Panajachel - river protection
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21 June 2010
Posted in
Lake Atitlan -News-
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A River Runs Through It ...
For almost 60 years, the Rio San Francisco passed quietly through the town of Panajachel. Between 1948 and 2005, the river slept. People forgot. The town grew.
Today, with the totally unexpected and unprecedented arrival of Tropical Storm Agatha, Panajachel is facing the new reality that its cycles, for reasons unknown, have changed. Whether it’s the result of global warming or simple chance is irrelevant. The reality is that Panajachel cannot continue with the environmental and economic politics of yesteryear, a policy that forgot the mortal danger that the passage of a river through the heart of the town represents, a policy that now makes us pay dearly again and again with each major storm.
For the very survival of Panajachel at this point there’s no alternative; the problem of the river must be solved. Further Inaction against the backdrop of the catastrophic results of each major storm is not an option. The human and economic losses are not bearable either individually or collectively. At the national level, and if only for the importance Panajachel represents to the national tourism infrastructure; the problem of the river running uncontrolled through Panajachel must be resolved.
The goals of this document are several: first, to provide a basic understanding of the problem using the tools that hydrology, economics and engineering afford us. This will allow us to properly frame the problem as we consider solutions. No human settlement can live with a wild river running through it, and the strategy employed in municipalities and countries around the globe is always the same: to harness the river. Panajachel cannot prosper if it does not change the politics of forgetfulness it has practiced ... to continue to ignore the river, to spend in response to disaster instead of prevention. Sticking our collective heads in the sands of the river is not a policy, it is a recipe for disaster, and this paper re-examines the problem and proposes other solutions.
The good news is that there are many solutions to the problems that flood-affected rivers present to municipalities. They are simple solutions, legally, economically and politically viable and feasible. The best news is that these solutions cost far less than the existing policy of “prevent nothing, respond to disaster”. Above all, they resolve the real and potential threat represented by the Rio San Francisco and would allow Panajachel to realize its potential, to be a proper gateway to Lake Atitlan, and to regain and retain the growth and prosperity it needs and deserves.
Rivers Without Borders
I. Potamology 101: From the Dictionary of Hydrology
"A flood plain is the orthographic part of a watershed that contains a variable channel that gets flooded by high waters of the river."
“Many times the topography of the coastal plains formed by the flooding rivers is in the form of cones , called alluvial fans , which means that the river bed can be moved fairly easily, flooding outlying areas. These areas are interesting areas for the development of irrigation due to favorable topography to divert water from the river to any point on the alluvium. It is all a vulnerable areas."
“Rivers of this kind are generally directed by man, thereby protecting agricultural as well as urban areas. In addition, for easier access to water, cities were often built near rivers, which makes them more vulnerable."
“River controls should provide clearly identified points of overflow with the completion of landfill possible to reduce the risks of uncontrolled levee break in order to manage rather than suffer the consequences of exceptional events."
GENERAL SUMMARY:
1. Upon entering the alluvial fan, the river by definition has no fixed channel, but naturally each bed is filled with eroded material and the river jumps to another place, creating the alluvial fan.
2. The only protection against this movement is not widening the river bed, but the establishment of a channel via riverwall construction.
SUMMARY FOR PANAJACHEL
1. Panajachel’s safety is guaranteed only with defined river walls, not with a wide channel. No river channel width will protect the town if there are no river walls.
2. A syllogism: If there are no walls, there is no channel; if there is no channel, there is no security.
Example: The Rio Quiscab and its Travels
Its "Channel" Before and After Tropical Storm Agatha
These photos show that once in the floodplain, uncontrolled alluvial rivers are only stopped by the walls of the canyon itself. In this case, the bed of the Rio Quiscab traveled more than 650 meters laterally in a single storm, from the center to the edge of the flood plain.
The Rio San Francisco, geologically identical, also without walls, is capable of the same.
Just imagine the results of that.
Rivers Without Borders
II. Potamology 102
Why is it that alluvial rivers don’t stay in their channels?
The answer is not in the water, but lies in a combination of the geology of an alluvial basin and the violence of the storms that batter them. Alluvial rivers, by definition, are products of morphologically soft watersheds. When big storms arrive, their water enters easily in the upper watershed land, penetrating and softening to the point that landslides are produced. The rocks and mud within these slides are then carried downstream by the river below.
