Year One Post Construction Monitoring Report
(August 2011 to June 2012)
The 2011 renourishment of the South Amelia Island Shore Stabilization project placed approximately 2.1 million cubic yards (Mcy) of beach quality sand along roughly 3.2 miles shoreline. The 2011 project was the second scheduled maintenance of the original 1994 SAISSA Nourishment Project and the first maintenance nourishment following completion of the Phase II structural stabilization project. The first renourishment was completed in 2002. Since 1994 approximately 6.5 Mcy of sand has been placed along the South Amelia Island shoreline as part of the SAISSA Nourishment Project. As of June 2012, the 2011 project shoreline has approximately 2.8 Mcy more sand relative to the pre-1994 project condition. This is exclusive of the large spit formation within the Amelia Island State Park.
Based upon the June 2012 beach monitoring survey the 2011 renourishment of the South Amelia Island Shore Stabilization project has met the project goals. Despite a relatively severe wave climate, the 2011 renourishment performed slightly better over the first monitoring year than the 1994 and 2002 beach fills, due in part to the stabilizing structures constructed in 2004. In the net, the 2011 renourishment lost approximately ‑86,600 cy or 4 percent of the total placed volume over the first 10-months following project completion within the project limits. By comparison, the 1994 project lost -450,200 or 15 percent of the approximate placed volume over that project’s first monitoring year (12 months). Additionally, the 2002 project lost ‑394,200 or 25 percent of the approximate placed volume over that project’s first monitoring year (14 months). These losses do not include the post-project volume changes south of the 2011 project area.
During the first monitoring year following the most recent SAISSA nourishment (August 2011 to June 2002), the project area experienced a net loss of ‑86,600 cy (i.e. sand unaccounted for within the project limits). However, despite the relatively small net loss, comparison of the monitoring surveys indicates a significant level of post-fill beach equilibration. Based upon beach profile surveys, the project beach fill area lost roughly -537,100 cy above the MHWL. The measured loss above the MHWL is consistent with the average measured shoreline retreat at the MHWL (-107.8 ft) and the berm (-127.2 ft). Shoreline adjustments extended to deeper depths, to roughly -6 ft-NAVD, where the measured volumetric change was ‑941,200 cy. In keeping with expected beach equilibration processes, almost all of the measured “losses” along the upper beach were offset by “gains” in the nearshore zone, principally between -6 and -20 ft-NAVD. Between ‑6 and -20 ft-NAVD, the project area gained +854,600 cy. Hence the small net loss noted above.
The relatively small net loss, roughly 4 percent of the total placed volume, occurred in a year of an atypically severe wave climate. The average significant wave height at the Fernandina buoy during the monitoring period was 3.15 feet, roughly 11 percent higher than the long-term average significant wave height at the buoy. Most notable in the wave record are the occurrence of three storms during the period, Hurricane Irene in late August 2011, a long-duration nor’easter in early October 2011 and Tropical Storm Beryl in late May 2012. These storms contributed to the significant reconfiguration of the project fill.
As noted previously, the Amelia Island State Park (AISP) was formally incorporated into the South Amelia Shore Stabilization Project beginning with the first renourishment in 2002. That project included a Phase II component which called for the construction of a 1,600 ft. terminal structure at the juncture of the Park oceanfront with Nassau Sound, and a 400 ft long detached breakwater near the north limit of the Park oceanfront shoreline.
During the design of the most recent (Summer 2011) 2.1 Mcy beach renourishment project, it had been predicted that a federal disposal event would occur in the fall/winter 2011 - 2012. The location of the fill would be immediately southward of the detached breakwater. As a result, the design beach fill minimized the volume of borrow material to be placed at that location in the summer of 2011. Unfortunately, the federal disposal operation has been delayed – until summer of 2013. As a result, the under-filled section of Park shorefront intended for beach disposal has experienced chronic net erosion and recession due to its downdrift location relative to the detached breakwater and the occurrence of several tropical storms and nor’easter “level” events which have occurred over the past 12 months, mol.
In the last week of December, 2011, the Park authorized minor scarp removal and beach enhancement south of R-75 in the area of highest erosional stress adjacent to the breakwater. Subsequently in March/April of 2012, a contractor was retained by the Park Service to excavate some 1,850 cy of sand from the breakwater salient and move the material to the scarp line southward thereof as a temporary means of dune protection.
The Jacksonville District advises that the requisite AIWW maintenance contract has been rescheduled for construction in the Summer of 2013. The anticipated beach disposal volume is 500,000 cy. It is Olsen Associates, Inc.’s recommendation that virtually all of that material be placed within the currently located hot spot immediately south of the detached breakwater. For more information on the Year One Post Construction Monitoring Study, please Click Here [44-pgs].