One of the physical water quality parameters that we monitor at Utah Water
Watch is called turbidity. Turbidity is the amount of suspended material in a
stream or in a lake. This could be sediment such as soil or plant material
like algae particles that are in the water. Basically turbidity is a fancy
word for water clarity. In a stream we use what's call a turbidity tube, to
monitor how clear the water is. If you look at this tube it has a ruler on it
with centimeters and way down at the bottom is a white and black disc. We fill
this tube all the way up with water, and then we can lower it to the level when we
can just start to see the white and black disc.That tells us how clear the water is.
So the first step is to go into the stream and to fill it up. Go to your monitoring
location and when you are at your monitoring location you want to sample the
water that's coming from up stream. You don't want to sample the water down stream
after you have stirred up the sediment. Take your turbidity tube you don't want to
sample right at the surface just right below a little bit below the surface. So
stick it down underneath and then put the whole thing up and let it start to fill
all the way to the top.
Now once you've filled it all the way up you want to make sure that you can look
through the tube and be able to see. If you can fill it all the way to the top and
look through the tube then you will record that the whole water column is clear.
So what this means is on your data sheet you would select the greater than symbol
and write down 60 centimeters because in theory if I had a longer tube I could fill
this tube up to increase the clarity of the water. So this is what happens when
you have very clear water, a very clear stream. Now let me go demonstrate if you
are on a different stream such as like the Colorado River or the Green River. They
naturally have a higher sediment a higher turbidity to the water.
So now for demonstration purposes I've artificially increased the turbidity.
Stirred up the water so we have all this suspended sediment. So now when I look
down through the tube I can no longer see the white and black disc.
So no we're just letting the water drain out just so we can just start to see the
outline of the white and black disc.
You want to make sure that you do this in an even amount of light, so either all sun
or all shade. And right there, now when I look down I can just start to see the
white and black outline. So then I would go on the scale and look we have 10, 20,
25 centimeters. So this is what I would record on my data sheet. I would record
I would circle the equal signs because it equals 25 centimeters.
Once you have a measurement of the turbidity level using your turbidity tube
you can then on your chart convert that to the units that we use to monitor turbidity
They are called NTUs is the unit of measurement. Turbidity is something that
varies naturally in all streams. Think about how clear this stream is versus the
color of the Colorado River. What we don't want to see with streams is extremely
large changes in them. They have seasonal changes from when we have high flows in
spring during our, the snow melt in the high run off periods. But we don't want to
see very large changes in them because that could be a sign of something in the
watershed is going on and we are getting to much erosion, to much sediment, or too
much plant growth in a stream. In Utah for recreation and for fishery we never want
to see an increase greater than 10 NTUs from our previous measurements. So that's
the water quality standard for recreation and warm water and cold water fisheries.
This is a variation of how we do this in lakes. In lakes we use the same secchi
disc it's just an 8 inch disc that we lower down into the water column and if
you are interested in seeing that watch our video on monitoring turbidity in lakes