# Micro-level water-resources engineering—7: Dealing with the [upcoming] summer

Last monsoon, we’ve mostly had excess rain-fall in most parts of Maharashtra, even over India, taken as a whole.

Though the weather in Maharashtra still is, for the most part, pleasantly cool, the autumn season this year (in India) is about to get over, right this month.

Therefore, right now, i.e. right at the beginning of February, is the perfect time to empirically check the water levels in all those check-dams/farm-ponds you have. … That’s because, evaporation is going to happen at an accelerating pace from now on…

Between end-October (say Diwali) and March (say Holi), every solar year in India, the reduction in the levels of the stored water is dominated by the following two factors:
(i) seepage (i.e. the part which occurs after the rains cease), and
(ii) usage (i.e. the irrigation for the “rabbi” (i.e. the winter agricultural) season).

But from now on, the dominant factor is going to be the third one, namely, (iii) evaporation, and it is going to be increasingly ever more important throughout the upcoming summer, i.e., until the arrival of the next monsoon.

As I had earlier pointed out in this series  [^][^], in Maharashtra, the losses due to evaporation are expected to be about 5–8 feet (or 1 to 1.5 “puruSh”) deep.

Don’t take my word for it. … Go out and actually check it out. (Take snap-shots for your own record, if you wish.)

The beginning of February is also the perfect time to start executing on your plans for any maintenance- or new construction-activities on any check-dams/farm-ponds/residential water conservation that you might have thought of, in your mind. If you start executing on it now, you still have a very realistic framework of about 4–4.5 months left, before the next monsoon rains are slated to arrive [give or take about a half month here or there].

…Just a reminder, that’s all.

Keep in touch, best, and bye for now…

[As usual, I may come back and edit this post a bit after its publication, say, after a couple of days or so… I don’t know why, but things like that—viz., thinking about what I did happen to write, always happen to me. But the editing wouldn’t be too much. … OK. … Bye [really] for now.]

# Summer, boredom, city skyline, etc.

Boredom. That’s what my life has become of late. … Boredom. … Pure boredom.

Life is boring.

Nothing interests me. Don’t feel like writing anything.

No, it’s not called a writer’s block. To have a writer’s block, first you need to be a writer. And my problem is that I don’t even want to be a writer. Not even just a plain reader. Both are boring propositions.

Life, somehow, has become boring to that great an extent.

Summers always do that to me.

While at IIT Madras, we (a few friends of mine and I) had begun using a special term for that: (Sanskrit) “glaani.”

Usage pattern:

“Did you work out those lab calculations?”

“Ajit, did you complete those lab calculations?”

“Machchaa…”

The fellow turns around, lethargically. [He, too, doesn’t have much energy left to pursue anything; the heat has been that bad…] … Begins to drag his feet back to his room.

“glaani.” [One attempts some answer, some explanation.]

The fellow does not even care to look back.

The use-case scenario is over.

Currently, it’s summer time, and this year in particular, I am finding it even more lethargy-inducing and boring than it usually is…

Here is an idea I had. I wanted to expand it in a blog post. But since everything has become so summer-ly boring, I am not going to do that. Instead, I will just mention the idea, and let it go at that.

How do you visually estimate the water requirements of a human settlement, say, a city? Say a city with skyscrapers, like Mumbai? (Skyscrapers? In Mumbai? OK, let’s agree to call them that.)

Start with a decent estimate of per capita water requirement. Something like, say, 135 liters/day/person. That is, $1.35 \times 10^2 \times 10^{-3} = 1.35 \times 10^{-1}$ cubic meters. For one year, it translates to $0.135 \times 365 = 49.275 \approx 50$ cubic meters.

An average room in an average apartment is about 10 feet X 12 feet. With a standard height of 10 feet, its volume, in cubic meters, is: $3.048 \times 3.6576 \times 3.048 = 33.98 \approx 35$ cubic meters.

Of course, 135 liters/day is an estimate on a slightly higher side; if what I recall is right, the planning estimates range from even as low as 50 liters/day/person. So, taking a somewhat lower estimate for the daily per capita requirement (figure out exactly how much), you basically arrive at this neat nugget:

Think of one apartment room, full of water. That much volume each person needs, for the entire year.

If one person lives in one room (or if a family of four people lives in a 2BHK apartment), then the volume of that apartment is their yearly water requirement.

