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

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Orange County Coastal Regional Sediment Management Plan the tidal characteristics are similar at coastal locations throughout Orange County. Tidal characteristics computed for the tidal epoch from 1983 to 2001 for the Newport Bay entrance are presented in Table 2.1 (NOAA, 2003) in relation to the Mean Lower Low Water (MLLW) vertical datum. Each of these represents either extreme recorded events or defined vertical means as calculated by NOAA over the tidal epoch and are given relative to a fixed vertical survey datum. The North American Vertical Datum of 1988 is the most recent vertical survey datum available for this area. Mean Lower Low Water (MLLW) is the common low tide datum used for describing tides. Table 2.1 Tidal Characteristics at Newport Bay Entrance DATUM OR LEVEL ELEVATION (FEET, MLLW) Maximum Measured Water Level (Jan 28, 1983) 7.67 Mean Higher High Water (MHHW) 5.41 Mean High Water (MHW) 4.67 Mean Tide Level (MTL) 2.80 Mean Sea Level (MSL) 2.77 Mean Low Water (MLW) 0.92 North American Vertical Datum of 1988 0.18 Mean Lower Low Water (MLLW) 0.00 Lowest Measured Water Level (Jan. 20, 1988) -2.35 Source: NOAA (National Oceanic and Atmospheric Administration),2003 Sea Level Rise USACE and many California State agencies have issued guidance for incorporating sea level rise into federal or state projects. USACE guidance states that potential sea level change must be considered in every USACE coastal activity as far inland as the extent of estimated tidal influence and recommends a multiple scenario approach to address uncertainty and help develop better risk-informed alternatives (USACE, 2011a). These scenarios cover a broad range of sea level changes termed low, intermediate, and high as shown in Figure 2.4. In this figure, the low scenario is an extension of historical global rates (1.7 millimeters per year), since the local Newport Beach tide gage did not record long enough for confident extrapolation. This Everest International Consultants, Inc. 2.7
Orange County Coastal Regional Sediment Management Plan global rate is between other, nearby local rates observed at La Jolla and Los Angeles (2.1 and 0.8 millimeters per year, respectively). The intermediate and high scenarios are based on equations provided by USACE. The State of California has provided ranges of interim sea level rise guidance (CO-CAT, 2010) to be used until a final report from the National Academy of Sciences is available. Sea level rise projections in this interim guidance are shown in Figure 2.4 labeled “CA Interim Guidance.” Which projection to use should be based on agency and context-specific considerations of risk tolerance and adaptive capacity. Additional regulation and policy on sea level rise was provided by the Office of the Governor (2008), SCC (2009) and the California Ocean Protection Council (2011). 80 Sea Level Rise (inches) 70 60 50 40 30 USACE High USACE Intermediate USACE Low CA Interim Guidance Range High CA Interim Guidance Avg High CA Interim Guidance Avg Med CA Interim Guidance Avg Low CA Interim Guidance Range Low 20 10 0 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 Year Figure 2.4 Sea Level Rise Projections The National Academy of Science report (National Research Council, 2012) on sea level rise provides updated southern California sea level projections for year 2100 at 37 inches higher than those found in year 2000, with the projected range being from 17 to 66 inches. The CA Interim Guidance is expected to be replaced with new guidance for California based on these results. Everest International Consultants, Inc. 2.8
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