A crumbling rock and concrete jetty largely buried and forgotten beneath the sand at the mouth of the Russian River has become the focus of renewed interest amid studies to determine its impact on the adjacent estuary.
No one knows, for instance, how deep the remnants of the 84-year-old jetty and adjoining seawall extend below the mutable surface of Goat Rock State Beach, nor how they affect the shifting sands and mingling of salt and fresh water where the river meets the sea.
But that's expected to change.
A series of geophysical tests that began Wednesday and are scheduled to extend into next week are aimed at resolving some of the mysteries of the historic structures and how they interact with environmental forces at the river's end in Jenner, the Sonoma County Water Agency said.
Scientists from Lawrence Berkeley National Laboratory and elsewhere plan to use high-tech gadgetry, including ground-penetrating radar, to build a picture of subsurface structures left behind by failed attempts to tame the sea with more than 100,000 tons of stone carved from Goat Rock, as well lumber and steel.
The overall effort is intended to provide information that will help the Water Agency and other entities optimize fish habitat in the estuary, where threatened steelhead trout spend their summers, senior environmental specialist David Cook said.
In particular, biologists want to know how much fresh and saltwater seepage goes on beneath the surface of the sand and gravel spit that encloses most of the estuary and how it might affect the volume and salinity of the water within.
They also want to understand the extent to which the jetty — a failed attempt to keep the mouth open for transit by gravel barges decades ago — still affects the natural dynamics that might otherwise close the outlet all summer long.
"At this point, much of the structure is buried, so we really have to go off of what documentation there was for the construction of the jetty, which there's not a whole lot of," said Chris Delaney, senior engineer with the Water Agency. "Since we can't see much of it, because it's buried in the sand, we have to turn to other methods to really get a better picture of what the composition of the jetty is."
There are no plans currently to destroy or modify the jetty, but it may be that the studies indicate that's appropriate, agency personnel said.
The jetty project was begun in 1924 with the opening of the quarry at Goat Rock and construction of a narrow-gauge rail system to transport stone 3,500 feet up the beach to the point where the eventual stone jetty abruptly angled left and out toward sea.
The jetty itself was completed years later, its foundation built into excavated sand to a depth of perhaps 16 feet and with a height of about 17 feet, according to historical documents.
The money put forward by businesses ran out before the jetty was complete. The state later became involved, in part to keep the passage open for migrating fish. Ensuing periods of construction and reinforcement continued until 1948 but never managed to beat back the forces of nature, Cook said. The manmade structures fell apart, subsided, degraded and were largely buried.
A portion of the concrete covered jetty still remains visible, as do several hillocks of enormous rock chunks, a few wooden posts and two lengths of rusted and pitted railway.