Micro-level water-resources engineering—10: A bridge to end droughts?…

Let me ask you a simple question: Why are bridges at all necessary? I mean to refer to the bridges that get built on rivers. …Why do you at all have to build them?

Your possible answer might be this: Bridges are built on rivers primarily because there is water in the rivers, and the presence of the water body makes it impossible to continue driving across the river. Right? OK. Good.

In India, “kachchaa” (untarred) roads often exist on the sides of the main road or a high-way, as we approach a bridge on a river. These side-roads usually aren’t built after planning, but simply are a result of the tracks left by the bullock-carts plying through the fields, on both sides of the road. People from nearby villages often find such side roads very convenient for their purposes, including accessing the river. The sand-smugglers too find such approach-roads very convenient to their purposes. The same roads are also found convenient by journalists and NGO workers who wish to visit and photograph the same river-bed as it turns totally dry, for quite some time before summer even approaches.

Somewhere in there lies a certain contradiction—a technical contradiction, I should add.

If there were to be no water, ever, in these rivers, then no bridges would at all be necessary. Yet, these bridges are there. That’s because, in monsoon, it rains so much that these rivers begin to flow with full capacity; they even overflow and cause extensive flooding in the adjacent areas. So, naturally, bridges have to be built.

Yet, come even just late winter time, and the river-bed is already on its way to going completely dry. The bridge might as well not have been there.

Thus, the bridges, it would seem, are both necessary and not necessary in India. That’s the contradiction I was talking about.


But why not turn this entire situation to your advantage, and use the very site of a bridge for building a small check-dam?

After all, the very fact that there is a bridge means:

there is enough water flowing through that river, at least during monsoons. We only have to find a way to use it.


Here are some of the advantages of building check-dams nearby a bridge—or may be even directly underneath its span:

  • The patterns of water-flow across the pillars of the bridge, and even the pattern of flooding near the site of the bridge, has become well known, even if only because there is a better access to this site (as compared to other potential sites for a check-dam)—because of the existence of the main road.
  • There is already a built structure in place. This means that the nature of the rocks and of the soil at the site is already well studied. You don’t have to conduct costly geological surveys afresh; you only have to refer to the ready-made past reports.
  • Another implication of there being a pre-existing structure is this: The nearby land has already been acquired. There is no cost to be incurred in land acquisition, and the cost and other concerns in relocating the people.
  • Columns/pillars of the bridge already exist, and so, the cost of building the wall of a check-dam can come down at least a bit—especially if the wall is constructed right underneath the bridge.
  • Many times, there also is a lower-level cause-way, or an older and abandoned bridge lying nearby, which is no longer used. It can be dismantled so that the stones used in its construction can be recycled for building the wall of the check-dam. It’s another potential reduction in cost (including in the material transportation cost).
  • The existence of a bridge at a site can often mean that there is likely to be a significant population on either sides of the river—a population which had demanded that the bridge be built in the first place. Implication: If a water body comes to exist at this same site, then the water doesn’t have to be transported over long distances, because a definite demand would exist locally. Even if not, if the check-dam is equipped with gates, then the stored water can be supplied at distant locations downstream using the same river—you don’t have to build canals (starting from the acquisition of land for them, and further costs and concerns down the way).
  • Easy access to transportation would be good for side-businesses like fisheries, even for building recreational sites. (Think agro-tourism, boating, etc.)

Of course, there are certain important points of caution or concern, too. These must be considered in each individual case, on a case-to-case basis:

  • The local flow pattern would get adversely affected, which can prove to be dangerous for the bridge itself.
  • There is a likelihood of a greater flooding occurring in the nearby locations—esp. upstream! A blocked river swells easily, and does not drain as rapidly as it otherwise would—the causeway or the spillway can easily turn out to be too small, especially in the case of small dams or check-dams.
  • The height of the bridge itself may be good, but still, the river itself may turn out to be a little too shallow at a given location for a check-dam to become technically feasible, there. Given the importance of the evaporation losses, the site still may not turn out to be suitable for building a check-dam. (For evaporation losses, see my last post in this series [^].)

But overall, I think that the idea is attractive enough that it should be pursued very seriously, especially by students and faculty of engineering colleges.


We all know that there has been a great proliferation of engineering colleges all over the country. The growth is no longer limited to only big cities; many of them are situated in very rural areas too.

