Changes in Beach Profile and Grain Size after Beach Renourishment

Transcription

1 Kevin Bodge, PE PhD Krista Egan, EI olsen associates, inc. and Mike McGarry Brevard County Natural Resources Mgt. Dept. Changes in Beach Profile and Grain Size after Beach Renourishment February 2018 Beach Preservation Tech. Conf.

2 How does beach profile shape change after a beach renourishment event? How does sand grain size change across the profile after a beach renourishment event? We ll contrast Pre- and Post-Project Conditions and first 2 years after a renourishment.

3 Brevard County, Florida Merritt Island Banana River CCAFS Sand Bypassing North Reach CSI Offshore Borrow Area CSII Shore Protection Project Atlantic Ocean Patrick AFB South Reach

4 Sand Grain Size varies across the Natural Beach Beach Profile

5 Sand Grain Size varies across the Natural Beach Offshore Beach Nourishment Sand Brevard Native Beach* Median Sand Size ( ) Beach Profile CSII *Cape Canaveral Air Station

6 Sand Grain Size Distribution

7

8 Canaveral Shoals II offshore sand

9 The existing post project sand matches the pre project sand by depth zone 2013 Samples (3 8 yrs post renour) Native Berm (pre project) Canaveral Shoals II offshore sand BERM

10 The existing post project sand matches the pre project sand by depth zone 2013 Samples 3 8 yrs post renour. Native Intertidal (pre project) INTER TIDAL

11 The existing post project sand matches the pre project sand by depth zone Native Subtidal (pre project) 2013 Samples 3 8 yrs post renour. SUB TIDAL

12 EXPECTED CHANGE IN SAND SIZE? OFFSHORE MIGRATION FINER SAND COARSER BERM AFTER EQUILIBRATION?

13 Beach Profiles Cocoa Beach R 36 Pre Nourishment ( )

14 Beach Profiles Post Nourishment ( ) Cocoa Beach R 36 Pre Nourishment ( )

15 Beach Profiles Composite Profiles N 3 rd St to S 11 th St R 33 to R43 Pre Nourishment (2000/01)

16 Beach Profiles Post 2005 Nourishment (May 2005) Composite Profiles N 3 rd St to S 11 th St R 33 to R43 Pre Nourishment (2000/01)

17 Beach Profiles May 2012 (7 Yrs Post Nour.) Post 2005 Nourishment (May 2005) Composite Profiles N 3 rd St to S 11 th St R 33 to R43 Pre Nourishment (2000/01)

18 What happens immediately after beach renourishment construction? We examined: Beach profiles: 6 nourished and 3 non-nourished. Sand grain size at 6 depths along each profile at pre-construction and 0-, 3-, 6-12-, and 24-months post-construction. o 54 beach profile surveys, and o 324 sand samples

19 Beach Fill Areas x xxxxx x xxxxx x xxxxx x xxxxx x xxxxx x xxxxx North Reach Nourished Profiles ( ) Nourished (2014) Control (No Fill) Sand Samples x x x RENOURISHMENT (Brevard County) x xxxxx Control Profiles (No Fill) x xxxxx x xxxxx South Reach

20 Beach profiles shifted to Mean High Water alignment Control 0 MONTHS Nourished Control 3 MONTHS Nourished COMPOSITE PROFILES

21 Nourished 6 MONTHS Control Control 12 MONTHS Nourished COMPOSITE PROFILES

22 Nourished 24 MONTHS Control COMPOSITE PROFILES

23 0 MONTHS 3 MONTHS NOURISHED 6 MONTHS 12 MONTHS 24 MONTHS CONTROL

24 Elevation (ft, NAVD88) +7.5' MSL +3' MSL -1.5' MSL -10.5' MSL Elevation (ft, MSL) BEACH SLOPE ANALYSIS ZONES

25 Elevation (ft, MSL) NR SR SLOPE ANALYSIS: BERM CONTROL Steeper

26 Elevation (ft, MSL) NR SR SLOPE ANALYSIS: INTERTIDAL Steeper

27 Elevation (ft, MSL) NR SR SLOPE ANALYSIS: SUBTIDAL Steeper

28 Elevation (ft, MSL) Nourished Control SLOPE ANALYSIS: BERM

29 Elevation (ft, MSL) Nourished Control SLOPE ANALYSIS: INTERTIDAL

30 Elevation (ft, MSL) Control Nourished SLOPE ANALYSIS: SUBTIDAL

31 Elevation (ft, NAVD88) +7.5' MSL -9' MSL Elevation (ft, MSL) SURF ZONE WIDTH

32 Elevation (ft, MSL) SURF ZONE WIDTH

33 SEABED SAND SAMPLES

34 R 36 GRAIN SIZE DISTRIBUTION +3 MSL R mos. 0 months Beach Fill Beach Fill Profile

35 Beach Fill Profile GRAIN SIZE VS. ELEVATION

36 Beach Fill Profile GRAIN SIZE VS. ELEVATION

37 Control Profile GRAIN SIZE VS. ELEVATION

38 MEAN GRAIN SIZE Nourished BERM Control Nourished +3 MSL Control

39 MEAN GRAIN SIZE Nourished -3 MSL Control Nourished -6 MSL Control

40 MEAN GRAIN SIZE Nourished -9 MSL Control Nourished -12 MSL Control

41 Summary Profiles Post-project beach profile conforms to native pre-project profile, except for steeper beachface slope (as expected from restoration of eroded beach). Negligible difference in average beach profile shape between nourished and non-nourished, at 0- to 24- months. Change in nourished beach slopes similar to or lesser than non-nourished profiles from pre- to 12- to 24-months. Temporal changes in profile slope and surf zone width similar between nourished and non-nourished profiles. Surf zone widths increasingly converged at 12- to 24-months.

42 Summary - Sand Existing post-project sand matches native sand, by depth. Grain size at nourished berm slightly increased at 0-6 months, returned to pre-renourishment within months. Little net change in grain size at/below MHW..changes were less than non-nourished profiles. Negligible changes below -9 ft MSL anywhere. Temporal variations in grain size are significant -- mostly greater at non-nourished profiles, and obscure trends.. though there is limited indication of increasing coherence at 12- and 24-months post-construction.

43 Kevin Bodge, PE PhD Krista Egan, EI olsen associates, inc. and Mike McGarry Brevard County Natural Resources Mgt. Dept. Changes in Beach Profile and Grain Size after Beach Renourishment February 2018 Beach Preservation Tech. Conf.