The graph that you see at the top of this post shows the water temperatures in the shellfish lab’s two tanks from 3 PM on June 5 to 3 PM today, June 12. Since the tanks get water from the same pump in Bunkers Harbor, the temperatures go up and down together as night turns to day and tides move in and out. That’s always been true until today. Between 2 and 3 AM, the orange line from Tank 2 started increasing slowly as the green line for Tank 1 started dropping. Then, at 7 AM, Tank 1 started warming quickly while Tank 2 continued its gradual increase. By 3:30 PM, Tank 1 reached 59.5°F, while Tank 2 was still 55.5°, a four-degree difference! What was going on?
Before digging into that question, it is worth spending a moment with another one: How did we even know this was happening? The answer is that the picture at the top of this post is a screenshot from an online site that anyone can visit to check on the water temperatures in the lab at the moment and over the past day and week. Here is a link you can use to access the graphs. When you click on the link, the good people at Adafruit, who store our data, will show a banner telling you that you need an account to see streaming data. But you can see what’s happening now and over the past week without an account. Accounts are free, so sign up if you like, but you don’t need to.
We do not expect many readers to follow the changes in the lab’s water temperatures from day to day, but it is interesting to look every once in a while. For example, note that the water coming into the lab from Bunkers Harbor almost reached 62° today. That’s unusual in mid-June in Downeast Maine. You can also see an area in the middle of the graph where the temperatures were more steady. That was on June 9, a foggy, quiet day.
For those of us managing the lab and its more than 300,000 resident clams, online access to what’s happening in the lab is essential. When I saw that the temperatures in the two tanks were no longer tracking together, I knew it was time to head over to the lab to see what was going on.
What was worrisome was that the orange line for Tank 2 began holding steady after 3 AM. I knew that low tide occurred around 3:17 that morning, which meant that cooler water would begin moving into the harbor just after that. The dropping temperature in Tank 1 fit that pattern. Why wasn’t the temperature dropping in Tank 2? My best guess was that the flow of fresh seawater into Tank 2 had stopped. There is an air pump providing aeration in Tank 2, so the clams would be OK for a while without water circulation, but if my guess was right, it was a problem we needed to address.
The lab is only about 10 minutes from my house. When I got there, I stuck my hand under one of the Tank 2 inlet pipes and felt no water movement, but did notice that the water, at 55°, felt really cold. I checked the other Tank 2 inlet. Same thing. Then, I went to the back room to put my hand under the inlet in Tank 1. Lots of flow and, wow, at just under 62° it felt almost as warm as the water in the pool at the YMCA.
The tanks are plumbed in series with Tank 1 getting the water first and Tank 2 getting what does not flow into Tank 1. Readjusting the valves controlling the flow into Tank 1, shutting them back a bit so that there would be water that could make its way to Tank 2, took just a few minutes. When the water started flowing to Tank 2 it came with a lot of air — big bubbles coming out of the inlet pipes. That told me that flow to Tank 2 really had stopped. But why?
Thinking about this question raised another one: What was the pump doing around 3 AM? In addition to water temperatures, we track the electrical power that the pump uses minute by minute. On the left you see the wattage that the pump drew between 4 PM on June 11 and 9 AM this morning, June 12. Note that the pump started drawing less power right around 3 AM, a situation that continued until just before 4.
So, we have evidence that the pump encountered some kind of difficulty around the same time the water stopped flowing into Tank 2. Putting the pieces together, it seems likely that the pump stopped moving water at its usual rate and perhaps was pumping a combination of air and water. Once it settled down to pumping water again, air that was trapped in the pipes between the tanks had the effect of sending all the flow to Tank 1. It wasn’t until I “burped” the pipes (with big bubbles coming out of the pipes in Tank 2) that both tanks were getting water again. The graph on the right shows Tank 2 began getting warmer as soon as I got water flowing again. The temperatures in the tanks were the same by 8 PM and continued moving together again after that.
So, we “sort of” know what happened early this morning, but still don’t know why the pump hiccuped. We have a record of the voltage reaching the pump and it stayed steady between three and four, indicating that the problem was not caused by a fluctuation coming down the power line. The problem happened right around low tide, when the pump is most likely to be sucking air along with water, but the tide this morning was only 0.3 feet below mean low tide, which is not unusually low. Perhaps there was some swell coming into the harbor? We’ll probably never know the whole story.
Two things ARE clear. The first is that it is a good thing that we have a remote monitoring system. The second is that we need to keep an eye on what the system is telling us.
Do take a moment and visit our temperature dashboard to see what is going on. It’s always at least a llittle bit interesting and sometimes gets TOO interesting.
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