Micro-level water-resources engineering—5

Important Update added on 2015.04.22!

See near the end of this post.

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Today is (Sanskrit) “akshay tritiya.” In the Khandesh area of North Maharashtra (in which the Shirpur town of the famous Shirpur pattern falls), in the local lingo, the day is known as “aakhaaji.” In Khandesh, it is a festival of women visiting their (Marathi) “maaher” (i.e. their parents’ home, or the home before marriage). There are traditional songs in the local “AhiraNi” dialect, and dance of the Gujarathi garbaa style, but played only by women. When I was a school-boy in that region, the dance would be done with “Tipri”s, but as far as I remember, without any dhols (i.e. drums), loud-speakers, or any large-scale organization, even if all the streets of the town would overflow with women playing “Tipri”s. I don’t know what the situation is like today.

Festivals mark days of relief. But otherwise, summer is a time of gruelling hard work for rural women. Maharashtra’s population is already 11.4 crores. Even if you take only 20% population as drought-affected, that makes it about 2 crores. (In the 2013 drought, the estimates were about 3 crores.) That means about 1 crore drought-affected women. So, as a rough estimate, there must be at least about 50–75 lakh women facing water-scarcity in a normal year—e.g., right now! Imagine, some tens of lakhs of women having to daily carry pots on their heads for several kilometers a day, just for fetching water—often only poor quality and soily/brackish water, but something that allows them at least cooking food for their families for their barest sustenance. What can we do to spare them the hardship? Obvious.

Find out cost-effective water resources strategies and solutions that can be within their means, without remaining dependent either on government or even on charity.

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I have been browsing a lot of material, but have found that in this area, even some of the simplest questions are so hard to answer.

For instance, the data about the local geology. Or, even the data about local morphology—I mean, maps with contour lines having 1, 2, or even 5 m resolution, and not 20 or 30 m resolution. Digital DEMs with say 5 m resolution are impossible to find, and so, some creative solutions have to be found out. Here, I first thought of an idea, and later on found a part of it mentioned in a Marathi official document for irrigation department that my father gave me. I will write about it, and address many such questions some time later in this series.

In this post, instead, let me touch upon another simple question.

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How much of the fallen rainwater really runs off the ground to the rivers? Why don’t some of the dams fill up every monsoon?

In Maharashtra, Marathwada is the region of the lowest rainfall (about 65 cm/annum). The river Godavari flows through this region. There is a big dam called the Jayakwadi project [^]; the reservoir is called “Naath Saagar;” it is named after the great Marathi poet-saint Eknath Maharaj.

The simple question is this: Why does the Naath Saagar reservoir does not fill up to its full capacity every rainy season?

An easy answer would be to say: “Because the rainfall is deficient.”

Let us see whether, starting from some simple basic assumptions, this answer turns out to make any sense or not. Let’s try to do a quick, back-of-the-envelop estimate for how much water should flow into the Jayakwadi dam every year. (My objective behind working out this simple exercise was to get some kind of a datum for the small check dams.)

The basic source of water is the rainfall. To estimate the total water received via rainfall, we have to know the watershed area of the dam. The Wiki page on the Jayakwadi dam [^] notes the catchment area as 21,750 square km. Referring to the rainfall for the upstream catchment area of this dam [I used the map in the book River Basins of India (p. 66)], I estimate the average rainfall for this region as about 65 cm (which also is the figure quoted by P. R. Pisharoty as noted in an earlier post in this series). So, the total annual water received via rainfall in the Jayakawadi watershed is about 1.41375E10 cubic m. Raghunath’s text on hydrology [^] on page 5 notes that for India’s total annual rainfall water of 370 million ha-m, the total runoff into all the rivers is 167 million ha-m. Thus, the runoff to the biggest river in a basin should be about 45% of the total water received from the skies. Assuming that a similar figure applies here, I get the runoff calculations as the following Python code shows:

# Assumed data
dRainfall = 0.65 # meter, assumed
dRunoffCoefficient = 0.45 # for all India
dCatchmentArea = 21750.0*1000*1000 # meters
# Calculations
dRainwaterVolume = dRainfall*dCatchmentArea
dEvaporationLoss = dRainwaterVolume/3.0
dRunoff = dRunoffCoefficient*dRainwaterVolume
dSeepageIntoSubsoil = dRainwaterVolume - dEvaporationLoss - dRunoff
print ("Total Volume: %E, Runoff: %E, Evaporation Loss: %E Seepage: %E" % (dRainwaterVolume, dRunoff, dEvaporationLoss, dSeepageIntoSubsoil))

On Ubuntu, open a terminal, type “python” in it, and at the Python prompt (say >>>) copy-paste the above lines, and hit enter. (On Windows, you will have to install a suitable Python environment first.) Or, use the online interactive Python terminal here [^].

