HomeMy WebLinkAbout; ; Beach Reconnaissance Report No 2; 1988-03-01TON-138
CITY OF CARLSBAD
BEACH RECONNAISSANCE
REPORT NO. 2
DECEMBER 1987
SUBMnTED TO
CITY OF CARLSBAD
BY
CHOULE SONU
TEKMARINE. hiC.
PASADENA, CA
MARCH 1988
Bi-Monthly Beach Reconnaissance
December 28, 1987
Executive Summary
In the preceding inspection performed during October 13 and 21, 1987,
beaches between Oceanside Harbor and the public beach south of the Agua
Hedionda entrance jetties, a distance of about 6 miles, were essentially
sandy. At that time, cobbles made their first substantial appearance at
Manzano Drive, progressively increasing in volume further to the south. In
the current (December 28, 1987) inspection, cobbles began to appear in sub-
stantial quantity already at Mountainview Drive (at the outlet of Buena
Vista Lagoon), only about 3 miles south of Oceanside Harbor. This meant
that the sandy belt extending southward from the south fillet of Oceanside
Harbor has shrunk about 3 miles in the intervening two-month period, a
result of the usual seasonal cycle.
This seasonal erosion has occurred in the form of the thinning sand veneer
on the beach surface at distances beyond 3 miles from Oceanside Harbor.
Since the sand veneer is underlain immediately by the resident cobbles,
cobbles became exposed in varying amounts in proportion to the degree of
sand removal. As a result, beach elevations have become lower along the
stretches where sand has been lost, allowing the leading edge of the waves,
called swashes, clash directly on the riprap at a number of locations. A
low beach elevation was particulary noticeable at Wisconsin Avenue, merely
2 miles south of Oceanside Harbor.
The reconnaissance inspection at this time further demonstrated that the
City of Carlsbad shoreline and the shoreline further to the south, as far
as Moonlight State Beach, Encinitas, are typically " source-starved", mean-
ing that there is insufficient sand to absorb the full wave energy
available for littoral transport. Cobbles are the dominant beach material
at Pine Avenue (at the north end of the seawall) and as far south as
Moonlight State Beach, Encinitas. There is also little or no indication
that cobbles are undergoing significant longshore movements; they appear
essentially a resident deposition. The inspection at this time has
revealed no unusual events nor occurrences.
Note: Prior reconnaissance
October 13 and 21, 1987.
December 28, 1987
WISCONSIN AVENUE (OCEANSIDE)
The beach is quite flat; but is reasonably wide, consisting
dominantly of sand.
December 28, 1987
FORSTER AVENUE (OCEANSIDE)
The flatness of the beach is clearly indicated by the high ground
water on the beach surface south of the rock groin in the upper
photo. There is slightly more sand on the upcoast than on the
downcoast sides of the rock groin, attesting to the southward
movement of littoral drift.
December 28, 1987
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OCEANSIDE BOULEVARD (OCEANSIDE)
The beach is even narrower here. The downcoast view reveals
rapidly diminishing beach widths in that direction.
December 28, 1987
CASSIDY STREET (OCEANSIDE)
The beach is all but non-existent; the swash front is directly on
the riprap. The slope is approximately 1 : 30.
December 28, 1987
MOUNTAIN VIEW DRIVE (CARLSBAD) (BUENA VISTA LAGOON OUTLET)
Cobbles begin to make their presence felt at this location, and
the rock foundation outcrops on the beach surface - both the in-
dications that the sand veneer is now very thin.
December 28, 1987
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BEECH AVENUE (CARLSBAD)
The amount of cobbles on the beach increases progressively south-
ward, much of them piled against the base of the riprap.
December 28, 1987
PINE AVENUE, CARLSBAD (NORTH END OF NEW SEAWALL)
Cobbles become more dominant than sand at this location. The
beach face is somewhat steep here owing to the abundance of
cobbles on the upper beach.
December 28, 1987
ACACIA AVENUE. CARLSBAD (CARLSBAD STATE BEACH)
Cobbles are present on the upper beach, but the beach elevation
is generally low because sand has been lost from the beach. Note
that the rock foundation underlying the seawall is now exposed.
December 28, 1987
AGUA HEDIONDA LAGOON (CARLSBAD)
The public beach in front of Agua Hedionda Lagoon is now essen-
tially a cobble beach. A steep escarpment dividing the patches
of cobble and sand marks the limit of erosion from a previous
storm, which removed both cobble and sand from the beach. Only
cobbles have returned to the beach subsequently, in amounts which
are apparently insufficient to heal the escarpment.
December 28, 1987
MANZANO DRIVE (CARLSBAD)
The beach is made up entirely with cobbles.
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December 28, 1987
ENCINAS CREEK OUTLET (CARLSBAD)
Sand is completely absent on the beach face.
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December 28, 1987
POINSETTIA LANE (SOUTH CARLSBAD STATE BEACH)
Essentially a cobble beach, except for a narrow strip of sand
along the water's edge.
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December 28, 1987
BATIQUITOS LAGOON OUTLET (CARLSBAD)
The beach is covered fully with cobbles. The entrance to the
lagoon is closed.
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December 28, 1987
MOONLIGHT STATE BEACH (ENCINITAS)
A fully cobble beach.
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