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posted by Fnord666 on Tuesday May 29 2018, @06:07AM   Printer-friendly
from the flood-insurance-FTW dept.

Common Dreams reports

A Maryland city was devastated [May 27] after 6-inches of heavy rain caused a downtown flash flood. Major damage is reported and many cars have been swept away.

Ellicott City was still recovering from a flash flood two years ago that killed two and forced the historic city to rebuild much of its Main Street. Residents said Sunday's flood seemed even worse than the storm in July 2016--which was called an extremely rare "one-in-1,000 year event", and cost the city tens of millions of dollars in damages.

Additional information at:
The Baltimore Sun
The Washington Post
USAToday


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  • (Score: 2) by qzm on Tuesday May 29 2018, @06:20AM (25 children)

    by qzm (3260) on Tuesday May 29 2018, @06:20AM (#685461)

    Perhaps a bit less spending on civic improvements like parks, cycleways, pedestrian precincts, and mostly on many many many meetings, public consultations, and consultant investigations in to those.

    Perhaps a little more spending on basic infrastructure and maintenance, even when it is not 'sexy'.

    These floods are not caused by more water, but by less ability to handle the normal amounts of water.
    As more land is urbanised, the required support engineering is simply being ignored.

    Starting Score:    1  point
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  • (Score: 2) by c0lo on Tuesday May 29 2018, @06:30AM (8 children)

    by c0lo (156) Subscriber Badge on Tuesday May 29 2018, @06:30AM (#685463) Journal

    These floods are not caused by more water, but by less ability to handle the normal amounts of water.

    [Citation needed]
    No, seriously, when I hear "1 in 1000 years flood", it makes me think at "water in excess of the normal amounts".
    As you claim that is actually "normal amounts of water", I think you should present the evidence for it.

    So, how about you present the median/average for the last 50 years and compare with the one in the latest event?
    Here, a helping hand: the 2018 flood event saw 8 inches of water falling in two hours [wikipedia.org]

    --
    https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
    • (Score: 2) by Runaway1956 on Tuesday May 29 2018, @02:01PM (7 children)

      by Runaway1956 (2926) Subscriber Badge on Tuesday May 29 2018, @02:01PM (#685601) Journal

      Your request for citations is not unreasonable - but I'll pass on it just the same.

      Meanwhile, it is a known fact that urban sprawl continues. A ten acre Walmart parking lot is not known for it's permeability - nor are the hundreds of miles of streets, sidewalks, and concrete foundations and driveways in a typical medium sized neighborhood. There is little place for water to soak in, and many ephemerals are just paved over, preventing water from freely running off.

      Your citation of 8 inches of water in two hours? Interesting - but, how widespread was that? Did it extend a hundred miles in every direction, or was that a local event that only involved a hundred square miles? From the paragraph above your direct link,

      Floods

      The town is prone to flooding from the Patapsco River and its tributary the Tiber River. These floods have had a major impact on the history of the town, often destroying important businesses and killing many. Ellicott City has had major devastating floods in 1817, 1837, 1868,[58] 1901, 1917, 1923, 1938, 1942, 1952, 1956, 1972 (Hurricane Agnes), 1975 (Hurricane Eloise), 1989, 2011, 2016, and 2018.

      So, one has to ask, just how far outside the ordinary is this particular flood? Hmmmmmm . . . Only 7.4 inches of rain fell, compared to 8 inches in the article you cite. But, was this truly a "worse flood" than all those others recorded in the town's history? Maybe this kind of thing happens every fifty years on average?

      when I hear "1 in 1000 years flood

      it makes ME think, "How in hell do these guys know that? There are no records going back 1000 years, they must be pulling numbers out of their asses! In most of Europe, China, and parts of the mideast, where people actually kept written records, they probably have a pretty good idea how often bad floods happen. In the US? Written language was introduced with the arrival of the Europeans, and we haven't deciphered the various records maintained by previous civilizations. Tying knots in yarn is probably perfectly understandable, to the people who were raised tying knots - but we don't understand it at all. Mayan and Aztec both had something roughly equivalent to cueniform writing, but we haven't truly deciphered that either. So - where are the records?

      I know for a fact that all of the rivers in America flooded routinely before the Euros started reforming the land to their liking. There were no dams, except beaver dams. Torrential downpours rolled straight down from Bimidji, to New Orleans, with nothing to slow it down.