Thus, the total quantity of water rushing into the Jayakawadi dam every year should be 6.36E9 m^3 (i.e. cubic meters). The Wiki page on the Jayakwadi dam notes that the total capacity of the dam is just 2.91E9 m^3.

Thus, the total quantity of water flowing into the dam should be about 2.1 times the dam reservoir capacity. The dam should more than overflow every year.

Yet, the dam doesn’t even fully fill up every year—it does so only about 2–3 times in a decade.

Even if we take a lower runoff coefficient, say as low as 0.35 (e.g., to factor in the presence of the relatively smaller dams upstream, and also an increased forest cover—which must be a very unrealistic assumption), and even if we take the annual rainfall in the watershed region to be as drastically low as just 40 cm (i.e. the worst drought situation, because they declare a drought if the rainfall is 20% lower [^], and the average for the catchment area of Jayakawadi is above 65 cm), you should still get some 3.045E9 m^3 of water into the Jayakawadi reservoir—more than enough to fill it up fully.

Indeed, there is a further irony. This dam has already gathered a lot of silt (because it is situated in a relatively flatter region, with more loose soil), and the live storage has gone down by 14% (as per Wiki).

[Incidentally, there has been some criticism that the project was moved 100 km upstream. Chances are, the reservoir then would have covered even a flatter area of loose topsoil.]

All of which means that the Naath Saagar reservoir should fill up and overflow even in the worst drought-hit years.

In practice, it doesn’t.

What gives? Any idea? I have no clue.

There must be something the wrong with the way the run-off calculations are performed—they are going off the mark by some 250%. That is too big an error. Has anyone looked into this aspect more carefully?

Exercise: Undertake the same exercise for the Ujjani dam. It is supposed to supply water to another severely drought-prone region in Maharashtra, viz. that of the Solapur district and the nearby areas. It too doesn’t fill up every year.

Realize that big dams like Jayakwadi and Ujjani have comparatively huge catchment areas. For a check dam, the catchment area (or the watershed area) is very small—and therefore, subject to even wider fluctuations from year to year. This is one sobering point we must keep in mind in our enthusiasm for the micro-level projects.

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The Evaporation Loss, the High Intensity Rains, and Seepage vs. Storage:

As Raghunath’s book [^] shows on page 5, the water balance equation is:

total rainfall = evaporation loss + runoff + seepage into sub-soil.

The item of seepage into subsoil is further split into two parts: (i) a slightly bigger part (53%) of the contribution to moisture (which is the part that is used by the shrubs and the trees in their life-processes; this is the part that is ultimately released to the atmosphere via transpiration), and (ii) a smaller part (47%) of the recharge into groundwater.

Thus, the biggest items here are (1) runoff and (2) evaporation.

This primary importance of the runoff quantity in the overall quantitative scheme was the reason why I decided to check whether the simple runoff factors or calculations are realistic or not. If they were to be OK, I could use them as they are, in my detailed calculations concerning computational watershed modelling.  But as the above example of the Jayakwadi dam showed, at least at a gross scale, the runoff factors are not reliable. Now, even if there are some more detailed (say GIS based) models and micro-models for computing runoffs, I am not sure how reliable they would be. And, if the runoff factor itself is wrong, we are basically regressing back to the stage of empirical data collecting and validation, and so, coarsening out of the micro-models to macro-models (even if using GIS) would be an even more distant a step … Anyway, to proceed further….

For India, the runoff figure is several times higher than the total groundwater recharge.

Further, in the Deccan trap basalt region of Maharashtra, the seepage mechanism is not as efficient as it is in the alluvial soils (for instance, of Aravali region of Rajasthan, or in the Tapi and Purna basins of Maharashtra (the area of the Shirpur pattern)).

Recall Pisharoty’s paper I quoted in my last post in this series [^]. In Maharashtra, half of the annual rainfall occurs within only 15 to 20 high-intensity hours, which occur sometime over only 35–45 days of any actual rainfall.

Thus, in the Deccan trap region of Maharashtra, first there is an overall inefficiency of seepage. It is further compounded worse due to the infrequent high intensity bursts of rains. If the same amount of rainfall were to occur as a slow drizzle over a long period of time, say a continuous stretch of weeks, then such a rainfall pattern would be better conducive to seepage. On the other hand, a sporadic high intensity pattern implies less seepage and more runoff.

