Plotting High-Water Marks in the Field Using SAC-GUI

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Detailed Description

This video describes how to use SAC-GUI in the field to plot high-water mark profiles. Plotting high-water marks in the field is required for most indirect measurement techniques


Date Taken:

Length: 00:06:17

Location Taken: Las Vegas, NV, US

Video Credits

Office of Employee Development, Mark Smith, Carly Venghaus, Hartley Delvalle, Todd Geiger


Hi, this is Megan Poff and I’m the Field Office Chief at the USGS in Las Vegas, Nevada.  In this video, I’ll be discussing how to input data into a program called SAC-GUI to plot high water marks and view high-water mark profiles in the field, steps that are required for most indirect measurement techniques.  There are other programs you can use to plot high-water marks in the field, but I’ve found SAC-GUI to be the most straightforward.  I should mention as a caveat here that SAC-GUI is no longer supported and may stop working at some point, depending on the user’s operating system.  In the event that SAC-GUI does not work, analysts can use iRIC SAC, the replacement for SAC-GUI, although it’s currently not as user-friendly for field plotting. 

Before you even go to the field and survey any type of indirect measurement, make sure you have SAC-GUI on your computer.  You can download it at  We’re now in the field and have surveyed all the high-water marks.  If you surveyed the high-water marks in Cartesian coordinates, i.e. northings and eastings, all you have to do is export your data as either a tab, comma, or space-delimited ASCII file from the data collector and put the file on your computer.  I typically will export files as .csv files so I can easily edit or manipulate them using a program like Excel prior to importing to SAC-GUI.  If you surveyed the high-water marks in polar coordinates, i.e. angles and distances, you will need to convert the angles and distances into northings and eastings first.  This is discussed in the SAC conversion spreadsheet video.

SAC-GUI has some specific naming formats for all surveyed objective points and high-water marks.  I’m going to check over my file and make sure I’m following the format first.  More information on the naming formats can be found in the SAC-GUI factsheet (FS 2012-3112).  The objective points can be called BM, RM, or HUB, then a dash, then a number.  For example, we should see things like “RM-5” and “HUB-1.”  If you have other things in your file, just remove them for now. High-water marks are either LH or RH (for left or right high-water mark), a dash, a number, and an optional second dash and quality.  For example, you could have RH-3-G or just RH-3. I encourage you to include the optional quality code.

I’m now going to finish my file by removing any extra columns and column headers, and adding in a column that will serve as a sequence identifier.  Each point must have its own unique number.  Now I’ll hit save, and say yes when Excel complains about the .csv format.

Let’s crank open SAC-GUI and get started.  Click Maximize on the upper right of the screen so you don’t lose buttons later on.  We’ll use the New Indirect Wizard to get the data into the SAC-GUI.  Click File à New Indirect.  The first screen that opens up is the Project Info screen.  Because we’re just using this program to quickly plot high-water marks in the field, you get to skip filling anything out on this screen.  Hurray!  Click Next on the bottom right.

The following screen is the Survey Data Input screen.  Click Browse on the upper right to navigate to wherever you saved your file.  Once you find the file, you can either double-click it, or single click and then click Open.  The program is now asking me for a delimiter.  My file is comma-delimited, so I’ll pick that.  The data should now be arranged in columns for you.  Click the appropriate header for each column.  In my file, the first column is the sequence number, so I’ll leave that as selected.  For the next few columns, I always export my data as NEZ, meaning northing-easting-elevation.  I’ll change the column headings to reflect that.  Keep in mind that SAC-GUI defaults to show easting and then northing.  It can’t actually determine which of your columns is easting and which is northing, that is just the default display order.  If you export in NEZ like I do, make sure you have your columns set correctly.  The next column is already set to point ID, and the final column contains any remarks. Click Next on the bottom right.

We’re now at a Review/Edit Data screen.  If anything is immediately wrong with your data, SAC-GUI will highlight the field in red.  My data is fine though, so I’m going to click Next on the bottom right.

This is the Plan View Plot screen, and what we do here is define a baseline so the program knows where downstream is and where the centerline of the channel is so all the points will plot properly.  Click Add Baseline in the lower right.  I’m going to click on the screen to define my upstream and downstream baseline points, making sure I follow the shape of the flood channel and I define the baseline upstream and downstream of the extent of my data (that is, beyond any high-water marks surveyed at the upstream and downstream ends of the reach).  If the legend is in the way, you can easily right click and remove it.  You can also zoom in or out by right-clicking and choosing Zoom In or Zoom Out.  Next, tell SAC-GUI which baseline point is the downstream point by clicking in the box.  Hit Save.  You should now have a baseline with numbers appear in the Plan View Plot.  If you don’t see the baseline, or if you get an error, double-check that your baseline extends upstream and downstream of your data.  You may need to zoom out to help with this.  Once you see the baseline with numbers on it, click Next on the lower right.

Ta da!  It’s the High Water Marks Profile plot!  I can use this to easily view where to place cross sections for slope-area measurements.  The plot defaults to showing both the left and right bank high-water marks on one screen, but you can also use this plot to view and delineate left- and right-bank high-water marks separately.  This will give us more information about slope breaks in the water-surface profile and where best to place cross sections.  Cross sections should be placed at those breaks as discussed in the slope-area videos.  The SAC-GUI plotting tool is also good for other indirect methods, including contracted-opening measurements (to plot water-surface approach profiles) and culvert measurements (to plot approach profiles and evaluate ponding upstream from the culvert). 

If you are surveying a slope-area measurement, write down the high-water marks at or near the locations where you’d like to place cross sections, and save your SAC-GUI project for reference back in the office.  When you start surveying again, you can use the stake-out function on your surveying instrument to have it lead you straight to the points where you’ve decided to place your cross sections based on the high-water mark profile plot. 

If you need help in the field, call your supervisor, surface-water specialist, or indirect measurement specialist.