Tuesday, May 22, 2012

Accretion Cycle in Overdrive at the North End

Excess sand at the north end - Why not truck this down to S. Sloat? (photo: Mike Martinovich)

We are eagerly awaiting the official unveiling of the Ocean Beach Master Plan as well as the start of the implementation phase...

Meanwhile, our chapter has been busy talking with City officials and government agencies about a near term plan for Sloat. As much as there needs to be a long term plan, there is no reason why we can't begin reversing the damage now.

We hope to see a new interim policy featuring rubble clean-up, aggressive sand replenishment (sand coming from clearing the Great Highway and parking lots), and the commitment to use sandbags instead of quarry stone for emergencies. Additionally, we could use more attention to maintaining safe access to the beach.

The last few months our seasonal northwest winds have settled in, triggering major sand movement. At the north end, so much sand has piled up that it has reached the top of the esplanade and has begun to spill over into the parking lot. This is nothing new or unnatural. It is an example of our beach's native accretion process, the return of sand to beachscape. Our new document The History of Coastal Erosion at Ocean Beach (see prior post) features a photo of the same exact condition taking hold in 1942.

Unfortunately, at the south end of Ocean Beach, the erosion cycle continues. Our contention is that the exposed fill and quarry stone south of Sloat is only exacerbating the problem. The area in front of the 1997/1998 revetment is particularly troublesome. In this stretch (south of the 1st parking lot) a sand scouring effect is present due to wave reflection off the rocks. This has produced a deep hole or trough that never seems to move or fill in with sand. Normally, troughs at Ocean Beach are temporary, shifting position, disappearing and reappearing as currents and wave energy change the contour of the bottom. The stationary hole at S. Sloat has become permanent. It has been there ever since waves began consistently reflecting off the rock. Check out this video of the hole:  http://youtu.be/SSECoX2WB2Y

It is well known that coastal armoring often lead to this kind of scouring / feedback loop.  Such phenomena inhibit a shoreline's accretion process, causing what is known as "passive erosion". This why we believe the time is now to remove whatever rubble we can and to replace it with sand.
We will update the blog as soon as we reach any progress on this and other issues. Thanks for checking in and staying engaged!