Levees and the illusion of flood control

A post by Anne JeffersonResearchBlogging.orgMy hometown lies on a sandbar, squarely in the floodplain of the Upper Mississippi River. Winona (Minnesota) benefited from its position along the river, rapidly growing to wealth as a steamboat port and lumber town. The second railroad bridge across the Mississippi was built there, and in 1900, Winona had more millionaires per capita than any other town in the country. In the last hundred years, the lumber industry in Winona has declined, but my town is still a major port on the Upper Mississippi and the river is the lifeblood of the community.

Panoramic map of Winona (1889, Minnesota Historical Society)

Panoramic map of Winona (1889, Minnesota Historical Society)

But the same river that gave so much to my hometown also wrought destruction on Winona. From its founding in the 1850′s through the 1960′s, parts of Winona were repeatedly inundated by spring floods of the Mississippi River. Record flooding occurred in April 1965, and disaster in Winona was averted only by frantic sandbagging and the mysterious blow-out of a railroad dike a few miles downstream that released floodwaters into a wildlife refuge.

Flooding in Winona, 1880 (Minnesota Historical Society)

Flooding in Winona, 1880 (Minnesota Historical Society)

Winona levee, image from Winona Daily News

The Winona riverfront, protected by its high levee. Image from the Winona Daily News.

Following the 1965 flood, which crested at 20.77 feet, Winona built a massive 11-mile long levee that is designed to protect the city up to a river stage of 22 feet. The levee took nearly 20 years to complete, but now high spring flows pass Winona with little incident. The second largest flood in 81 years of record at Winona occurred in 2001, with the river cresting at 20.07 feet. A small parcel of parkland outside the levee was inundated, as it is many years, but otherwise the high water brought nothing but casual observers.

What is to be concluded from Winona’s story? Levees are good at protecting bits of land and communities where we’ve deemed it unacceptable that they be exposed to repeated floods. It’s not realistic to relocate all floodplain communities to higher ground – Winona, for example, has 25,000 people on a few square miles of land and is hemmed in by 500 ft bluffs – and if we are going to continue to use major waterways as transportation corridors, we need ports to get stuff on and off boats. Levees do a great job of minimizing impacts from moderate size floods. Ten out of 26 years since the Winona levee was completed have had peak flows above flood stage, so that’s nearly 40% of years where the levee has prevented flood damage and produced an economic benefit that will eventually equal its construction costs. In my mind, there’s no question that Winona is a place that benefits from and deserves its levee. I do acknowledge my bias in the matter, however, and I know that there are some serious negatives that come with levees.

People are drawn to settle on floodplains – because rivers provide transportation corridors, but mostly because floodplains are the most fertile soils on Earth. Those fertile soils are there because flooding creates floodplains, bringing in the sediment and nutrients that make rich, agriculturally-productive soils. I’d wager that every floodplain-dwelling person thinks that his or her home, farm, and community deserves protection from floods.

All along the Mississippi River and its tributaries, as settlers built farms and towns, their experiences echoed that of Winona. The river gave their land value (whether they realized the soil connection or not), but it also gave them misery. They wanted the benefits of the river, but not its floods. So they built levees, but often the locally-built levees were inadequate and failed repeatedly. In the late 1800s, the federal government took over and the US Army Corps of Engineers began a policy of building levees along the whole length of the Mississippi River from Cairo, Illinois, to its mouth – protecting millions of hectares of fertile farmland and hundreds of riverside communities. Or so they thought.

Flooding in Arkansas, along the Mississippi River, 1927 (Corps of Engineers photo)

Levee overtopping and failure was so widespread in the 1927 Mississippi River flood, that sometimes there was no dry land left except atop the levees. Here, flood victims camp on a levee at Arkansas City, Arkansas (Corps of Engineers photo)

The great Mississippi River floods of 1927 showed the folly of depending on hundreds of miles of continuous levees to keep the floodplain dry. The 1927 flood was larger than anything that had come before it in the historical record, and the levees broke in at least 145 places, flooding 70,000 sq. km. In one spot, the flooding was 80 km wide (check out this spectacular – and large – map of the flood extent). More than a million people were displaced by the floods, and the cultural, social, and political ripple effects of the flood changed the nation’s history (I’m not exaggerating; read John Barry’s book Rising Tide for the gripping story).

