As part of the agreement between Indian River County and Coastal by johnrr1

VIEWS: 4 PAGES: 3

									Sector 1 & 2 Fill Performance & Hardbottom Impacts – 2004 Hurricanes
General: Coastal Tech applied the Mike 21 model to assess the fill performance and hardbottom impacts in the Sector 1 & 2 Project Area that:  occurred as a result of the 2004 hurricanes, and  might have occurred if the Sector 1 & 2 Project had not been constructed. Coastal Tech specifically applied the Mike 21 - LITPROF storm profile model to predict cross-shore profile changes caused by Hurricane Frances and Jeanne - applied to the conditions with and without beach nourishment. The “with nourishment” condition is represented by the August 2004 profile; while the January 2003 profile is used to simulate the “without nourishment” condition. The October 2004 profile is considered to be the measured post-storm profile by which the LITPROF “with nourishment” poststorm profile is compared. Coastal Tech evaluated the performance of the beach fill via LITPROF storm profile model at R-8 in Sectors 1 & 2. The Sebastian Inlet Wave Gauge historical data (maintained by Florida Institute of Technology and Sebastian Inlet Tax District) for Hurricane Frances & Jeanne was used as a forcing storm event. The forcing storm event and LITPROF were run for the time period of August 17, 2004 to September 27, 2004. The LITPROF post-storm profile representing September 27th condition is compared to the available post-storm measured profile (October 2004). Figure 1 shows the pre(August 2004) and post-storm (October 2004) measured profiles. Figure 2 shows a comparison of the LITPROF post-storm profile compared to the post-storm measured profile. The following observations are noted:  The LITPROF 9/27 post-storm profile shows an overall higher erosion across the beach-face (at elevations higher than MLLW), than the post-storm measured October profile. At lower elevations, the LITPROF simulation shows more offshore deposition than the post-storm measured profile. The LITPROF predicted 9/27 profile and measured October post-storm profile suggests that the beach-profile partially recovered by movement of sand during the post-storm calm conditions – beyond the wave record available drive LITPROF. This partial recovery was personally observed after the 2004 storms by Coastal Tech staff (Walther, 2008, personal communication); such partial recovery is expected after extreme storm events.  LITPROF simulations predict cross-shore sediment transport out to approximately -20ft NGVD and correspondingly show that extensive hardbottom areas were likely buried immediately after the storm. The measured profile indicates that much of the buried hardbottom became re-exposed during the more calm conditions after the storm.  Storm-profile models are based on cross-shore sediment balance, therefore any effect of longshore transports are not accounted for. Some discrepancies between the measured and the computed might be attributed to this fact.

A comparison of the LITPROF simulations in Figures 2 and 3 “with nourishment” and “without nourishment” indicates the “without nourishment” condition is predicted to have comparable hardbottom impacts. Based on the above results, it can be concluded that:  Fill placement at low fill densities – as for the Sector 1 & 2 Project Area - would not likely result in any significant additional impacts to hardbottom during a Hurricane Frances & Jeanne-type event.  Hardbottom impacts are ephemeral and very much dependent upon water-level and wave climate.

Figure 1 - Pre- and post-storm measured profiles

Figure 2 – LITPROF “with nourishment” output profile compared to post-storm measured profile

Figure 3 – LITPROF “without nourishment” output profile


								
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