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5— Santa Margarita River South through Oceanside and Carlsbad
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Cobble Beaches

In southern California beach cobbles are derived from two sources: from rivers as the result of floods, and from sea cliff erosion (Emery 1955). The longest cobble beach in southern California is found in south Carlsbad (Emery 1960:184) (fig. 23a ). During the storms of January 1983, the beach cliff eroded six to ten feet in places (fig. 23b ). In 1960, Emery noted that the cobbles of this beach, which is presently owned by the State of California, were the result of local cliff erosion. Today, however, the cobbles are much larger and were most likely dredged from the Oceanside small-boat harbor to the north, as early as 1963.


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Figure 24a
September 1979 view looking north along The Strand at Oceanside. The structure and road were located on the
former beach. Riprap was placed to protect the concrete seawall and road.
Photo : G. Kuhn.

Figure 24b
February 1980 view looking at the same site as that in 24 a . The road and seawall were undermined and collapsed
between 12 and 15 February 1980; the waves were less than six feet high.
Photo : G. Kuhn.


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During the storms of 1978 from the south, the beach sand was rapidly removed by storm surge, and the cobbles were withdrawn by the waves and thrown like artillery against houses at Oceanside (Kuhn and Shepard 1980). The cobbles became a destructive element again in the winter of 1980, contributing to the undermining and collapse of the beach road (figs. 24a , 24b ) and to the damage to apartments and homes along the shore (figs. 25a , 25b ). In south Oceanside, roofs collapsed and windows were broken as the cobbles again became projectiles (fig. 26), although the waves were consistently less than six feet in height. Even where riprap protected the shore, the cobbles moved as far as twenty feet up the beach (fig. 27a ). The stones were seen to move along the shore and by June 1978 had largely disappeared (fig. 27b ).

The Army Corps of Engineers (Hales 1978:27–32) suggested several alternatives for stabilizing the sand and creating a buffering beach at Oceanside. These included rock revetments, concrete seawalls, groin systems, sand-fills, breakwaters, and a permanent sand bypass system. At the present time sand-fills are the only method being attempted.


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Figure 25a
View of beach cottages south of Wisconsin Street in Oceanside, 4 January 1978.
Photo : G. Kuhn.

Figure 25b
View at the same site as that in 25 a , taken 17 February 1980. Wave and beach cobble
abrasion damaged houses along the shore during the February storms. Property damage
occurred as the result of cobbles being thrown by waves less than six feet in height.
Photo : G. Kuhn.


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Figure 26
February 1980 view of the damaged beach cottage in south Oceanside.
Note that the windows were shattered and the roof collapsed as a result
of cobbles being thrown by relatively small waves.
Photo : G. Kuhn.

Figure 27a
January 1978 photo of beach cobble abrasion in south Oceanside. Cobbles
moved up the beach eighteen to twenty feet, covered the riprap seawall in
places, and eroded lawns behind the seawall.
Photo : G. Kuhn.

Figure 27b
June 1978 view at the same site as that in 27 a . Only remnant
pockets of cobbles remain.
Photo : G. Kuhn.


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Figure 28a
April 1978 view of eroding beach at Carlsbad.
Photo : G. Kuhn.

Figure 28b
July 1980 view of the same site in Carlsbad. The sand did not return to the beach this year during the summer.
The cobbles have eroded behind and around the seawalls and the riprap and adjacent to the building.
Photo : G. Kuhn.


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