The extensive leveeing of the Lower Mississippi River made the 1927 floods worse, just as all levees today carry consequences for current and future floods. While levees are good for individual communities in small- to moderate-size events, levees are bad for the river system’s overall capacity to deal with flood flows.

By literally walling off large sections of the floodplain, levees give the river much less room to spread out horizontally. This is obvious. It’s the reason that we build levees: to keep the river confined and out of our way. But levees basically do nothing to change the discharge, or volume, of the flood. So if the water can’t spread horizontally, it has to either speed up or get higher – and mostly the flood waters get higher. At St. Louis, the 1993 Mississippi flood peaked at a stage of 49 feet. In ~1927, the same volume of water at St. Louis would have reached only 39 feet. In the 66 years between the 1927 and 1993 floods, the cumulative changes to the Mississippi channel – including continued levee building – increased flood stage by 10 feet. At Chester, Illinois, the difference is 16 feet. In short, levees increase flood heights.

Google Earth image of Winona, Minnesota and the levees (red) and natural floodplain extent (blue)

Winona is protected by levees, shown as red lines, and railroad dikes act as levees on the opposite side of the channel. The blue lines illustrate the approximate geomorphic extent of the floodplain. Above flood stage, the Upper Mississippi River has access to much less horizontal extent than it would naturally have, because of the levees. The magnitude of floodplain width reduction on the Lower Mississippi River is even more dramatic. (Image from Google Earth)

Levees even increase flood heights where they are not. The river is flowing along, flooding, and the flood wave is moving downstream, occupying the floodplain as it goes. Suddenly, it gets to a place where it is constricted by the levees, which are acting somewhat like a convergent nozzle. Some water goes through the constricted opening, but other water backs up and ponds behind the constriction.

Dynamiting the Mississippi River levee in St. Bernard Parish, 1927 (Corps of Engineers photo)

Dynamiting the Mississippi River levee in St. Bernard Parish, 1927 (Corps of Engineers photo)

Removing levees immediately decreases flood height, by giving the river back temporary storage space on the floodplain. In Winona, in the 1965 flood, the town was saved from inundation by the breaking of a railroad levee ~15 km downstream. When that levee broke, the water at Winona dropped more than 20 cm in a few hours – just enough to keep the top sandbags above water. When the Bird’s Point Floodway was opened on May 3, 2011, water levels in the Mississippi at Cairo dropped more than 30 cm within hours. In 1927, powerful citizens of New Orleans decided to blow up a levee downstream of the city, flooding the residents of St. Bernard’s parish, in order to save themselves. As it turns out, unintended levee breaks that occurred a few hours before the dynamiting, upstream of New Orleans, would have kept the city dry anyways.

Not only do levees actually exacerbate floods, they are a static solution to a dynamic, probabilistic problem. Levee heights are based on knowledge of the past history of floods on the river system, estimates of precipitation that is likely to occur, and hydraulic analyses. On the Mississippi, the “project design flood” was developed in 1956 based on “the largest storm series considered to have a reasonable chance of occurrence in the season when floods are likely to occur over the Mississippi River Basin.” For reference, the Mississippi River at Vicksburg is currently flowing at 2,330,000 ft3/s (~66,000 m3/s), and the project design flood is 2,710,000 ft3/s. On Friday, the Mississippi River at Natchez is predicted to crest at 62.5 feet, almost 4.5 feet higher than the highest flood on record there. So the flood of 2011 on the Mississippi River is within the design standards of its levees, but what happens when a bigger flood comes along? Or what happens when a big flood comes along on a river where the levees aren’t so well designed and maintained?

