Surfrider Foundation: Mitigation Through Surf Enhancement

CHAPTER 3
(Page 3 of 7)

The necessary parameters required by REF/DIF 1 to propagate waves over a bathymetry grid are the wave amplitude (1/2 the wave height ) at the farthest offshore row of grid cells, the wave period, and the wave direction. In order to accurately model waves in the El Segundo area the wave climate was determined and input into the model. Because surfable waves do not occur in a regular or predictable manner, it was determined that waves with a 1.5 meter height represented an average surfable wave (Noble, 1992). The average period of the waves approaching El Segundo was determined to be 12 seconds (O'Reilly and Guza, 1993, & personal communication). Examination of O'Reilly's Spectral Model of Southern California (O'Reilly and Guza, 1993) and results from the Noble (1990) report indicated that the majority of waves approaching El Segundo are nearly shore normal because shadowing and refraction due to the Channel Islands. The Channel Islands are found offshore to both the north and the south of El Segundo [See Figure 3.6].

Spectral Model of waves approaching So. Cal.

Figure 3.6: A map from O'Reilly and Guza's (1993) spectral model of waves approaching the Southern California Bight. This map is updated daily and can be observed on the Internet.

With the "typical surfing conditions" established and the reef bathymetries created, the next step was to run the REF/DIF 1 [See Appendix A for a discussion on REF/DIF 1 operations]. Once the wave climate conditions and the bathymetry are input into REF/DIF and the model is run, REF/DIF outputs three files important to this project: wave height, depth, and break point. The wave height file is used as a visual check to see that the model ran correctly and contains the wave response, as expressed in height, to the shore and the reef. My model results are analogous a test of the model performed by Kirby and Dalrymple (1994), therefore as a visual check, I expected my results to have a similar pattern. The depth file is used as a check to ensure that the bathymetry was correctly input into the model. The wave breaking file consisted of a line that indicated where the model broke the wave. This file is also used to observe wave response to the reef. Over thirty model simulations were run in an effort to test the model, investigate whether the model would simulate wave breaking over a reef, and to explore reef characteristics that would enhance surfing and create a surfable wave in El Segundo. Each parameter was tested independently. The specific results are considered in more detail below [See tables 1-4].

Table of wave climate without reef

Table 1: Shoreface, wave climate and wave response for a planar beach without an artificial surfing reef. These conditions are characteristic of El Segundo, CA (O'Reilly and Guza, 1993)

Table of Reef Parameters of wave modeling

Table of Reef Parameters of wave modeling

Table 2: Reef Parameters used in wave modeling. Bold indicates parameters that were changed while all others were held constant.

Table of REF/DIF parameters

Table 3: Ref/Dif parameters input as initial conditions for each model run. Bold indicates parameter that was changed while all others were held constant.

Table of wave response for each model run

Table 4: Wave responses for each model run. K1, K2 and the Iribarren number are dimensionless parameters decribing wave shape. Down-line velocity measures the rate of progess the bore makes along the wave crest. Ride length measures the ridable part of the breaking wave. Length2 is included for waves which approached the beach at and angle because they broke assymetrically. Italics respresent interesting results which are commented on in the Discussion.

table of contents

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