August 28, 2007

  • Excess moisture

    A trivia note unrelated to anything really.  One of the bridges that crosses the Mississippi in Minneapolis to the North is the Broadway Bridge.  It is said to cross exactly at at 45 degree latitude or exactly half way between the equator and the north pole.  Might be true.  Earlier this summer, after (ironically) crossing the now collapsed 35w bridge my Garmin wrist GPS put 45 degrees N less than one hundred years north of Broadway Avenue and 35W.  I remember as a child walking around the edge of the Keller golf couse in St. Paul I saw a bronze plaque noting 45N.  Once I got a GPS I decided to try to replicate, ironically on a trip on 35W.

    Moisture may have played more of a role than people might figure.  St. Anthony Falls is maybe a half mile upstream.  There is a small hydro plant there but, except in extreme drought conditions, there is always water over the dam face.  This is decorative of course but it also helps to add oxygen to the river water that goes over the dam so it is designed for maximum turbulence on the spillways to both give the illusion of a larger volume of water falling and to add more oxygen to the water.  It’s a cheap effective strategy but it also tends to add a lot more moisture to the air.  If you have ever been in a Glen below a waterfall you have noticed this moisture. 

    At the point of St. Anthony Falls the river is flowing almost directly eastward and the prevailing wind here is from the West.  Below the falls, the Mississippi forms a deep gorge that tends to funnel the high humidity waterfall spray right past the collapsed 35W bridge.  I recall a few years back I was down there below the 35W bridge “playing” with an Isuzu trooper I them owned.  There were a number of piles of dirt left there that had settled so it was a fun place to “play” with 4 x4′s.  I noticed that the area seemed very humid.

    Extra humidity alone wouldn’t’ be enough to brings down the bridge but a lot of the likely culprits be they road salt or “pigeon poop” or my favorite “bearing-hingle “scalling/sticking” are accelerated by moisture.  To coin a term we might call this the “boathouse effect”.  A boathouse is exposed to higher humidity and I’m still sticking (pun intended) with the bearing-hinge sticking/scalling as a contributing factor.  I haven’t heard the extra humidity mentioned in stories.