Hardly surprising. In the traditional water-harvesting in Rajasthan, they would have single-storied houses, and roughly the same volume for an underground reservoir of water. Last year, I blogged quite a bit about water resources and water conservation; check out tags like “water resources” [^].

So, the next time you look at a city skyline, mentally invert it: imagine a dam-valley that is just as deep as the skyline’s height, containing water for that skyline. That would be the residential water requirement of that city.

Of course, if the population density is greater, if one apartment room accommodates 2, 3 (or even more number of) people (as is the common in Mumbai), then the visualization fails. I mean to say: You then have to imagine a deeper (or wider) dam valley.

… I used to be skeptical of residential water harvesting schemes. I used to think that it was a typical NGO type of day-dreaming, not backed up by hard data. I used to think that even if every 3-story apartment building covered its entire plot area (and not just the built-up area) with a 1 to 2 story-deep tank beneath it, it wouldn’t last for even a couple of months. But when I did the actual calculations (as above), I became convinced of the utility of the residential water harvesting schemes—if the storage is big enough.

Of course, as one often hears these days, if common people are going to look after everything from electricity (portable gen-sets, batteries and inverters), water (residential water harvesting), garbage (composting in the house/terrace garden), even security (gated communities with privately paid watchmen), then what the hell is the government for?

If your anger has subsided, realize that only the last (security) falls under the proper functions of government; the rest should actually be services rendered by private businesses. And if government gets out of every thing but the defense, the police and the courts, the economic progress would so humongous that none would bother reading or writing blog posts on residential water conservation schemes—there would be very competent businesses with private dams and private canals to deliver you clean water very cheaply (also via private trains, if the need be)… But then, I am not going to write about it.  Writing is boring. Life is boring. …. So, just look up Ayn Rand if you want, OK?

… Yawns. Life is boring.

BTW, did you notice that boring also means digging, and I was somehow talking about inverting the skyline, i.e., imagining wells and valleys. Kindaa double meaning, the word “boring” happens to have, and I happen to have used it in both senses, haven’t I?

Oh well. But really, really speaking, I meant it only in the simplest, most basic sense.

Life is boring. … Yawns….

[E&OE]

# 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.

* * * * *   * * * * *   * * * * *

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.

* * * * *   * * * * *   * * * * *

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.

* * * * *  * * * * *   * * * * *

“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.

* * * * *  * * * * *   * * * * *

[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?

* * * * *  * * * * *   * * * * *

A Song I Like:
(Hindi) “ni sultaanaa re…”
Music: R. D. Burman
Lyrics: Majrooh Sultanpuri

[E&OE]

# Micro-level water-resources engineering—3

The deccan trap basalt as the most widespread feature of the geology of Maharashtra:

The geological map for India shows a large uniform portion for the deccan plateau. It consists the hard basalt rock, and not soft or sandy alluvial soils. The deccan trap basalt portion goes over Maharashtra, MP, Karnataka, and the adjacent areas from other states. (To my surprise, it seems that the geologists do not include the south Karnataka region in the same deccan trap basalt region.)

As far as regions of water-scarcity go, there is a very wide continuous band in India. Take India’s map, and mark two slanted lines: the top one going across Rajasthan, MP, Orissa, and the bottom one going across Gujarat, Maharashtra, Karnataka, Telangana and AP, even Tamil Nadu. Statistically speaking, the greatest number of the most severe droughts seem to occur in the regions falling in between these two lines.

The area of my interest is in Maharashtra. The worst drought-prone regions of Marathwada, South Maharashtra and parts of Vidarbha and Western Maharashtra all fall in between those two lines.

If Maharashtra is seen at a large, national, scale [say, 1 cm:100 km], the topmost geological layer is comprised mostly of the deccan trap basalt.

The water-seepage characteristics of the deccan trap basalt:

Speaking in general terms, if you take, say, a 10 cm X 10 cm X 10 cm cube of basalt, you will find it to be a hard, impermeable rock. You might therefore conclude that it is not very easily conducive to groundwater seepage.

However, when viewed at a larger scale, even a top-layer of basalt is not uniform either in composition or in shape (i.e. in terms of its surface morphology). First of all, there are inhomogeneities introduced and fissures formed right at the time of formation of these geological layers aeons ago. Then, there are earth-quakes, introducing cracks and fissures. Further, there also are some very slow processes that nevertheless make their effects felt over the geologically long time-scale of tens, even hundreds of thousands of years.