Once in the floodplain, the water slows and can no longer carry the large rocks and stones that came from above, and they are deposited in the floor of the existing bed. In major storms, the bed is thus quickly filled with these stones and sand, and then the water has only to look for another low point to follow its path to the lake. At this point, it establishes a new direction and a new bed, sometimes very distant from the original. It is for this reason that the location of these rivers can only be controlled with containment walls, thereby defining a fixed route as they pass through the floodplain.
If only it was this overflow that was facing the engineer looking for containment solutions, it would be easy. Build high walls. What complicates the design of retaining walls is the other behavior of an alluvial river... the feature that shows up when storms are not as strong and do not contain the amounts of water needed to create landslides. .. but are still strong enough to do damage. In these cases, instead of leveling and filling, the river carves down, like all other rivers, threatening the wall that contains it along its lower edges below instead of above, as is the case in large storms.
The fact that these rivers can cause problems from both below (undermining) and above (overtopping) complicates the engineering ... but there are several solutions that solve both problems and make the alluvial rivers stop their uncontrolled travels and stay where they are put.
Causes, Channels, Costs and Calculations
Given the foregoing, it is an inescapable truth that a failure to channel the alluvial river that runs through the town of Panajachel will cause damage, loss and death with every big flood. This is an inconvenient fact. Widening the channel is not and can never be a solution in itself, if not done in conjunction with river retaining walls. The only importance of the channel width is whether it is wide enough, in combination with the height of the walls, to allow controlled passage of the maximum flows and to protect the village. The cause of our disasters is not a restricted channel, but the lack of appropriate walls.
Again: If there are no walls, there is no channel; if there is no channel, there is no security.
Rivers Without Borders
III. Economics 101: Un-economical Economics
Over the past five years and in the wake of Hurricane Stan, many have asked the city leaders "When will you channel the river?" The answer, of course, is always the same - "We have no money." But seen in those purely economic terms, we can compare the cost of inaction to action, and see which of the two really is more expensive. How much does the policy of inaction - the decision by the authorities to spend on repair rather than spending on prevention -- really cost?
For obvious reasons, it is difficult to quantify accurately certain elements of the costs of disasters in general. However, the following table is a summary of the costs directly related to the damage done by the uncontrolled passage of the Rio San Francisco on its way through Panajachel during Tropical Storm Agatha.
Rivers Without Borders
Historical Maximum Flow Calculation
For better or worse, today the river is an average 50 meters wide due to historical factors of growth. If we wanted to make, as UNIRIOS insists, a channel of 150 meters, the city would have condemn a great deal of private land, compensate the owners, take away the land and then build the wall. Given the legal, political and economic realities in the village, this solution is very difficult if not impossible to achieve. The following table shows the comparative costs of three approaches, varying the width of the river:
From this table what is apparent is that the proposal of making the channel 150 mt. wide is economically impossible, not technically necessary… and therefore not real. However, the loss of millions of Quetzals’ in damages that every big storm brings is real, and to this real threat we have to offer real solutions, not unattainable dreams.
A practical, effective, workable and desperately needed solution.
The control of a river like the Rio San Francisco is usually done in the manner shown this photo to the right. There is a channel lining edge to edge, including the bed of the river. The benefit of this style is that it denies the undermining of the river walls and guarantees the integrity of the channel. The main disadvantage is that it is more expensive. In Panajachel, there are other disadvantages that are both economic and political. There are many people who make their livings out of the river, selling the sand, gravel and stones the river delivers each year. Given the political and economic forces held by the “areneros”, a system that leaves open the main channel while protecting the edges, as shown the picture at left, is the best option.
This requires, especially where water velocities are high (as they are in Panajachel), a special design to protect the "foot" of the walls and preventing them from being undermined. This additional cost, however, is much less than the cost of the concrete floor of the canal, and is offset by the income of the ‘areneros”.
A River With Borders
Civil Engineering 101: Design of Levees and Channels
Water, as mentioned several times, takes the shape of its container according to its use. If you want tea, it’s put in a cup. If you want to swim, we put it in a pool. And if we want to protect ourselves from it, we put it in channels. The design below is a practical, economical way to control the Rio San Francisco in its course through the town. It is not the only or necessarily the best solution ... but it is a solution.
The following design parameters are the ones we have reviewed and verified:
- • It handles a maximum flow of 717 MT3 / s (TT Agatha plus 30%)
- • It provides foot wall protection (water speeds up to 9 m/s)
- • Leaves space for fill (1 meter, Agatha)
- • Still leaves extra security as "freeboard" (70 cm)
- • Easy, quick and inexpensive to build (and in its time, any repair work)
- • Proven design is recognized and used around the world
The costs presented in the previous page (Q250 mt2) are based on this design.