Land use changes in a watershed can increase flood flows. As urbanization spreads impervious surfaces (e.g., parking lots) over larger areas, rainfall makes its way to rivers more quickly, contributing to increasing floods. Agricultural drainage and conversion of wetlands to farm fields also increases flooding. Levees built to withstand floods in a watershed with little urbanization and agricultural drainage may be inadequate after the land use patterns have changed.

Precipitation and snowmelt patterns also change, changing the frequency and magnitude of floods along with them. Increasing intensity of precipitation, a likely outcome of anthropogenic climate change, will contribute to increased flooding in the Mississippi watershed and elsewhere. Already, analysis of long-term flood records on the Upper Mississippi and Missouri suggests that annual peak flows are increasing in some areas, and that the likely cause is climate change (Olsen, 1999). This means that we need to recalculate the probability of a given size flood occurring each year. What was once thought to be a 1% probability event (“100-year flood”) now occurs with much higher probability. But, in a dynamic climate, it’s not entirely clear how to calculate flood probabilities in the way we’ve done in the past.

Levees aren’t designed to hold back every conceivable flood, and they are not perfect performers even when they are faced with more routine floods. Dams are often required to be designed to operate safely to the probable maximum flood worst-case scenario, but levees are usually built to a much more relaxed standard, something like the 1% probability (100-year) flood. When a flood comes along that’s bigger than that design standard, the levee will be overtopped or fail. And sometimes, levees fail even when the floodwaters are within the design criteria. One reason for opening the Bird’s Point Floodway in early May was concerns about levee failure at Cairo – even though they would have had several feet above the predicted crest, prolonged flooding could still have caused undermining or erosion that led to failure and catastrophic flooding of the city. The American Society of Civil Engineers (ASCE) report card on infrastructure gave the U.S. levee system a grade of “D-”, because more than 85% of the nations levees were privately built more than 50 years ago, are privately maintained (if at all), and were not designed for the current level of development behind them. The ASCE estimates it would take 100 billion dollars to repair and rehabilitate the levees of the U.S.

Elsberry, MO, June 20, 2008 -- A levee in the Elsberry levee district breaks, flooding farmland and houses in the area. - Jocelyn Augustino/FEMA - Public domain image

A levee breach on the Mississippi River near Elsberry, Missouri in the 2008 flood. (photo: Jocelyn Augustino/FEMA)

Every thoughtful analysis, from 1927 to 2011, has concluded that levees are not the sole solution to the Mississippi River’s flooding. After the 1927 flood, the Corps of Engineers added three floodways to their engineering arsenal. The Bird’s Point Floodway provides temporary floodplain water storage in a critical area just downstream of the Mississippi-Ohio junction. The Bonnet Carre and Morganza Floodways divert water from the river via alternate routes to the Gulf of Mexico. (All of these floodways are currently in operation.)

A levee protecting the town of Valley Park, Missouri from 2008 flooding of the Meramec River, a tributary of the Mississippi. (photo by the City of Valley Park)

A levee protecting the town of Valley Park, Missouri from 2008 flooding of the Meramec River, a tributary of the Mississippi. (photo by the City of Valley Park)

But levees continued to be built all along the Mississippi River and its tributaries, and more people come to live and work on the floodplain. Since the 1993 floods on the Upper Mississippi River, more than 72 square kilometres of floodplain lands have been put behind levees in the St. Louis area alone (Pinter, 2005). Much of this land was under water in the 1993 flood. In the St. Louis area, 28,000 new homes have been built and 26.8 square kilometres of land has been developed for commercial and industrial use on land that was submerged in 1993. That means 10s of thousands of people are now living in the floodplain, protected only by an earthen wall. Land behind levees is open to any form of development, doesn’t show up as high risk on FEMA floodplain maps, and residents often don’t have flood insurance. Some don’t even have any idea that they are living on a floodplain. And that’s probably the biggest problem with levees. Levees create the illusion of safety that promotes further settlement and development of floodplain lands.

