Beach Nourishment Impact on Beach Safety and Surfing in the North Reach of Brevard County, Florida

Transcription

1 Beach Nourishment Impact on Beach Safety and Surfing in the North Reach of Brevard County, Florida Prepared by John Hearin, Ph.D. Coastal Engineering Vice Chairman Cocoa Beach Chapter

2 Port Canaveral Patrick Air Force Base Cape Canaveral Net littoral sediment transport 350,000 cubic yards per year Brevard County North Reach: Port Canaveral Jetty (FDEP monument R-0) to Patrick AFB (FDEP Monument R-54). FDEP monuments are spaced approximately 1000 feet apart. Total length of North Reach is 9.4 miles. Sebastian Inlet

3 Issue US Army Corps of Engineers plans to nourish the North Reach this fall/winter using the Canaveral Shoals offshore borrow site. Canaveral Shoals borrow site was used for 2001 and 2005 nourishment projects. Borrow sediment grain size was coarser than existing beach.

4 Result Coarser sediment caused increase possibility of rip current formations and had a negative impact on the surfing wave climate

5 Major Cause of Beach Erosion Port inhibits alongshore sediment flow 188,000 cy per year (Olsen 2012) Port Canaveral Predominate Sediment Flow

6 Reasons for Beach Nourishment Protect Upland Structures from Storm Damage Preserve Beach as an Economic and Recreational Resource

7 Wider Beach = Additional Storm Protection December 2000 April 2001

8 Cape Canaveral AFS Port Canaveral North Reach Nourishment Methods: Emergency Nourishment Net littoral sediment transport 1972: 200,000 yd 3 (R-0 to R-14) (Brevard County, 2011) Minutemen Causeway R-36 Patrick Air Force Base

9 Cape Canaveral Port Canaveral Minutemen Causeway Net littoral sediment transport R-36 North Reach Nourishment Methods: Port Canaveral Trident Basin Dredge 1974: 2,850,000 yd 3 (R-0 to R-14) (Brevard County, 2011) Patrick Air Force Base

10 Cape Canaveral AFS Port Canaveral North Reach Nourishment Methods: Port Canaveral Harbor Sand Bypass Project Minutemen Causeway Net littoral sediment transport R : 783,000 yd 3 (R-0 to R-8) 1998: 1,035,000 yd 3 (R-3 to R-14) 2007: 750,000 yd 3 (R-4 to R-10) 2010: 650,000 yd 3 (R-1 to R-10) (Brevard County, 2011) Patrick Air Force Base

11 Cape Canaveral Port Canaveral Canaveral Shoals II Minutemen Causeway R-36 North Reach Nourishment Methods: Shore Protection Project ,798,000 yd 3 (R-3 to R-54) ,600 yd 3 (R-8 to R-18) and (Brevard County, 2011) (R-33 to R-54) Patrick Air Force Base

12 Sediment Grain Size Classes (Wentworth scale). < mm: Silt mm: Very Fine Sand mm: 0.25 mm: 0.5 mm: 1 mm: Fine Sand Medium Sand Coarse Sand Very Coarse Sand 2 mm: Gravel (shell)

13 Class Weight (%) North Reach Beach Composite Grain Size Distributions Mode R Native Beach Sample R Beach Sample R Beach Sample R Beach Sample R Beach Sample R Beach Sample North Reach Mean Fine Sand Modes Very Coarse Fine or Fine Sand 10 Fine Coarse Grain Size (µm)

14 Class Weight (%) Brevard County Composite Grain Size Distributions (Olsen, USACE) 50 R-36 North Reach 1989 R-64 Patrick AFB 1989 R-93 Mid Reach R-125 South Reach 1989 Borrow: Canaveral Shoals II 1998 Canaveral Shoals II Fill Mean Medium Sand Mode Medium Sand Fill Coarser than North Reach & Patrick AFB existing beaches Grain Size (µm)

15 Class Weight (%) North Reach Composite Grain Size Distributions R36 Composite 2001/2005 Fill Composite 2005 R21/R29 Composite Beach Mean Medium Sand Mode Medium Sand Grain Size (µm)

16 Class Weight (%) 50 North Reach Composite Grain Size Comparisons R-36 Composite 2005 R21/R29 Composite /2010 Updrift Fill Composite: Borrow Data 2003 Cape Canaveral AFS 2011 R36 Composite 2011 Shoreline Mean Fine Sand Mode Fine Sand Grain Size (µm)

17 Class Weight (%) R-36 Cross Shore Grain Size Distributions 1989 and Coarse Sand on Dune & Berm was not present on existing beach in Coarse sand result of 2001/2005 Fill. Dune & Berm R36 Dune 2011 R36 Dune 1989 R36 Berm 2011 R36 Berm 1989 R36 MHW 2011 R36 MHW 1989 R36 MLW R36 MLW 1989 R36 Trough R36 Trough 1989 R36-12ft R36-10ft Grain Size (µm)

18 Fill Templates Based on Grain Size Natural Foreshore Slope 1:50 Cape Canaveral AFS Fill Slope = 1:25 Canaveral Shoals II Fill Slope = 1:

19 FDEP Sand Rule Rule 62B (2)(j), Florida Administrative Code (Established 1992 / Amended 10/23/2001) Use beach fill material that maintains the general character and functionality of the material occurring on the beach and in the adjacent dune and coastal system. Characteristics include the sediment properties of grain size distribution, color and mineral composition (quartz and carbonate) and bulk properties of cementation and compaction.

