1. Cross-Shore, Along-Shore, and Vertical Correlation of Rotary Spectra in the Nearshore

2. Outline
RIPEX
Problem
Analyses
Summary of Conclusions

3. Nearshore Rip Cells 50 to 100 m spacing
Strong rip currents scour channels
Crescentic bars between
Waves break farther offshore over bars
COAST LINE

4. Cross-shore Instruments
Location ~ 100m offshore
Centered around MWL
Approx. 0.5m – 3m depth
Recorded from ~April 15, 2001 to ~May 15, 2001

5. Tower and Goal Post Electromagnetic Current Meters
Conductivity Sensors
Capacitance Wave Staff
BCDV
Camera
Scanning Acoustic XY Altimeter
Recorded April, 2001

6. Instrument Locations
ADV
Tower
PUV
ADCP

7. Observations Storm Event on April 22, 2001.
Bed forms in the surf zone prior are 20-50cm across, 10-20cm high.
Bed forms after the storm have been eliminated.
Character of forcing changes substantially

8. Before

9. After

10. Days
Days
Data Coverage f
Semi-diurnal tide

11. Question
Can the nearshore wave spectra (outside beakers) be correlated to surf zone forcing?
If so, does this correlation change in different wave environments?

12. Methodology 2.4-hour periods are examined
Day 110 (prior) and Day 113 (after)
Times are centered on high tide to ensure complete data coverage and similar conditions (MWL, etc)

13. Rotary Spectral Analysis
Examines rotational frequencies of vectors
Inner spectra examine co-rotation
Outer spectra examine cross-rotation
Autospectra correlate to single variable spectra
Cross-spectra and coherence examine interactions

14. Data Selection
Storm event

15. Pressure Spectra Narrow-band swell peak
Swell peaks
Surf beat
Infragravity
Narrow-band swell peak
Low infragravity energy outside surf beat
Broad-band swell peak
High infragravity energy
Three distinct surf beats

16. D110
Vertical
D114

17. Cross-Shore Coherence
D110
D114

18. Results (Not shown) No coherence with inner spectra observed
Exception is minor coherence at swell peak
Outer coherence appears scattered through frequecies
Outer cross-spectra show opposing peaks at Surf beat and Swell frequencies:
High energy at swell peak when combining ADCP anti-clockwise with others’ clockwise
High energy at surf beat when combining ADCP clockwise with others’ anti-clockwise
More prominent in low infragravity energy case (20 Apr)

19. Conclusions
Vertical rotary spectral analysis shows expected coupling within the water column
Inner spectra are not significantly correlated
Outer cross-spectra show opposing cross-correlation at surf beat and swell peaks.
Likely due to opposing positions within rip cell
ADCP outside rip cell outflow
PUV inside rip cell outflow
ADV outside adjacent rip cell
ECM inside adjacent rip cell
Surf beat is more energetic because of longer period