For the last couple of days, the tide has seemed extraordinarily low during our Albany Bulb swims, the water incredibly shallow. Yesterday when Angie and I swam to the point, we could still touch bottom more than half a mile offshore. Today, Charlotte and I walked out for a good long way before I finally suggested we flop in because it was never going to get any deeper.
In my memory (corroborated by after-swim chats with others), we haven’t slogged through the muck like this since last spring (or summer—the collective memory isn’t that specific). I can say with certainty that since I have been blogging these eighty-two days, the water has not been so shallow as touch ground half a mile out.
Does the depth of the bay change so dramatically from season to season? Is there a cyclical nature to it? I tried to find some answers, but couldn’t quite. I learned a lot. The San Francisco Bay, an estuary that swirls with salty water from the Pacific Ocean through the Golden Gate and the freshwater of the Delta, fed by the Sacramento and San Joaquin rivers, is one of the most altered estuaries in the United States. The ground beneath is constantly changing due to tides and currents as well as because of human interventions like dredging and dumping. Here is a cool map detailing the complex underworld of the bay.
But I couldn’t find anything to explain what seems like short-term dynamics. In our post-swim chats, we debated the possibility that we’d simply not swum at the bulb at low tide in a long time. I couldn’t fathom that this was true, but after drawing blanks on any info regarding depth change, I decided to take a look at the tide charts and low and behold, maybe it is.
Through much of January, the morning low tide didn’t correspond with our swimming times for the bulb and when it did, it wasn’t very low. On January 6 low tide was at 7:52, for instance, but it was a 2.7 tide and January 22’s low tide was at 8:00 but was a 2.2. To put those numbers into perspective, today’s low was -0.1. February and early March were the same; most of the morning low tides didn’t match up with our swims and were not that low anyway.
Strangely, all of the negative lows of January, February, and early March occurred during the second low tide of the day. Now I’m wondering if there’s some pattern to that? Some meaning? Despite my best efforts to understand them, tides continue to confound me. Many things I thought I knew (which I wrote about here) don’t seem true when I study the tide charts. It’s frustrating and wonderful at the same time; it seems right that the tides are a little bit magical and unknowable, but, also, my mind is itchy with wanting to make sense of them.