Tag Archives: Forstbaumschule

A different kind of drop photography today…

After all the professional drop photography I talked about yesterday, here is some of my own from a walk that I took after the amazing and slightly overwhelming experience of giving the laudation speech at the opening of an art exhibition.

Below, I really liked how the wave rings have such different sizes and amplitudes depending on whether they were made by rain drops or ducks (you might have to click the image to enlarge to see what I am talking about).

And below, I love so much about this picture. The long waves with the very small amplitude that are coming into Kiel fjord from some far-away storm. The short waves and small scale turbulence that is created where wave crests just manage to flood a step on the staircase, but the water then flows off it again during the next wave trough. The small speckles made by rain drops. The fact that it seems to almost be summer again because the beach chairs are back! And, of course, that I caught the splash and the flying drops of the wave.

I read this poem by E.E. Cummings on Saturday that really speaks to me. It ends in

“For whatever we lose (like a you or a me)
it’s always ourselves that we find in the sea”
E.E. Cummings

Balances of dyed and un-dyed waters

Oh look, a plume of (almost) un-dyed water hitting the green lake!

I am really fascinated by the balance between green water leaking out of the pipeline and into the rain drainage, the rain falling on the lake, and the rain water coming into the lake through the rain drainage system. Right now, the water coming out of the drainage is a lot less green than the water in the lake, which is itself being diluted by rain. So much so that you can see a clear plume entering before it is mixed so much, entraining so much lake water, that you loose track of it in the green.

This makes me think about all kinds of stuff: how long between it raining on the catchment area that drains into the lake and the water actually reaching it? And how large might the catchment area be relative to the area of the lake (i.e. how large are the respective influences on the color)? So much entertainment just stemming from a little green dye :)

It’s all about the right equipment: That’s why I now own a UV lamp! I see a lot of fluorescent tracer spotting in my future!

Before I start gushing about my awesome new UV lamp (thanks for encouraging that purchase, Uta! :-)), some other updates on the state of green in the park across the road from my house (don’t know what I am talking about? Check out previous posts on the fluorescent dye tracer).

The lake is still bright green and very well mixed, similar to what it looked like in this post. But what is a lot easier to see now is the green water coming out into the Kiel fjord. It was very hard to see on the pictures I took the other day on our fluorescent night walk, and I didn’t see any by eye the first couple of days, but for the last days it has been clearly visible:

It’s still a lot clearer by eye than on the pictures, but even in these pictures you see the plume going out of the storm drain, don’t you?

In other news: my UV lamp arrived today and I am so excited!

So here is a water sample I took out of the green stream, photographed in normal daylight and then lit by my UV lamp. Pretty cool, ey? :-)

Who wants to come fluorescent water-spotting with me? :-)

Fluorescent night walk — following the stream through the lake into Kiel fjord!

Luckily some of my friends are crazy enough to bring the UV lamps and go on a night walk with me, following the green fluorescent stream! (Don’t know what I am talking about? Check out the previous posts (post 1, post 2) on why there is fluorescent dye in a lake across my street and why that is exciting)

Following the water

It looks very spooky when all of a sudden in the middle of a park you come across something looking like the picture below. Well, you would probably not come across it if you didn’t know where to look, but you get my point. And once you found it, you can follow it downhill.

But don’t let yourself get distracted by signs on the trees, someone is trying to lead you in the wrong direction ;-)

Because what we were looking for was, of course, the same lake I have been posting about today and yesterday, except now it looks like the picture below. If you thought it was creepy by day you know nothing of creepy!

Creepy, but also fascinating! Of course I have to inspect it more closely.

Below my hand holding the UV torch while I was looking at all kinds of critters in the water (poor things!)

Science is, of course, team work. Especially when you want pictures, too ;-) Thanks Maria and Tom for such a spontaneous and exciting adventure!

Below, Tom is shining the UV lights down the little water fall so we can take pictures.

And here you see the view from the upper lake down the water fall into the lower reservoir. Next time I will definitely not do such a fluorescent night walk without a tripod and a better camera than my phone!

It might have been a bit of a hassle to find if you didn’t know where to look, but since I know exactly where that lake drains into Kiel fjord, we could follow the fluorescent water out the storm drain into the fjord!

Here we are at the top of the sea wall, looking down, and you see eddies of fluorescent water coming out of the storm drain and into the fjord. Super cool to see that the flow was coming out on the edges of the drain, and that it was eddying. And that, even though there was not a large flow coming out, it could be seen quite far into the fjord, at least as far as our torches could still light the surface. Very very cool tracer oceanography! That was one exciting evening!! :-)

Dye tracer “in the wild”, day 2

This morning, the green lake looked different yet again.

If you remember yesterday’s pictures, we ended the evening with the lake being a fairly well mixed green color (picture on the right).

Now imagine my surprise when I came back in the morning and it looked like this:

The right side of the lake is still green, but the direct connection between inflow and outflow is an even brighter green! And the green inflow detaches once more at the tip of that little island (which it only did during the first observation yesterday, and two hours later the mixing had progressed around the tip).