      • (Score: 4, Informative) by c0lo on Tuesday May 29 2018, @02:21PM (6 children)

        by c0lo (156) Subscriber Badge on Tuesday May 29 2018, @02:21PM (#685615) Journal

        when I hear "1 in 1000 years flood

        it makes ME think, "How in hell do these guys know that?

        Their specific meaning [usgs.gov]

        The term “1000-year flood” means that, statistically speaking, a flood of that magnitude (or greater) has a 1 in 1000 chance of occurring in any given year. In terms of probability, the 1000-year flood has a 0.1% chance of happening in any given year.

        ---

        here are no records going back 1000 years, they must be pulling numbers out of their asses!

        Learn first, be dismissive later (if you still feel the need) 100-year flood/Probability [wikipedia.org]

        A common misunderstanding is that a 100-year flood is likely to occur only once in a 100-year period. In fact, there is approximately a 63.4% chance of one or more 100-year floods occurring in any 100-year period. On the Danube River at Passau, Germany, the actual intervals between 100-year floods during 1501 to 2013 ranged from 37 to 192 years.[5] The probability Pe that one or more floods occurring during any period will exceed a given flood threshold can be expressed, using the binomial distribution, as

        Pe = 1 − [ 1 − ( 1/T ) ]N

        where T is the threshold return period (e.g. 100-yr, 50-yr, 25-yr, and so forth), and N is the number of years in the period. The probability of exceedance Pe is also described as the natural, inherent, or hydrologic risk of failure.[6][7] However, the expected value of the number of 100-year floods occurring in any 100-year period is 1.

        --
        https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
        • (Score: 0, Troll) by khallow on Tuesday May 29 2018, @02:50PM (4 children)

          by khallow (3766) Subscriber Badge on Tuesday May 29 2018, @02:50PM (#685631) Journal
          You didn't answer the question. Runaway wasn't asking about the definition, but about how they know.

          As to the 1 in 1000 year event, what of stalled hurricanes (that is, very slow moving hurricanes)? They can dump a lot more than 6 inches in a very short period of time. And I bet any place in Maryland (even far inland) would get more than one of those things in a millennium.

          I think there's a simpler explanation here. The flash flood wasn't a 1 in 1000 event.
          • (Score: 3, Insightful) by c0lo on Tuesday May 29 2018, @03:00PM (3 children)

            by c0lo (156) Subscriber Badge on Tuesday May 29 2018, @03:00PM (#685641) Journal

            You didn't answer the question. Runaway wasn't asking about the definition, but about how they know.

            It was you that took pride you had maths at least as a hobby?
            If so, would you mind to explain to Runaway how do you determine that N when you assume a binomial distribution and have a representative data set, even if you don't have the full 1000 years "population"?

            --
            https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
            • (Score: 1) by khallow on Tuesday May 29 2018, @03:18PM (2 children)

              by khallow (3766) Subscriber Badge on Tuesday May 29 2018, @03:18PM (#685652) Journal

              If so, would you mind to explain to Runaway how do you determine that N when you assume a binomial distribution and have a representative data set, even if you don't have the full 1000 years "population"?

              I wouldn't do that since that wasn't what he asked. But I'll also note that weather is not a binomial distribution. It commonly has a long tail.

              • (Score: 1) by khallow on Tuesday May 29 2018, @03:23PM (1 child)

                by khallow (3766) Subscriber Badge on Tuesday May 29 2018, @03:23PM (#685654) Journal

                But I'll also note that weather is not a binomial distribution.

                And by that, I mean that the size of extremes are not determined by normal weather conditions. The binomial condition you described doesn't give you a means to extrapolate extreme weather conditions. It merely describes how often those extremes are expected to occur assuming certain conditions (such as independence of weather from year to year), and the span of time that one looks at.

                • (Score: 2) by Osamabobama on Tuesday May 29 2018, @06:22PM

                  by Osamabobama (5842) on Tuesday May 29 2018, @06:22PM (#685774)

                  The important thing here is that there is some distribution being used, with the data being fit to it, leading to probability estimates about possible flood levels. Let's assume the model uses the appropriate distribution.

                  Does the model get updated, though? For instance, if a farm upstream were to build a levee around a field in the flood plain, the crops in that field may survive the flood (yay!), but some measure of water would no longer be able to spend a few days flooding that field, instead being diverted downstream to flood someplace else more severely.

                  Or, maybe the models are accurate, and we hear about a 1000-year flood in one location, but nothing about the 999 other locations that get a normal level of flooding. This one seems less likely, especially when the same location gets more than one such flood in a lifetime.

