There are three entrances to the Berkeley Marina: North, Middle, and South. Keelboaters know to avoid the North in low tides, and that the South is the only safe entrance in very low tides. But what are the numbers? That is, what's the tide level threshold for avoiding the North entrance? How about the Middle entrance? And is the South entrance absolutely safe in all tide levels?
Here's a shot of the marina entrance with this highlighted along with the lower depth area on the west side of the north-south channel (which is now marked by white hazard buoys).
Unfortunately, we don't have reliable data to answer most of the questions above except the one about the South channel entrance. The "channel" into the South entrance is a federal navigation channel, which is why mark 3 (or Olympic Circle D mark) exists. Because of this, the US Army Corps of Engineers conducts annual sounding surveys, and the last one was in February 2023
If you blow up the South entrance in the diagram for this survey, you see this
The numbers on the chart are soundings adjusted for Mean Lower Low Water, in other words tide level 0.0. I'm not entirely sure of the purpose of the three parallel "course lines" into the marina, but the data shows that if you stay inside of the rightmost one, you will have at least 6 feet of depth at 0.0 tide
For reference, these are the drafts of our boats: Commander – 3'9", Merit – 4', J80 – 5'. So with care, all of these boats can go use the South entrance in low tide with some margin.
To reiterate, the soundings show that you can safely transit with 6 feet of depth at 0.0 tide, which means you can safely transit the South entrance with 5 feet of depth at -1.0 tide, which is close to the limit of the J80.
Tide predictions and depth charts are imprecise, so you have to use caution. For tides, the predictions are based on models and observations over a very long timescale that cannot take into account variations caused by factors on very short timescale, such as drought, rain, snowpack melt and runoff, etc. The nearest NOAA tide station for which you can get predictions vs. actuals is Richmond Inner Harbor
The differences can be as much as a foot in either direction, so it's a good idea to look here and factor the differences into your calculations. And you can be conservative in very low tides by transiting on a risiing tide.
I'll end with an anecdote. A few years ago, I skippered a Commander in the annual Berkeley Parade of Lights in December, where a whole flotilla of Christmas decorated boats paraded out of the Marina past the Yacht Club, along the pier, and back in again. For whatever reason, the start of the event was in the late afternoon at exactly the low tide, which was about -1.4 that day. Nobody grounded, although a couple of boats drawing 7 or so decided to turn around at the Yacht Club and not exit the marina.
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