Model Interpretation and Conservative Assumptions.

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portion. In the spring and summer, small waves resulted in the return of sand to the beach and shallow

water area, thus completing the cycle. Cut and fill depths on the order of two to three feet are common

inshore of 25 feet MLLW, and sand depth changes of one-half to one foot are common at depths greater

than 25 feet MLLW.

Model Interpretation and Conservative Assumptions. The indirect sedimentation analysis is based

on model-predicted, worst-case outputs from the GENESIS model. Input parameters into the model were

conservative with regards to wave energy, gross longshore sediment transport, five year time frame, and

negligible offshore losses except at Scripps Canyon in La Jolla. Worst-case model outputs were

interpreted conservatively with the initialscreening based on persistence of project-related sand deposition

for one year or more, regardless of model-predicted sand depth. Finally, worst-case, model-predicted

sand depths were compared to reef heights and resources on that hard substrate to determine the potential

for substantial burial of sensitive resources.

As previously stated, there would be no significant impacts from direct deposition of sand at the receiver

sites. In evaluating indirect sedimentation impacts, the focus was on hard substrate with sensitive resources,

particularly where such resources may experience worst-case, model-predicted persistent sedimentation

of greater relative depth. In general, those locations of greater sand persistence and greater depth

(sedimentation risk) are located where there is an indented shoreline or gradual bathymetry. Less

sedimentation risk would occur at offshore coastlines that curve outward as headlands or have steeper

depth profiles. Locations near receiver sites off South Oceanside, south of North Carlsbad, near

Batiquitos, near Moonlight Beach, north of Solana Beach, north of Del Mar and offshore Imperial Beach

are predicted by the model to have a greater risk for sedimentation (depth and duration). The model

indicates that other receiver sites would not have the same risk of indirect sedimentation, specifically South

Carlsbad North, Leucadia, Cardiff, Torrey Pines, and Mission Beach.

Sediment deposition at the Cardiff receiver site is not predicted by the model to have duration of one year

or greater and is therefore not identified with the seven locations above as having greater sedimentationrisk

with possible long-term impacts. However, nearby resources were evaluated for potential short-term

impacts. Some sedimentation is predicted by the model to occur offshore the receiver site to a maximum

distance of 1,400 feet from shoreline and to the north toward Cardiff reef. Cardiff reef is a high relief reef

with heights of five to seven feet at the southern edge, closer to shore, and three to four feet further

offshore. Worst-case, model-predicted sand depths of one to two feet would be limited in movement up

and over the reef by its height, and sensitive resources on top of the reef would not be exposed to project-

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Regional Beach Sand Project EIR/EA

99-69\SANDAG EIREA 4.1 to 4.13.wpd 7/17/00