Costs and Benefits
It is impossible to quantify the actual cost of a disaster. The loss of one house can mean the family must move to another place. That may mean that the family cannot pay schooling for the children, and they lose forever their education and their chance to contribute meaningfully to an educated and prosperous country. In this way the country is impoverished by disaster… but no figures can grasp or measure these losses.
What we can be measure are the costs of works, property values and damages to them, and in this fundamentally flawed way were the following calculation done… based on actual costs and values:
IN SUMMARY
The hydrologic, economic, and political math
• Every river that runs through a settlement must be controlled to prevent continuous tragedies and foster security and development.
• The case of Panajachel is more dangerous yet due to the type of river running through it.
• Controlling an alluvial river is not achieved by widening the channel, but by strengthening the walls.
• The solution for the design of this work must be based on engineering, not politics.
• The main design parameters are a) to establish with certainty the flow that is to be controlled, b) to secure the width that exists for the channel, and c) to then design a channel that will handle the calculated flow.
• With a cost:benefit ratio of 11:1, it’s clear that if just in financial terms, it is a sound investment.
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2010-06-24 19:31:28 - | Marco
True, we are already blessed with flood walls but i think they are incomplete. On my side of the river, close to las manos i do not have a wall to my knowledge, nor las manos or mayan families have any protecttion. Without it lots of properties will be lost, as well as ones on the other side of the river, where there is a wall but people did build houses on the side of the river bed. (example, a friend is renting a house in the riverbed, just outside of the protected area, Q 500 he paid to house his family, dangerous but payable in his case. After agatha he search for a new location, the offer of the owner to pay Q 300 a month from now on made him stay).
Panajachel is small, we could surely need some extra (safe) space.
Without protection, the park will overflow every x amount of years; the problem is that this will be including the stones/boulders that will run randomly through the riverbed. Destroying a park or anything else constructed there.By giving the river a core running 'highway' for sediments and boulders to run straight to the lake it may overflow without causing any structural damage to whats build beside it.
It will create much needed space for a park, water treatment plant, schools, etc.
I am curious as to how wide our friendship bridge exactly is. More or less then 70m, to get an idea of the width.
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2010-06-24 20:01:20 - | Soaring Bear - one place or another
All the boulders and sediment tumble down the mountain until reaching the relatively flat Pana where it settles out and adds to the height of the flooded area. This creates a persistent problem for either a park or walls. Pushing all that muck and rock to the mouth of the river instead of along the sides of the river (as they are currently doing) would preserve the town and extend it further into the lake. This would take cost something and change the lakefront.
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2010-06-24 20:19:52 - | Sid
Soaring Bear:
A couple of things. First, the river walls built in 1948 your refer to are totally ineffective as 'river walls'. Building behind them offers exactly 0 protection. Because of the lowering of the lake level over the past 40 years, the river has dropped accordingly (otherwise, it would have a 7 meter waterfall at the mouth). Because of the geology of the alluvial plain, gravel and sand, there is nothing to keep the river from cutting a deeper and deeper channel, which is exactly what it's done. If you stand at any point of the river bottom and look upstream or downstream, you will see that it is a perfectly straight line of descent, as we would expect. What this has done to the old '48 river walls is leave them 20 feet in the air, and at this point they offer no protection from the erosion of the river at all... twenty feet below them.Regarding all the soil brought down by the river, it is actually only brought down in major floods, like 1948, Mitch, Stan, and now Agatha. The areneros take care of these deposits and actually help keep the river 'canyon' at a steady height, a height determined by the drop in altitude, not by their removal of material.
Third, to your point that the river should be allowed to 'meander'... that would only make sense if Panajachel didn't exist. As shown by the recent changes if the channel on the sister plains of the Jaibal, the river can 'meander' the entire width of the plains. Therefore, by definition, any structure anywhere on the Panajachel plains would be at risk. As there are now 12,000 + people living here, meandering is not an option unless one likes to see repeated loss of life and property.
Last, you are right that it needn't be concrete. I proposed, nearly 20 years ago, the creation of a river park from the yellow bridge to the lake... there's no reason that can't still be done, including the construction of landscaped walls that would protect the walls of the existing channel and allow a beautiful park to be built. The mayor at the time was interested, but after developing full plans, he decided that there was no money...
