A methodology for predicting future coastal hazards due to sea-level rise on the California Coast

Sea-level rise will increase the risks associated with coastal hazards of flooding and erosion. Along the active tectonic margin of California, the diversity in coastal morphology complicates the evaluation of future coastal hazards. In this study, we estimate future coastal hazards based on two scenarios generated from a downscaled regional global climate model. We apply new methodologies using statewide data sets to evaluate potential erosion hazards. The erosion method relates shoreline change rates to coastal geology then applies changes in total water levels in exceedance of the toe elevation to predict future erosion hazards. Results predict 214 km2 of land eroded by 2100 under a 1.4 m sea level rise scenario. Average erosion distances range from 170 m along dune backed shorelines, to a maximum of 600 m. For cliff backed shorelines, potential erosion is projected to average 33 m, with a maximum potential erosion distance of up to 400 m. Erosion along the seacliff backed shorelines was highest in the geologic units of Cretaceous marine (K) and Franciscan complex (KJf). 100-year future flood elevations were estimated using two different methods, a base flood elevation approach extrapolated from existing FEMA flood maps, and a total water level approach based on calculations of astronomical tides and wave run-up. Comparison between the flooding methods shows an average difference of about 1.2 m with the total water level method being routinely lower with wider variability alongshore. While the level of risk (actual amount of future hazards) may vary from projected, this methodology provides coastal managers with a planning tool and actionable information to guide adaptation strategies.

[1]  Paul D. Komar,et al.  An Application of LIDAR to Analyses of EI Nino Erosion in the Netarts Littoral Cell, Oregon , 2002 .

[2]  D. Inman,et al.  Climate Change and Potential Hotspots of Coastal Erosion Along the Southern California Coast , 2009 .

[3]  J. Titus,et al.  Greenhouse effect and sea level rise : a challenge for this generation , 1988 .

[4]  D. Cayan,et al.  Second California Assessment: integrated climate change impacts assessment of natural and managed systems. Guest editorial , 2011 .

[5]  N. Sitar,et al.  Processes of coastal bluff erosion in weakly lithified sands, Pacifica, California, USA , 2008 .

[6]  L. Robinson.  Marine erosive processes at the cliff foot , 1977 .

[7]  R. Gutierrez,et al.  Rain, waves, and short-term evolution of composite seacliffs in southern California , 2009 .

[8]  Hilary F. Stockdon,et al.  Empirical parameterization of setup, swash, and runup , 2006 .

[9]  R. Flick,et al.  Sand volume needs of Southern California beaches as a function of future sea-level rise rates , 2009 .

[10]  Peter H. Gleick,et al.  Assessing the costs of adapting to sea-level rise: a case study of San Francisco Bay , 1990 .

[11]  William G. McDougal,et al.  EXTREME WATER LEVELS, WAVE RUNUP AND COASTAL EROSION , 1997 .

[12]  Billy L. Edge,et al.  Ocean Wave Measurement and Analysis , 1994 .

[13]  P. Gleick,et al.  Potential impacts of increased coastal flooding in California due to sea-level rise , 2011 .

[14]  Paul D. Komar,et al.  Climate Controls on US West Coast Erosion Processes , 2006 .

[15]  W. Pilkey,et al.  The concept of shoreface profile of equilibrium: a critical review , 1993 .

[16]  C. Storlazzi,et al.  The Relationship Between Incident Wave Energy and Seacliff Erosion Rates: San Diego County, California , 2000 .

[17]  Emily Young,et al.  Climate change-related impacts in the San Diego region by 2050 , 2011 .

[18]  John J. Marra,et al.  Wave runup, extreme water levels and the erosion of properties backing beaches , 2001 .

[19]  Hilary F. Stockdon,et al.  Sea-cliff erosion as a function of beach changes and extreme wave runup during the 1997–1998 El Niño , 2002 .

[20]  A. Trenhaile.  Modeling the development of marine terraces on tectonically mobile rock coasts , 2002 .