                  It's like a hypothetical statistician and a gambler, both observing a series of coin flips come up heads over and over. The statistician is confident in his knowledge that, eventually, it will even out to about 50-50 heads/tails. But the gambler will quickly start to suspect that the coin isn't fair.

                  --
                  Appended to the end of comments you post. Max: 120 chars.
        • (Score: 0) by Anonymous Coward on Tuesday May 29 2018, @03:11PM

          by Anonymous Coward on Tuesday May 29 2018, @03:11PM (#685648)

          WTF, that's the geometric distribution, not binomial. https://en.m.wikipedia.org/wiki/Geometric_distribution [wikipedia.org]

          Besides that, it also assumes that there is no correlation for the reasons behind any two floods and that the probability of a flood is exactly the same every year. If this is the type of back of the napkin, first-pass analysis being used you should be scared for your town. There is no reason to expect those assumptions to hold, so no reason to be surprised that the model predicts the wrong thing, and so no reason to try attributing it to any specific cause.

          And anyway, even if those assumptions were good enough, we need to know many towns are seeing too few or the expected rate of "hundred year floods", keeping track of a bunch and only reporting the places with "excess" floods is cherry picking.

          There are so many things wrong here, its total cargo culting. I don't see any hope of coming to a correct conclusion using this process.

  • (Score: 0) by Anonymous Coward on Tuesday May 29 2018, @07:11AM (14 children)

    by Anonymous Coward on Tuesday May 29 2018, @07:11AM (#685470)

    East of Atlanta, there is a rainstorm nearly every day. You can track it back to Atlanta, where the urban heat island effect disturbs the weather.

    So, did something upwind of that Maryland city change in the past 1000 years? I'm betting it did.

    Not that a couple occurrences mean the "1000 year" forecast is wrong of course! The next event might be 4321 years away. These events don't go on a perfect 1000-year cycle like clockwork.

    On the other hand, "1000 year" may have been nonsense from the start.

    • (Score: 3, Informative) by c0lo on Tuesday May 29 2018, @08:01AM (12 children)

      by c0lo (156) Subscriber Badge on Tuesday May 29 2018, @08:01AM (#685483) Journal

      On the other hand, "1000 year" may have been nonsense from the start.

      "One in X years" is conveying the statistical "reality" of "the chance of one such event in any given year is 1/X".

      So, "1 in 1000 years" should just tell you "the probability that we derived from our model** of such an event to happen in any given year is 0.1%".
      This is actually used by the insurance companies - they seems pretty good to make money from such a "non-sense", so maybe, just maybe, there's actually some sense into it?

      ---

      ** yes, of course, the derived chances have the same credibility as the model they used to derived it from.
      Somehow, I don't expect the insurance companies to share this model with the rest of us.

      --
      https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
      • (Score: 0, Troll) by khallow on Tuesday May 29 2018, @03:26PM (6 children)

        by khallow (3766) Subscriber Badge on Tuesday May 29 2018, @03:26PM (#685657) Journal

        so maybe, just maybe, there's actually some sense into it?

        Are you going to continue to try to snow us with mathematical non sequiturs or are you going to admit that these estimates can sometimes be in error?

        • (Score: 2) by c0lo on Tuesday May 29 2018, @03:36PM (3 children)

          by c0lo (156) Subscriber Badge on Tuesday May 29 2018, @03:36PM (#685661) Journal

          My post @Tuesday May 29, @08:01AM
          Yours @Tuesday May 29, @03:26PM

          Are you going to continue...

          This thread is done, happy now?

          --
          https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
          • (Score: 0, Redundant) by khallow on Tuesday May 29 2018, @03:55PM (2 children)

            by khallow (3766) Subscriber Badge on Tuesday May 29 2018, @03:55PM (#685682) Journal
            That depends. Do you understand the gist of my posts? The mathematics of the frequency of 1 in N events doesn't inform you of the size of the 1 in N event. Plus, we have here a confounding factor of the urbanization of the region and the building of large parts of the town on a flood plain.

            I think there's an alternate scenario here. The 1 in 1000 estimate was bullshit, provided as political cover for the leaders of the town in question (and perhaps a number of state-level officials as well). Having this extreme event happen again so soon (and being able to easily visualize much worse flooding events like stalled hurricanes that are likely to happen inside of a thousand years), indicates to me that the original statement was likely in error - and probably deliberately so.
            • (Score: 2) by c0lo on Tuesday May 29 2018, @04:21PM (1 child)

              by c0lo (156) Subscriber Badge on Tuesday May 29 2018, @04:21PM (#685698) Journal

              someone found some details [soylentnews.org], you may want to check.

