Design Scenarios

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7_BEACON Tech Report (FINAL)

Sediment samples were collected along two transects at each of the beach fill sites. The samples

were collected on the beach and out to a depth of 30 feet (Figure 3-2) to characterize the native

beach gradation. The samples were analyzed for grain size and the results are contained in

Appendix A. The median grain size (D50) for the composite sample is 0.144 mm, with a fines

content of 13% (passing the #200 sieve). The offshore portion of the profile contains the highest

percentage of fines. The samples taken at depths between 18 and 30 feet ranged from 18 to

39% fines. These existing data indicate a relatively high percentage of fines offshore. Although

these fines exist, sensitive resources (offshore reefs and kelp beds) also exist offshore and

downcoast of the beach fill site. Fine-grained particles tend to settle offshore in the vicinity of

these resources. In order to minimize the volume of fines that may adversely impact the reef and

kelp beds, beachfill with up to 25% fines is proposed at the Goleta Beach fill site.

3.1.2

Design Scenarios

The beach fill material will be placed either below the mean high tide line, as a layer over the

beach surface as a berm, or as a dike along the revetment or back of the beach. One or more of

these design scenarios may be used at the same time depending on site conditions. Beach fill

concepts are described below.

Below Mean High Tide Line

Beach fill will be placed below the mean high tide line if the material is darker colored

and finer grained than the existing beach sand. Sand will be delivered to the beach and

pushed by bulldozers to the water's edge. At low tide, the material will be pushed as far

seaward as possible and left in a low berm below the existing berm so that it can be

reworked by waves during the following rising tide. The fines will be gradually

winnowed out of the material by waves and currents, carried offshore, and sand will be

left behind.

Beach Berm

Beach fill may be placed as a layer over the existing beach as a berm. The beach-berm

concept at Goleta Beach is shown in Figure 3-3. More discussion of the concept of

design profiles versus natural profile evolution is presented in Section 3.7. The berm

would be a level surface extending a certain distance from the back of the beach toward

the ocean, then sloping gradually into the water. The elevation, width, length, and slope

of the berm will vary for each sand placement opportunity, depending upon the quantity

of material to be placed, its qualities and the condition of the beach at the time. Figure 3-3

shows the maximum proposed berm width over the existing profile (maximum envelope)

for the maximum amount of material at the site (100,000 cy/yr). All projects will fall

within this envelope.

A typical berm at the Goleta Beach site for the maximum volume proposed would be

elevated to near +12 feet above mean lower low water (MLLW) and extended 75 feet

seaward, then sloped at 10:1 (horizontal to vertical) to the water. The length of the beach

fill may extend up to 2,200 feet.

3-2

Moffatt & Nichol Engineers