Micro-level water-resources engineering—4

Further Update on 2015.04.13: The debugged version is online.

Here is the zip file for the debugged version [^]. I have updated the link in the main text below, too. The bug consisted of a single change: In the file CCheckDamsSeries.cpp, line 228, it should be dEX1 = dX2 - dEWaterLength; in place of dEX1 = dX2 - dWaterLength;. That’s all. (Copy-pasting codes always introduces errors of this sort.)

What I have now uploaded is only the (corrected) first version, not the entirely rewritten second version (as mentioned in the first update below). Two reasons for that: (i) The first version itself is good enough to get some overall idea of the benefits of check dams, and (ii) I have decided to try Python for the more elaborate and completely rewritten version. The reason for that, in turn, is that I just got tired of compiling the binaries on two different platforms.

That way, I am new to Python, and so, it will take a while before you get the expanded and rewritten version. I am learning it the hard way [^].  May be a couple of weeks or so for the next version… Bye for now.

Important Update on 2015.04.12: The software is buggy.

I have noticed (at least one) bug in the software I wrote (see details below). It came to my notice today, once I began completely rewriting the code with a view to study how the economics would work out at different gradients of the river (keeping all the other variables constant, that is). The bug concerns the calculation of the water volume after evaporation, in each dam.

Please give me a few days’ time, at the most a week, and I will upload a (hopefully) correct and a much better written code.

In the meanwhile, I am keeping the current buggy code at the link provided below just in case you want to debug it or play with it, in the meanwhile. Once the new code is ready, I will remove the current buggy code and replace it with the new code.

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The last time, I had suggested an exercise to you. I had not actually undertaken that exercise myself, before writing about it on the blog.

Once I began calculating manually, I realized that the calculations were highly repetitive. I therefore decided to write a quick-and-dirty C++ program about it.

It takes a few input parameters concerning the geometrical dimensions of the highly simplified model river, generates a series of check dams, and calculates the volumes of water that would get stored.

The program also takes into consideration a thumb-rule for the evaporation losses. However, the seepage losses are not considered. That will be quite a different game.

The program also calculates the number of people whose daily personal water needs would be fully satisfied by the available water storage (after deducting the loss due to evaporation, though not by the seepage).

Finally, I also threw in a very rough-and-ready calculation for estimating the costs of building the system of check-dams, and the one-time per-capita cost (for the supported population) for the round the year availability of water (assuming that all the dams do get fully filled up during the monsoon each year).

Let me hasten to emphasize that the cost calculations here are too simplistic. Don’t rely on them; take them as just rough, preliminary and merely indicative estimates.

The cost calculations also do not include any maintenance aspects—which, IMO, is an even more serious drawback for this software. I believe that dam-maintenance must be factored in right at the stage of design—including periodic maintenance for the mechanized removal of the accumulated silt.

Further, costs for lift-irrigation or pumping of water are not included in this program.

Despite these limitations, it has turned out to be an interesting toy to play with!

I am sharing a link to a zip file (stored on Google Docs) containing the source code as well as the pre-compiled binaries for both Windows 7 and Ubuntu 14.04.01 LTS (both 64 bit), here [ (.zip, < 40 kB) ^]. Enjoy!

Things you could check out:

After altering some of the input parameters, I found that the total amount of water available (and hence the population that can be supported, and hence the per-capita expense) is highly sensitive to the depth of the river gorge at the mouth (i.e. at the extreme downstream end, where it joins a bigger river). Realize that this is a very simple model: the volume of the pyramid is directly proportional to the area of the base rectangle, and the fact of the slope restricts the possible storage volume in such a way that the depth of the river bed at the mouth then perhaps becomes the most important parameter in this model.

If you spot some other peculiarities, I would love to hear from you.

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These days, I have been discussing these ideas with my father a bit. Not much, but I just passingly mentioned to him that I had written a blog post and that I mentioned about what he had told me about the geology of the Shirpur region.

Next day, he dug out from somewhere the proceedings of an all India seminar he had attended. Here are the details of the seminar: “Modern techniques of rain water harvesting, water conservation and artificial recharge for drinking water, afforestation, horticulture and agriculture,” jointly organized by the Rural Development Department of Government of Maharashtra and the Directorate of Ground Water Surveys and Development Agency, in Pune, on 19–21 November, 1990!