Hence, in the Deccan trap regions of Maharashtra, it is the surface storage strategy which is likely to prove better than the underground seepage strategy.

For the above reasons, our solutions should be able to handle arresting the high intensity runoff, for storage.

Next, in India in general, evaporation also is several times higher than the groundwater recharge.

Evaporation is a really bad factor in hot climates like India. At the level of large-scale dams and even for check dams, there is precious little that can be done about it. (Solutions have been sought, e.g., spreading some chemicals on top of the water, but their side effects is a worry.)

Realize that evaporation is a surface phenomenon. Dams with a shallow and wide-spread reservoir (e.g. Jayakwadi) tend to have a relatively higher percentage of evaporation losses, as compared to the deeper dams. Ditto, also for check dams. (That is the reason why the nallah-deepening aspect of the Shirpur pattern makes good sense—provided the cost of excavation is low enough. For the time being, let’s focus on evaporation.)

Evaporation maps for Maharashtra show losses as high as 1.5 m to even 2.5 m per year. Thus, if you build a check-dam with a 3 m high wall, expect to lose more than half of the water to evaporation alone. (The famous bund of the bund-garden in the Pune city used to be actually shallow; it would hold a nice expanse of water simply because the bigger Khadakvasla dam upstream would periodically release water into the river.)

For the same reason of evaporation, most nallah-bunding and contour-trenching works, such as those by Anna Hazaare in Ralegan Siddhi, or those typically undertaken under the socialist programs like MNREGA, don’t translate to anything at all for storage, or for that matter even seepage. Typically, the bunds are less than 1 m tall, and theoretically, water in them is expected to plain evaporate out right before December. Practically, that anyway is the observation! No matter what Anna Hazare might tell you, it is a waste of money and effort.

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Farm Ponds:

Before closing, let me mention farm ponds as an effective storage strategy, apart from check-dams.

One big advantage with check dams as compared to conventional dams is that there is no cost incurred in the acquisition of land, and for rehabilitation of the displaced people. Speaking purely costs-wise, I read somewhere (or heard in Suresh Khanapurkar’s interviews) that about half of the cost of the conventional dams is on just these two counts.

However, in the case of check dams, if the natural depth of the river gorge is not sufficient (try the small software I wrote earlier in this series), then in order to reduce the percentage loss due to evaporation and thus to make the project economical, some extra expenditure may become necessary in deepening the nallahs.

Now, in the Deccan trap region of Maharashtra, since small rivers and nallahs tend to run through regions of hard rocks (the top soil layer can be as thin as just 0.5 to 1 m or even zero, in them), the excavation work to deepen the nallahs can easily prove to be too costly—this is a factor going against the Shirpur pattern. (More on the economics of excavation in check dams, and of farm ponds, in a later post.)

An advantage with the farm ponds, when compared to check dams, is that since they are built in the field, i.e. in a deeper layer of soft soil, deepening the ditch turns out to be much more economical.

On the downside, as compared to check dams, the storage capacity of farm ponds is much smaller. They also eat up what otherwise could have been a productive farm land.

But, as we saw, a deeper water body means lower percentage of evaporation losses.

Thus, overall, costs-wise, there are many oppositely directed factors, and it’s not possible to draw general conclusions. It’s the cost balance that really determines whether a farm pond makes sense in a given location or not, or is it a check dam for storage, or a check dam for seepage. (I will write another post covering the economics of check dams vs. farm ponds vs. conventional dams).

Second, as far as evaporation is concerned, there is an incredibly creative solution which I ran into only today. It suggests that if you cover a farm pond with a floating layer of the used plastic bottles, then the evaporation loss (at least for very small experimental ponds) can be cut by up to 40%! [(1.7 MB .PDF file) ^]. The work has been done at the well-known Vigyaan Aashram at PaabaL near Pune; guess they also have some kind of collaboration with COEP and MIT (USA). Anyway, coming back to evaporation losses, this is a huge, huge advantage at a throw-away price! The suggestion right now is only at a preliminary stage. I think it should be seriously taken up for studies on a larger scale of a realistic pond. But yes, as an engineer, I simply marvel at this idea—it again takes a perceived problem (“Gee, even Indians have started buying bottled water, huh?” and “Now how do we deal with this mess of all this plastic waste!”), turns it around on its head, and provides a cost-effective solution to another pressing problem. Neat!