There are only two ways I can think of how that could have happened:

a) During the night, there was a lot of un-dyed water added to the lake. Maybe through rainfall? But the effect would have been that the green color in the lake would have gotten diluted and, when the rain stopped, the inflowing water appears a lot greener than the surrounding lake water. Possible, even though I didn’t notice any rain during the night.

The other option is this:

b) Someone added more dye to the leaking pipes. This is the more probable explanation to me. The effect would be the same as above: A more intense inflow into a less intense lake.

In any case, the plume we are seeing now can only have been flowing with that intense a coloring into less green water for a couple of hours, otherwise the whole lake would have been mixed through and through.

I guess the easiest way to know which explanation is right would be (well, in addition to asking them directly) to have an objective measure of how green the water is, so that we would know if that changed over night or if the plume is really more intense now than yesterday. But with light that is always changing that is really not possible to say.

But this new green inflow is definitely beautiful: Look at the instabilities where it meets the stagnant lake water!

And more instabilities on the other side.

So those pictures were taken at around 7 in the morning. When I came back in the afternoon, the lake looked like this (sorry about the confusing lighting with the shadows and directly lit spots, can you ignore those and imagine what the color would look like under better light?):

Completely mixed and very very green! Interesting, isn’t it? So apparently the inflow stayed as intensely green as in the morning and, over the course of the day, mixed the whole thing.

P.S.: The company that puts the dye tracer in said on my Instagram @fascinocean_kiel that they are using uranine as dye, and that it’s completely safe for the environment. And, interestingly, that’s what we use in tank experiments under the name fluorescin, and that means that it is a fluorescent dye! I really need your UV light, Uta!! :-)

Dye tracers “in the wild”

You know I love dye tracers (remember the beautiful fluorescent green we used in the 2017 experiments in Grenoble, when we got to play with the 13m diameter rotating tank?) but today I found some “in the wild” again — on the way back from my morning run & swim no less, in Kiel’s Forstbaumschule.

I’ve seen a dye tracer here several times before, and it’s basically just an indicator for a leak in the district heating (and everybody claims that it isn’t harmful to the environment despite its color).

Dye as a flow tracer

Spotting leaks would be very difficult if you just had normal water running into places where there is other normal water. Last winter you could clearly see that the dyed water was quite a lot warmer than the rest because it melted ice away where it went, but at temperatures like to day you might be able to see a thermal signature with thermal imaging equipment, but it is nowhere near as obvious as during winter.

But today my timing was lucky: The pipes can’t have been leaking for very long yet, because there were clear boundaries visible between the “old” lake water that wasn’t dyed yet, and the plume of dyed water entering into the lake and leaving it on the other side.

Dye as age tracer

So in a way the dye also acts as age tracer (since there are currently no other inflows into that lake. It would obviously be different if there were): the “old” water is still dye-free, whereas the “young” water is bright green. And then there are the regions where older and younger water mix and the color isn’t quite as intense.

Dye to visualize mixing

On the boundaries between the dyed water and the old lake water you see mixing in form of tiny eddies, and I’m pretty sure that when I go back this afternoon, the whole lake will be this awesome fluorescent color. And I am curious to see if there will still be flow structures visible or if it’ll all just be bright green :-)

Update: 2 hours and 11 hours later

And I went back. Twice.

Below you see how the coloring changes at the inflow mixes more and more with the lake water: left the picture taken at 7:15 am, then 9:15 am, then 7 pm. Fascinating! :)

Moving sandbanks

A while ago I wrote a blog post on how the sand banks in this little creek form. Below you see the picture I showed then:


Then, about two weeks ago, I passed that spot again when it was raining, and this is what it looked like:


Now we can actually see the flow field, and we can see that the sand bank in the far back has moved quite a bit. We also see that during the night it must have rained more at some point, since the leaves on the sandbank on the left that got stranded there, must have been carried there by a higher water level.

I went back later that day when it had stopped raining, and then it looked like this:


Now that the water level has sunk again, you can clearly see that the sand banks have shifted compared to where they were in the first picture a couple of weeks ago.

Funny how much you can discover if you actually look at the world around you :-)

The building of sand banks

The eroding force of moving water can be seen in so many places when you pay attention. For example in a park where I sometimes go for walks, the really well-maintained paths are forever eroded and washed away by the heavy rains we’ve had recently.


In the picture below you see a green pipe opening into the pond, and what you can’t see is a second, larger pipe just to the right of the first one. Both pipes drain water from the park’s paths. Water then flows through the pond and eventually into Kiel fjord. And what happens is that all the pebbles and sand from the park’s paths end up in the drainage system and get washed into that little pond, where they get deposited in a sand bank.


Interestingly enough, water exiting the pipes seems to typically do so at such a high velocity that all the debris doesn’t get deposited right then and there, but carried downstream until the water has slowed enough that a sandbank can form. And on the sandbank you can see that larger rocks get deposited first while smaller ones are carried further with the current before they settle.