Hi, this is Megan Poff and I’m the Field Office Chief at the USGS in Las Vegas, Nevada.
I’d like to talk about field notes for indirect measurements.
I will also talk about pictures, site sketches, and some of the other metadata that you’ll
want to collect to ensure a quality indirect measurement.
First off – the field notes.
What do you want to record in the field about your visit?
If you are visiting a regular gaging station site, use SVMAQ for your site inspection notes.
At minimum, your SVMAQ notes indicate that you were at your site, and it’s always a
good idea to record some gage heights and perform a control inspection.
Your Water Science Center Surface-Water Quality Assurance plan will state exactly what you
need to do during a gage inspection, so make sure you follow that.
What else goes in your notes when you are running an indirect measurement survey?
Well – the high-water mark ratings need to be recorded somewhere.
Unless the flagger recorded all the high-water mark ratings, it will be up to you as the
surveyor to document this valuable information.
You could either record these in the high-water marks section of SVMAQ, or you could record
them in your survey notebook, or (my favorite way) you can record them directly in your
surveying software.
If you’re using a handheld controller to operate a Total Station or GPS, there are
often note spaces where you can enter valuable information.
You could also embed the rating of each high-water mark in its name – for example, LH-1-G,
where the “G” stands for “good.”
Regardless of where you record the information, you must record the rating and the type of
mark.
To save time in the field, I like to use abbreviations when I record marks and ratings.
For example, a note of “GSL” would be a “good seed line” and “GDL” would
be “good debris line.”
That way, if I’m looking at drawing my high-water mark profile through one mark versus another,
I can determine what might have been the more reliable mark.
A seed line is usually better than a debris line, right?
Without knowing the type of mark, it’s difficult to weight one mark over the other when you
have two marks with the same quality rating.
Let’s move on to talking about pictures.
Pictures are worth a thousand words, and useful pictures will help anyone who checks or reviews
the indirect measurement later.
At a minimum, you’ll want to have pictures showing an overview of the entire reach, pictures
of each cross section, and pictures upstream and downstream of any structures used in your
computation.
For your reach pictures, try to get one looking upstream and one looking downstream.
When you take your cross section pictures, try to get at least two: one looking from
one bank to the other and the second taken from within the middle of the channel looking
downstream with your rod person standing with the rod held horizontally at the water surface
elevation.
The rod person should also indicate the cross section number.
This can be done by holding a sign with the cross section number or by holding up a number
of fingers showing the cross section number so you don’t forget which cross section
was which.
Another good picture to get would be some scale examples for estimating channel roughness.
If you have a representative area of substrate, put an object like a water bottle on it and
snap a photo.
Obviously this is easier in dry parts of the channel!
If you have a structure like a culvert or bridge, take good photos of the geometry – the
entrances, the exits, maybe with a person in each for scale if you can pull it off.
Be sure to take photos of any non-standard aspects of the structures along with important
items that affect the discharge coefficient computation, such as concrete beveling.
If you are running a whole bunch of indirect measurements, it will help you to take your
photos the same way every time.
That will help you with naming each photo later.
You can also put your photo numbers and locations from where they were taken on your site sketch.
Speaking of site sketches, these are great for helping tell the overall story of your
flood.
It’s tempting to skip doing a site sketch, but these are a requirement for any indirect
measurement survey.
Even though I can’t draw and my site sketches look more like scribbles than anything else,
I’m always happy when I have a sketch to refer to, particularly with complex systems.
Draw in things like what the cross sections look like, and add the bed material, locations
and types of plants, and an estimated roughness coefficient.
For the plants, you don’t have to note that you saw 15 quercus alba, you can just say
that there were moderately dense trees with the trunks in the water.
If you have multiple channels, show each in relation to each other.
Show which way north is located, or at least show where your gage is located in relation
to the reach itself, and indicate the flow direction.
You could also take a screen capture from a program like Google Earth and add lines
for cross sections and reach locations.
However, make sure you do your electronic or hand-sketch in the field.
You can also add notes in your sketch about where your base station or Total Station was
set up, and things like the width of the road for road overflow measurements.
Sketches of the cross sections should be done as well.
Show how different roughness elements are distributed across the channel.
What other metadata do we need to record in the field?
For one – collimation tests on instruments.
If you’re running a conventional level, you can use SVMAQ to record your collimation
test.
However, if you’re running a Total Station, you might only be able to see a collimation
test on the screen of the unit itself.
Take a picture of that screen, because you might not be able to record it anywhere else.
For either a conventional level or a Total Station, you will need to record the reciprocal
leveling information.
This will include a tape-up from each hub to the instrument and the rod offset.
There are a few more things to check and record with Total Stations specifically.
First, check the prism offset in both the rod and the gun and make sure both are set
the same.
Second, check and record the air temperature and the barometric pressure.
Third, check the vertical datum of the instrument periodically throughout the day of the survey
by comparing the vertical angle through two faces of the scope.
In angle/distance mode on the gun, sight a point in direct telescope mode.
Note you aren’t actually doing a shot on the prism, just comparing angles.
Record the vertical angle in degrees, minutes, and seconds.
Now, invert the telescope by flipping the scope and rotating the instrument.
Site the same point and record the vertical angle again.
Sum the direct and inverted angles – they should add up to 360 degrees, 0 minutes, and
0 seconds.
If you note a significant difference of greater than 5 seconds, run an internal instrument
calibration.
Also important to note is the location of the indirect measurement in relation to the
gage.
Give the distance from the gage, a GPS coordinate, or even just a good description.
If you don’t run the indirect measurement at a regular gaging station, then the location
is even more important so it can be properly documented in NWIS.
You may need some other items.
For example, if you’re doing a culvert indirect, it’s a good idea to have a list of everything
you need to measure and then fill out the list like a worksheet in the field.
Always tailor your approach to the type of indirect measurement you’re surveying.
If you need help in the field, call your supervisor, surface-water specialist or indirect measurement
specialist.