Several People Asked: Hey Adam, ever since Hurricane Marie lit up Southern California a lot of sandbars have been trashed. How long will it take for them to recover? How long does it take for a spot to rebuild its sandbars?
Adam Wright – Solspot Forecaster:
Hurricane Marie was definitely something special…it is easy for us West Coasters to forget how powerful and how destructive large hurricane swells can be…and Marie really cranked up the juice there for a couple of days.
Despite the size of her surf, which don’t get me wrong was impressive, it was the wave-size combined with the consistency that really demolished the sandbars. Marie basically had big sets stacked up with 15-20 waves per set and very little downtime in-between…it was this beating action that started the incredible side-currents, which along some beaches looked like rivers flowing along those inside sections. Those side currents quickly eroded any stable sand we had in both the inner and outer bars (if your spot had a 2 sandbar system…like Huntington Beach for example) and then pulled it out into deeper water as strong rip-currents (moving away from the beach) began to form as all of the swell-surge tried to find ways to drain off our beaches.
So how long it will take for the sand to recover? Unfortunately there isn’t a quick and dirty answer to that. There are a number of factors that go into creating sandbars…first you need to have a source of new sand. The quickest way to get new sand would be from runoff, where we get enough rain to push more sand out the various river basins or even erode it right off the sandier cliffs close to the beach. Naturally we are in the middle of a drought, so we may not have this as a realistic option until the bigger weather patterns change.
A backup source of sand, and the one more likely to help reform our bars (until we get some rain) is to have it slowly pushed around from other nearby beaches. This can happen when you have a mix of small short-period windswells (usually from the WNW-NW) and a fairly decent amount of tidal swing. The short-period waves can make it almost completely to the shorebreak without disrupting the chewed up sandbars on the outside, grab a little bit of sand from the onshore berm and the slop it back out into the lineup and eventually letting it settle and reform the bars. This is a pretty common occurrence for most of the West Coast…in fact Oceanographers refer to this process as the ‘longshore bar current’ and is one of the main ways we see sand transported around. Essentially it is a much smaller version of what Marie did, but going from the North to South along the coast, (and in a much less catastrophic fashion).
Socal unfortunately doesn’t have the most efficient longshore current…just the nature of our coastline which swings around to face more to the south as you drop past Point Conception slows down a lot of sand movement. This is compounded by all of the development we have along the coast, big harbor jetties, piers, even the random headland, all get in way and keep the current from making a nice smooth transition like it does along a lot of the Northern and Central California beaches. (Of course it helps that those areas also get some good run-off during the winter too).
If you are just worrying about the sandbars you actually want this minor windswell to be the only swell in the water when it is trying to shuffle the sand along. A bigger swell from another direction would disrupt the transportation and wouldn’t give the sand the time to settle into a dense feature, instead it would keep it fairly fluid and the bars wouldn’t improve. That sort of sucks for us surfers since we would like to have something to ride most of the time…and crappy little windswell doesn’t really do it for us.
So how long till the sandbars return…not really sure…I have seen them bounce back pretty quickly, sometimes in just a matter of weeks if the conditions are right, but I have also seen areas that can take years to get back up to speed. Generally the wider, longer, more uniform the beach the faster it recovers…of course if the guy in charge of the weather decided to dump a ton of rain on our region we would see it recover even quicker (especially if we only got the rain and not a lot of swell).Tags: longshore bar current, sand transportation, sandbars, Solspot Q and A