When a problem to be studied touches on the lives of people, say a student or two, it becomes easy for them to turn serious about it. Speaking from my own personal experience, I can say that BE project-reports from even relatively lower-quality engineering colleges have been surprisingly (unexpectedly) good, when two factors were present:

(i) When the project topic itself dealt with some issue which is close to the actual life of the students and the faculty, to their actual concerns.

For instance, consider the topic of studies of design of check-dams and farm-ponds, and their effectiveness.

During my stint as a professor, I have found that rural students consistently show (across batches) reporting of the actual data (i.e., not a copy-paste job).

In fact, even if they were not otherwise very bright academically, they did show unexpectedly better observation abilities. The observation tables in their reports would not fail to show the more rapidly falling water levels in check-dams. Invariably, they had backed the data in the tables with even photos of the almost dried up check-dams too.

Yes, the photos were often snapped unprofessionally—invariably, using their cell-phones. (Their parked bikes could be easily visible in the photos, but then, sometimes, also the Sun.) No, these rural students typically didn’t use the photo-quality glossy paper to take their printouts—which was very unlike the students from the big cities. The rural students typically had used only ordinary bond-paper even for taking color printouts of their photos (invariably using lower-resolution ink-jet printers).

But still, typically, the set of photos would unambiguously bring out the fact of multiple field visits they had made, per their teacher. The background shrubs showed seasonal variations, for instance; also the falling water levels, and the marks of the salt on the dam walls.

Invariably, the photos only corroborated—and not even once contradicted—the numbers or trends reported in their observation tables.

Gives me the hope that one relatively easy way to identify suitable bridges would be to rely on students like these.

(ii) The second factor (for good, reliable field studies) was: the presence of a teacher who guides the students right.

No, he doesn’t have to have a PhD, or even ME for that matter. But he has to know for himself, and pass on to his students, the value of the actual, direct and unadulterated observations, the value of pursuing a goal sincerely over a course of 6–8 months—and the fun one can have in doing that.


OK, a bit of a digression it all was. But the point to which I wanted to come, was academics, anyway.

I think academic institutions should take a lead in undertaking studies for feasibility of converting a bridge into a check-dam. Each academic team should pick up some actual location, and study it thoroughly from different viewpoints including (but not limited to):

  • CFD analysis for predicting the altered water-flow and flooding patterns (with the water flow possibly designed to occur over the main wall itself, i.e. without a side-weir), especially for a dam which is situated right under a bridge);
  • FEM analysis for strength and durability of the structures;
  • Total costs that will be incurred; total savings due to the site (near a bridge vs. far away from it at some location that is not easy to access); and overall cost–benefits analysis; etc.

The initiative for such studies could possibly begin from IITs or other premier engineering colleges, and then, via some research collaboration schemes, it could get spread over to other engineering colleges. Eventually, this kind of a research—a set of original studies—could come to take hold in the rural engineering colleges, too. … Hopefully.


Should the government agencies like PWD, Irrigation Dept., or “private,” American concerns like the Engineers India Limited, etc., get involved?

Here, I think that the above-mentioned academic teams certainly are going to benefit from interactions with certain select institutes like (speaking of Maharashtra) CDO Nasik, and CWPRS Pune.

However, when it comes PWD etc. proper, I do think that they operate rather in a direct project-execution mode, and not so much in a “speculative” research mode. Plus, their thinking still remains grooved in the older folds such as: either have multi-purpose large dams or have no dams at all!, etc.

But, yes, CWPRS Pune has simulation facilities (both with physical scale-models, and also via computational simulation methods), and CDO Nasik has not only design expertise but also data on all the bridges in the state. (CDO is the centralized design services organization that is responsible for engineering designs of all the dams, canals, bridges and similar structures built by the state government in Maharashtra.) The cooperation of these two organizations would therefore be important.


In the meanwhile, if you are not an engineering student or a faculty member, but still, if you are enthusiastic about this topic, then you can do one thing.

The next time you run into a site that fulfills the following criteria, go ahead, discuss it with people from the nearby villages, take a good set of snaps of the site from all sides, write a very small and informal description including the location details, and send it over by email to me. I will then see what best can be done to take it further. (The fact that there were so few engineering colleges in our times has one advantage: Many of the engineers today in responsible positions come from the COEP network.)