We’ve taken away enough of the natural floodplains of the Mississippi and other rivers. At the very least, it is time to stop building levees in undeveloped areas. But I think it is also time to make some more difficult choices about what areas we are going to return to floodplain functionality – giving the river back some space for spreading out and temporarily storing water during floods. Doing that will be better for the river ecosystem and safer for the more than four million residents of the Mississippi River floodplain.

Update: Steve Gough of Riparian Rap takes on some of these same issues, in the context of the on-going Mississippi River floods, in his post “Never ending flood suffering. A recipe.

References Cited:

Barry, John M. 1998. Rising Tide: The Great Mississippi Flood of 1927 and how it Changed America. Simon and Schuster. 528 p.

Leopold, Luna B., 1994, Flood Hydrology and the Floodplain, in Coping with the Flood: The Next Phase, White, G.F., and Myers, Mary F., ed., Water Resources Update, Spring issue, p.11-15.

Olsen, J., Stedinger, J., Matalas, N., & Stakhiv, E. (1999). CLIMATE VARIABILITY AND FLOOD FREQUENCY ESTIMATION FOR THE UPPER MISSISSIPPI AND LOWER MISSOURI RIVERS Journal of the American Water Resources Association, 35 (6), 1509-1523 DOI: 10.1111/j.1752-1688.1999.tb04234.x

Pinter, N. (2005). ENVIRONMENT: One Step Forward, Two Steps Back on U.S. Floodplains Science, 308 (5719), 207-208 DOI: 10.1126/science.1108411

Categories: by Anne, geohazards, hydrology, society
Tags: , , , ,

Comments (19)

  1. Anna O. Zacher says:

    Interesting article. I’m dismayed that you think that people generally do not know that they are living on/in a floodplain an what that entails, that there are no FEMA maps showing potential flooding areas, and no flood insurance available, as my experience is (was, I’m retired now) entirely opposite. This is pretty common knowledge, IMO, and the information is available everywhere. Many people DO know, i.e. surely most people investigate when buying/building any land, a home, or planning a farm, and can’t remain ignorant at least of the local history.

    The problem as I see it, is that many people go ahead anyway, ignore, rationalize, or refuse to accept the facts, cross their fingers, and then blame and seek govt action when structures fail. (Some few exceptions of course.) They should instead accept that it is their choice to live in a floodplain, and they should embrace the old saying , “You pays your money and you takes your chances”.

    • Hi Anna – Perhaps I wasn’t clear. I know that floodplain residents – outside of the levees – are well aware of the risks of floodplain living, etc. They see the rivers rise and fall every year.

      My sentences about lack of FEMA maps, flood insurance, and awareness are specifically about people living in areas protected by levees. FEMA can “accredit” levees if they deem the levees provide adequate protection for the 1% probability flood. In that case, flood insurance is recommended but not mandatory. While some levee-protected residents may well buy flood insurance, as you say, many people will choose not to. I didn’t say that flood insurance was unavailable; you can buy flood insurance for properties well outside the floodplain. Here’s some information from FEMA on flood hazard mapping and flood insurance categories for people living in leveed areas: http://www.floodsmart.gov/toolkits/levee/files/pdfs/Living_Behind_Levees_Property_Owners.pdf

      • CherryBombSim says:

        Well aware of both the risks and benefits, sometimes. I know that “bottom land” along the Illinois River is generally worth a lot more than other farmland. The occasional flood losses are balanced out by the awesome yields, and the farmers there are mostly well-informed about how the process works.

        The Corps has been a lot stricter about levee conditions since Katrina hit New Orleans, but unfortunately, the emphasis seems to be still on building them higher and stronger, rather than smarter.