BTW, the farm ponds need not always get only“naturally” filled, i.e., with the surface-running rain-water falling from the sky on the same field. Sometimes a combination of a lift-irrigation scheme + a farm pond can also be cost-effective.

Further, as has been practically demonstrated at many sites (e.g. in the Ahmednagar district, by actually practising farmers) a farm pond can also be very easily used for farming fish, as a side business (read side income)! Farming for fish requires relatively little labour—mostly, only some aeration (if at all required) and throwing food into the pond regularly (like twice/thrice a week or so), that’s all. Fish is not only very tasty food, it also is a very high quality and easily digested protein.

The side-walls of the farm-ponds can be also be planted with the kind of trees that give lush green shadow while making do with less water demand. A welcome sight, and a welcome spot for rest, on a hot summer afternoon.

Finally, talking of water bodies, trees, and how beautiful and (literally) cool a surroundings they can go on to make, and of side-businesses, and of creativity, here is yet another creative side-business that has come out of a bigger farm pond; check out the Saguna Baug in Neral near Mumbai [^].

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Important Update added on 2015.04.22:

Python scripts for predicting the extent to which the Jayakwadi and Ujjani dams should fill, at a given rainfall level. Also, analysis of results, and some comments:

Since writing this post yesterday, I studied more closely the topic of the rainfall–runoff relationships in standard textbooks on hydrology.

There are quite a few models that allow you to calculate the expected runoff volume from the rainfall extent. These are specific to soil types, gradients, type of surface, etc. For Maharashtra, there is a well-known model by Inglis and De Souza (1929); e.g. see p. 180 here [^]. This is an empirical (curve-fitted) model that gives you two separate equations.

For the ghat region:
R = 0.85P - 30.5

and for the Deccan plateau:
R = \dfrac{1}{254} P \left( P - 17.8\right)

where R is the annual runoff and P is the annual rainfall, both in cm.

Since the formulae seemed to give far lower values for the runoff coefficient, and hence the runoff volume even for the average rains, I decided to write a Python script to find out the extent to which the Jayakwadi (and later, also Ujjani) dam would fill up, given different levels of rainfall.

Here is a link to a zip containing the Python script files and their outputs, in the CSV format [^]. In my code, I calculate the R parameter using both the above equations and take their average. Effectively, I assume that half of the watershed region is of the ghat region, and the other half is of the Deccan plateau. Though the zip file doesn’t show it, there aren’t very glaring differences in the values of R as estimated via the two equations.

The files make it clear that at the average rainfall level of 65 cm in the watershed (i.e. the catchment) region, the Jayakwadi dam is expected to fill only to 89.6%. If there is a drought year and so the watershed region receives some 45 cm rains, this dam would fill only to 21%!! For this dam to fill 100%, an above average rainfall of 67–68 cm would be necessary. Little wonder that the dam has filled only rarely.

The figures for the Ujjani dam are not much different, only slightly different. For instance, it would take 77–78 cm rain in its catchment area for it to fill up. The catchment area of the Ujjani dam does receive a somewhat higher rain, and so, let’s say the normal rainfall there is 70 cm. At this level, the Ujjani dam is expected to fill only to 73% of its full capacity!

There are other methods to estimate runoff too. But given the informal general knowledge about these dams, Inglis and De Souza’s correlations would seem to hold well.

I am no expert in dams design. To my lay engineer’s eyes, these are decidedly wasteful designs. After all, bigger-than-necessary designs imply greater-than-necessary expenditures, too. The Wiki page informs us that Jayakwadi project has cost more than Rs. 10,000 crores by now. … What portion of this huge amount are wasteful?

Among the Maharashtrian “intellectual,” “chattering” etc. classes  (and also among the NRI community, esp. that settled in the USA, esp. in California), it has become a fashion to blame politicians for every conceivable ill concerning water scarcity in Maharashtra.

Do you think that these civil engineering designs were done by politicians? Do you think that, for instance, say Vasantrao Naik, would have knowingly ordered a deliberately bigger and costlier dam, just to score some political high point for himself or his party? (I mention him because the Wiki informs us that the Jayakwadi dam design was finalized when he was the CM. Similarly, the Ujjani dam got designed when he was the CM.)

If you think such things are possible—things like increasing a dam size just to score some political high point for oneself or one’s party—then I would say that you just don’t know the way a typical politician thinks and operates. Yes, even in a mixed economy.

