Thursday, January 19, 2012

Golden Gardens

This time of year, the highest tides arrive right around sunrise. A couple of days after Christmas I headed out early to Golden Gardens to see the effect of the month's highest water levels. The predicted high tide was 12.7' above MLLW (Mean Lower Low Water or a "0" tide).  According to the Seattle tide gauge, the actual water level may have come in a couple inches higher.   These photos were taken 15-30 minutes after the peak tide.

This is not an unusually high tide.  A 13' tide (these numbers hold for central Puget Sound, but would need to be adjusted for other areas) occurs an average of 7-8 times a year, although the annual variability is huge.  Some years never see a 13' tide at all.  And in El Nino years, we may get 20 or 30!  (Alki Beach:  January 2010).  

The number of high tides at progressively higher levels falls off quickly.  In Seattle, Mean Higher High Water (the average of the highest high for every day of the year) is 11.35' - and we can expect a couple hundred every year.  As noted, 13' tides average less than 8 times a year.  And 14' tides take extraordinary conditions:  either a strong El Nino, like January 2010, or a big storm with a strong surge (February, 2006). Seattle's highest high tide was 14.5' and occurred on January 27, 1983 (another El Nino year).

In these photos at Golden Gardens, we see that the still water level is probably a foot or so below the sandy berm, but that the runup of the waves is just enough to send water over the berm crest.  Berm elevations vary and can depend on wave exposure and the abundance of gravel, among other factors, but 2' above MHHW is often a good place to start.


More on Golden Gardens:
Golden Gardens:  July, 2011

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