  2. John Welch says:

    Fascinating article. I was directed here by a link from GeoEvelyn. The article ought to be required reading for at least the one-third of the country drained by the Mississippi. I just started reading John Barry’s book when the the 2011 flood started hitting the news, and I’m right in the middle now (literally – Mounds Landing levee just failed). What strikes me the most is how flood control decisions, which require the very best technical analysis and understanding (which admittedly isn’t always consistent) are made very often with huge pressures from other real-life concerns. My way of saying we have a long way to go before a force as powerful as the Mississippi is accommodated.

  3. Brian Romans says:

    Fantastic post. Makes me wonder if we ought to keep numerous areas along the river un-leveed on purpose — the “strategic flooding reserve system”, or something. The trick would be convincing the public that they can NEVER develop this land (habitation or agriculture) even if a flood doesn’t occur for 80 years. These areas could also be nature/wildlife reserves … I don’t know, just thinking out loud. The real hard part would be trying to reclaim such a “flooding reserve” from already developed land.

  4. Alec says:

    Mrs. Jefferson,
    I really appreciated your article. I thought it was a great and timely introduction to the issues of levees. As an architecture student who just finished a design studio dealing with issues of water infrastructure in New Orleans, for me it was a nice article that explicitly and clearly showed the connections between the architectural (hardscape), infrastructural, and hydrological conditions.

  5. Lab Lemming says:

    Following Brian’s point, are the various cypress swamp state parks/game reserves in Ar/LA/MS leveed, or open to the river?

  6. Jessica says:

    It occurs to me that, in the long run, creating levees around most of the former floodplain areas will also rob them of the very thing that draws farmers to them and makes them valuable: their fertility.

  7. Gaythia Weis says:

    Excellent article.
    I’ve just returned from a journey from CO to the east coast and back, past expansive regions of soggy cornfields. We took a largely “blue highways” non-Interstate route. Winona sounds as if it is an exception, but one of the things that stood out for me was the number of towns that have their older residential and retail commercial centers up on bluffs away from the rivers, but now have Big box stores and new developments right on what ought to be the floodplain. Many older farmhouses were tucked up against the hillsides, with the fields stretching out towards the rivers. I know that there was a lot of publicity starting several months ago that people needed to sign up for flood insurance 30 days before the event. This leaves plenty of time to calculate snowpack levels, and, in my opinion, no real incentive to exercise common sense.
    As a nation, I think that along with expanding natural, wildlife refuge floodplains, we could institute policies that make distinctions between polices that extend needed help after flooding, and re-enforcing bad decision-making.

  8. Dan McShane says:

    Thanks for a well thought out write up on the Mississippi and flood risk in general. We have a long way to go to figure these issues out on all of our rivers.

  9. Commander Awesome says:

    My own home was hit hard by flooding this year (though nothing in comparison to what people on the mississippi got). I was wondering whether there would be any benefit to building man-made river structures instead of dikes, to try to provide more “horizontal” flow space instead of outright constraining river flows. I know the cost would be extremely high, at least the initial construction costs. Would there be sufficient gain? Or is it just a crazy pipe dream?

  10. Bill says:

    Hello from the other end of the Mississippi!

    Excellent post, with many great points. You might be interested in the NSF report headed up by Robert Bea from Berkeley on flood protection of New Orleans and the reasons for the levee failures (flooding Eastern NO, St. Bernard Parish, and the Lower 9th Ward) and the flood wall failures (flooding the areas from Downtown to the lake). The report not only details the engineering failures, but also documents the history of the development of the overall system.

    http://www.ce.berkeley.edu/projects/neworleans/

  11. nails says:

    I want to respond to comments about letting rivers flood.

    FEMA is facing a daunting task. And they sure can get cross-ways with this environmental scientist.

    FEMA wants to make sure that no new development increases flood risks for anybody. The upshot is a preferance for development that increases local drainage rates.

    But that’s what got us into this mess in the first place: steepened hydrographs (throughout the watershed) exacerbate downstream flooding. I’m very concerned that FEMA is institutionalizing this process, now especially on higher-order streams.

