EVEREST June, 2013 - California Department of Boating and ...

Orange County Coastal Regional Sediment Management Plan
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Sediment loss due to land subsidence has been estimated at 72,000 yd 3 /year.
From 1934 to 1975 elevation decreases of as much as 6 feet were observed at
the Huntington Beach oil fields.
Offshore loss of sediment from the littoral cell was estimated at 78,000 yd 3 /year.
Other losses were negligible.
• Net longshore sediment transport is highly varied along the cell, depending on time
period and location within the cell, with rates ranging from 34,000 to 492,000 yd 3 /year, all
to the southeast (USACE, 2002b).
• For the entire littoral cell, the 1963 to 1997 period was marked by an average increase in
beach width of 4.1 feet/year and a corresponding volume increase of 4.7 yd 3 /foot-year
(Gadd et. al., 2006).
The lagoon at the Bolsa Chica Ecological Reserve with a direct tidal connection to the beach
and ocean was constructed in 2006. This lagoon requires periodic maintenance dredging to
maintain adequate tidal prism and habitat distribution. The lagoon has been dredged twice (i.e.,
2009 & 2011) since opening with material being placed on the beach between the inlet jetties
and the Huntington Cliffs. This temporary sediment sink has little effect to the long-term
sediment budget of the littoral cell since material entering the lagoon is eventually replaced on
the beach within the littoral system.
2.3.3 Laguna Beach Littoral Cell
The Laguna Beach Littoral Cell extends 13 miles from the Newport Bay Entrance in the
northwest to Dana Point Harbor in the southeast. This cell includes from northwest to southeast
the neighborhood of Corona del Mar (within the City of Newport Beach), Crystal Cove State
Park, the City of Laguna Beach, and the City of Dana Point. This cell is sometimes referred to
as the Laguna Beach Mini Littoral Cells due to the presence of 23 littoral sub-cells that exist
within the boundaries. This region is characterized by a high-relief coast which is irregular in
plan, consisting of small sandy pocket beaches backed by seacliffs and separated from one
another by headlands with reef extensions that function like underwater groins, retarding the
alongshore movement of sand.
A sediment budget was performed for the period from 1927 to 1984 revealing the following key
quantitative sediment components (USACE, 2002b):
• Sand discharge from streams represents the largest natural source of littoral material in
these cells, with 1,900 yd 3 /year coming from the Laguna Canyon watershed, 12,000
yd 3 /year from Aliso Creek, 1,200 yd 3 /year from Salt Creek, and modest quantities
coming from numerous smaller streams and creeks. These quantities are being
reduced, however, as the watersheds become developed.
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