Understanding Larry's Creek Watershed and Turbidity
First, you'll need some background information about Larry's Creek. Read the Larry's Creek Watershed Profile Fact Sheet (Acrobat (PDF) 1.3MB Mar25 16) from the Susquehanna River Basin Commission, and then answer the questions:
- How large is the Larry's Creek watershed?
- In what county is it located?
- Describe the land use in the watershed?
- Based on the land use in the watershed, would you expect the stream's water to be normally clear or muddy? Why?
- What percentage of Larry's Creek is considered to be impaired? What is the source of impairment?
- Where is the water monitoring station located on Larry's Creek?
- Where does the water in Larry's Creek go?
- How many gas well pads are located in the watershed?
- Is any water permitted to be extracted or discharged into the creek from natural gas development?
Ask the question: What is turbidity and how is it measured? Provide the explanations below.
- Turbidity is the measure of the relative clarity of water. Turbid water is cloudy or opaque because fine particles in the water scatter the light.
- Materials that make water turbid include clay, silt, organic matter, algae, or plankton. Sediments can wash into rivers during rainstorms causing turbidity. High water velocity water also stirs up sediments and makes the water cloudy.
- One way to measure turbidity is to shine a light through the water. Turbidity meters have sensors that "read" how much light is reflected back.
- Turbidity is reported in nephelometric turbidity units (NTUs).
Ask the question: Is there a relationship between turbidity and precipitation? Have the Students study the graph below. This graph shows precipitation and turbidity data recorded at Larry's Creek earlier in 2011.
Follow up with questions about the graph:
- This is a time series graph. Time is the variable on the x-axis. What is the time range for this graph?
- This graph has two y-axes, one for turbidity and one for precipitation. Why is it necessary to have two y-axes?
- What is the unit for turbidity? What is the unit for precipitation?
- Do you notice the gaps in measurements? Why might this be?
- What is the highest measurement of turbidity shown on this graph? For precipitation?
- Do you see a relationship between precipitation and turbidity? Describe this relationship.
- With your pencil, sketch a line that connects the lowest turbidity measurements between precipitation events.
- Between precipitation events, what is the general measurement of turbidity in Larry's Creek?