2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

More documents

Recommendations

Info

Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report 2.2. TIDAL MONITORING Introduction Tidal monitoring is fundamental to understanding the factors influencing physical and biological structure of the Bolsa Chica Lowlands. As a non-estuarine system with minor surface freshwater input, oceanic tides combined with winds are the principal forces driving the hydrodynamics within the wetlands. Conversely, as these factors act to sculpt the physical and biological environments, feedback loops associated with alteration of basin bedform and shoreline conditions influence tidal conditions within the system. Ultimately, roughness associated with the development of vegetation will influence tidal conditions; presently, this is an inconsequential variable in assessing system conditions. At the present time, accretion and erosion of sand within the flood shoal of the FTB has the greatest impact on tidal conditions, resulting in tidal lag and muting. While it is anticipated that the future opening of the central and east MTBs (in addition to the west which was opened in Marsh 2008) will influence the shape of tidal curves in the FTB, it is expected that the principal factor influencing the performance of the entire system will be the tidal drain and fill parameters between the ocean and the FTB. The restoration and opening of the Bolsa Chica Lowlands to the Pacific Ocean allowed nearshore littoral sands to be drawn into the FTB, forming a flood shoal that restricts and retards tidal flows at the entrance of the FTB (refer to Section 2.1). Tidal monitoring provides a means of tracking the tidal lag and muting to provide information regarding the functionality of the system and the need for maintenance dredging. The tidal monitoring program also offers insight into intertidal mudflat and vegetative habitat development within intertidal elevation ranges. Tidal muting and loss of drainage affect inundation frequency within the intertidal zone that further affects oxidation-reduction potential in the sediments. These changes in tidal hydroperiods and associated factors can have substantial consequences on mudflats and marshland development. Methodology Tidal monitoring was begun in the FTB on December 21, 2006 at 11:06 and has been continuous since then with data collected at 6-minute intervals. The tidal data were collected with a RBR Instruments TGR2050 pressure gauge. The TGR2050 has a depth accuracy of ±5 mm and a resolution of ±0.1 mm. A second TGR2050 pressure gauge was deployed nearby, on shore and used to correct the submerged pressure gauge for atmospheric pressure. The pressure data obtained from the submerged and atmospheric pressure gauges were used to calculate water depth at the sensor with the following formula: Depth = (P w – P atm ) / (λ * 0.980665); where depth is the water depth in meters at the pressure gauge, P w is the pressure in deciBars read at the in-water pressure gauge, P atm is the local atmospheric pressure in deciBars, λ is the density of seawater measured at the study site (1.027 g/cm 3 ), and 0.980665 is a gravitational constant (RBR 2007). Merkel & Associates, Inc. 107
Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report The tide logger was held in an aluminum bracket mounted to the FTB bulkhead at the east water control structure. The initial bracket configuration resulted in a sensor elevation of –0.05 m NAVD. This elevation was not sufficient to capture the lower low tides during spring tidal cycles. On January 19, 2007 at 13:00, the bracket was extended, resulting in a sensor elevation of –0.68 m NAVD. A subsequent elevational measurement of the FTB bulkhead by Coastal Frontiers resulted in adjustment of the sensor elevation to –0.72 m NAVD. This sensor elevation was used for data reported in the 2007 annual report. In 2008, it was learned that nearby Orange County elevational benchmarks had been adjusted 7 cm to account for local subsidence. Thus, the tide stations sensor elevation was corrected to –0.79 m NAVD. This change, along with a minor calculation error discovered during analysis of the 2008 data, resulted in minor changes to previously reported values. When appropriate, these corrections are provided in the below text. Tidal elevations were calculated by adjusting the 6-minute water depth data with the sensor elevation. The tidal muting analyses are based on data collected from January 20, 2007 through December 31, 2008. Recorded tides were compared with tides measured at the nearest tidal station, located 22.5 km (14 miles) north in Los Angeles Outer Harbor (LAOH) (NOAA Station 9410660). The NOAA gauge is located immediately adjacent to the open ocean, and the recorded tides represent the ocean tidal conditions. The data were obtained from the NOAA Tides and Currents website (http://tidesandcurrents.noaa.gov). The obtained data were not temporally corrected based on distance to the study site because the correction is less than the logging period. Results Comparison of the lower low tide data for each sampling date since January 20, 2007 against the NOAA tide data for LAOH shows that the FTB does not completely drain to local oceanic sea levels during lower low spring tides (Figure 2-5a). Moreover, the data indicate that tidal muting trends observed in 2007 were continued and became more pronounced during 2008. In 2008, lower low tides in the FTB only went as low as LAOH during very mild neap tides. Plotting the differences between the minimum observed tidal elevations for all daily lower low tides at LAOH versus the FTB numerically illustrates increased tidal muting (Figure 2-5b). From January to December 2007, tidal muting within the FTB had increased by an average of 0.07 m (previously reported as 0.10 m). Muting accelerated during 2008. By the end of 2008, tidal muting averaged approximately 0.40 m. The maximum low tide differential between LAOH and the FTB was 0.86 m on July 2, 2008. Notably, on infrequent occasions the tidal elevation of the ocean tides marginally exceeded the elevation within the FTB. This occurred principally at periods of neap tide and may be the result of a variety of factors including inlet morphology, tidal lag influences, or instrument variance at particular times. Table 2-2 summarizes the bi-weekly spring highest and lowest tidal elevations observed in the FTB and LAOH. Because the FTB gauge was lowered on January 19, 2007 only a partial spring-neap tidal cycle was analyzed for the first cycle in January 2007. The column identified as “Difference” under “Spring High Tide” show the spring high tide differences as calculated by subtracting the highest tide in the FTB by that at LAOH. A negative number indicates that the ocean high tide is higher than that in the FTB, and a positive number indicates the FTB has a higher high tide than that in the ocean. The general change from slightly positive values in 2007 to negative values in 2008 may be associated with Merkel & Associates, Inc. 108
Page 2 and 3:
Bolsa Chica Lowlands Restoration Pr
Page 4 and 5:
Bolsa Chica Lowlands Restoration Mo
Page 6 and 7:
Page 8 and 9:
Page 10 and 11:
Page 12 and 13:
Page 14 and 15:
Page 16 and 17:
Page 18 and 19:
Page 20 and 21:
Santa Barbara Los Angeles Outer Bol
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
BS PM Rep3 Muted Pocket Marsh BS PM
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Topsmelt January April July October
Page 60 and 61:
Page 62 and 63: Bolsa Chica Lowlands Restoration Mo
Page 74 and 75: 22 Temperature 20 Temperature (C) 1
Page 78 and 79: PM 50 66 47 Full Tidal Basin Future
Page 94 and 95: Zone PM 2 9 10 11 12 13 14 19 20 21
Page 108 and 109: Aug06 to Jan07 Jan07 to Jun07 assum
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Total Future Full Tidal Basin FFTB
Page 170 and 171:
Page 172 and 173:
Western Snowy Plover Nesting at Bol
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
Page 204 and 205:
Page 206 and 207:
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
Page 218 and 219:
Page 220 and 221:
Page 222 and 223:
Page 224 and 225:
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Page 244 and 245:
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
Page 254 and 255:
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Page 262:
show all

2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?