Stream flow measurement lab preparation

The first lab activity is to go into the field and get some practice collecting data using the velocity-area and dilution gauging techniques. Please study the following videos so you already understand the basics and can start practicing with the equipment as quickly as possible. While I recognize it is not possible to completely learn how to use these instruments from these videos, studying them will save time in that you will know what you are looking for when you actually get a chance to put your hands on the equipment.

A top-setting wading rod is a deceptively sophisticated (and expensive) piece of equipment. The ability to use its slide-rule like function takes time to learn, but it allows you to quickly put the velocity sensor at 4/10 depth from the bed without removing it from the water and saves an experienced team hours in the field. Let's start with an introduction to the wading rod (2:32 min).

The side of the wading rod on which you measure depth does not have numbers on the tick marks. I suspect this is by design because the numbers are hard to see near the water line, anyway. Understanding how to read the tick marks and knowing how to read backward from higher values that are above the water line are the keys to efficient use of a top-setting wading rod (2:54 min).

Once you know the depth of the water, you are going to want a quick way to set the velocity sensor at the 4/10 depth from the bed. Preferably, you would prefer to be able to do this without removing the rod from the water or being able to see what is going on below the water surface. The reason a wading rod is called "top-setting" is because it has a slide-rule like feature that lets you set this depth from the top of the rod (i.e., the part of the rod easiest to get at when you are out standing in a stream). Study this video to understand how this feature works. (3:30 min).

Wading rods with imperial units work on the same principle, but the spacing looks a little different. Here is a review of the differences in using a wading rod based on imperial units (2:42 min).

With those skills in hand, here is the step-by-step process for the velocity-area gauging method (5:27 min).

Here is an example of students trying their first velocity-area gauging transect. You might be able to pull data off this video if you want to figure out the discharge they measured using the spreadsheets described below. If you don't want practice data, there is probably not much point in watching this whole video, but you might want to watch it through the first couple velocity measurements. I wouldn't consider this an example of all the best practices in this technique, but we all have to start somewhere and perfect technique requires many more hours of training and practice (11:48 min).

The flow meter used in these videos is a Marsh McBirney "Flo-Mate 2000". There are only a few buttons on the device, so configuring it can be a little cryptic. Here are the details on configuring this type of flow meter (4:19 min).

We will also be performing a dilution gauging tracer experiment as part of the field exercise. Please be familiar with the dilution gauging protocol.

Click this link to download the postscript PDF document 

Once you have the field data from velocity-area or dilution gauging methods, you need some computer skills to calculate a discharge estimate from those data in a reasonable amount of time. 

Make sure you go to the course management website, download the materials for the associated homework assignment, and get started on the homework. If you get started on the homework before lab and come to lab with questions for the instructor and ready to work with your peers, you will likely be able to finish most of the homework associated with this lab activity during the lab session. This is by far the most time-efficient strategy for completing the homework assignments, and probably the best strategy for maximizing the amount you learn and retain from each laboratory activity.

If you want to follow along with the following exercise, you might want to use the homework assignment template or download the Microsoft Excel template for velocity-area gauging.

Link to download MS Excel template for velocity-area gauging 

Here is a detailed review of how to build a Microsoft Excel spreadsheet for velocity-area gauging calculations (13:50 min).

If you want to follow along with the following exercise, you might want to use the homework assignment template or download the Microsoft Excel template for dilution gauging.

Link to download MS Excel template for dilution gauging 

Before processing dilution gauging data, you will want to trim the data down to only the part of the breakthrough curve when the tracer is meaningfully influencing the solute concentrations in the stream. Because the background can shift, including a lot of data that is different from background that is not caused by the tracer will cause inaccuracy in the flow estimate. Creating a plot of the breakthrough curve to visually assess when you are back to background concentrations is helpful toward decisions about trimming the data (14:56 min).

And here is a detailed review of how to build a Microsoft Excel spreadsheet for dilution gauging calculations (20:33 min).