Tuesday, December 22, 2015

Happy Solstice!

Hey Everyone!  As I am sure you are aware, yesterday was the summer solstice down here, or the winter solstice for most of you.  The sun has now reached its highest point in the northern sky.  This is an event of interest for us down here, especially because the sun is the primary control of stream flow.  The days won't be getting any shorter now (still 24 hours of sunlight) but the sun will begin to spin around our heads lower and lower in the sky.

165 cfs flowing at Vanda gauging station.
It was fitting that we visited the largest river in Antarctica on this day, and even more fitting that we measured such a large flow rate.  The Onyx River at the Vanda gauging station (near the outlet of the river into Lake Vanda) was measured with a flowtracker to be flowing at 165 cfs.

Flowtracker Explanation:
If I haven't described what a flowtracker is yet, and if you are just dying to find out, I will explain.  The flowtracker is what we use to get an accurate manual measurement of the volumetric flow rate (volume of water passing a certain spot per unit time) of a stream. The flowtracker is an acoustic doppler velocimeter, which I am sure you all are very familiar with.  Many times scientists, engineers, and others with poor social skills like to come up with big words to make what they are doing seem important or advanced, and this name is an example of that.  This piece of technology sends out sound pulses that bounce off of particulates in the water (small sediment particles) and based on the return of the sound signal it can estimate the velocity of the water at that point.  It uses the Doppler effect to measure the velocity. This is the same phenomenon that makes a train sound different when it is traveling towards than when it is travelling away from you.  So, the instrument determines the velocity of the water at a specific point in the stream.  We measure the velocity of the stream at 20 to 30 equally spaced points across the channel at a cross section that is perpendicular to the stream flow.  The depth of our measurement is simply 40% of the depth of the stream at that point.  For example if the stream is 1 ft deep at a point, we would measure the velocity at a depth of 0.4ft (see figure below).

Where d is depth, and the x-axis represents velocity of the stream at each depth. i.e. a value of zero at the bottom due to friction with the stream bed, and maximum velocity at the top of the stream.  Average velocity is 0.6d from the top or 0.4d from the bottom.
The reasoning here is that, due to friction on the flow from the stream bed, this point is the depth averaged velocity (add up velocities at all depths and take the average).  The velocity, the location across the stream, and depth of each velocity measurement is recorded in the flowtracker program.

Cross section geometry of the stream as measured with the flowtracker.  Each area slice is calculated, the average velocity of each slice is then determined, and the two values are multiplied to yield volumetric flow rate per slice.  The flow rates are then summed to determine a total. 
Using these three pieces of information we can estimate the volumetric flow rate.  The distance between measurements and the depth of each measurement allow us to estimate the cross sectional area of the stream.  The cross sectional area is broken up into little slices that are bounded on each end by a measurement location (see figure above).  The area of each little slice is multiplied by the average velocity of that slice.  Area multiplied by velocity gives us a volumetric flow rate for that little slice.  This is done for all slices across the channel, and the results are summed to yield a total volumetric flow rate.

  We attempted to measure the flow at the upper reaches of the Onyx at the Lower Wright gauging station, but the stage of the river was too high to safely wade across.

Stage was too high to safely wade across the river and gauge flow at Lower Wright Valley gauging station (beginning of Onyx River)
Some weather rolled in last night and has been hanging around today.  I don't think it has impacted the helo schedule too much yet, but it has really affected our streams.  Von Guerard (the stream running by our home here at F6) turned off today, along with Harnish.  It makes our lives a little easier when there isn't any flow present. However, Christa (one of my teammates) has a PhD project to work on that requires a decent amount of flow, so hopefully things turn back on for her sake.

Some nasty looking clouds rolled in over Taylor Valley yesterday afternoon.

I also have been getting some Christmas gifts this year which has been such an amazing surprise!  I feel like a little kid when South Pole Santa (the helicopter pilot) hands you a package from back home.  My mom and Annie sent packages, and I would feature them here if I hadn't already ate all of the contents of them.  Thank you so much guys!  My aunt Natalie sent me the card and zombonis featured below.  These are little wind up zambonis driven by zombies that you assemble yourself.  Mikey and I built one each and raced them.  He had a little bit better craftsmanship, so his drives straight.  I haven't won yet, but I am hoping for a Christmas miracle.  Thanks so much Natalie!!!

Racing zombonis
 I just received a package today from my Grandpa and Grandma Sudman.  I apologize for not waiting for Christmas day, but since nobody is here to tell me otherwise I broke into my presents early... They sent some tasty brownies, and cookie bars, along with a super great letter, and this awesome book.  Mikey was talking about this book earlier in the season.  He said he read it last season and it was really nice to read about someone in a warm climate while you are freezing your butt off.  I thought it sounded super interesting and I was bummed he didn't bring it down.  Well ask and you shall receive!  Sure enough this book showed up along with a large detailed national geographic map of the area to follow along with Teddy Roosevelt's trip through the jungles of the Amazon .  Thanks so much guys this is amazing!!

To all my friends and family back home reading this, I miss you guys and wish I could spend the holidays eating bunches of cookies and drinking too much eggnog with you!  Thanks for all the emails, phone calls, letters, and packages.  It sure helps to make the holidays great even away from home.  Another thing that really helps is that I am surrounded by such great friends down here!

Goodies from Grandpa and Grandma Sudman!

1 comment:

  1. Glad you got the zombonis Zach! Wish you were here, AND also glad you're on an adventure in Antarctica! Merry Christmas love Natalie