Due to the inhomogeneity of their composition and morphology, the daily thermal expansions and contractions experienced by the surface layers of rocks are inhomogenous. These inhomogeneities lead to thermally induced mechanical stresses. Over the geological time-scale, the repeated thermal stresses result in local fractures, especially near the surface (where the temperature gradients are the greatest). Further, the mechanical effects of erosion due to water flow leads to deposition of sand; it also serves to erode the fissure openings. The chemical action of dissolved minerals and chemicals lead to enlargement of fissures and opening of cavities at surface as well as deeper layers. Even in a nominally hard rock like basalt.

Thus, due to fracturing and weathering at the surface layers, if you consider relatively bigger patches, say those at the scale of, 10 m to a few hundreds of m (or bigger), even a top layer of a nominally hard rock like the basalt, can begin to act like the more permeable alluvial layer.

Since the cracks are highly irregular and elongated, percolation from a surface water body into the deeper underground layers is highly inhomogeneous and anisoptropic.

In the above discussion, we have considered the seepage from the surface layers. As far as the underground flow through aquifers goes, there is a presence of local sub-layering within an overall top layer of basalt. Further, fissuring and cavitation also has occurred deeper underground. Therefore, local underground aquifers are observed to exist even within an overall basalt layer. Such aquifers often are quite directional, and not too criss-cross. Hence, anisotropy (or directionality) to the local underground flow is only to be expected.

As an example of a locally restricted fracturing/fissuring, observe the groundwater falling over the passing trains and buses in the tunnels of the Khandala ghat on the Mumbai–Pune routes. (BTW, in case you have ever wondered whether these fissures/fractures pose risk, don’t worry!  Their presence is already factored in, while designing for tunnels—fracture mechanics, by now, is a fairly well understood technique.)

One notable reference here is by Prof. Deolankar of Uni. of Pune: Deolankar, S. B. (1980) “The deccan basalts of Maharashtra, India—their potential as aquifers,” Ground Water, vol. 18, no. 5, September–October 1980, pp. 434–437 [(.PDF) ^]. Note the comparisons to the basalt layers elsewhere, and the quantitative estimates for parameters such as porosity, yield, transmissivity and specific capacity.

To conclude, (i) a top layer of basalt layer also allows for seepage of water, even if (ii) the effect varies greatly from place to place (due to the inhomogeneity of fracturing) and the flow is directional (due to anisotropy).

Therefore, groundwater seepage, and therefore artificial groundwater recharge work, appears feasible even in the deccan trap region of Maharashtra. However, it is only to be expected that the seepage aspect won’t be as pronounced as in the regions having a sandy alluvial top layer.

The importance of the local geology:

Due to the local inhomogeneity and anisotropy, there also arise certain difficulties or challenges.

The main difficulty is that unless a detailed geological study of the local hydro-geology is carefully conducted, it would be impossible to tell whether any underground water recharge work would at all be feasible in a given village or not.

Artificial groundwater recharge work may lead to very impressive results in some village or a cluster of villages, but it may not at all give economical returns even in some nearby  villages—even if all of them fall under the same governmental administrative unit of a taluka (or even a block). [The same Collector; the same Block Development Officer! … Two results! (LOL!)]

Thus, in Maharashtra (and similar regions), it becomes crucially important to know what kind of local geology there is—the surface geology, as well as the geology and morphology of the underground strata.  The depth to which these features should be known would vary from place to place; it may range from 10 m to even hundreds of meters.

Unfortunately, the geological surveys in the past were conducted only at much grosser scales. The relevant geological data at the micro-level of villages (i.e. covering just 5 km X 5 km areas) are simply not available.

If experts (say GSA) are asked to conduct such surveys at the micro-level for the entire country, it would be a very time-consuming and costly process.

However, realize that what you need for the water-conservation work is not the most elaborate kinds of surveys. You don’t need surveys of the kind that GSA or the mining engineers make. You aren’t really interested in things like detailed rock-compositions, percentages of minerals, etc. Your main interest is things such as: what kind of strata run where underground, what kind of intermediate layers occur in between the layers of hard rocks and at what depths, the depth and the direction at/in which the local fissures and aquifers run, whether a given fissure extends up to surface or not, etc.

Some of this data (concerning the local geological strata) can be gathered simply by observing the traditional wells! Often-times, the wells are either not at all covered with walls, or even if there is a masonry work, it does not extend beyond a certain depth, and so, the underground layers stand adequately exposed at the traditional wells. Other data can be had by observing the exposed surfaces of nallahs, rivers, hill-sides, etc.

