### Onesquethaw Creek Stations 1 through 6

Strata (geology)

Superposition (Principle of)

Station #1: Gradient vs. Velocity

Elevation: 200.6  meters       Latitude: 42o34’29” N       Longitude: 73o57’50” W

Background Information:

Factors Affecting Transportation of Sediments
Running water is the primary agent of erosion on Earth. Most running water is found in streams and rivers. There are many factors that affect the movement of sediments in a stream.

Gradient (slope), discharge, and channel shape influence a stream’s velocity. Sediments carried by a stream become rounded due to the grinding action of the water on the rocks, a process called abrasion.

The average velocity (speed) of a stream depends on its slope and discharge, which in turn help to explain the carrying power of a stream. As the velocity of the stream water increases, the size of the particles carried in the stream also increases, a direct relationship.

Streams carry materials in 4 distinct ways:

1.      Floatation - floating of particles less dense than water

2.      Solution - dissolved particles

3.      Suspension - tiny particles can travel within the water without touching the stream bed

4.      Bed Load - bouncing (saltation) and dragging (traction) of sediments along the stream bed

## View the following:

Powerpoint of jake stick Use (only works in IE)

Video of Eye Level

Station 1 Photos from the Field Trip (only works in IE)

## Activities

1) In this activity students measure the velocity and gradient of the stream at two different locations. Location A is the upstream location.  The table on the next page must be completed in its entirety using the steps in this process and the data given.

Each student is assigned to either the Location A team or the Location B team.

You are assigned to the Location A team.

(a) Determine the gradient of the stream for location A – Students will determine the gradient using jake sticks, sight levels, and a tape measure.

1.  Using the tape measure the students assigned to Location A determine the horizontal distance between the two canisters representing the start and finish points to be 25.8 meters.  Enter this data in the table below in the appropriate space.

2.  The student with the sight level determines their eye height to be 155 cm for the Location A team.  Enter this data as the starting elevations in the appropriate space.

3. The student with the sight level stands at the starting point while the student with the jake stick stands at the finish point.  The person with the sight level determines the new jake stick reading to be 209 cm.  Enter this data as the finish elevation in the table.

4. Complete the calculation for change in elevation and stream gradient (use the formula found on the front cover of the Earth Science Reference Tables) and enter them into the table.  The first four columns of line one in the table should now be complete.

5.  Since only one reading for the gradient is taken, no average needs to be calculated. Therefore, enter the same data for columns 1-4 on line 4 of the table as well.

b) Determine the velocity of the stream for location A – Students will determine the velocity of the stream using ping pong balls, a timer, and a net.    The same distance will be used as determined for the gradient.

1.  The velocity of the stream is determined over the same distance as for the gradient.  Convert the distance measured (25.8 meters) to centimeters and enter that data in the table on lines 1-4 since it remains the same for all three trials.

2.   A student drops a ping pong ball (or orange) into the fastest moving part of the stream at the starting point.  A student simultaneously starts the timer.

3.  When the ping pong ball (or orange) reaches the finish point the timer is stopped and the ping pong ball is caught in a net.

4.  This process is repeated with two more ping pong balls.

5.  The times are as follows:  Trial 1 =  23.90 seconds

Trial 2 =  25.32 seconds

Trial 3 =  26.25 seconds

Enter this data as the travel times on lines 1-3 of the table.

6.      Determine the stream velocity for each of the three trials using the rate of change formula found on the front cover of the Earth Science Reference Tables.

7.      Complete line four of the table by finding the average values for trials 1-3.

c)  Complete the table for Location B using the data provided.

 elev. start (cm) elev. finish (cm) change in elev (cm) distance (horiz.) (m) stream gradient (cm/m) travel time (sec) distance (horiz.) in cm. !! stream velocity (cm/sec) location A / 1 location A / 2 XXXX XXXX XXXX XXXX XXXX location A / 3 XXXX XXXX XXXX XXXX XXXX location A  (average) location B / 1 160 275 30.24 13.90 location B / 2 XXXX XXXX XXXX XXXX XXXX 11.55 location B / 3 XXXX XXXX XXXX XXXX XXXX 12.35 location B  (average)

2) (a) Using the data from your chart on the previous page, and the Earth Science Reference Table page 6 “Relationship of Transported Particle Size to Water Velocity” graph, determine the size of the sediment the stream could carry at locations A and B.  Record both sizes below:

Size of particle that should be carried in location A: _________ cm

Size of particle that should be carried in location B: _________ cm

Draw to scale a sediment with the maximum size that could be transported at Location A and Location B in the space below

 Location A Location B

(b) Using a ruler the students found pieces of sediment of the approximate sizes that the chart showed could be transported.  They took the sediment samples to the stream, dropped them in one at a time and observed what happened.

Here are their results:

Location A: Of two particles, one particle failed to move, the other bounced downstream along the bottom.

Location B:  Of two particles, one particle failed to move, the other rolled downstream along the bottom.

## Questions - Station #1

1) (a) How did the velocity of the stream at Location A compare to Location B?

(b) The stream discharge at both locations is the same.  In light of this, explain the difference in the velocities below.

2) (a) How did the size of the sediment that could be carried by the stream at location A compare to location B?

(b) Explain the difference in the size of sediment that can be transported.

3) (a) Did all the sediments dropped in the stream keep moving?

(b) Assuming that the student calculations and measurements were correct, what factors might account for sediments that were not carried?          (Hint: Carefully examine ESRT page 6)

(c) By what method did sediments of the maximize size that were transported at Locations A and B move?

Location A:

Location B:

4) State the relationship that exists between:

a) gradient and velocity:

b) velocity and particle size carried by stream: