Hydrology Field Methods

Open Channel Flow Measurements

Flow in a channel requires the measurement of the flow velocity across the channel.

• We commonly select a section of channel that is straight, with few obstructions, and with uniform depth and velocity.

• We then subdivide the channel into at least ten subsections, measuring the width, average depth, and average velocity of each subsection.

• The velocity is determined using a flow meter, such as the:
  • Gurly-Type flowmeter
  • SonTek flowmeter

• The estimated discharge (flow, in cfs) in each subsection is the product of the width (feet) times the average depth (feet) times the average velocity (feet per second).
  • Q = W L v

For additional information:

• Washington State Department of Ecology
• Methods of determining flow in open channels.
• USGS Website
• Streamflow Gaging
• Methods of Conducting and Evaluating Measurements of River Flows, Inflows, and Tributary Flows

Assignment:

1. Purchase a bound laboratory notebook.
2. Put your name on the inside front cover, along with your phone number and email address.
3. Leave the first three pages blank for now. These will be your table of contents.
4. Every page should be numbered (either front or back, or just the front) in the upper corner.
5. Use a different numbered page for each day of class.
6. Put the day and date of the class on the top of each page.
7. I suggest that you leave the back of each page blank, so that you can tape or stable inserts on it.
8. On the back of one of the pages, tape or staple the attached class list (phone numbers and email).
9. Working in teams of three, develop a simple guidance document explaining how to measure flow in a stream.