Yes, it’s important for a typical politician in a mixed economy (regardless of the party to which he belongs) to show that he is doing something meaningful, whether something actually meaningful gets done or not; yes, it is possible that given a choice, he would always pick up that choice which benefits his own constituency; yes, it is possible that he might even bring a bit of pressure on the officers to tweak solutions so that his constituency benefits. (They even publicly admit if not boast about such things.)

But a deliberate increase of size of a dam for absolutely no conceivable benefit to anyone? No way. No politician even in a mixed economy—and esp. in reference to a country like India—ever operates that way.

Here, if you say that an increased dam size means an increased budget, and therefore greater bribes to him/his party-men, then I would say, you just don’t understand the system. Even if I grant you the premise that every politician is always on principle on the look-out for kickbacks and bribes, granted that, a typical politician still wouldn’t want to increase a dam’s size, because—and get this right—he doesn’t have to. He can easily use the same amount of the additional (wasteful) budget on some other project without ever affecting the total quantum of his bribe, so why should he insist on making just one dam/project bigger than necessary, at the expense of all other possible dams/projects? If he can build two dams in the same budget—note, the amount of bribe has stayed the same—since he stands to get double the publicity with the same budget-money, he would rather go in for that.

Thus, all this “logic” is simply the smart “white-collared” Indian’s way of saving the “behind” of his own—or of groups of people he regards similar to him—nothing else.

Are bureaucrats and even engineers ever going to admit there might have been some mistakes here? More importantly, how many Indians of the “intellectual” kind are going to be willing to even think of such a possibility? (Even Anna Hazaare’s all-water-vaporizing nallah-bunds seem almost innocuous by comparison; they must have involved relatively smaller amounts, say of a mere few hundreds of crores. In contrast, wasteful big projects like these would involve thousands of crores.)

And, even more importantly, is there anyone willing to have an honest second look about the socialistic nature of the system that produces costly errors of this kind? (Not just costs. Since a wrong datum for the capacity of the dam has been established, now there also are fights: Marathwada people think that if the Jayakwadi dam doesn’t fill up fully, the reason must be that the smaller dams upstream have been criminally diverting water that is rightfully theirs… Think of the bigger and bigger mess it all gets into.)

…Anyway, since I can’t do anything about it, let me wind down on that topic, and instead, let me focus on what I can do.

What this exercise means is that I can use some of these even simple text-book methods to build computational models for the check dams/farm ponds with acceptable enough accuracy; they would be accurate at least to a first-order. (After all, Inglis and De Souza’s second equation shows that a quadratic dependence of the runoff on the rainfall. Also, the other rainfall-runoff models show different kinds of nonlinear relations. So, they should be accurate at least to the first order in further usage.)

One more point before we close. Let me note a couple of good links on the topic of farm ponds. Here they are:

“Farm Ponds: A Climate Resilient Technology for Rainfed Agriculture: Planning, Design and Construction” [(13.1 MB PDF) ^]

“Rainwater Harvesting and Reuse through Farm Ponds: Experiences, Issues and Strategies” [(5.4 MB PDF) ^]

Also, a useful reference on the topic of evaporation: “Potential Evapotranspiration Estimation for Indian Conditions: Improving accuracy through calibration coefficients” [(3.8 MB PDF) ^]

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A Song I Like:

[I recently randomly stumbled on a listing of this song, and then listened to it after a long, long time—long enough that reading only through the words, I was not able to place the song; I had to listen to it to “get” it back…  A relaxed tempo, and a beautiful melody by SD. … I don’t know if RD assisted SD for this song or not (this one is from 1963), but going by the orchestration, there is at least a hint of the young RD here, esp. in those interludes of the sax and guitar. I doubt if Dada Burman, in 1963, could have given that much of a freedom to Manohari Singh (an assistant and the probable sax player) sans RD’s presence. The tune, of course, is unmistakably SD’s own. … It’s the kind of a tune which you inadvertently catch yourself humming aloud sometime later, perhaps even a few days later, and it still surprises you, and it still makes you want to re-listen to the song…  Shailendra is at his lyrical best… And yes, it’s Suman Kalyanpur, not Lata.  Enjoy the brilliant simplicity of SD (possibly with a small assistance coming from RD)…]

(Hindi) “ye kis ne geet chheDaa…”
Music: S. D. Burman
Singers: Mukesh, Suman Kalyanpur
Lyrics: Shailendra


[PS: Though the content will not change much, tomorrow, I might come back and add just a few links to some good documents on design/experience/economics of farm ponds that I have downloaded. Done. Also added Python scripts for computing the percentage of dam capacity to which the Jayakwadi and Ujjani dams would fill up, at various levels of rainfall in their respective catchment areas.]