zone, that portion of the shore lying
between the upper limit of wave wash at high tide and the ordinary low water mark.
Both of these boundaries usually lie on a sand or shingle beach. The foreshore
zone is not designated on Figure 2, since the transient shingle/beach deposits are
not shown. More importantly, insufficient sand beach exists today to support the
backshore, or elevated beach, which typically remains dry and defines the landward
edge of the foreshore. Thus, at Solana Beach, the foreshore extends to the sea cliff
and allows waves, on a daily basis, to impact directly upon, and actively erode, the
coastal bluff.
2.3.2 Classification of Bluff Geometry
Assessing the rate of coastal retreat requires an understanding of the dynamic
relationship between the upper bluff and seacliff. Emery and Kuhn (1982)
developed a global system of classification of coastal bluff profiles, and applied that
system to the San Diego County coastline from San Onofre State Park to the
southerly tip of Point Loma. In their regional study, the Solana Beach area is
designated as Type AC (c)@ (see Figure 3). The letter AC@ designates coastal bluffs
having a resistant geologic formation at the bottom, and less resistant materials in
the upper parts of the bluff. The relative effectiveness of marine erosion of the lower
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