In case you have no idea what they are, here is a story on them. Basically they are small (about the size of an apple it seems) black balls that they are using in California to reduce the lose of water in their reservoirs. The black balls work to reduce the growth of algae as well as reflect the sunlight back off the water, reducing evaporation. They will supposedly save the state 300 million gallons of water a year (which is a drop in the bucket for what they use, but I guess every bit helps).
I don’t know if this is going to be worth doing from a cost benefits perspective, or if this works if other states, especially in the south west (and maybe other countries with outdoor reservoirs in dry or arid parts of the world) will try it as well. I wonder if there would be any unintended ecological effects from doing this, though I can’t imagine that such a small amount of evaporated water vapor or sun deflection would have any measurable effect. Just saw the video and figured I’d share.
I heard about this here on the Dope. I was wondering why nothing had been done to stop evaporation in reservoirs. Some responders didn’t think there was a drought concern at all I think, but somewhere in this country there’s always a drought, and tremendous loss of water through evaporation. The black balls seem to be intended to limit biological life in the water, I would have thought the concern would be not to interfere with it, but lack of water is reaching a critical level in California right now, preserving the water would be the primary concern.
I would have thought white would be best, but I guess they are using black balls filled with water to maybe absorb the sunlight to, I guess, help with the algae control part (black water filled balls would absorb the sunlight and heat up, perhaps killing the algae?).
Or, maybe they are black because it’s the government and that seems to be the color the public associates with them.
Well, these are in reservoirs so I assume there aren’t any fish or other things in there except algae. I don’t think it would have much of an effect on the food chain except perhaps migratory birds that might want to land there (and I have no idea if they do in these reservoirs)
Evaporation is prevented by the presence of the balls more than by the color - the balls disrupt the contact between the water surface and the air, which is the physical pathway for evaporation. If they’re packed tightly enough, they can also trap a layer of vapor-saturated air at the water surface and below the influence of the wind, which could further reduce evaporation.
Black balls might result in slightly warmer water at the surface, but I don’t think that’s really significant. In a reservoir, the solar energy absorbed by the black balls would be absorbed more efficiently by the water column if they weren’t there. By intercepting solar radiation, the balls will reduce the total heat content of the water column. At the surface, the balls will be warm, but I’m not sure how efficiently that heat would transfer to the water itself. Regardless, the surface water temperature is less significant to evaporation rates than the characteristics of the air.
I don’t think they need to worry about ecological impacts on the SoCal reservoirs mentioned in the OP’s article, but ecology be an important consideration in other multi-use reservoirs. I can see the balls driving oxygen depletion, especially with low inflows. The other thing to consider would be seasonal turnover. In the fall, the water on the surface cools and its density increases. When it gets cool enough, it plunges downward, mixing with the water below it and “turning over” the lake. The mixing brings oxygen down to the lake bottom, which mobilizes nutrients in the bottom sediments and distributes them in the water column. I can see the balls interfering with that process - the water loses all that heat through the surface, and the balls will slow that heat loss in the same way they slow evaporation. Not a big deal for LA reservoirs, but it’s an ecologically important process in, for example, the Sierra Nevada reservoirs that are managed for recreation and fishing as well as water supply.
Oh, and white plastics break down in sunlight really fast - black plastics can be made with UV-resistant materials, but those materials are dark and generally aren’t compatible with white plastics.
According to the article, the primary purpose of the balls isn’t preventing evaporation. The state uses chlorine in the water to sterilize it. But if the chlorine gets hit by too much sunlight it causes chemical reactions that result in bromate ions being in the water, which are a suspected carcinogen. So the balls are dumped in the water as a cheap means of blocking sunlight.
I can’t really wrap my head around the linked story. Most reservoirs in San Diego and many in Los Angeles are man made lakes. The EPA has mandated they all be covered? How would that work exactly? Lake Hodges, for example, is 1200 acres. That’s a big tarp! Or, I guess, a shit ton of black balls. Even the smaller ones like Lake Poway, Lake Miramar, and Lake Murray are 100 to 200 acres, and they absolutely have ecosystems … fish, waterfowl, and an array of plant life (including fishermen).
Yeah, this ball technique is exactly what restaurants use when doing extended sous-vide preparations to retard evaporation (lots use ping-pong balls). There’s no sunlight to reflect/block, so it’s totally a physical process that prevents the evaporation.
the patchy self-organization of the balls reminds me of metals, in which the atoms form crystalline grains that butt up against adjacent grains whose crystal orientation is different.
Ah, thank you for this. I’ve long noticed these in the reservoir up the street from me when I go walking past it (the Ivanhoe Reservoir, as pictured in Machine Elf’s link), and have always meant to look up what they were, but always forget.
