Freaky Flood Year?

May 24, 2011 by  

[Chuck Selden and Mike Malone contributed the following regarding the seemingly endless bad water we've had this year.  Apparently, it could be a lot worse!  We feel better already.  (Sort of.)]

It really has been quite a spring.  [Great for ducks, not so much for rowers.] Alarming news regarding high water on March 12, April 18 and May 19.  PBC floats closed on and off again to boat launchings.  Shovel and broom brigades clearing away endless amounts of mud.  When is the next one?  Will it ever stop?

Below is historical flood data taken at Little Falls.  Just click on an image to make it bigger (and more readable) or visit the NOAA site (click) here. [Chuck will have the most recent data posted soon. Read on for Chuck's analysis.]

So far, in 2011, our flood water has remained below 12 feet, and we haven’t had to move boats to higher ground. In 1937 and 1996, two floods required us to move boats to the ballroom and upper decks.  In the last 80 or so years, there were only 10 times with water over 15 feet that forced us to move most of our boats upstairs, and a few times when waters were over 13 feet, forcing us to move a few of our lower boats upstairs and anchor our floats.

So, what is our risk now of another flood in 2011, you ask? Well, we could make a prediction by looking at the number of years with three or more high water events. During thirteen of the last 80 years, we’ve had at least three high water events per year, and of those, only during four of those years, we had more than three. During seventeen years, we had only one above 9 ft event.  During 34 years (1/3 of the record), we had not one above 9ft event at Little Falls. Chances are that we’re done with high water for the year.

Or are we? [Place your bets, ladies and gentlemen.]

Well, we usually get flooding, if at all, in the spring, and although they are less common in May, we did just have one.  Still, going by the data we have available, if we do get another flood this year, most likely, it will be in the fall.

We will be posting a “to do” list for reacting to predicted river levels by the logbook and on line at the PBC web site that gives tips, insight and rules on when to row; when to stay ashore; who might be able to risk going out; when club boats are not allowed to go out at all; at what depth we must detach the ramps and floats and anchor them downstream; and the circumstances that dictate which boats to move upstairs and when.

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Comments

2 Responses to “Freaky Flood Year?”

  1. Bob Hirsch on May 25th, 2011 7:46 am

    Nice write up, but I noticed that the tables you presented have an error in the second entry. That flood was 168,000 cubic feet per second not 16,800. Don’t know what other errors there might be in this list. You can find the data for the largest flood of each year at http://nwis.waterdata.usgs.gov/md/nwis/peak?site_no=01646500&agency_cd=USGS&format=html

    I took a look at the total amount of streamflow in March and April combined and could see that it is the 4th largest since 1932. I’ll make a calculation for the combination of March, April and May at the end of May. I’m guessing that will stack up as one of the highest. I’ve also looked at the size of the annual floods for the Potomac all the way back to 1895 and the overall record doesn’t show any signs of a trend towards larger floods.

    Bob Hirsch

  2. admin on May 25th, 2011 9:57 am

    Hi, Bob!

    Thanks so much for your comment and discerning eye for precise data! Chuck had sent a few other tables that may have been more accurate, but unfortunately, we weren’t able to format them for the site. Our tables came from the NOAA Middle Atlantic River Forcecast Center at http://www.erh.noaa.gov/marfc/Rivers/FloodClimo/.

    Here is an excerpt from the NOAA site:

    This area is devoted to flood frequency analysis information for the MARFC forecasting area. It contains information on how many times floods have happened in a specific month, percentages of flood occurrence for each month, probability, and average height above flood stage.

    The main function of this project is to give the user historical flood statistics for most of The Middle Atlantic River Forecast Center (MARFC) forecast points. MARFC has received numerous requests from our customers in regards to historical flood information. This project answers these requests for the much needed information.

    If you have any questions, input or see any bad links, please contact Charles Chillag (Charles.Chillag@noaa.gov) or Alaina Macfarlane (Alaina.MacFarlane@noaa.gov).

    Interestingly, as you found, they say on the site that their flood data isn’t necessarily up to date, so thanks, again, for catching the error!

    Penelope Walz