    To be more specific, local ordinances that are inspired by FEMA (44 CFR 60 &etc.) require engineering review (a “no rise” certificate). That sounds swell at face value, but as these local requirements find their feet across the nation, they’re killing the very sorts of proejcts that might actually save us. This FEMA-inspired process has resulted in local planners (and more than a few FEMA insurance experts) to deny environmental projects, such as those that would increase a stream’s natural access to a floodplain. The mandated engineering review (“no rise” certificate) often exceeds all other project costs.

    FEMA approaches all of this like an old hound-dog I once knew: every time he opened his eyes, it was a new world. I say this because FEMA bases all of this on conditions right now. FEMA maps lock us into today’s channel morphology — at least plan view (flood-prone areas) and X-section (base flood elevations). But today’s morphology is generally the product of anthropogenic destabilization in the watershed. Here in New Mexico, much of this can be attributed to railroads: they ushered in urbanization (hard surfaces and road borrow-ditches that main-line precipitation from the uplands into the streams), made it economical to overgraze (including woody encroachment and a host of other changes that shift from infiltration to sheetflow), caused deforestation (railroad ties &etc., again to increase runoff curves), and directly encroached on stream channels (less meandering equals steepening). Many of these effects resulted in incision, further limiting access to floodplains that might otherwise attenuate floods.

    In my estimation, streams are generally in a recovery trend from the impacts of the 1880′s – 1920′s. This natural recovery process often involves bank erosion, as a stream tries to reestablish its floodplain at teh new, lower elevation. All of that erosion has caused a lot of damage to aquatic ecosystems. I remain hopefull that we’ve seen the worst of that — but this new FEMA stuff doesn’t inspire confidence.

    I work with floodplain managers a lot. We sure agree that it’d be best if folks just kept their hands off the rivers — preservet he whole floodplain! But we part company when it comes to restoration — they often shut down the very projects necessary to put things back to right.

    FEMA needs a bigger view. I have a lot of respect for their hydrologic engineering, but I think their leadership is all insurance experts and politicians. Their science, as far as it goes, seems pretty cracker-jack. But they really need to raise their gaze a few degrees. (In the political marketplace, flooding homes apparently sells better than dirt-loving tree-huggers.)

    That’s what I think, anyway.

  12. Abbas Raza says:

    Hi Anne,

    You’ve won 2nd place in the 3QD Science Prize. See here: http://www.3quarksdaily.com/3quarksdaily/2011/06/the-winners-of-the-3-quarks-daily-2011-science-prize.html

    Come and leave an “acceptance speech” comment at 3QD if you like, and email me so that I can arrange to send you the money.

    Congratulations!

    Best wishes,

    Abbas

  13. arvind says:

    Congrats on the 3QD prize, Dr. Jefferson!

  14. Bill says:

    Congrats on the 3QD prize!

  15. Winfield J. Abbe says:

    While the engineering profession has had many successes in general, the dismal failure of the engineers and government to deal with flood control along the Mississippi River, and lesser rivers as well, in any way other than short time levees or flooding others out, is one of the great failures of our time, and for the past centuries as the article noted.
    The funny thing is, that aqueducts are nothing new are they? Shortages of water are also nothing new. Flooding is nothing new either is it?
    Aqueducts move water from the Colorado River to the Los Angeles area to provide it for the most trivial of uses like watering lawns and washing cars, but without it Los Angeles would be dead.

    Why the failure to do the same thing with the Mississippi River? This is both a failure of engineering and politics and is the greatest failure of our government in our time. All that mostly pure water ends up in the ocean rather than for use by populations deprived of it because government wasted so much money on other less important ventures, like wars and the failed war on drugs and the failed war on cancer and welfare and so many other wasteful activities in which our government engages.
    I didn’t see anything in the article about the potential use of aqueducts to transfer the higher energy water on the Mississippi River to other areas where needed with a system of aqueducts and gates and pumps. After all, aqueducts are basically controlled man made rivers .
    Yes this engineering program would cost a lot of money, but it would be a much better use of it than the many wasteful projects of government. The economic benefits would return much of the costs.
    Again, the failure to lead in this direction is one of the great failures of engineering and government of our time. How often to you hear one of our mentally impaired politicians talk about this? Yet this problem is one which only a strong federal government could solve. The vast land area and vast costs could only be dealt with by the federal government which has so dismally failed in this vital area.
    It would be like an interstate system to transfer vital water, not automobiles.

