WATER QUALITY: HYDROLOGY
1. Turbidity Tube Test
Turbidity means how clear or cloudy the water may be. Dirty water blocks
sunlight that plants need for photosynthesis and makes it hard for animals
and plants to “breathe” the oxygen present in the water.
Fill the plastic tube all the way with water from the stream. While looking
through the top of the tube, allow water to leave the tube by opening the
small plastic tube at the bottom. Record the level at which the black and
white disc at the bottom of the tube becomes visible. Use the numbers on
the white tape on the outside of the plastic tube for your results.
2. Stream Flow
Hydrologists calculate flow on rivers and streams to understand how much water
is available for human consumption, agriculture, livestock, industry, and for
wildlife habitat. The amount or volume of water that flows through the
stream is also important to the water quality of the stream. Higher stream
flows have higher oxygen levels, dilute unwanted or dangerous chemicals,
and clean the stream bottom and vegetation of unwanted silt. Traditionally,
stream flow is calculated as the unit "cfs" (cubic feet per second).
Stream Flow: Velocity
You will need a partner for this test. Measure off 100 feet in distance
along the stream bank. This may already be marked for use with flags by
your station leader. Have your partner stand at the downstream flag with a
stopwatch. Have one student at the upstream flag toss a ping pong ball into
the middle of the stream and shout “go!” The downstream student will
start the stopwatch at this point and stop the stopwatch when the ball
passes by their position. Record this time in seconds on your data sheet and
calculate the stream flow rate.
Stream Flow: Estimated Area
Width: Choose a cross-section halfway between the two markers. Two students
measure the width of the creek. The measuring can be done with a tape measure.
Have the recorder write down the measurement in feet on the worksheet.
Depth: Use the yardsticks to measure the depth of your stream at three
places. This should be measured near the middle and both sides of the
stream bed. Record the measurements in inches. Add these three numbers
and divide by 3 to find the average depth in inches. The recorder will write
down the measurements. {The worksheet has a work area, which will allow
students to convert the measurements to feet and calculate the average depth.}
Area: Multiply the width times average depth to get an estimated cross-section
area.
Calculate Flow:
Multiply the velocity by the area to find the flow in cubic feet per second (cfs).
BANK FULL
Identify the highest point on the bank where you are standing. Send one
student (make sure there is an adult on the other bank) to the other side
of the river to identify the highest point on that bank. Measure the
distance between these two points. Estimate the height of the water from
the streambed to the tape measure.
Calculate the area using the formula on your data sheet
Questions: Reflect on these questions as time allows.
Based on what you know about the flow of the water today, what
affect would this amount of water flow have on the stream and
surrounding area?
At what season of the year would you expect the highest stream flow?
Why?
Have you ever noticed flooding in downtown Harrisonburg?
Is there a flood plain for Blacks Run as it moves through the city?
What is the surface on either side of Blacks Run?
How are floods important to the health of a riparian buffer?