Monitoring Methods: Streamflow

In a stream, a person holds a net to measure and record the depth of the water. Another person writes on a clipboard.

Two volunteers measuring and recording the depth of the water

 

Monitoring Methods

When Do You Monitor?

Time Needed

Equipment Needed

Monitor streamflow once each month, May through October. 

 

 

 

 

 

 

 

 

 

20- 30 minutes

 

 

 

 

 

 

 

 

 

 
  • Tape measure
  • Yardstick or marked D-frame net pole
  • Surveying flags/flagging tape
  • Net (can use D-frame net to catch the float)
  • Stopwatch (or smartphone)
  • Calculator (or smartphone)
  • WAV Baseline Monitoring Datasheet Links to an external site.
  • Pen/pencil
  • Hip boots or waders
  • Stakes (to secure the tape measure)
  • Waterproof gloves (optional)

 

 

 

 

Determining Streamflow (Area v Velocity = Flow)

The method you are going to use in determining streamflow is known as a velocity-area approach.  The task is to find out the volume of water in a 20-ft. section of stream by determining both the stream’s velocity and the area of the stream section.  You will first measure the width of the stream, and then measure water depth at a number of locations across the width to find the average depth at your monitoring site.  Then by multiplying the average depth by the width, you can determine the average cross-sectional area (ft2) of the stream.  Water velocity (ft/sec) is determined simply by measuring the number of seconds it takes a float to travel along the 20' stream length.  Since water velocity varies at different depths, (surface water moves more quickly than subsurface water because water moving against rough bottom surfaces is slowed down by friction) you will need to multiply velocity by a correction factor to adjust your measurement to account for the effect of friction.  The actual equation used to determine flow is this:

Flow = Area x Corrected Velocity

 

Measuring and Calculating Streamflow

Here is a brief synopsis of the process.  The detailed step by step process is on the fact sheet "Streamflow: Flow Speaks Volumes". Links to an external site.

    1. Measure 20' along the length of your chosen stream segment and mark the up and downstream ends of the section.
    2. Measure stream width at the midway point of the 20' length.
    3. Measure the water depth at one-foot intervals across the stream width.
    4. Track the time it takes a floating tennis ball to move the marked 20' length a total of four times at different locations across the stream.
    5. Determine the correction factor based on the stream bottom.

 

DNR SWIMS

The DNR SWIMS online database will calculate stream flow for you when you enter your measurements and findings into the system.

lined paper If you want to learn how to do the actual calculation by hand so you can determine the streamflow while you're in the field, you can use our WAV Streamflow Worksheet Links to an external site..

 

Video Demonstration

Watch this video to learn WAV's monitoring streamflow method.