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 Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 9
The Oceanside Littoral Cell is supplied with sediment by San Juan Creek in Orange
County, the Santa Margarita, San Luis Rey, and San Dieguito Rivers, and the San Onofre,
Las Pulgas, Buena Vista, Agua Hedionda, San Marcos, Escondido, and Los Penasquitos
Creeks. Presently over 40 percent of these rivers are controlled by dams and flood control
facilities; however, more importantly, significant sand mining activities within the upland
watershed has severed the majority of this beach building material to the coastline.
2.5
Littoral Sediments
In the historical past, the Solana Beach coastline has, at times, had a sand beach as much
as 100 yards wide (USCGS, 1887-88). Average beach width may have been on the order of
100 feet, recognizing that seasonal beach width fluctuations may also be on the order of
100 feet (Everts, 1991). Although the source of sand from the upland watershed is
episodic, only reaching the coastline during significant flood events within the geologic
past, sand from the upland watershed has continued to supply the littoral system with an
annualized sediment discharge volume estimated by various researchers to vary from
53,000 to 426,000 cubic yards per year, assuming similar climatic conditions (USCOE,
1991). Best-guess estimates for fluvial sediment production range from 160,000 to
200,000 cubic yards per year. The sediment contribution from coastal bluffs is more
difficult to evaluate, with coastal erosion contributions estimated to range from 10 percent
to 100 percent of the upland fluvial contributions.
Robinson & Associates, under contract to the U S Army Corps of Engineers (USCOE,
1988), estimated the total volume of beach sediments contributed from coastal bluff
erosion from 1889 through 1969 to total 28 million cubic yards for the Oceanside Littoral
Cell, averaging 351,000 cubic yards per year or approximately 100+ percent of the pre-
anthropic inland fluvial contribution. All things considered, this study appears to be flawed,
recognizing that along the entire 52-mile stretch of the Oceanside Littoral Cell,
approximately 0.7 foot per year of coastal bluff erosion would be required to generate this
volume of sediment on an annual basis. This suggests that in the last 80 years, over 50
feet of coastal bluff erosion should have occurred along the entire Oceanside Littoral Cell.
On the contrary, at least within the study area, little if any measurable coastal bluff erosion
occurred within the first 70 years of this century (Shepard and Grant, 1947; USCOE, 1960;
Everts, 1991; USCOE, 1991). Considerable beach nourishment has also occurred on
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