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

More documents

Recommendations

Info

Orange County Coastal Regional Sediment Management Plan Storms Storm-induced changes in nearshore water levels arise from storm surge (from lowered barometric pressures, wind shear, and wave set up) and fresh water runoff. For example, the lowest locally recorded barometric pressure occurred during a storm on January 18, 1988. The combined storm induced changes resulted in water levels that were 0.7 feet above predicted astronomical levels at the Los Angeles Outer Harbor tide gage (USACE, 2002b). The fresh water component includes rainfall runoff and dam release and is particularly important for inland beaches such as those within Newport Bay and Huntington Harbour. Climatic Oscillations El Niño Southern Oscillations and Pacific Decadal Oscillations are global scale cyclic climatic variations that impact the local sea levels in the Project area. El Niño Southern Oscillation has a frequency of every four to seven years and results in temporary increases in sea level on the west coast of North and South Americas. For example, during the major El Niño Southern Oscillation event of the 1997-1998 season, monthly mean sea levels in southern California were increased by up to one foot (Flick, 1998 as reported in USACE, 2002b). On a longer time scale, the Pacific Decadal Oscillation was recently shown to be a likely cause of suppressed sea levels on the west coast of North America and may lead to a rapid increase in local sea levels in the near future (Bromirski et. al., 2010). 2.2.3 Waves Waves are the driving force in generating longshore currents, sediment transport in the littoral zone, and shoreline changes. Ocean waves impacting the Orange County coast are produced by the following four sources (USACE, 2002b; Moffatt & Nichol, 2009a). Northern hemisphere swell is derived from extratropical cyclones that occur in the northern Pacific Ocean. This comprises the most severe waves reaching the Orange County coast, and these waves usually have the greatest impact of all the wave sources. These swells generally approach from a swell window of from 275 degrees to 285 degrees (USACE, 1996a). The literature is less than clear as to whether long-term historical northern hemisphere swell activity has been increasing or remains steady and how it will trend in the future (Graham et. al., 2002; Inman et. al., 2006; Graham, 2005; Seymour, 2011; Bromirski et. al., 2002; IPCC, 2007). Tropical storm swell is derived from hurricanes off the west coast of Mexico during the summer and early fall. Most of these hurricanes take a westerly track sending swell out to the Pacific Ocean. On occasion, a northwest track sends swell up to southern California, with the swell window ranging from 155 degrees to 200 degrees (USACE, 2002b). Everest International Consultants, Inc. 2.9
Orange County Coastal Regional Sediment Management Plan Southern hemisphere swell is derived from extratropical cyclones from the South Pacific Ocean with the majority occurring from spring through early fall. These swells approach from about 170 degrees to 215 degrees, decaying significantly as they traverse across the Pacific Ocean. Local sea is the term applied to steep, short period waves which for this project are generated by local winds and northwest winds in the outer coastal waters. The local winds can be further separated into pre-frontal winds from the southeast, gradient winds during the passage of a winter low pressure system from the west, and westerly sea breezes. With the predominance of wave energy reaching the Orange County coast from the northern hemisphere, wave driven currents typically run from northwest to southeast throughout the winter and spring and cause the majority of longshore sediment transport. As this coast is also significantly exposed to southern swell, seasonal reversals in longshore sediment transport occur, typically in the summer. These seasonal longshore transport components tend to be much greater than the net difference between the two. Thus the combined gross longshore transport (south transport + north transport) is much greater than the net longshore transport (south transport – north transport). Variable climatic cycles result in a range of conditions from dominant southeastward sediment transport over certain periods, followed by periods of more balanced sediment transport directions. The shoreline morphology has equilibrated over time to follow predominant conditions and over the long-term is oriented to southeastward sediment transport, with sediment inputs to the littoral cells typically from the northwest and outputs from the littoral cells typically in the southeast. 2.3 Sediment Transport and Beaches The Plan covers the entire 39 mile coastline of Orange County extending from the San Gabriel River in the north to the San Mateo Creek in the south. This stretch of coastline can be divided by many possible features, of which the physical process of sand transport seems most appropriate for a RSM plan. These physical processes are most easily described by a sand accounting system called the sediment budget and a geographical grouping method based on the littoral cell. The sediment budget approach was developed to understand the impact of coastal processes on shoreline change. The sediment budget conceptually accounts for inflows (sources), outflows (sinks), and storage of sediment within a littoral cell. A littoral cell is a coastal compartment or physiographic unit that contains sediment sources, transport paths, and sediment sinks (USACE, 2002b). A littoral cell is typically a portion of the coastline that does not significantly transport to or receive littoral sediment from another cell in either the upcoast or downcoast direction (USACE, 1991). Most cells, however, are not absolutely separated and do have some leakage between them. Orange County has four major littoral cells as shown in Figure 2.5. These littoral cells are the Seal Beach Littoral Cell, the Huntington Beach Littoral Cell, the Laguna Beach Cells (USACE, 2002b), and the northern portion of the Oceanside Littoral Cell (USACE, 1991). Everest International Consultants, Inc. 2.10
Page 1 and 2: Prepared for U.S. Army Corps of Eng
Page 3 and 4: Orange County Coastal Regional Sedi
Page 29: Orange County Coastal Regional Sedi
Page 81 and 82:
Orange County Coastal Regional Sedi
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
show all

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

Create successful ePaper yourself

Delete template?

Save as template?