              --
              https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
              • (Score: 1) by khallow on Wednesday May 30 2018, @01:18AM

                by khallow (3766) Subscriber Badge on Wednesday May 30 2018, @01:18AM (#686026) Journal
                Ok, I checked. First, it's not based on actual measurements as suspected. Second, it's on a fine enough scale that there's potential for a lot of 1 in 1000 events, even if their estimates were accurate. Just look at the map and the graph of rainfall. They have potential for several dozen 1 in 1000 events just on that map based on location and time span. They'll have a significant degree of dependence with neighboring regions, but it's not a stretch to generate many mostly independent possibilities from such a scale plus, a region the size of Maryland (not to mention the entire East Coast). For example, get 100 mostly independent observations and you have a 1 in 10 chance of a 1 in 1000 event every year.
        • (Score: 3, Informative) by aristarchus on Tuesday May 29 2018, @09:38PM (1 child)

          by aristarchus (2645) on Tuesday May 29 2018, @09:38PM (#685919) Journal

          It's statistics, khallow! Are you innumerate?

          continue to try to snow us with mathematical non sequiturs

          This is NOT about Anthropogenic Global Warming! Just because it was snowing in Maryland in May does not mean that the overall average global temperatures are not rising? And just because you have two once-in-a-thousand-year floods back to back does not mean that they were not both once-in-a-thousand-year events. Please, khallow, argue in good faith, and do not go to the dark side of Runaway.

      • (Score: 0) by Anonymous Coward on Tuesday May 29 2018, @03:31PM (3 children)

        by Anonymous Coward on Tuesday May 29 2018, @03:31PM (#685658)

        This is actually used by the insurance companies - they seems pretty good to make money from such a "non-sense", so maybe, just maybe, there's actually some sense into it?
        [...]
        Somehow, I don't expect the insurance companies to share this model with the rest of us.

        I doubt they are making money by using the "binomial" (actually "geometric") distribution (see my other post above). At a minimum I would expect them to include info about basic stuff like how if an area just flooded it will be more likely to flood again for some period of time since the groundwater has been "recharged", etc.

        • (Score: 2) by c0lo on Tuesday May 29 2018, @03:40PM (2 children)

          by c0lo (156) Subscriber Badge on Tuesday May 29 2018, @03:40PM (#685664) Journal

          I doubt they are making money by using the "binomial" (actually "geometric") distribution

          Likely they are using more refined models. The thingy with binomial distribution on Wiki was the only model I could publicly find.
          I'll appreciate if someone could link to more relevant papers.

          --
          https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
      • (Score: 2) by HiThere on Tuesday May 29 2018, @06:38PM

        by HiThere (866) Subscriber Badge on Tuesday May 29 2018, @06:38PM (#685786) Journal

        It's an estimate of the probability based on that data available at the time it was calculated. It's also highly rounded. You don't see reports of "it's a 1 in 997 year flood".

        The numbers aren't updated as frequently as they should be, but even if they were you shouldn't take them that seriously...they aren't intended to be taken that seriously. They are *estimates*.

        --
        Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
    • (Score: 2) by MostCynical on Tuesday May 29 2018, @08:52AM

      by MostCynical (2589) on Tuesday May 29 2018, @08:52AM (#685498) Journal

      "Rainstorm" is not the same as a "1 in 1000 year flood event".

      Something that happens every other day
      VS
      Something that is likely to happen, on average, once in a thousand years.

      Insurance companies are very good at this.

      Also, "1-in-a-1000" events *could* happen several times in a week, and *still* be 1-in-a-thousand events (although actuaries *do* review their tables, and if something becomes, or is assessed to be, more likely, your premiums will go up.)

      --
      "I guess once you start doubting, there's no end to it." -Batou, Ghost in the Shell: Stand Alone Complex
  • (Score: 0) by Anonymous Coward on Tuesday May 29 2018, @07:00PM

    by Anonymous Coward on Tuesday May 29 2018, @07:00PM (#685802)

    yeah, the "news" showed feet of water rushing down main street. that water didn't just come from some light rain shower. something goddamn overflowed. why the presstitutes don't bother mentioning what all the fat leaches in various bureaucracies have been doing all this time or where these damn yankees built their stupid town is beyond me. if you depend on leaches to protect you from flood waters, then you get flooded and the news will lie about it like it's Gaia mad at your carbon footprint.