How USGS Streamgages Work

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Detailed Description

This video explains how streamgages are used to measure the height and flow, or speed, of streams. By monitoring the height and flow of streams, the people who manage water infrastructure can have advanced noted of when the water is rising and how fast it’s coming. This helps to prepare for flooding, mudslides, and other hazardous impacts that a lot of fast-moving water can have. NOTE: The video was created for third graders. Some of the concepts have been simplified accordingly.
 

Details

Date Taken:

Length: 00:14:59

Location Taken: Yolo County, CA, US

Video Credits

Flume tank demonstration by USGS Hydrologist Chuck Hansen.
 

Transcript

How USGS Streamgages Work – Video Transcript

 

[ON-SCREEN TEXT: HOW USGS STREAMGAGES WORK]

 

[STEVE ACKLEY SPEAKING]

 

[ON-SCREEN TEXT: STEVE ACKLEY U.S. GEOLOGICAL SURVEY (USGS)]

 

Hi, I’m Steve Ackley from the U.S. Geological Survey, also known as the USGS.

 

And this is one of our streamgages or gage houses.

 

The USGS has thousands of streamgages throughout the country.

 

More than 500 of them are right here in California.

 

This streamgage is located near Putah Creek in Northern California.

 

Steamgages are used to measure the height and flow, or speed, of streams.

 

[ON-SCREEN TEXT: WHY IS IT IMPORTANT TO MEASURE THE HEIGHT AND SPEED OF A STREAM?]

 

Can you think of reasons why that might be important?

 

Let me put it another way...

 

Here's what Putah Creek looks like a few miles downstream from here.

 

This was from February of this year, 2021.

 

Now, here's what it looked like at the same place, two years ago, after a big winter storm.

 

You can see how the water is much higher and going much faster.

 

[ON-SCREEN TEXT: WHAT DO YOU THINK THE IMPACTS MIGHT BE OF ALL THIS WATER MOVING DOWN THE CREEK?]

 

What do you think the impacts might be of all this water quickly moving down the creek?

 

Here are some clues.

 

Flooding and mudslides are a couple of hazardous impacts that a lot of fast-moving

water can have.

 

These impacts can be made even worse when several streams, with a lot of fast-moving

water, come together.

 

However, there are ways we can be prepared.

 

By monitoring the height and flow of streams, the people who manage water infrastructure

 

can have advanced notice of when the water is rising and how fast it’s coming.

 

[ON-SCREEN TEXT: WORD ALERT: “INTRASTRUCTURE”]

 

The word infrastructure refers to things like dams and floodgates

 

that can help control water, either by slowing or redirecting the amount of water flow.

 

Or, in the case of drought when there isn’t enough water, more water can be released

from lakes and reservoirs.

What I want to talk to you about today are the ways the height and speed of streams are measured.

 

Then, when we’re done, I want to give you a couple of activities, so you can see for yourself

how these methods work.

 

[ON-SCREEN TEXT: MEASUREMENTS AT THE GAGING STATION OF GAGE HOUSE]

 

First, I’d like to show you one way the gaging station or gage house

works to measure the height of a stream.

 

In this picture you can see what's called the bubble system.

 

With the bubble system, a tube is hooked up to a

pressurized tank of gas.

 

The other end of the tube is under the water.

 

And then a small amount of gas bubbles out of the

tube under the stream.

 

The amount of pressure it takes for the gas to get out of the tube

shows how much water is

pushing down from above. 

 

As the depth of the water increases, more pressure is required

to push the gas bubbles

through the tube.

 

A sensor on the tube is linked to a computer inside the gage house.

 

This pressure is calculated on the computer and the information is

communicated by a satellite antenna

on the top of the gage house.

 

[ON-SCREEN TEXT: HOW A “HYDROLOGIST” MEASURES STREAM HEIGHT]

 

Now, I’d like to show you another way a person called a hydrologist measures stream height.

 

[ON-SCREEN TEXT: WORD ALERT: “HYDROLOGIST”]

 

A hydrologist is someone who knows about water.

 

The first part of the word “hydro” means water or relating to water.

 

The second part of the word “ologist” means to have knowledge of something.

 

You may have seen “ologist” used in other words.

 

[ON-SCREEN TEXT: GEOLOGIST]

 

A geologist is someone who knows about the earth.

 

[ON-SCREEN TEXT: ASTROLOGIST]

 

An astrologist is someone who knows about the stars.

 

So, a hydrologist is someone who knows about water.

 

[ON-SCREEN TEXT: DOPPLER: ANOTHER WAY TO MEASURE STREAMS]

 

In addition to the bubble system, another way hydrologists measure both the height

and speed of water in the stream is by using sound waves

 

that are sent form a raft that is pulled across the stream.

 

[ON-SCREEN TEXT: HEIGHT AND SPEED MEASURED TOGETHER = “DISCHARGE”]

 

The height and speed measured together is called discharge.

