Objective

Calculate the flow of Medano Creek above.

1. Press pause to stop Medano Creek.
2. Calculate the flow at that moment.
3. Enter the flow into the cfs field.

Calculating Flow

The diagram above has four parts, based on data from a gauging site on Medano Creek where scientists have monitored the creek's flow since the early 1990s. An estimated monthly flow for this gauging site is continually being charted in the animation above.

• Top-left: This cross-section of the creek bed contains vertical lines every two feet. To estimate the area, record the depth measurement at each line that intersects water.
• Top-right: The vertical profile provides a velocity meter.
• Middle: The wide-angle view of the dunes shows the creek in its yearly progression. Notice that the sand below the creek bed must be saturated with water before the creek can proceed downstream (left). Hydrologists call this upper-level aquifer a perched aquifer. It is perched because it sits atop a non-porous layer of earth.
• Bottom-left: This monthly chart provides a continuous view of the estimated yearly flow from the gauging site.

To begin measuring, press Pause to stop the animation. Your task is to calculate the creek's flow at a given moment with the data available. If you are correct within 10 percent of the actual calculation, you will receive a clue.

The basic equation for calculating flow is:

flow (cfs or ft³/s ) = area (ft²) x velocity (ft/s)

Step 1: Calculate the Area (ft²) of the Creek Bed Cross-section

To calculate the area of a complex shape like a creek bed cross-section with the best accuracy, scientists use calculus. For this activity a simpler method will be used. To determining the area of a simple shape such as a square, length is multiplied times width (in this case depth times width). The first step in this activity is to determine the average depth of the creek.

• Refer to the cross-section and add up all the depths for each marker that is covered by water.
• Next divide by the total number of these markers.
• Then multiply this average depth times the width of the creek (you will need to estimate this measurement using the feet markers under the cross-section).

This final number is the area of the creek cross-section.

Step 2: Record Velocity (feet per second)

Since water at the edges of a creek flows more slowly than water at the center of a creek (due to friction with the banks), researchers usually measure velocity at multiple locations to determine the average velocity. In this activity, the average velocity of the creek is provided in the upper-right corner.

Step 3: Calculate Flow = Area (ft²) x Velocity (feet per second)

Multiply area from Step 1 times velocity from Step 2. This is Medano Creek's flow (cubic feet per second, cfs) for the moment when you pressed pause. The flow level tells hydrologists how much water is passing the gauging site at a given moment in time.

Step 4: Check Your Answer

Enter your answer in the box provided and press Check. If correct, you will gain a clue. If not, please try again and check your figures!

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