2.0 Alternatives Considered
is dispersed up and down the shoreline. This simplified model is appropriate for these sites because they
are geographically isolated from other fills, they have relatively straight coastlines, and lack sensitive
resources.
Numerical modeling was used for the remaining receiver sites because the northern coast of the San Diego
region is more varied with coves, promontories, lagoons, and built structures, and there would be multiple
beach fills in close proximity with overlapping effects. The model used for this project, the Generalized
Model for Simulating Shoreline Change (GENESIS), predicts sand movement up and down the coast only
(longshore) and does not predict on and offshore movement. Instead it assumes that sediment movement
on and off the beach (cross-shore) is seasonal and averages over the long-term and therefore, there would
be no long-term change in the beach profile. The GENESIS model is the most current technology. There
is no available model to simultaneously consider both longshore and seasonal cross-shore sediment
transport, which is the natural process.
GENESIS is intended to provide a generalized long-term trend in shore line response. The results can
indicate anticipated general areas of sand gain (deposition) or erosion at orders of magnitude over large
scales. While modeling shoreline change over time is inherently imperfect, there is no better or more
accurate alternative available at this time. The modeling of longshore sediment transport was supplemented
by GENESIS with analysis of seasonal beach profile changes using an analytical method. The method
involves converting the new mean sea level position predicted by GENESIS into a new beach profile at
each beach profile location. The purpose of the work was to quantify the depth of sand cover in the
nearshore zone in the vicinity of the beach fills to assess potential effects to biota. A depth of sand cover
was calculated over the average winter profile at each location (for winter conditions) and over the average
summer profile at each location (for summer conditions). This was done at six month intervals for five years
after project construction to represent end of winter conditions (May) and end of summer conditions
(October) for each year. Once the depth of sand cover was calculated at each beach profile location, the
depth of cover at areas in between the profiles was interpolated from that at the profiles. A computer
program was prepared to calculate the depth of sand cover in between the profiles using a relationship that
was developed for all North Countybeaches betweenpredicted changes in shoreline position and the depth
of sand cover along the length of the profile.
The modeling results were used in this process to guide the development of alternative receiver sites,
alternative footprint locations and to assist in estimating potential sedimentation impacts to marine biological
resources. Model-prediction in this inherently dynamic system are estimates only and cannot be considered
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