20 Research Findings Fill material used in the 2001 and 2005 fill projects did not maintain the general character of the sediment occurring in the existing North Reach coastal system. The mean & median grain size for the fill sediment was triple that of the existing beach and the mode was double. The result was a nourished beach with a very different character than the existing beach.

21 (wright & short,1984) Modal Beach State Ω > 6 Dissipative fine sediment flat slopes rip currents low % spilling breakers wide surf zone 1< Ω < 6 Intermediate medium sediment steeper slopes rip currents high % plunging breakers variable surf zone Ω < 1 Reflective coarse sediment steepest slopes rip currents high % surging breakers narrow surf zone

22 R17-R22 R17-R22 R1-R16 R36 Dimensionless Fall Velocity (Ω) R28-R31 near shore R2 R0-R8 R1-R9 R3-R14 R29 R4-R10 R36 R3-R54 R8-R19 / R33-R54 R1-R10 North Reach Beach and Fill Modal Beach States Composite Active Beach Sediment Samples Composite Fill Port Channel (1994 sample) Composite Fill Cape AFS (1994 sample) Composite Fill Cape AFS (1995 sample) Composite Fill Canaveral Shoals II (1998 sample) Composite Fill Cape AFS (2003 sample) Dissipative Ω > Intermediate 6 > Ω > Reflective Ω < 1 Date

23 Research Findings Fill material used in the 2001 and 2005 fill projects changed modal beach state of North Reach from dissipative to low intermediate. North Reach (R-36) returned to dissipative state by 2011.

24 Rip currents develop more in intermediate and reflective beach states compared to dissipative ones. In other words, the steeper the beach, the more rip currents and the more danger for users. Charles W. Finkl, Ph.D., Editor-in-Chief Journal of Coastal Research (JCR) Professor Emeritus Department of Geosciences Florida Atlantic University

25 On the Atlantic coast of Florida, dissipative beaches are less susceptible to the development of strong rips during most of the year. On intermediate beaches, even on calm days it is possible that many strong rip currents are present. BENEDET, L.; FINKL, C.W. and KLEIN, A.H.F., Morphodynamic classification of beaches on the atlantic coast of Florida: geographical variability of beach types, beach safety and coastal hazards. Journal of Coastal Research, SI 39 (Proceedings of the 8th International Coastal Symposium), Itajaí, SC, Brazil. ISSN

26 Brevard County Ocean Rescue staff has noted that recent changes and intensity of rip currents have appeared to coincide with recent beach renourishment. Brevard County Ocean Rescue Lifeguard Report for the period of 2007

27

28 Impacts to Surfing Wave Environment R-36: Most Data Available Nine survey profiles from (FDEP) Six year synthetic wave data set (surfbreak engineering) 17,530 individual wave records ( ) Surfing Parameters Analyzed Breaking wave height Break point (surf zone width) Seabed slope at breakpoint Breaker type: spilling, plunging, collapsing

29 Research Findings Impacts to Surfing Wave Environment North Reach Pre Fill (Before 2001) Dissipative beach, flat profile, low sand bars Wide surf zone width at all tides Primarily spilling breakers at all tides Occasional plunging breakers at higher tides

30 Research Findings Impacts to Surfing Wave Environment North Reach (R-36) - Post Fill (2001 to 2010) Intermediate beach, steep profile, variable sand bars Tidally dependent surf zone width Spilling breakers at lower tides Plunging breakers at higher tides Collapsing breakers at high tides were un-surfable

31 Elevation (ft) NAVD88 North Reach Monument R36 Bathymetry Profiles 15 MHHW MLLW 10 Nov-00 Pre Fill Jan-01 Post Fill High Tide: 2000 Median Surf Zone Width = 210 ft 2001 Median Surf Zone Width = 50 ft Horizontal Station from Monument (ft)

32 Research Findings Impacts to Surfing Wave Environment North Reach (R-36) 2011 to Present Beach returned to dissipative state Surfing similar to pre fill conditions (2000) Surfing impacted from

33 (Olsen, 2010)

34 Goals Maintain the existing nature of the beach in the North Reach Avoid future adverse impacts to beach safety and surfing in the North Reach

35 Current Post Construction Beach Monitoring Requirements Sea Turtle Requirements Nesting (daily during nesting season for 3 years) Escarpments (weekly during season for 2 years) Sand compaction (annual for 3 years) Beach Tilling (if compaction test results dictate) Engineering Requirements Beach sediment samples of dune and berm (one time immediate post fill) Annual beach and bathymetric surveys (3 years) Biannual surveys until next nourishment (after 3 years)

36 Current Post Construction Beach Monitoring Requirements Engineering requirements are insufficient to monitor and assess: Beach and bathymetric profile equilibration Sediment redistribution and natural sorting Modal beach state transition Rip current formation An independent long term monitoring program is needed to resolve fill compatibility and equilibration issues

37 Post Construction Beach Monitoring Recommendations Monitoring should occur at several representative locations along the North Reach: Beach & bathymetric surveys (bi-monthly 5 years) Sediment samples (quarterly 5 years) Nearshore wave data (daily 5 years) Rip current monitoring (daily 5 years) Surfing statistical assessment (daily 5 years) Would provide valuable data for all future projects in Brevard County