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Pacific Coastal and Marine Science Center

PCMSC Seminar Series

Wednesday, August 23rd, 2:00 pm

Robert McCall

Deltares, South Holland, Netherlands

Modeling incident-band and infragravity wave dynamics on rocky shore platforms

Illustration from the speaker's upcoming talk.

Summary:
Approximately three-quarters of the world’s coastline consists of rocky and cliffed coasts. Rocky shore platforms, low-gradient rock surfaces that occur within or close to the intertidal zone, play an important role on such coasts by dissipating waves and reducing the amount of wave energy reaching the base of the cliff. However, despite recent investigations of wave dynamics on rocky shore platforms few data exist with which to develop and validate numerical models that can be used to accurately predict wave transformation across shore platforms and wave impact at the cliff. The WASP (Waves Across Shore Platforms) project was set up to address the current lack of data and models for these types of coasts. To this end, field deployments were carried out during the winter of 2014–2015 at four rocky shore platforms in the UK and one platform in Ireland. Water levels were recorded at 4 Hz over 8–13 tides by a cross-shore array of 12–15 pressure transducers spaced approximately 10–15 m apart across the width of the intertidal shore platform. Shore platform morphology was surveyed using RTK-GPS to determine a representative cross-shore profile through the cross-shore instrument array, as well as using a Leica P20 terrestrial laser scanner to map platform roughness at high resolution (3.1 mm at 10 m distance). The field data were used to set up, calibrate and validate one-dimensional, cross-shore profile XBeach models. At each field site the incident-band wave height was calibrated by varying the incident-band bed friction factor used in the wave action balance in XBeach (fw), the incident-band wave breaker parameter (γ), and the infragravity wave related friction factor used in the non-linear shallow water equations in XBeach (cf). Model validation was carried out using wave height data from the 7–12 tides not used in the model calibration. The results of the model simulations show that after calibration of the three free model parameters, XBeach is able to simulate incident-band and infragravity-band wave height transformation well. Interestingly, the calibration method shows that the optimal value for the infragravity wave related friction factor (cf) for particularly the rougher sites depends on the level of bathymetric / topographic detail given as input to the model. It is thought that this is because the explicit inclusion of bed roughness elements in the model bathymetry in itself leads to infragravity wave energy loss in the non-linear shallow water equations.

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Street map of our location.
[Larger version]

From the San Francisco Bay Area:
Take your favorite highway to Hwy 17 South to Hwy 1
At the Hwys 17+1 merge, keep right
Follow signs to “Hwy 1 North, Half Moon Bay, UC Santa Cruz”
Stay on Hwy 1 North (keep in right-most lanes)
Hwy 1 is also named Mission Street — Follow Mission for about 2 miles
At the Western Drive stop light, turn left onto Western Drive
The building right in front of you is the
USGS Pacific Coastal and Marine Science Center
2885 Mission Street

From the south coast or from Hwy 17:
Take Hwy 1 North to west Santa Cruz
At the Western Drive stop light, turn left onto Western
The building right in front of you is the
USGS Pacific Coastal and Marine Science Center
2885 Mission Street

From the north coast:
Take Hwy 1 South to west Santa Cruz
At the Western Drive stop light, turn right onto Western
The building right in front of you is the
USGS Pacific Coastal and Marine Science Center
2885 Mission Street

Parking:
Limited parking spaces may be available in the parking lot located on the NE corner of Western Drive and Mission Street
Limited parking is available along Mission Street and along Natural Bridges Drive
Entrance to PCMSC is at 2885 Mission Street

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