And, of course, data about the local underground strata can always be had by drilling observation bore-wells (though it would be a costlier method).

The economic relevance of computational modelling:

In places like Maharashtra, since the groundwater seepage, flow, and water-holding characteristics crucially involve local variations and directionality, 3D computational models should prove to be of definite use.

Use of 3D computational models would not only streamline the collection of data, it would also lead to far more accurate predictions concerning economic feasibility of projects—ahead of spending any money on them.

A case in point, here, is that of a small check-dam built at the initiative of the IIT Bombay alumni. More details can be found at the CTARA Web site. As a measure of the difficulty in making predictions for underground water flow, notice that in spite of certain geological studies (of conductivity measurements etc.) conducted by the IIT Bombay experts prior to building of this check dam, it still has not resulted in any enhanced ground-water seepage downstream. Chances are, if a 3D model were to be built by drilling observation bore-wells, either a significant amount of money could have been saved, or deployed at a more suitable location.

An apparent counter-case in point is that of the success of the Shirpur pattern, at its original location, viz., near Shirpur (where else?). No detailed micro-level 3D computational modelling was conducted for it. Still, it was successful. How come?

The local geology of the Shirpur region as not being representative of the entire state of Maharashtra:

As it so happens, my father, a retired irrigation engineer, had worked in the Shirpur area. (I thus happened to have had a considerable stint of my school education in and around Shirpur.) I had discussed the issue with my father quite a few years ago. From whatever I now recollected, he had mentioned that the local geology there indeed was more conducive to underground seepage. There were sandy soils at the top level, and some hard rock well underneath. Both these factors lead to better seepage characteristics. The strategy of deepening and widening of the nallahs, as followed in the Shirpur pattern, therefore is a good strategy. As to the rest of Maharashtra, the local geological characteristics differed, he had mentioned it.

[I guess we had this conversation some time in 2007 or 2008. I have been having this idea of not getting discouraged if there is no water at a bore-well location, but instead turn the situation on its head and use the out-coming data regarding the underlying geological strata, to build better predictive computer models at a very fine level of granularity. I have been having this idea since at least 2008, and so, our conversation must be that old. As to the appreciation of having to carefully build 3D models, I owe it to my training in materials engineering, in particular, stereology.]

Anyway, in the recent weeks, I therefore checked the local geology for the Shirpur region, consulting some of the references listed in my earlier post in this series. It turns out that the depth to the water level near Shirpur is at roughly 20–30 m bgl (i.e. below ground level); see ref. here: Aquifer Systems of India, Central Ground Water Board, Plate XXVII on page 58 [(34 MB) pdf ^]. Now, this is a region through which Taapi, a major river, flows. As any school-boy in Shirpur would know, the river has enriched the top layers with a rich black soil. What is the official geological nature of this top layer? Turns out that it is “alluvial.” The black soil does not have the best permeability. However, in the Shirpur region, the alluvial deposits also are sandy in nature, esp. as you go below a certain depth (of 1 m to a few meters). Next, check out the distinctive yellow patch of the alluvial region in this map, standing in sharp contrast to the green patch for the basalt layer for the major parts of Maharashtra [(370 kB pdf) ^].

A top layer of alluvial soil, esp. if deeper than 10 m, if it is then also supported underneath by a highly impervious layer (e.g. basalt in Maharashtra), then the approaches that seek to enhance ground-water seepage do make good sense.

In contrast, if there is a top layer of basalt itself, then, in general, it is less conducive to groundwater seepage; it is more conducive to construction of check-dams for water storage (as in contrast to water percolation/seepage), or for the Kolhapur-type weirs for both storage and redistribution, etc.

As an inevitable conclusion, the local geology holds very important implications for selection of effective water conservation strategies.

Naturally, you can’t just go ahead and apply the Shirpur pattern everywhere in Maharashtra.

“Give me the funds for a few Poclains per taalukaa, and I will make everything green,” is a statement therefore strongly reminiscent of “Give me a place to stand and with a lever I will move the whole world.” The point is not that the whole world won’t be moved; the point is the natural difficulty in providing the guy with a place to stand (complete with air to breathe etc.), not to mention the engineering difficulty of supplying him with a strong enough, and long enough, a lever. And, of course, the difficulty of arranging a place to keep the fulcrum of that lever.

