Beach Berm Dam - Doheny State Beach EarthCache

This Earthcache is located at Doheny State Beach. There is a parking fee if you want to park in the park, but there are shopping centers just across the street. This cache will look at the geomorphology of a sand berm that dams a creek and the formation of laminations in sandstone.

Secondary Coordinates: N 33 27.724 W 117 41.060 The secondary coordinates are provided incase the primary ones are in the middle of the creek and for the confirmation pictures.

The coordinates place you in the middle of a sand berm that usually blocks the San Juan Creek from emptying into the Ocean.

This berm forms whenever there is low flow in the creek, which is usually since we don’t get much rain. Water pools behind the berm like a dam and provides habitat for a variety of species. Water still flows into the ocean. It just moves slowly down through the sand.

October, 2004
source: http://www.californiacoastline.org/

(Hydrogeology info can be obtained from the Municipal Water District of Orange County (Michelle Tuchman at (714) 593-5014 or mtuchman@mwdoc.com) by asking about the testing in Dana Point begun in March 2005. (http://www.mwdoc.com/documents/March2005Currents.pdf))

Unfortunately, the water is highly polluted because most of the water in San Juan Creek is runoff from streets in the watershed and receives accidental releases from the sanitary sewer system. Note the many no swimming signs. (Don't tell the birds).

Only when there is high flow in the creek does the creek actually empty into the ocean.

July, 2003
source: EagleAerial

Following a storm, water builds up behind the sand berm until it over flows. The creek then erodes a channel through a portion of the berm and drains the ocean. This also drains the contaminants into the ocean resulting in typical beach closures following storms.

The channel the forms allows you to view the layering in the berm.

source: Ron Blakey (ronald.blakey@nau.edu), Department of Geology, Northern Arizona University
http://jan.ucc.nau.edu/~rcb7/bermcutDanaPt.jpg

Once the flow of the creek goes down again, the waves begin to transport sand back up onto the beach. Sand is only deposited in the channel during high tide, so the layering is a reflection of minor differences in sand composition between high tides, sand grain size differences between incoming and outgoing tides due to wave energy differences, and the accumulation of additional material (wind blown sand, wood, etc.) on top of the sand during low tide.

source: BikeNfind Earthcache log date May 13, 2006

These layers, called laminiation because they are so thin, are present beneath the entire beach. Feel free to dig a small trench of your own to try to find the lamination down near the water. If anyone asks, just tell them you’re building a sand castle, or the truth. The high tide will fill it back in.

If the beach were to be buried, the lamination would be preserved and become lamination in sandstone that could be used later to help reconstruct the environment in which the sand is deposited.

Logging requirements:
Send me a note with :

1. The text "GCPZYK Beach Berm Dam - Doheny State Beach" on the first line
2. The number of people in your group.
3. Post pictures of the channel walls. Describe them if you don't have a camera
4. If there is no channel, you will need to do some digging.

The following referenced were used in generating the above information:

• http://jan.ucc.nau.edu/~rcb7/Oceanography.html
• http://www.ocwatershed.com/watersheds/sanjuan_reports_studies_Qtr1_section2.asp
• http://ceres.ca.gov/wetlands/geo_info/so_cal/san_juan_creek.html

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