Northern Shenandoah Valley Watershed Investigation
Hydrogeology Experiment on Surface-Groundwater Interactions: How Do Our Actions Affect Water Quantity and Quality? Teacher Virginia Science SOLs: 6.1, 6.7, 6.9
Prepared for the Southwest Texas Educators Workshop Spring 2007. Developed by Jessica Gordon, Graduate Research Assistant, Jackson School of Geosciences Outreach Programs, The University of Texas at Austin. Modified by Blandy Experimental Farm Education Staff 2/2011
Learning Objective: Students will learn how different surfaces influence water runoff and groundwater recharge and how pollution travels through creeks, streams, and aquifers.
Key Concepts & Skills: Different surfaces affect the movement of water in various ways. Students will make observations and predictions about surface runoff and groundwater. Students will collect, record, and analyze data.
Investigative Question: What impacts do different surfaces have on surface water runoff, groundwater recharge, and stream pollution?
Materials Vocabulary Hydrogeology models Runoff Beakers Aquifer Watering cans Recharge Water Groundwater Buckets Stormwater Calculators Watershed Graduated cylinders Impervious surface Stopwatches Pervious surface Student Worksheets Permeable
Background Information: Water is an essential resource for all living things. Half of the drinking water in the United States comes from groundwater sources, water stored underground in cracks and spaces in soil and rocks. Groundwater needs to be restored to provide freshwater and this occurs through precipitation. Ideally, most precipitation would go into recharging (i.e. replenishing or restoring) the groundwater supply and to plant up-take. However, runoff occurs when precipitation cannot infiltrate the soil. This occurs when there is a lot of precipitation but also happens today due to anthropogenic (human) causes such as impervious (impenetrable) surfaces. When there is an excess of precipitation, much of the water runs off land and becomes stormwater. Stormwater runoff is generated when precipitation from rain and snowmelt events flows over land or impervious surfaces and does not seep into the ground. An aquifer is a geologic formation made of a layer of permeable rock (fluids can pass through) that has large pockets of water. Water can enter an aquifer through faults,
PreK-12 Programs at Blandy Experimental Farm and 1 The State Arboretum of Virginia www.virginia.edu/blandy Northern Shenandoah Valley Watershed Investigation fractures, sinkholes, or seep through the soil in a process called recharge. How we live on our watershed (the area of land that drains into a body of water) can impact water quantity and quality. It is important to maintain the quantity and quality of groundwater in order to be able to continue to use this resource.
Post-experiment question ideas: 1. Which surface had the most run-off? Why do you think this happened? 2. What does impervious mean? 3. What commonly sits on concrete? [cars] Do you ever see any liquid leaking from a parked car? [oil] Where will this oil eventually go? 4. Which surface had the most water recharge? [bare soil] 5. What did the water look like? [dirty] What’s in the water? [dirt] 6. What do we call that process when soil funs off with water? [erosion] 7. Did the recharge water from the plant surfaces look different from the bare soil surface? [yes; little or no soil] Why do you think this happened? [roots keep the soil from eroding] 8. Lots more potential questions to ask your students!
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9. Hydrogeology Experiment: Use the hydrogeology models to determine how surface type affects runoff and groundwater recharge. Then, design an experiment that produces the least amount of runoff and the greatest amount of recharge.
Hydrogeology Model: The Effect of Groundcover on Surface Runoff and Groundwater Recharge
For this investigation, hydrogeology models have been built to demonstrate how impervious and pervious surfaces (concrete, soil, non-native grass, and native plants) influence surface runoff and groundwater recharge. Discuss the features of the different surfaces.
Type of Surface Examples of this type of surface Concrete Sidewalks, parking lots, roads, roofs Bare soil at construction sites, disturbed areas of Soil land in a lawn, dirt roads, livestock loafing areas Grass Lawns, fields Native Plants Woods, native plant gardens, native wetlands.
Use the table below to predict how water will move through the different surfaces.
