Coastal Process Lab

Part I:

Case Study: Santa Monica Beach

About $1905,$ a pier was built at the end of Colorado Avenue $($photograph A$,$ page $3).$ Almost

immediately, it was obvious that the pilings of the pier were interfering with the longshore drift.

The beach widened as sand built outward from the pier.

Notice on each photograph a baseline $($R$-$S$-$T$-$U$)$ has been drawn. This represents the shoreline

before the pier was built.

In $1934,$ the City of Santa Monica completed a breakwater seaward of the pier to provide safe

anchorage for boats. The engineers thought that a breakwater that was not attached to the shore

would permit sand to be transported along the beach while providing protection for small boats.

Using reference points R$-$S$-$T$-$U shown on the figures, measure the width of the beach at each

point from the baseline and record it in the following table. Make a paper ruler using the scale on

photograph C $($page $4).$

How did the beach change as a result of the construction of the breakwater.

It did not change over time because the length of the coast is the length of the beach. The width

did expand between $1928$ and $1949.$

Determine the rate of advancement of the shoreline at point $T$ during the period from Dec.

$1937$ through Oct. $1949(11\mathrm{.}8$ years$).$ Hint: Your answer will be in $f\frac{t}{y}r.$

$25\mathrm{.}42$ feet$/$year

Engineers now understand that unconnected breakwaters built at a distance from the shore

that is less than three times their length are likely to be joined to the shore by deposition in the

wave shadow behind the breakwater.

a$.$ What is the length of the breakwater in feet?

$-2125$

b$.$ What is the distance from the breakwater to the $1928$ shoreline? $($hint $-$ measure on figure B

from the breakwater, along the pier, to the small $"x".$ This $"x"$ represents the edge of sand in

$-2,000$ feet approximately

Given the rate of sand growth, how many years following $1928($and its shoreline$)$ do you

think it would be before the breakwater and the shoreline joined together?

$-78\mathrm{.}67$ years $-79$ years

How might they have engineered the breakwater differently in order to prevent it from joining

the shoreline?