    Winfield J. Abbe, Ph.D., Physics
    Athens, GA

    • nails says:

      Winfield,

      I appreciate your comments. But I honestly think this is the kind of thinking that got us into this mess in the first place. I do not share your enthusiasm for this kind of engineering solution.

      The word “rivals” derives from an original meaning of “people who live on the same river”. Streams have always been a source of conflict among those of us suffering from human ambition. Anthropologists have long studied the importance of surface waters – from Dr. Neal W. Ackerly:

      As an anthropologist, I have spent considerable time studying past civilizations in arid lands that relied on surface water. Most of these societies failed. Analyses suggest that they failed for three reasons:
      1. They overestimated the amount of water available in the rivers on which they depended;
      2. They underestimated annual variability in discharge, and
      3. They underestimated the frequency, persistence, and recurrence intervals of extreme low-flow events
      Unlike earlier societies, we have employed two pieces of technology that buffer annual discharge fluctuations: storage dams and groundwater pumping. However, storage dams are not necessarily effective and, as the 1950s drought so amply demonstrated when Elephant Butte Reservoir was virtually dry, this technology has already failed once in our lifetime. What saved us during the 1950s drought was our ability to pump groundwater. Thanks to this technology, what should have been a wake-up call turned into a moderate inconvenience.
      Today, we find ourselves not only relying on surface water to meet our water needs, but, as well, pumping groundwater to meet these needs. It is not hard to envision a scenario, perhaps
      unfolding sometime between A.D. 2010 or 2020, when drought once again dramatically reduces surface water supplies. Unlike the 1950s, however, our continued withdrawals during the intervening years will have significantly depleted groundwater reserves and we will then find out, in spades, whether we should have used water in the fashion to which we are now accustomed.
      When–not if–this does happen, it may come as a shock to find that we, too, have repeated the
      mistakes of past civilizations and, like them, are faced with a water crisis.

      In response to your rhetorical questions, I reply that water engineering failures are nothing new, either. Most of my professional work revolves around misguided attempts (for the record, generally not engineered) to get rivers to “behave”. I’ve seen a lot of environmental damage associated with efforts to make a river stay put, as an example.

      Your analogy to Los Angeles is interesting. Nothing against L-Aliens, but if I could rewrite history, I’d prefer to leave LA “dead” and keep the Owens River alive. (Hate to date myself, but at Humboldt I remember singing “ding-dong, the ditch is dead” after political defeat of the “peripheral canal”.) So, I’m thinking your referenced “politics” along the Mississippi might actually be working, at least in this narrow regard.

      For my part, I’d prefer to see more of that “pure” water stay in the stream and support aquatic ecosystems. I’d prefer to see folks leave the floodplains alone, and let the rivers flood like god intended. Here in the arid southwest, I think my Indian friends would say the same. They’re the descendants of some of those “past civilizations” that Ackerly mentioned, and they’ve earned insight into sustainability. Respectfully, I trust them more than the engineering approaches you describe.

  16. Matt B. says:

    Parking lots are not impervious; they are impermeable. There is no such word as “anyways”. Climate change does not make people, therefore it is not anthropogenic (“-genic” means “making”, not “made by”).

    This article is really interesting. It’s analogous to evolving a polite society; one might gain advantage by stealing or killing, but if everyone does it, it’s bad for the society as a whole. Likewise, building levees helps locally, but makes things worse for a larger region. We need a generic name for this phenomenon.

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