Micro-level water-resources engineering—9: Your enemy no. 1 is…

I am not sure how the elections affect the actual, on-the- ground activities related to the water conservation efforts, this year. However, the point I want to emphasize here is urgent—and it is technical in nature. It is also of very real consequences. I have made this same point several times over the past few years, but still find that, unfortunately, it still remains worth repeating even today. The point I want to remind you is the following:

Regardless of the scale of your water conservation project (whether farm-pond, small check-dam, big check-dam, KT weir, percolation tanks, dams, etc.), and regardless of whether it’s the building of a new structure or just the maintenance of an old one, remember that:

Evaporation loss is the least appreciated but also a most real factor that is actually operative in India.

Expect that depth-wise, water body that is about 8–10 feet deep will simply get evaporated away in a single year. There is nothing you can do about it. (So far, no suitable technology has ever been invented to cost-effectively counter or circumvent the evaporation losses.)

Also, realize that

A small pond (say 5 feet by 5 feet in area) and a large dam (say 1 km by 5 km in area) both lose the same height of water in the same time period.

For ease in visualization, remember, 10 feet is the height of a typical single storey building.

10 feet also is the height of a typical passenger bus.

Thus, if your farm-pond has water 20 feet deep when fully filled (say at the end of a monsoon), then expect that it will come to hold only about 8–10 feet deep water during the month of May next year—even if no one has taken even a single liter of water out of it, for any use whatsoever.

Further, realize that in any water-conservation structure, you are going to have some clearance in between the top level of the water-body and the top level of the dam-wall (or the pond-wall).

Thus, to have a water body that is at least 20 feet deep, you must have the top of the wall at a height of about 24–25 feet or more, when measured from the bottom of the water body. In contrast:

If the wall of your farm-pond or check-dam itself is only about 12 feet tall, then expect it to go absolutely completely dry during summer.

Don’t blame the failure of a shallow check-dam on any one. Most of all, don’t blame it on the vagaries of nature, don’t blame it on a lack of enough rain-fall “last year.” Blame it squarely on your own ignorance, your own poor design choices.

If your check-dam is not deep enough so as to fully overcome the evaporation loss, and further hold some additional useful depth of water, then it is by design going to be completely useless, absolutely non-functional. It is going to be a pure waste of money.

So, this year even if you are planning to undertake only the maintenance of older structures, drop from your list all those structures which won’t have at least 20 feet deep water body when fully filled (or 25 feet tall walls).

Remember, a penny saved is a penny earned. The same money can be used for building check-dams at better geographical sites, or even doing away with the whole idea of building check-dams (if no suitable site exists nearby a given village, as often happens in the Marathwada region of Maharashtra) and instead going in for just a set of farm-ponds—of sufficiently deep water bodies.

Just throwing money at schemes—whether by government agencies, or NGOs, or even by private parties—is not going to help, if you don’t pay attention to even simplest technical points like the minimum depth of water body.

Foreign authors don’t always adequately highlight this factor of the evaporation loss, because is not very significant in their climates. But it is, to us, in India.


If you are in water conservation, remember:

In India, your enemy no. 1 is not a lack of enough rain-fall. It is not even the uneven or non-uniform pattern of the rain-fall, though these certainly are a matter of concern. But they are not your enemy no. 1.

In water resources engineering in India, your enemy no. 1 is: the evaporation loss.

And realize, no feasible technological solution has ever been found to counter it.

All that you can do is to just build farm-ponds or check-dams that are deep enough—that’s all. … Having deep enough water bodies is the most intelligent way of going about it.

I wish all of you ample water supply at least during the next summer—if you spend money intelligently, this summer.

My two cents.

Addendum: My past blog-posts dealing with the topic of water resources may be found here: [^]. In general, the posts which appeared earlier in the series are more technically oriented; the posts that appeared later have been more in the nature of topical repetitions. The post with a high technical content—and also a simplest Python script to estimate evaporation losses—was this one [^]. Also see the next one in the series, here [^].

A late thought: A good project for ME/MTech in water resources engineering:

Given a geographical area (such as a state, region, district, or otherwise, a region defined via watershed areas), estimate the extent of floods that occur every monsoon. Then, estimate the potential amount of storage possible, and the amount actually realized. Be realistic for the second estimate—include seepage and evaporation losses, as well as cost considerations. Develop methodologies for making estimates of all kinds (flooding, seepage and groundwater storage, total on-surface storage potential, the potential that is realized). In the end, consider whether the following statement is defensible: So long as news of floods keep flooding in, we cannot say that the root-cause of water scarcity is the lack of sufficient rains, or uneven (in time) and non-uniform (in space) patterns of rainfall.




