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Resource Issues: Landslide and Debris

Ecology of the Big Sur Coastline

The Big Sur coastline along the central coast of California is unparalleled in natural beauty, an incredible mix of high cliffs, rugged canyons and crashing surf. This stretch of coastal wilderness is an international treasure and a special place for residents and visitors alike. Big Sur is also a unique and special area in the sanctuary, where the continental shelf is narrow, hugging the coastline and several deep, submarine canyons come close to shore. Deep, cold, nutrient-rich waters are upwelled at Point Sur, supporting plankton blooms and providing the foundation for a rich diversity of marine life, including algae, invertebrates, kelp forests, rockfishes, seabirds, sea otters, sea lions and migrating marine mammals. Onshore, a relatively thin series of coastal watersheds drain the coastal terrain, connecting land and sea through steep canyons of oak woodlands or towering redwoods.

History of Highway 1

Highway 1 along the Big Sur coastline was constructed in the 1930's and opened in 1937. Parts of the highway north of Big Sur follow the Old Coast Road, completed from Monterey to Big Sur by Monterey County in the 1880's. Construction of the highway involved extensive excavations that utilized steam shovels and blasting of this diverse geological landscape. Fill was placed in minor canyons and bridges constructed across major canyons. The highway has a long history of landslides that have both landed on the highway and undermined the road bed. Road closures have been common, with long-term closure mainly due to large landslides in years of heavy rainfall.

Landslide Management History

In conducting landslide repair work on Highway 1 prior to the designation of the sanctuary, maintenance practices of the California Department of Transportation (Caltrans) often involved moving landslide and road repair debris into the adjacent marine environment. Maintenance and catastrophic road repair activities often deviated considerably from the natural patterns of slide movement and sediment transport in marine systems. The disposal of landslide debris affects marine habitats and biological communities by direct burial, sediment scour and turbidity plumes of fine suspended sediment.

The severity of winter storms in 1998 closed Highway 1 along the Big Sur coast for several months, and subsequent landslide and road repairs resulted in approximately 1 million cubic yards of excess material. Sanctuary regulations (http://montereybay.noaa.gov/intro/mp/regs.html#prohibitions) prohibit the discharge of material within its boundaries, and secondly, prohibit the disposal of material outside the sanctuary boundaries that subsequently enters the sanctuary and harms resources. However, sanctuary management allowed the disposal of some material between the highway and mean high tide line at specific sites, with specific criteria such as compaction of fill and revegetation.

Changes in Landslide Management

As a result of the storms of 1998, Caltrans moved forward on the development of a management plan for Highway 1 long the Big Sur coastline, from Carmel River in the north to San Carpoforo Creek in the south. This entire area is adjacent to sanctuary waters. The development of the Coast Highway Management Plan (CHMP) was led by Caltrans, in conjunction with other regulatory agencies including the sanctuary, and congressional and community representatives. As a result, Caltrans made a significant effort to identify land disposal sites as a proactive approach to deal with future landslides. However, the amount of cubic yards that these sites can accommodate is limited, and therefore Caltrans asked the sanctuary to consider ocean disposal in the future. So, even though the regulations prohibit side-casting of the land-slide materials (e.g., soil, rocks, vegetation placed down slope of the highway), Caltrans can request a permit from the sanctuary.

Ecological studies support landslide disposal management

Understanding the sensitivity of shoreline habitats to existing disposal practices is key to effectively minimizing the negative effects of landslide material deposition or redistribution on or near the shoreline. The sanctuary and the CHMP lacked such a thorough understanding of marine resources along typical landslide areas and sites where Caltrans may seek to dispose of rock and soil debris onto the shoreline and into the ocean. The Marine Resources Survey (http://sanctuarysimon.org/projects/project_info.php?projectID=100280), and subsequently the Big Sur Nearshore Characterization (http://sanctuarysimon.org/projects/project_info.php?projectID=100312), were among the first comprehensive studies to accurately characterize selected intertidal and subtidal communities of fishes, invertebrates, and algae that are potentially impacted by natural landslides and subsequent disposal management practices. Many of the results have been aggregated by sanctuary staff in a GIS database initiated by the CHMP. The resulting GIS project contains over 100 spatial data sets including shoreline types, aerial photos, geological data, and Hwy 1 postmiles. Sanctuary staff use this database to inform permitting processes and update it as new information becomes available (e.g., we have since added abalone critical habitat data).

landslide diagram

URL: http://montereybay.noaa.gov/resourcepro/resmanissues/landslide.html    Reviewed: March 05, 2014
Web Site Owner: National Ocean Service

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