Dramatic statements, both!

I will go ahead, stick my neck out, and say that the Shirpur pattern—inasmuch as it incorporates the seepage mechanism as a strategy—is not likely to be the most optimum solution at any places other than in the Tapi and the Purna river regions! Check out the map if you have not done so already [(370 kB pdf) ^]!

The idea of small dams as storage—and not seepage—devices:

Come to think of it, then, with all the due qualifications—i.e., speaking only in general terms, and only for most parts of Maharashtra (not all), and ignoring any fracturing present in the local geology—the idea of small-dams or check-dams as storage devices, rather than as a seepage devices (or as a groundwater recharge devices), has begun to make much better sense to me. …

[… Yes, the famous government-funded Poclains, and the government-funded work to be contracted out to some of the local parties, and the government funds to be timely released only to some of those parties…. The whole she-bang does stand to be applied also here; more on it, later, if at all necessary. …]

…For the time being, here is an exercise for you.

Exercise:

Take a smallish river (or a bigger nallah), say, 50 km (or 10 km) long. Build an enormously simplified geometrical model of the river, by assuming a rectangular pyramid for its water-carrying volume.

Thus, ignore all the bends in the course of the river and instead assume that the river looks like a long, acicular triangle in the plan (i.e. in the top view). Further, assume that the vertical cross-section of the river remains rectangular throughout; it goes on linearly increasing in area from zero at the origin of the river to a certain value at the end of the river.

Assume typical figures for the dimensions of the river/nallah: how about a vertical cross section that is 50 m wide and 2–3 m deep at the mid-length of the river (i.e. 25 km downstream from the origin)? Assume also a suitable slope for the river, so that water does indeed flow downstream: how about a fall in the height of the ground level of, say, 50 to 100 m, over its 50 km length?

Now, if a series of check dams were to be built on this “river” such that they would submerge some 75% of the total river area present in the plan view into water-holding areas, calculate how much total volume of water would be made available. Compare this volume to the storage capacity of a single conventional dam known to you. …

[While making your calculations, realize (i) that the max. height of the dam cannot exceed the depth of the river bed (because only the river area would go under water), (ii) that the bottom of the river slopes down, and therefore (iii) that the depth of river bed below the water surface goes on decreasing as you go upstream from the check dam location, coming to zero at some location upstream. The third factor severely delimits the total volume of water that can be held via the series of check dams.]

To put the water volume in context, assume that the per-capita consumption for daily individual consumption is some 135–150 liters. Using this assumption, determine the size of the town/city whose needs could be met by this series of check dams. (Note, this figure does not include demand for agriculture and industrial usages.)

Then, consult a practising civil engineer and find out the current cost of construction of all these check dams. Compare this cost with that of a single conventional dam.

Think about any advantages the series of check dams may have; consider water distribution, flood control, and sedimentation and maintenance aspects.

Include the costs of canal construction in the conventional approach. Include the costs of lift-irrigation schemes in the check-dams approach.

Include the fact that since check-dams won’t have a great height (say 2–4 m), the evaporation losses (estimated at about 20–30% in the conventional dams) may even lead to this circumstance: all the water in a check dam plain evaporates in the thin air even before the next summer season approaches. Realize here that, as a rule of thumb, evaporation losses over the eight non-monsoon months are as high as about 1.67 m of height loss per square m of the average of top and bottom surface areas in the plan. [To help put this figure in some kind of a context, the average annual rainfall in Maharashtra is about 110 cm—if no rainwater were to be lost to seepage, runoff or evaporation, and if all of it could be collected, a tank with a square meter of bottom surface area would hold a water body 1.1 m tall.]

Include the economics of maintenance and mechanization in the regions where there is no traditional “Rajasthan culture” of water conservation, but instead people expect government to bring them everything wherever they are.

* * * * *   * * * * *   * * * * *

I will come back later with some further notes and observations (including those on software) on this topic of micro-level water-resources engineering. In particular, I want to make a few notings related to the GIS software. However, I belong to those old-fashioned kind of engineers who, in their practical life (as in contrast to their avatars in blogosphere, for instance) always first do a quick back-of-the-envelop calculation before they switch on a computer to do any computational modelling. If you are like me, you should finish the above exercise first, so that the exploration of software is better grounded in reality.

* * * * *   * * * * *   * * * * *

A Song I Like:
(Marathi) “gangaa aali re, angaNi”