[21]  Gary B. Griggs,et al.  Formation, evolution, and stability of coastal cliffs : status and trends , 2004 .

[22]  Cheryl J. Hapke,et al.  National assessment of shoreline change part 4: historical coastal cliff retreat along the California coast , 2007 .

[23]  M. Overton,et al.  NUMERICAL MODEL FOR DUNE EROSION DUE TO WAVE UPRUSH , 1984 .

[24]  Melvin J. Dubnick.  Army Corps of Engineers , 1998 .

[25]  S. Leatherman.  Coastal geomorphic responses to sea level rise: Galveston Bay, Texas. , 1984 .

[26]  Michael D. Dettinger,et al.  CLIMATE CHANGE SCENARIOS AND SEA LEVEL RISE ESTIMATES FOR THE CALIFORNIA 2008 CLIMATE CHANGE SCENARIOS ASSESSMENT , 2009 .

[27]  Dana K. Wingfield,et al.  Spatial and temporal variability in oceanographic and meteorologic forcing along Central California and its implications on nearshore processes , 2007 .

[28]  R. Holman,et al.  Estimation of Shoreline Position and Change using Airborne Topographic Lidar Data , 2002 .

[29]  P. Bruun.  Sea-Level Rise as a Cause of Shore Erosion , 1962 .

[30]  T. Parsons,et al.  Vertical tectonic deformation associated with the San Andreas fault zone offshore of San Francisco, California , 2008 .

[31]  Daisuke Mizuno,et al.  A Semi-Empirical Approach to Projecting Future Sea-Level Rise , 2007 .

[32]  Vincent R. Gray.  Climate Change 2007: The Physical Science Basis Summary for Policymakers , 2007 .

[33]  P. Komar,et al.  Cliff Erosion along the Oregon Coast: A Tectonic-Sea Level Imprint Plus Local Controls by Beach Processes , 1993 .

[34]  P. Gleick,et al.  THE IMPACTS OF SEA-LEVEL RISE ON THE CALIFORNIA COAST , 2009 .

[35]  C. Everts.  Sea Level Rise Effects on Shoreline Position , 1985 .

[36]  M. Larson,et al.  An analytical model to predict dune erosion due to wave impact , 2004 .

[37]  P. Ruggiero,et al.  Increasing wave heights and extreme value projections: The wave climate of the U.S. Pacific Northwest , 2010 .

[38]  Robert G. Dean,et al.  Numerical simulation of time-dependent beach and dune erosion , 1985 .

[39]  T. Sunamura,et al.  Geomorphology of rocky coasts , 1992 .

[40]  C. Hapke,et al.  Rates and Trends of Coastal Change in California and the Regional Behavior of the Beach and Cliff System , 2009 .

[41]  R. Guza,et al.  A comparison of two spectral wave models in the Southern California Bight , 1993 .

[42]  Henry F. Diaz,et al.  Evidence for Intensification of North Pacific Winter Cyclones since 1948 , 2001 .

[43]  Kenneth O. Emery,et al.  Sea cliffs: Their processes, profiles, and classification , 1982 .

[44]  N. Knowles.  Potential Inundation due to Rising Sea Levels in the San Francisco Bay Region , 2009 .

[45]  T. Edil,et al.  MECHANICS OF COASTAL LANDSLIDES AND THE INFLUENCE OF SLOPE PARAMETERS , 1980 .

[46]  C. Carter,et al.  Coastal erosion: Processes, timing and magnitudes at the bluff toe , 1988 .

[47]  P. Ruggiero.  Impacts of Climate Change on Coastal Erosion and Flood Probability in the US Pacific Northwest , 2008 .

[48]  N. Kraus,et al.  MECHANISM AND CALCULATION OF SAND DUNE EROSION BY STORMS , 1997 .

[49]  A. Santo,et al.  A methodology for the study of the relation between coastal cliff erosion and the mechanical strength of soils and rock masses , 2000 .