Wow! 1990! The proceedings are by now some 25 years old!

Yet, browsing through it, it first seemed to be how little things had changed. The contents of that seminar a generation ago are almost entirely relevant even today!

… Of course, there must have been some changes. What I got here was only a compilation of the abstracts and not the complete proceedings of all the full length papers. It is difficult to make out the progress (or its absence) looking only at abstracts. … I notice that a lot (even majority) of the papers are mostly of the sort: “This thing needs to be looked into” or “We have begun this study,” or “this approach seems to be promising.” Concrete, quantitative results are rare in the book. May be that’s the reason why the material looks very “modern” even today.

Other noticeable points: Only one or two papers make reference to GIS or material generated by GIS, or to the satellite imaging/remote sensing technologies. None provides any kind of a computational modelling. All the diagrams are drawn on paper—not computer generated. The book itself was printed, not produced via desktop publishing.

There was a participant from a foreign country—a lone foreign participant, I think. His affiliation was with the Cornell University, USA.

The title of this paper was “Optimization techniques to study the impact of economic and technical measures in recovering aquifers polluted by farming activities” (italics mine).

Even in the abstract, the author felt it important to highlight this part: “the importance of a government body which assumes a key regulatory role in managing the quality of the aquifers cannot be understated” (italics mine).

Immediately later, he also simply added, as if it were an unquestionable kind of a statement: “Both economic and technical measures are at the disposal of the government” (italics, once again, mine).

The author had grandly concluded his abstract thusly: “A theoretical model is developed that may assist the government in determining proper policies under various conditions of economic priorities as well as under different scenarios for relative price ratios between inputs and agricultural production” (italics emphatically are only mine).

The more things change the more…

BTW, any one for the idea that participation from Ivy League schools uplifts the quality of Indian conferences?

It’s a 140 pages book, and I haven’t finished even browsing all through it. My father gave it to me only yesterday noon, and, as you know, I have been writing this program since yesterday afternoon, and so didn’t find much time for this book.

However, I did notice one very neat abstract. So neat, that I must share it fully with you. It forms the content of the next section.

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“Indian Rainfall and Water Conservation,” by P. R. Pisharoty, Professor Emeritus at Physical Research Laboratory, Ahmedabad.

Abstract

The average annual rainfall over the plains of India is 117 cm. The average for all the lands of the World put together is only 70 cm. per year.

In Maharashtra, 80% to 95% of the annual rainfall occurs during the monsoon period June to September. And that occurs in 85 days over the Konkan and in 35–45 days over the rest of Maharashtra. The monsoon rainfall over Konkan is 270 cm., Vidarbha 95 cm., Madhya Maharashtra 77 cm., and Marathwada 65 cm. Half of this amount (outside Konkan) falls in 15 Hours to 20 hours distributed within those 35–45 days. Being of high intensity, 3–5 cms. per hour, this half amount of total monsoon rainfall runs off the ground causing floods and much soil erosion.

This is our problem—particularly in the non-coastal Maharashtra. Only 35–45 days of any significant rain in the whole year, that too confined to the period June to September, half of the rain coming down with great intensity and running off the ground causing flood and much erosion.

We need innovative water conservation methods. We have to draw on our ancient wisdom. The characteristics of the rainfall in the European Countries and in north America are different. Their rainfall is distributed throughout the year and their intensities are not as high as those of Indian rainfall.

Construction of a very large number of water ponds, each a hectare or so in area and about 10 metres deep is one such method. It can be supplemented by check dams, underground check dams, etc. There are other water harvesting methods adopted in areas where annual rainfall is 20–30 cm. or less. Maharashtra is not that bad.

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[In the above reproduction, I have kept the typos (15 Hours to 20 hours), the mistaken convention for writing physical units (cm. instead of cm) and the italics emphasis exactly as in the original.]

Honestly, which one of the two abstracts you liked better? Why? What kind of epistemological issues seem to be at work?

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A Song I Like:
(Hindi) “ni sultaanaa re…”
Music: R. D. Burman
Singers: Mohamad Rafi, Lata Mangeshkar
Lyrics: Majrooh Sultanpuri

[E&OE]

 

 

 

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