Crescent City Groin EarthCache
Hidden : 12/20/2014
Difficulty:
2 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:

This Earthcache provides you with an excellent opportunity to learn about and closely study a groin structure placed here as a solution to the chronic beach erosion and sedimentation problems in the harbor.


Access to the Earthcache
Parking is available at the Posted coordinates. This is a public access area, and the additional provided Waypoints make for great views when it is not too foggy. The Low View Waypoint is a short walk and provides a good view of the groin (groyne in Europe) and beach area. The Harbor View Waypoint is a more challenging terrain and requires a bit of climbing. It is OPTIONAL, but affords you a great view to the NW into the Harbor Area (please be careful if you attempt this climb. It’s about a 3 Terrain rating.) The below photo is where the Low View area is and the tsunami dedication bench.



Background
Crescent City has been struck by tsunamis in 1964, 2006, and 2011. Offshore underwater geological features have been identified as the cause for the concentration of the tsunami surge in this particular area. This Earthcache, however, focuses on damage caused by daily wave and ocean action. The Crescent City Beach has been subject to the erosional forces of the waves and the longshore currents over the years, so the City Officials designed and installed many erosion control features to protect the Crescent City Harbor to the west and the Beach to the east.




Groin (Groyne)
Groins are generally piles of medium/large rocks or manmade blocks that are placed perpendicular to the beach or at an angle to the beach area to interrupt or redirect the natural forces of the ocean. Groins are a type of breakwater. They discourage erosion of land-based sand due to the physical pounding of the incoming waves and also encourage accretion (deposition) of suspended sand onto the beach area by interrupting the flow in the area, thereby building the beach. This process causes the suspended sand from the longshore drift (the ocean current that transports the suspended sand particles) to be deposited onto the shoreline/beach area and not "escape" out of the area or into the harbor through the harbor mouth. Some groins are constructed completely under water and are called submerged groins. At the earthcache location, you will be able to easily see the location of the groin. It is a deflecting groin because it tends to change the direction of flow, rather than completely repelling it.
If you look at the aerial photo and around you when at the posted coordinates or the other View Waypoints, you will also note the presence of other breakwater structures (jetties, seawalls, riprap boulders, etc.) designed to protect the harbor.

References: CoastalWiki, Wikipedia

Completing the Earthcache
To get credit for completing this Earthcache, please send your answers to the following questions to our profile Email. Incorrect answers may lead to further questions from us, or deletion of your find log. You may log your find after you have transmitted your answers.

1. From the sign near the Posted coordinates, what is the full name of this Groin?
2. Estimate how high above the sea-level the top of the groin is (in feet or metres)? Is it a submerged groin?

From the Low View Waypoint:
3. By observing the waves’ action against the rocks/boulders in the groin structure, would you say that the groin is decreasing or increasing the energy of the waves?
4. Observe the waves approaching the groin. Are the waves striking the groin straight on, or at an angle?
5. Observe the area behind and near the groin. Do you think that the groin is preventing beach erosion, causing some beach erosion, or both?

Photos are optional, but they are welcomed. Please do not include spoiler photos of the sign or groin. Thanks.


"When one tugs at a single thing in nature, he finds it attached to the rest of the world." - John Muir
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