Hydrogeology Models: The Effect of Ground Surface Type on Surface Runoff and Groundwater Recharge: Teacher s Version Virginia Science SOL: 6.1, 6.5, 6.7, 6.9 Virginia Mathematics SOL: 6.2 (could extend to 6.1, 6.3, 6.9, 6.14, 6.15, 6.16) Investigative Question: How do different ground surfaces impact surface water runoff, groundwater recharge, stream pollution, and erosion? Learning Objectives: Students learn how different ground surfaces influence water runoff and groundwater recharge, pollution and erosion. Key Concepts & Skills: Different ground surfaces affect the movement of water in various ways. Students make observations, predictions, and hypotheses about surface runoff and groundwater recharge on each of the surface models. Students identify experimental variables to collect, record, and analyze data of the models. Materials Hydrogeology models (1 set/group) Beakers (100ml, 2/group + 1 for each bucket) Watering cans (1/group) Water Buckets (5 gallon; 1/group) Calculators (1/group) Graduated cylinders (100ml, 1/group) Student Investigation Datasheets Vocabulary Aquifer Groundwater Impervious surface Infiltrate Permeable Pervious surface Recharge Runoff Watershed Background Information: Hydrogeology is the study of water as it moves in and through the soil and rocks. 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. As groundwater is used it needs to be replenished to continue to provide freshwater for our use. The source for more groundwater is precipitation. Ideally, most precipitation would go into recharging (i.e. replenishing or restoring) the groundwater supply and for plant up-take via their roots. Runoff occurs when precipitation cannot infiltrate (pass down through) the soil. This occurs when there is a lot of precipitation but it also happens due to anthropogenic (human) changes to the ground surface, such as creating non-porous (impervious) surfaces. When there is a large amount of precipitation, much of the water runs off these non-porous surfaces and becomes surface runoff. Surface runoff occurs when precipitation from rain and snowmelt flows over the land or non-porous surfaces (impervious) and does not seep into the ground. Porous surfaces, especially those that have large amounts of grass and plants, promote groundwater recharge and reduce the amount of erosion caused by heavy storm-water events mainly because the leaf and root surfaces slow down the movement of the water. Native plants (plants that occur naturally in a particular region without direct
or indirect human intervention) are particularly desirable ground surfaces because these plants are adapted to the soil and precipitation conditions typical to a region. Groundwater is stored in an aquifer, a geologic formation made of a layer of porous rock (fluids can pass through) that has large pockets of water. Water can enter an aquifer through faults, fractures, sinkholes, or it can seep through the soil in a process called recharge. How we manage 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. Hydrogeology Investigation The Models There are four hydrogeology models each with a different ground surface: concrete (mix and pour your own), bare soil (use your local top soil; do not use potting soil as it erodes too quickly and will clog your models), grass (either dig some up or ask a nursery to donate a scrap), and native plants. (We use Caltha palustris which we purchase by the flat from North Creek Nurseries in Pennsylvania; this plant is rugged and can withstand multiple applications of water from students.) For instructions to build the models, refer to the article published in the NSTA journal, Science Scope: How do our actions affect water quality? By Jessica Gorden, February 2008 Pre-experiment inquiry question suggestions: [potential answers in italics] 1. What do you think hydrogeology means? [hydro=water; geology = study of rocks & earth processes, etc] 2. Does anyone have a well at their house? Where does the water in your well come from? 3. What is groundwater? 4. How does water get into the ground? 5. What is runoff? 6. When there is a lot of rain, where does runoff go? [into sewers, onto the ground, onto the road, into rivers, etc] 7. Do you think the runoff is clean enough to drink? Why or why not?