 

Here’s a fast-motion video of one of our hydrologists pulling a raft across the stream.

 

The raft uses an acoustic doppler profiler.

 

[ON-SCREEN TEXT: WORD ALERT: DOPPLER HYDROLOGISTS USE “DOPPLER” TECHNOLOGY]

 

Doppler is a technology where sound waves bounce off of things, sort of like an echo.

 

The soundwaves then bounce back. And how quickly they bounce back tells us how

far away something is.

 

Just like the bubble system, this information is sent to a computer.

 

The amount of time it takes the soundwave to bounce off the bottom of the stream

is another way of learning how deep the water is.

 

[ON-SCREEN TEXT: “VELOCITY” = SPEED]

 

Another way doppler is used at the gage house is to measure the velocity or speed

of the water going by.

 

To measure velocity, an acoustic doppler profiler is placed under the water on the

banks of the stream.

 

The sound waves are then sent across the stream.

 

As the sound waves go through the water, they bounce off fine particles.

 

Then that information gets sent to a computer and calculations are made to show how fast

the water is moving.

 

So, we've seen how hydrologists at the gage house measure stream height using the

bubble system.

 

We’ve also seen how hydrologists use doppler technology to measure both stream height

and velocity, or speed.

 

Now, let's look at another way hydrologists measure the speed of a stream.

 

[ON-SCREEN TEXT: MEASURING VELICITY (SPEED) USING A CURENT (OR “PYGMY”) METER]

 

Pygmy meters turn in the current, the same way a windmill or pinwheel will turn in the wind.

 

The faster it turns, the quicker the water is moving.

 

To show us more detail on how a current or pygmy meter works. We’re going to go to our

warehouse and hear from one of our hydrologists.

 

[CHUCK HANSEN SPEAKING]

 

[ON-SCREEN TEXT: CHUCK HANSEN USGS HYDROLOGIST CALIFORNIA WATER SCIENCE CENTER]

 

Hi, my name is Chuck Hansen. I'm with the USGS California Water Science Center

in Sacramento, California.

 

My primary job as a hydrologist is to measure the quality and quantity of different bodies

of water in California, all over.

 

Whether that's water from under the ground, groundwater, or surface water in streams and lakes.

 

[ON-SCREEN TEXT: CURRENT OR PYGMY METER]

 

 

So, what I’m holding is called a pygmy meter or a current meter. This would go on the end

of a large staff like this.

 

It would connect down here.

 

And the hydrologist would go out to the stream and put the current meter down into the stream,

so down into the flow.

 

There are markers here so they can tell how deep the stream that they're measuring is.

 

And here on the pygmy meter there is a wheel that spins.

 

So, as current flows by the meter, the pygmy meter spins.

 

And you can see the orange indicator here.

 

So, you could go out and use a stopwatch and watch, if it’s slow enough, as the orange cone

goes past – that’s one rotation.

 

And if you count how many rotations it makes over course of a minute, you can then make

a calculation about how fast the water is moving.

 

[ON-SCREEN TEXT: THE PYGMY OR CURRENT METER IS USED TO MEASURE HOW FAST WATER IS MOVING (VELOCITY).]

 

Now, obviously, if the water is moving very quickly and you can’t count the number of times

the orange cone passes right here, we can hook up some headphones.

 

And they’ve had these for many many decades again. There’s a little battery pack here.

And the scientist would out this on their head.

 

And it actually will make a click every single time the orange cone passes the end of the

pygmy meter.

 

[ON-SCREEN TEXT: CHUCK HANSEN USGS HYDROLOGIST CALIFORNIA WATER SCIENCE CENTER]

 

So, they can count by the clicks how many times in a minute that the sensor makes a

full rotation, and then be able to calculate how fast the water is flowing through the stream.

 

Now, we have a demonstration back here. This is called a flume tank.

 

[ON-SCREEN TEXT: THE FLUME TANK REPRESENTS A REAL STREAM.]

 

We’re gonna set up a small stream with various obstacles for the water to flow past,

just like it was a real stream.

 

And we’re gonna take a measurement here with this smaller pygmy meter.

 

Different stream sizes require very small, sort of medium-sized, or we have much larger

pygmy meters for larger streams.

 

So, we’re gonna use this small pygmy meter. And we’ll be able to count the clicks and

be able to count how fast the water is moving.

 

So, here we are with our improvised stream set-up.

 

Here in the flume tank we have our small pygmy meter set up which is connected

to a battery and through a wire to this box here.

 

[ON-SCREEN TEXT: FOAM BLOCKS REPRESENT OBSTACLES LIKE LOGS, ROCKS, AND OTHER DEBRIS WHICH AFFECT FLOW VELOCITY.]

 

These obstacles represent things like logs and rocks and debris in the stream and they’re

gonna change the velocity of our flow.

