Wednesday, January 25, 2017

The Birth of the Restore Sloat Campaign: 1997-1998 El Niño and a Cycle of Wet WInters


Greetings Surfriders,

Sharp Park News: Briefly, we have news that the appeal hearing at the Board of Supervisors for the Sharp Park issue will take place on February 28th.  Look for a blog post with more details as we get closer to the hearing. 

Recently, it has been noted in news reports that this winter storm season has been the wettest since the 1997-1998 El Niño. We would like to point out that the 97-98 event was actually the culmination of a series of wet winters.  We may be in a similar cycle right now.

History does have a way of repeating itself.  This month we would like to reflect back to those wet years of the latter 1990's and how this whole campaign got started.

The erosion disaster at Sloat began during the winter of 1994-1995.  Before that year, Ca was locked in a series of drought years.  Surfers remember those years well as drought years deliver long stretches of world class surf to Ocean Beach. 

As the second half of the 1990's went on, wet weather began to dominate winter conditions again.  At Sloat, storms started striping sand away from the newly replenished beach and bluff.  In order to protect the road and the sewer infrastructure from the encroaching surf, SFDPW constructed the giant quarry stone revetment we now see between the north and south parking lots. Erosion and blight then began to spread to the adjacent areas, sparking the birth of this campaign.

BEFORE:

Circa 1993
This is Sloat's north parking lot after the sewer and road renovation project.  The parking lot was completely refurbished, with a landscaped bluff and a sandy beach.














AFTER:


1997-1998 El Niño















Five years later, this is what remained of the beach and the same landscaped bluff.  It has always been Surfrider's contention that infrastructure built during the 1980's was placed too close to the sea south of Sloat.  This is why we are calling for a managed retreat solution. Sand replenishment in front of the infrastructure has been ineffective  (The 2008 date is the year the photos were copyrighted). Photo Credit: Bob Battalio, PWA and Associates

Below is the chronology of the 1999's era erosion cycle.  Citation: Army Corps of Engineers Ocean Beach Storm Damage Protection Project page 55, Table 3-1of the 3.1 Sediment Transport Processes Update section.

1994/1995 Storm
Season
The bluff edge retreated 30 to 40 feet between the two parking lots, and somewhat less elsewhere in the reach south of Sloat Blvd.

1996/1997 Storm
Season
Precipitation runoff and wave action formed numerous erosion gullies in the bluff face. In March

1997, one storm formed a gully extending to the beach that eroded the bluff to within 15 feet of the highway in the area between the two parking lots

Fall 1997 Toe protection (A small Emergency Quarrystone Revetment) placed between the 2 parking lots as an interim measure to protect the bluff against storms.

1997/1998 Storm
Season
Loss of sand from the beach south of Sloat Blvd. resulted in extensive erosion of the bluffs. In some areas, beach elevations were lowered 10-15 feet compared to their summer/early fall elevations. The bluff edge retreated up to 30 feet in the unprotected areas at the south end of Sloat Lot. Another Emergency Quarrystone Revetment placed in February 1998 between the 2 parking lots in response to the large storms.
The bluff edge protected by the EQR retreated only 2-6 feet in localized areas between the two parking lots. Along the South Lot, bluff edges retreated 0-16 feet and there was an overall oversteepening of the bluff slope, making it likely that future wave undercutting would result in more extensive bluff erosion.

1998/1999 Storm
Season
The bluff edge retreated approximately 50 feet in places along the section of beach from the south end of South Lot to Funston Cliffs. Bluff slopes have been over-steepened along the entire reach and are more susceptible to slope failure and wave undercutting. Bluff slopes above the toe are 40 to 70 degrees or more. The slope of the face of the bluff south of South Lot was nearly vertical in places following the erosion in early 1999

October 1999 Approximately 20,000 cubic yards of sand placed along a 370-foot-long reach of the bluffs south of South Lot to form a temporary sand barrier

January 2001 12,000 CY of sand placed at the sand barrier again, in response to a loss of almost half of the sand between Oct ’99 and Apr ‘00

2000/2001 Storm
Season
All of the sand placed in Jan 2001, plus about 17 feet of the original sand barrier eroded away. The bluff south of the barrier eroded back by 7 to 13 feet.