Surface Motion
T he Erosion Study of 1955-58
In June of 1955 a steel construction known as a groin (a term more common on the east coast to describe an iron or stone jetty) was placed at Twin Lakes Beach as part of a study on beach erosion.
Test groin at Twin Lakes, 1955
Santa Cruz Sentinel photo
The photo is another example of the pre harbor cliff contact with the bay. The location appears to have been at the foot of the Fourth Avenue cliffs which then extended into the bay, and which today is a bluff behind at least 150 yards of beach.
The groin was designed to measure sand movement and wave action were a harbor to be constructed. The amount of sand piled against it would give an idea of the possible effects on the littoral drift down the beach from the San Lorenzo Rivermouth.
Commentary and speculation: A brilliant idea, to test the sand flow, but one that did little to stop the Harbor construction, which very likely had such political momentum that no environmental study could have stopped it. Not many local people remember this steel jetty and the study seems to have not been heavily publicized.
Santa Cruz history marks 1955 as a flood year, which would mean a tremendous amount of available sand at the Rivermouth. Since the date of the test groin is May and June of that year, most likely the sandbar had washed away by then. If not, it's hard to imagine that a great deal of sand wouldn't have collected against it. In that case rideable waves would have occurred there, perhaps the first at the harbor surf spot.