Procedure 1. For experiment- Students should be in groups of 5 per model in order for all roles to be filled. Groups of less than 5 will need students to perform multiple roles 2. Inform students that they will be conducting an experiment to see how water moves over different surfaces and how this impacts surface runoff, ground water recharge, pollution and erosion. Students will use the scientific process to guide their experiment. The question or problem to be considered for this investigation: How do different ground surfaces affect ground water runoff and recharge? 3. Have students look around or think about different surfaces at the school. What do they see? Think about surfaces in cities, parks, agricultural fields. (They can write answers on their investigation document or you could make a table and fill it in with the entire class. See example below.) Type of Surface Examples of this type of surface (where each might be found) Concrete (or other Sidewalks, parking lots, roads, roofs, basketball courts, non-porous surface) Soil Grass playgrounds Bare soil at construction sites, disturbed areas of land in a lawn, dirt roads, livestock areas, newly plowed agriculture fields Lawns, livestock fields, sports areas Native Plants Woods, native plant gardens, native wetlands 4. Inform students that they will use the models to explore how different surfaces affect where water goes when it rains. 5. Ask students: What is a model? Why are they important? Why would you want to use a model when designing a building? 6. Where does the water go when it rains? Referring back to the model there are two pipes located in the model to help show where the water flows when it rains. Water that flows out of the top pipe will run along the surface to join rivers and streams is called surface runoff. Water that flows out of the bottom pipe will help refill ground water (called recharge). 7. Tell students to make predictions as to what will happen when water flows over each surface. Table 1. Predict what you think will happen. Check one box for each question. Which surface will have the Concrete Soil Grass Native Plants most water runoff? the least water runoff? the most water recharge? the least water recharge? x x Have students formulate a hypothesis based off of their prior knowledge of precipitation and these surfaces: There are several possible hypotheses. Example: I believe the soil model will have the most recharge because soil has lots of space for water to move through and there aren t any plants that will soak up some of the water. x x
8. It is now time to EXPLORE! Have students practice pouring water over each surface to see what happens when it rains. We advise using 500 ml of water on each of the models. This will allow students to get an idea of how water flows. Students should record their findings on their data sheet (an example is below). No measurements are needed for the exploration. Use the models to explore what happens when rain falls on the different types of surfaces found around Blandy Experimental Farm. Use words or pictures to show what you have observed below. Grass: More recharge and less runoff. Less water emptied than we put in. Soil: Plants: Concrete: 9. Now that the students have explored using the models, inquire with students: How can you accurately test these models? What do we want to learn from this experiment? 10. Have students think about how to set up an experiment. What are the steps in a Scientific Experiment? Think of what you have already learned about experimental design- what are your variables? What things should you keep constant? What data should you collect to determine the model that creates the most recharge and the least runoff? What tools do you have available to collect your evidence? 11. Have students identify the variables in their experiment. a. Independent Variable (what you will be changing): Type of Ground Surface b. Dependent Variable: (what will respond to the change): (1) Amount of water in surface runoff and (2) amount of water in groundwater recharge; (3) cleanliness of the runoff & recharge water c. Constants: (what must remain the same/be held constant): (1) Speed of rainfall (water poured), (2) amount of water poured, (3) all poured water must be clean (fresh water used for each trial) 12. Ask students to read the roles of the team members BEFORE beginning the trials. Students can change tasks for each trial so that everyone has a chance to pour the water on the models. Student 1. Measurer- Fill the graduated cylinder with 1000 ml of water & pour the water into the watering can. Student 2. Rain-maker- Beginning with the concrete model, pour the water slowly and evenly over the surface. Student 3. Water Collector 1- Collect the runoff water flowing from the model using one of the beakers. Student 4. Water Collector 2- Collect the recharge water flowing from the model using one of the beakers.
Student 5. Recorder- Record the amount of runoff and recharge water in Table 2 & also describe the the water looks like (ex. cloudy, dirty, clear, etc.). *Change tasks and repeat the procedure with the other three models. Do as many trials as time permits. 13. Students will record the ml of runoff and recharge for each ground surface in the table. Have students describe the water color and dirtiness after each trial. How can you organize your data? Should you test your system multiple times? Starting Amount of Water: 1,000mL Trial 1 Surface: Concrete Surface: Bare Soil Surface: Grass: Surface : Native Plants Total Recharge Groundwater Recharge Water Color/Can you see through it? Water Dirtiness (particles in the water?) Trial 1 Surface: Surface: Surface: Surface : Total Runoff Surface Runoff Water Color/Can you see through it? Water Dirtiness (particles in the water?) Analysis: 14. Students will analyze their data and calculate average percentage of runoff and recharge for each model. Below are the questions students will answer. a. How much water was runoff? b. How much of the water remains in the model? Why does water remain in the model? c. How much of the water is recharge?
Display these numbers as a ratio, decimal, and percent of the total water added. Table 3. Calculate the average percent of runoff and recharge for each ground surface. (Example data) EXAMPLE: Average runoff was 150 ml. 150 ml/1000 ml x 100% = 15% Type of Surface average runoff (ml) % Runoff = X 100% l000 ml average recharge (ml) % Recharge = X 100% 1000Ml Concrete 95% 3% Soil 66% 17% Grass 22% 76% Native Plants 1% 93% 15. Using their supporting evidence above, students will write a scientific report to conclude their experiment. Conclusions (scientific report; provide guidelines for your students) Restate the research question (what were you investigating?) Provide important data (including descriptions) from your tables as supporting evidence for what you learned State any problems that you encountered Suggest improvements for this investigation Suggest further investigations you could do using the models Be prepared to present your findings to the class *Discussion questions below to help with supporting details Discussion Questions; Teacher Led 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. 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 a non-porous 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. 4. What is the most interesting thing that you learned? Did anything surprise you? Answers will vary. 5. What are the benefits and limitations of this model system? What would you change to make the models better?