And to think…

Many of you must have watched the news headlines on TV this week; many might have gathered it from the ‘net.

Mumbai—and much of Maharashtra—has gone down under. Under water.

And to think that all this water is now going to go purely to waste, completely unused.

… And that, starting some time right from say February next year, we are once again going to yell desperately about water shortage, about how water-tankers have already begun plying on the “roads” near the drought-hit villages. … May be we will get generous and send not just 4-wheeler tankers but also an entire train to a drought-hit city or two…


OK. Here’s something less depressing. [H/t Jennifer Ouellette (@JenLucPiquant) ]:

“More than 2,000 years ago, people were able to create ice in the desert even with temperatures above freezing!” [^]

The write-up mentions a TED video by Prof. Aaswath Raman. Watched it out of idle interest, checked out his Web site, and found another TED video by him, here [^]. Raman cites statistics that blew me!

They spend “only” $24 billion on supermarket refrigeration (and other food-related cooling), but they already spend $42 billion on data-center cooling!!

But, any way, I did some further “research” and landed at a few links, like the Wiki on Yakhchal [^], on wind-catcher [^], etc.  Prof. Raman’s explanation in terms of the radiative cooling was straight-forwards, but I am not sure I understand the mechanism behind the use of a qanat [^] in Yakhchal/windcatcher cooling. It would be cool to do some CFD simulations though.

Finally, since I am once again out of a job (and out of all my saved money and in fact also into credit-card loans due to some health issue cropping up once again), I was just idly wondering about all this renewable energy business, when something struck me.

The one big downside of windmills is that the electricity they generate fluctuates too much. You can’t rely on it; the availability is neither 24X7 nor uniform. Studies in fact also show that in accommodating the more or less “random” output of windmills into the conventional grid, the price of electricity actually goes up—even if the cost of generation alone at the windmill tower may be lower. Further, battery technology has not improved to such a point that you could store the randomly generated electricity economically.

So, I thought, why not use that randomly fluctuating windmill electricity in just producing the hydrogen gas?

No, I didn’t let out a Eureka. Instead, I let out a Google search. After all, the hydrogen gas could be used in fuel-cells, right? Would the cost of packaging and transportation of hydrogen gas be too much? … A little searching later, I landed at this link: [^]. Ummm… No, no, no…. Why shoot it into the natural gas grid? Why not compress it into cylinders and transport by trains? How does the cost economics work out in that case? Any idea?

Addendum on the same day, but after about a couple of hours:

Yes, I did run into this link: “Hydrogen: Hope or Hype?” [^] (with all the links therein, and then, also this: [^]).

But before running into those links, even as my googling on “hydrogen fuel energy density” still was in progress, I thought of this idea…

Why at all transport the hydrogen fuel from the windmill farm site to elsewhere? Why not simply install a fuel cell electricity generator right at the windmill farm? That is to say, why not use the hydrogen fuel generated via electrolysis as a flywheel of sorts? Get the idea? You introduce a couple of steps in between the windmill’s electricity and the conventional grid. But you also take out the fluctuations, the bad score on the 24X7 availability. And, you don’t have to worry about the transportation costs either.

What do you think?

Addendum on 12th July 2018, 13:27 hrs IST

Further, I also browsed a few links that explore another,  solution: using compressed air: a press report [^], and a technical paper [^]. (PDF of the paper is available, but the paper would be accessible only to mechanical engineers though. Later Update: As to the press report, well, the company it talks about has already merged with another company, and has abandoned the above-ground storage of compressed air [^])

I think that such a design reduces the number of steps of energy conversions. However, that does not necessarily mean that the solution involving hydrogen fuel generation and utilization (both right at the wind-farm) isn’t going to be economical.

Economics determines (or at least must determine) the choice. Enough on this topic for now. Wish I had a student working with me; I could have then written a paper after studying the solution I have proposed above. (The idea is worth a patent too. Too bad I don’t have the money to file one. Depressing, once again!!)

OK. Enough for the time being. I may later on add the songs section if I feel like it. And, iterative modifications will always be done, but will be mostly limited to small editorial changes. Bye for now.