Check the appropriate box. Concrete Soil Grass Native Plants Which surface will have the x most water runoff? The least water runoff? x Which surface will have the x most water recharge? The least water recharge? x
Based on your predictions above, write a hypothesis. Hypothesis: ______
______
______
Independent variable (what you will be changing): ___Type of Surface Dependent variables (what will respond to the change): ___Amount of Water in surface runoff and groundwater recharge______
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Controlled or constant variables (what must remain the same/be held constant): ______speed of rainfall, amount of water______
Directions Student A-Fill the beaker with 1000 mL of water. Student B- Beginning with the cement model, pour the water slowly and evenly over the surface. Student C -Transfer the runoff and recharge water from the large buckets into two beakers. Student D- Record runoff and recharge on the data sheet. Rotating students, repeat the above with the other three models. Fill in the table below as you conduct the experiment.
Table 1 (Example data) Measurements are in milliliters (mL). Concrete Soil Grass Native Plants Runoff Recharge Runoff Recharge Runoff Recharge Runoff Recharge Trial 1 1000 0 550 150 118 800 10 900
Trial 2 910 62 700 215 150 850 0 950
Trial 3 950 40 750 155 300 650 22 950
Total 2860 102 2000 520 568 2300 32 2800 Average 953 34 666 173 189 767 11 933 (Mean)
Calculate the average percent of runoff and recharge for each groundcover. Table 2 (Example data) Type of % Runoff % Recharge Surface (average runoff)/(1,000 mL)*(100) (average recharge)/(1,000 mL)*(100) Concrete 95% 3% Soil 66% 17% Grass 22% 76% Native Plants 1% 93%
Discussion
1. What is the importance of doing multiple trials?
Only doing one trial leaves doubt as to whether the experiment was conducted correctly. Replication, multiple trials increases the validity of the data.
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2. Do you think that conducting three trials was enough or should more trials be conducted? Why?
Answers may vary. In general, more replication gives more data. With more data, outliers (unexpected data) do not skew or distort the data as much.
3. How could you design a system that would decrease or reduce the amount of runoff from an impervious surface?
Multiple ways to do this. Plant roots stabilize soil, so more plants equals less soil erosion and more water going into recharge the groundwater! Designing a system to lower or reduce the amount of runoff could be an extension activity.
Conclusions (restate the research question, provide important data from your chart as supporting evidence for what you learned, and state any problems that you encountered). Be prepared to present your findings.
Answers will vary.
Table 3 (Example data) Surface Type of Pollution Potential surface locations? Heat, sediment, oils, any Sidewalks, parking lots, runoff rooftops, dumping oil down Concrete storm drain Sediment, fertilizers Construction areas, bare soil Soil areas Grass Fertilizers Home lawns, agricultural areas Fertilizers, if used Meadows, woods, wetland Native Plants areas, gardens
1. We have examined how surface type influences surface water runoff and groundwater recharge, but how do our actions affect water quality? What are some potential sources of pollution you have identified for each type of surface?
Answers will vary.
2. How has this activity changed the way you think about surface runoff, groundwater recharge, and how decisions you make can influence water quantity and quality?
Answers will vary.
3. What is the most interesting thing that you learned? Did anything surprise you?
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Answers will vary.
4. What are the benefits and limitations of this model? What would you change to make the model better?
Prompts for discussion: How are the models different from real life? Actual rainfall varies in amount of water falling in a particular event. Flood conditions versus a slow steady soaking rain for example. Precipitation varies; it is not as simple as the water coming out of the water container in this experiment. The experiment is a simulation. Is this the same as collecting actual data from four areas? Why is this model useful? (Can’t go into the groundwater recharge in real life and measure it.) Recharge is not immediate.
5. What can you do to help keep our creeks, rivers, and aquifers clean?
Plant gardens, encourage community to plant plants instead of leaving bare ground. Proper disposal of waste, use less fertilizers, use organic fertilizers, or use fertilizers properly.
Extension Activity for the classroom: a. Look at aerial photographs of your town. Identify the amount of different types of groundcover, potential sources of pollution, and what kind of impact each type of groundcover has on the water cycle. How has this changed overtime? b. Design a hydrogeology system that reduces runoff (see Discussion #3)
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