C'est la guerre.
Sid
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2010-06-26 17:50:11 - | Anonymous - Panajachel Flood map
I have seen a map made by SEGEPLAN and most Panajachel is highly susceptible of floods and the rest to mud slides.... And I agree the river has to be domesticated but before that they should be a total interdiction of building between the walls actually place...In order to prevent future destructions... It is a political decision that I'm not sure anybody wants to take as of today... then the river bed should be worked
in a more natural way than the channel proposed... Working with reforestation of the bank and to manage in an ordained way the extraction of sand, peebles and stones... Right now it is managed by a group with particular interest and no vision how to extract properly the materials... And any action in the river is first political based on a technical choice which ultimately needs financing and right now the finances are under extreme stress...
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2010-06-26 19:26:07 - | Marco
Definitely there should be a ban on building between the existing walls. By now there is not much left to construct on luckily, most is pure riverbed with big rocks, like building on the moon. What can be done is protecting the area inbetween the walls, including the buildings that still stand. Trees or no trees, a channel is needed as soon as possible. And imagine the land that can be developed as soon as a proper channel is constructed, enough space for many parks. Sell this upfront to McDonalds, Gallo for bodega space, hotels or restaurants and private peopl. The money taken in should pay for the costs of a channel which gives the area next to the river much more protection that it has at the moment, in my opinion (nothing). In my fantasy Panajachel will be gone for 50% (or more); in 50 years or less.
I think the wall that “protects” Jucanya will tumble after a few storms, as if it has never been build. And the next few could make a house on “Salpores” a riverside property until whatever cycle is going on, completes.
Can anybody explain me why “areneros” are a problem. The river “channel” we have has to be kept clean or it will overflow easily. They are a benefit to Panajachel.
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2010-06-27 09:03:17 - | Sid
Marco:
At a meeting on thursday, three river channel plans were presented to the 'community'. 150 mts., by UNIRIOS; 90 mts, by COVIAL; and 60 by FONAPAZ. It's my understanding that nearly all attendees were for the 60 mt. walls, as it would stop the river from 'meandering', bouncing from side to side as it would in a 150 mt. wide flood channel, and would also provide the most 'reclaimed' land for other uses, from park to ...?As shown in my document (above), the walls of a 60mt wide floodplain would only have to be 2.68 mt high to protect against an Agatha sized flood, that height including a 30% safety margin plus 1 meter of fill. This is easily doable within the present river channel, and as Marco's points out, the areneros can keep the river channel to it's required depth by cleaning out the channel every year.
For additional security, it would be easy to increase the height, as the entire lower channel is more than 2.68 mt. deep, and in the upper channel, the height of the berms is also over 4 meters presently. As to the old 1948 river walls and their place in the discussion, in my opinion they are irrelevant for the following reasons: they were built when the river flowed at ground level, not 3-6 meters below, and as such are totally innefective today in terms of river control; they were built when there were possibly 500 people living in Pana and there was lots of open space; and third, they were not designed from a factual study of what was needed, rather just a guess based upon the space they had.
We now know how to calculate, design and build walls of many types that could be used to make Panajachel both safer and more beautiful, and the old river walls are just that... old river walls... historical markers that have no place in the modern conversation about how to protect and beauify Pana.
Sid
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2010-06-30 05:14:53 - | Dora Kethler
I don't understand what prevents the river from undermining these proposed walls. I hate the look of concrete lined channels up north and am glad to hear there is an alternative. Bravo! What can I do to help?
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2010-07-03 09:54:14 - | Sid
Dora:
Undermining, IMO, is an overstated problem. By definition, when dealing with aluvial rivers, only small rivers scour, while large floods fill. That doesn't mean that scouring and undermining isn't a potential problem... it is. However, there are many ways to deal with that issue, from very deep footings on the walls to collapsable 'toe' protections.The point of my article wasn't to define designs, but to make the case that for the future of Panajachel, the river must be controlled. What is the best design to achieve that end is an open question... but continuing to ignore the river is not an option.
best
sid
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2010-07-11 11:58:23 - | soaringbear
Friday (9 Julio) was a fine example of the futility of trying to channelize and tame the river. An ordinary afternoon rain succeeded in reversing a weeks worth of work by 2 shovels and a bulldozer by the main bridge. Yesterday there was a nice channel under the middle of the bridge and big berm. Today that's filled in and the river snaked its way to the Jucanya side and also washed out the tuk-tuk bridge yet again. These lessons will continue until people give the river plenty of room.
