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

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Orange County Coastal Regional Sediment Management Plan northwest-southeast direction and is exposed to a complex array of sea and swell that drives sediment transport generally to the southeast. The beaches along this stretch of coast range from intermittently narrow at Surfside, wide at Bolsa Chica State Beach, narrow at the Huntington Cliffs, wide at the Huntington Beach Pier to West Newport Beach, narrow near the Newport Pier, and wide at the Balboa Peninsula in Newport Beach. As in the case of the Seal Beach Littoral Cell, human intervention has strongly influenced coastal processes in this littoral cell. Of particular importance are periodic beach replenishments at Surfside-Sunset Beach and West Newport Beach and modifications at Bolsa Chica Ecological Reserve, Huntington Beach Wetlands, and the Santa Ana River. Also, coastal subsidence resulting from petroleum extraction was observed focused around the Huntington Cliffs (City of Huntington Beach, 1996). Natural processes affecting the cell include sediment input from the Santa Ana River and bluff erosion at Huntington Cliffs; the transport of sediment in both the alongshore and cross-shore directions under the influence of waves and currents; and the loss of sediment to Anaheim Bay, Newport Bay, and Newport Submarine Canyon. Gadd et. al. (2006) found that the Surfside-Sunset Beach nourishment project provided substantial increases in beach width over time, not just at Surfside-Sunset Beach, but also farther southeast through littoral transport to Bolsa Chica State Beach, Huntington City Beach, Huntington State Beach and to West Newport Beach. They estimated that the project increased beach widths cumulatively at a rate of 5.2 feet/year at Surfside-Sunset Beach, 4.1 feet/year at Bolsa Chica State Beach, 1.6 feet/year at Huntington Cliffs, 4 feet/year at Huntington City Beach and 4.1 feet/year at West Newport Beach. These rates are substantial and indicate that the impacts of the project extend well beyond Surfside-Sunset Beach and have provided substantial increases in beach width over time. Key quantitative sediment components of this littoral cell include the following: • Beach nourishment at the Surfside-Sunset Beach has totaled over 20 million yd 3 from 1945 through 2009. The source of this material was Anaheim Bay and offshore (Mesa, 2011). • Newport Beach has received over 9 million yd 3 of nourishment from 1935 through 2009, of which over 1 million yd 3 was in the form of backpassing from within the Newport Beach area. The source of this material was the Santa Ana River, Balboa Peninsula, Newport Harbor, and Newport Beach (Mesa, 2011). • The following quantities were calculated from a sediment budget covering the time period from 1963 to 1995 (USACE, 2002b): o The Santa Ana River sand yield was estimated at 33,000 yd 3 /year. o Sediment losses were estimated at 10,000 yd 3 /year to Anaheim Bay; 3,000 yd 3 /year to Newport Bay; and 1,000 yd 3 /year to the Newport Submarine Canyon. Everest International Consultants, Inc. 2.13
Orange County Coastal Regional Sediment Management Plan o o o 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. Everest International Consultants, Inc. 2.14
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