The absolutely essential criteria that your site should fulfill are the following two:

  1. The river gorge must be at least 25 feet deep at the candidate location.
  2. The under-side of the bridge-girder should itself be at least 35 feet above the ground or at a higher level (so that there is at least prima facie enough of a clearance for the flood water to safely pass through the bridge). But please note, this figure is purely my hunch, as of now. I may come back and revise this figure after discussing the matter with some researchers/IIT professors/experienced engineers. For visualization, remember: 10 feet means one storey, or the height of a passenger bus. Thus, the road should lie some 4 stories high from the river-bed. Only then can you overcome evaporation losses and also have enough clearance for flood water to safely pass through without doing any damage to the bridge or the dam.

Further, the preferred criteria (in site selection) would be these:

  1. The upstream of the site should not have too steep a gradient—else, the storage volume might turn out to be too small, or, severe flooding might occur upstream of the check-dam! For the same reason, avoid sites with water-falls nearby (within 1–2 km) upstream.
  2. The site should preferably be situated in a drought-prone region.
  3. Preferably, there should be an older, abandoned bridge of a much lower height (or a cause-way) parallel to a new bridge. Though not absolutely necessary I do include this factor in searches for the initial candidate locations, because it indirectly tells us that enough water flows through the river during the monsoons that the cause-way wouldn’t be enough (it would get submerged), and therefore, a proper bridge (which is tall enough) had to be built. This factor thus indirectly tells us that there is enough rainfall in the catchment area, so that the check-dam would sure get filled to its design capacity—that one wouldn’t have to do any detailed rainfall assessment for the catchment region and all.

So, if you can spot such a site, please do pursue it a bit further, and then, sure do drop me a line. I will at least look into what all can be done.


But, yes, in India, bridges do get built in the perennially drought-prone regions too. After all, when the monsoon arrives, there is flooding even in the drought-prone regions. It’s just that we haven’t applied enough engineering to convert the floods into useful volumes of stored water.

… For a pertinent example, see this YouTube video of a bridge getting washed away near Latur in the Marathwada region of Maharashtra, in September 2016 [^]. Yes, Latur is the same city where even drinking water had to be supplied using trains, starting from early April 2016 [^].

So, we supplied water by train to Latur in April 2016. But then, in September 2016 (i.e. the very next monsoon), their local rivers swelled so much, that an apparently well-built bridge got washed away in the floods. … Turns out that the caution I advised above, concerning simulating flooding, wasn’t out of place. …  But coming back to the drought-prone Latur, though I didn’t check it, I feel sure that come April 2017, and it was all back to a drought in Latur—once again. Fatigue!


PS: In fact, though this idea (of building check-dams near bridges) had occurred to me several years ago, I think I never wrote about it, primarily because I wasn’t sure whether it was practical enough to be deployed in relatively flatter region like Marathwada, where the drought is most acute, and suitable sites for dams, not so easy to come by. (See my earlier posts covering the Ujani and Jayakawadi dams.) However, as it so happened, I was somewhat surprised to find someone trying to advocate this idea within the government last year or so. … I vaguely remember the reports in the local Marathi newspapers in Pune, though I can’t off-hand give you the links.

On second thoughts, here are the links I found today, after googling for “check dams near bridges”. Here are a couple of the links this search throws up as of today: [^] and [^].

… Also, make sure to check the “images” tab produced by this Google search too. … As expected, the government agencies have been dumb enough to throw at least some money at at least a few shallow check-dams too (not good for storage due to evaporation losses) that were erected seemingly in the regions of hard rocks and all (generally, not so good for seepage and ground-water recharge either). As just one example, see here [^]. I am sure there are many, many other similar sites in many other states too. Government dumb-ness is government dumb-ness. It is not constrained by this government or that government. It is global in its reach—it’s even universal!

And that’s another reason why I insist on private initiative, and on involvement of local engineering college students and faculty members. They can be motivated when the matter is close to their concerns, their life, and so, with their involvement the results can turn out to be very beneficial. If nothing else, a project experience like this would help the students become better engineers—less wasteful ones. That too is such an enormous benefit that we could be even separately aiming for it. Here, it can come as a part of the same project.


Anyway, to close this post: Be on the lookout for good potential sites, and feel free to get in touch with me for further discussions on any technical aspects related to this issue. Take care, and bye for now…


A song I like:

(Hindi) “chori chori jab nazare mili…”
Lyrics: Rahat Indori
Music: Anu Malik
Singers: Kumar Sanu, Sanjeevani

[A song with a very fresh feel. Can’t believe it came from Anu Malik. (But, somehow, the usual plagiarism reporting sites don’t include this song! Is it really all that original? May be…)]

 

 

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