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2010-08-18 06:40:11 - | Sid
Sand walls are not walls. They are sand, and knocking sand down demonstrates only that Jimmy Hendrix was right (... and castles made of sand, fall in the sea, eventually.)
s
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2010-07-19 16:44:21 - | Marco
you are right Bear, i saw it. what was it, maybe a few hours of rain, i did not see it in the late afternoon, but did hear the river get louder by that time. The sand walls in panajachel at the friendship protecting the bridge itself from being undermined at the side of the basketball court, are pretty much gone.
i disagree on the effectiveness of channelling a river. in my country they do the same, channel it, let it run in between dikes which are covered by concrete or stone walls to make sure it does not erode or suck itself full of water and keep it clean (digging it out once in a while, we have a whole industry for that). We do not make our levi’s or dikes pretty in any way, mostly we cover them by a road and an occasional house of the " watchman".
But such a channel of 2 dikes will prevent what happened the 9th of july or before. the panajachel river will swing its way from one side of the concrete wall to the other without causing problems. And it will have a path of at least 50 meters wide which is enough to hold a lot of it before it overflows. this is something that will happen in the future. It happens in holland now and then, the river pa**es through cities where we try to completely contain it between the two dikes, at these places its narrowed with the result that they get their feet wet with damages inside the houses, carpets, etc. no one is in real danger.
Problem with a wandering river is that you will be without bridges most rainy season. Like what you saw with the tuktuk bridge, once the river wanders around to one of the sides you can’t use the ramp anymore, or worst.
The 150 meter wide channel is a utopia. The Ubico bridge is like 70 meters wide, and it is at its maximum now. You can’t channel anything right if you have a piece that is narrower than the channel itself. That will blow out. So a channel of 50 meters is an option. A channel of 70 meters will take out the friendship bridge without any problem (but still an option) and something like 150 meters is not real.
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2010-07-20 23:10:58 - | M. de Boskabouter
There has not been too much movement going on in the river this month of July. There was some the first week repairing the damage from Alex but not like in June, when they were at it throughout the day with 8 to 12 heavy machines. Today i saw 4 machines in the river working so they might be picking it up again.
And i was thinking. How much do these machines cost compared to the total costs of working towards a more permanent solution. Correct me if i am wrong, but i heard these machines cost Q 500 an hour (machine, worker and fuel) and from the second of June and 30 days on there were 8 of them working about 10 hours a day. This would amount to 1,2 million quetzales.
The 50 meter wide channel proposed in this article would cost 11,5 million Quetzales.At the moment that money is invested in piles of sand that don’t need no biblical rains to crumble down, we see that now when it rains only for a few hours. These machines will have to keep on working this rainy season; climatologists are predicting a
Quote:wet canículathis year. http://www.prensalibre.com/noticias/comunitario/ano-canicula-humeda_0_301769924.html
Apart from the money invested in the current sand walls i think these temp. dikes could mean disaster for parts of Panajachel when the river breaks through them. It could prevent it from coming back into its path. (see Panajachel Bridges )
I hope the Panajachel municipality, Guatemala’s first lady or any person or institute will be able to free up the money that is required to pave these 50 meter wide sand walls that we still have with a coating that will survive a rainy day or two.
M.
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2010-07-30 11:38:10 - | Sid - Friendship Bridge
A brief comment on the above is that the Friendship Bridge has a clear channel of 45 meters...
That means that, according to the calculations above, the depth would have been approximately 1.6 meters at the flood crest. I was not at the bridge at that time, and am curious if anyone saw the crest at the bridge?
As the clear height of the bridge is about 5.5 meters, there should have been about 4 meters between the water and the bottom of the bridge...
sid
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2010-09-30 07:58:16 - | Ellen
I am arriving late to this conversation. Is there a plant similar to vetiver www.vetiver.org that is indigenous to the area that would be useful in this erosion control. Or will vetiver in fact work. Vetiver has so many other uses and benefits and looks a lot better than concrete.
Flood walls were already built some years ago and it is sad that so many people ignored them and put houses in harm's way.
People tend to underestimate the risk of infrequent hazards, and become startled when a hundred year flood occurs twice in a decade. Better to listen to nature's message and give the river enough room to deposit silt and meander the way it is inclined to do.
One of the options to consider is establishing a park which could be more attractive than an LA-style cement channelization along the river.