 

And, if you look close down here, our small pygmy meter is slowly making its way and

making rotations.

 

This has a red marking on it that we would normally count the number of rotations that

it’s making in a minute to calculate our flow velocity.

 

If it was going so [too] fast, we could listen to it, as I mentioned, with either our

box or with our headphones.

 

You can hear the clicks coming through every time it makes its way around a full rotation.

 

And the box here is calculating how fast the water is moving.

 

In this case, just a little less than one foot per second.

 

It’s moving pretty slow through our small stream.

 

But in a larger stream it can move up to many feet, or many meters, per second.

 

So, we need to be able to get out with large meters, capture very small flows or very

large flows in different streams throughout the country.

 

[ON-SCREEN TEXT: HANDS-ON ACTIVITIES FOR YOU TO TRY]

 

[ON-SCREEN TEXT: HYDROLOGISTS MEASURE THE HEIGHT OF STEAMS BY USING THE BUBBLE SYSTEM.]

 

So, we've seen how hydrologists measure the height of streams,

 

that's the amount of water going through the stream,

 

by using the bubble system at the gage house.

 

[ON-SCREEN TEXT: BOTHE HEIGHT AND SPEED (”DISCHARGE”) ARE MEASURED BY USING ACOUSTIC DOPPLER.]

 

And we’ve seen how both height and speed are measured by using acoustic doppler.

 

[ON-SCREEN TEXT: A CURRENT OR PYGMY METER IS USED TO MEASURE THE SPEED (OR “VELOCITY”) OF STREAMS.]

 

Then we had a demonstration from one of our hydrologists, Chuck Hansen,

showing us how to measure the speed of streams by using a current

or pygmy meter.

 

Now, I’d like to give you a couple of activities that you can try on your own to reinforce

some of these concepts.

 

The first activity I'm going to do is going to demonstrate the concept behind

the bubble system.

 

And for this activity, you're going to need a bike pump that has some drip irrigation

tube attached to it.

 

And then you're going to need a garbage can.

 

And then you're going to need a garden hose.

 

So, now I've taken the tube from the bike pump and I've taped it to the bottom of

the garbage can.

 

So, if you take the bike pump and just put air through it, the needle doesn't move

because there's nothing pushing against it.

 

So, now the garbage can is filled with water.

 

So, let's see how the gage on the bike pump reacts to the full garbage can.

 

Ok, now you can see that the needle is moving. That means it's taking more pressure

for those bubbles to go through the water in the garbage can. Just like the bubble system

on the creek works.

 

Now, you might not have a bike pump or a garbage can available. But here's

something really simple you can do.

 

Just take a glass and fill it with water. Then take an ordinary straw.

 

Blow through the straw. Then take the straw and put it in the glass and blow again.

 

Your own mouth will tell you that it takes more pressure for that air to go through the water.

Just like the gage on the bike pump.

 

The next activity I have for you will reinforce the concept of a pygmy or current meter.

 

And for that, we're going to use a pinwheel and a garden hose.

 

So, what I've done is I've taken a pinwheel and I've colored one of the tips. In this case,

it's a yellow pinwheel and I've colored one of the tips black.

 

Now I'm going to hold it under a tiny trickle of water.

 

And we're going to count the rotations using the black tip. Just like they do on the

current or pygmy meter.

 

So, I hold it under the trickle of water - make sure it's stopped - hold it under the trickle of water.

 

And start counting the number of times it turns.

 

One, two three ... and you keep counting for an entire minute.

 

And then when the minute is over, you take the total number of times that the pinwheel

has turned. And you use the chart that has been provided...

 

And you can figure out how many feet per second the water is coming out of the hose.

 

[ON-SCREEN TEXT: POINTS TO REMEMBER]

 

Here are a couple of things I'd like you to remember.

 

[ON-SCREEN TEXT: MEASURING STREAM HEIGHT AND SPEED HELPS US PREPARE FOR FLOODS AND DROUGHT.]

 

First, it's important to measure stream height and speed because it helps us prepare for

major water events, like flood and drought.

 

[ON-SCREEN TEXT: MEASUREING STREAMS HELPS PEOPLE WHO MANAGE WATER “INFRASTRUCTURE” KNOW WHEN TO RELEASE OR STORE WATER.]

 

It also helps people who manage water infrastructure to know when to release or store water.

 

Second, there are different ways a person called a hydrologist measures the flow of water.

 

[ON-SCREEN TEXT: “HYDROLOGISTS” USE DIFFERENT WAYS TO MEASURE THE FLOW OF WATER.]

 

The methods we've seen used today are the bubble system, doppler, and the current

or pygmy meter.

 

I hope you've enjoyed this lesson on how streams are measured and why it's important.

 

If you're interested in knowing more, there are some links in the review sheet.

 

Thank you for spending your time with us today and learning about the water science

of the U.S. Geological Survey.