Prompts for discussion: How are the models different from real life? Actual rainfall varies in the 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 ground surface types? Why is this model useful? (Can t go into the groundwater in real life and measure the recharge.) Recharge is not immediate. 6. What can we do to help keep our creeks, rivers, and groundwater systems clean? Plant gardens, encourage communities to install plants instead of leaving bare ground. For construction sites, install a plant barrier at the edges of the sites to help reduce soil erosion. Proper disposal of waste, use less fertilizers, use organic fertilizers, or use fertilizers properly (only apply the recommended amount/area and don t apply right before a rain storm). Post-experiment inquiry question suggestions: [potential answers in italics] 1. Which surface had the most run-off? Why do you think this happened? 2. What commonly sit on concrete? [cars] Do you ever see any liquid leaking from a parked car? [oil] Where will this oil eventually go? [into our sewers and then, into our streams] 3. Which surface had the most water recharge? [native plants or grass] 4. What did the soil recharge and run-off water look like for the soil model? [dirty] What s in the water? [dirt; soil] 5. What do we call that process when soil runs off with water? [erosion] 6. Did the recharge water from the plant surfaces look different from the bare soil recharge water? [yes; little or no soil] Why do you think this happened? [roots keep the soil from eroding] 7. Did the amount of water you recorded for run-off and recharge water add up to 1000 ml, the amount of water you poured onto the models? If not, what happened to the rest of the water? [it was absorbed by the surface material; this happens for the concrete, too. Some of the water may pool at the top of the surface, as well.] 8. What would happen to our groundwater if all the ground was covered with non-porous surfaces? [eventually, we would use it all up; there would be no more water to pump into our wells] 9. There are many more potential questions to ask your students! Questions to Think About We have examined how ground surface type affects surface water runoff and groundwater recharge but, how do our actions affect water quality? What are some potential types of pollution you can identify for each type of surface? Record your answers in Table 4. Table 4. Potential types and sources of pollution (Example data) Surface Type of Pollution Potential sources of this pollution?
Concrete Heat, sediment/dirt, oil Heat: concrete warms up and retains heat Oil: leaks out of cars and trucks Sediment/dirt: Washed on to the concrete from stormwater Soil Sediment/dirt, fertilizers Sediment/dirt: Construction sites because they remove all the plants Fertilizers: farms, gardens Grass Fertilizers Housing areas, business landscaped areas Native Plants Fertilizers, if used Gardens with native plants Extension Activities: a. Design a hydrogeology system that reduces runoff (see Discussion Question #3). A couple of potential scenarios: 1. Reducing runoff and erosion from a construction site near a river 2. Reducing runoff from an urban area with lots of buildings and roads (lots of non-porous surfaces) Try it out and record your data as you did for this investigation. b. Look at aerial photographs of your town. Identify the amount (proportion) of different types of ground surfaces (non-porous, vegetated, buildings), potential sources of pollution, and what kind of impact each type of ground surface has on the watershed. If you have aerial photographs taken at different dates (1937, 1968, 2000, for example), determine how the ground surface has changed over time.
Student Sheet Hydrogeology Models: The Effect of Ground Surface Type on Surface Water Runoff and Groundwater Recharge Investigation Question: What impacts do different ground surfaces have on surface water runoff, groundwater recharge, and stream pollution? For this investigation, we will use hydrogeology models to demonstrate how non-porous and porous surfaces (concrete, soil, non-native grass, and native plants) affect surface water runoff and groundwater recharge. Think and Discuss: Concrete, bare soil (no plants on it), grass, and native plants are common ground surfaces in our area. In your group, discuss where we might find some of these different ground surfaces. We might find concrete surfaces at: We might find bare soil surfaces at: We might find grass surfaces at: We might find native plant surfaces at: Think, Predict, and Hypothesize Table 1. Predict what you think will happen. Check one box for each question. Which surface will have the... Concrete Soil Grass Native Plants most water runoff? least water runoff? most water recharge? least water recharge? You have just made some predictions! Choose one of your predictions from Table 1 and write a hypothesis (For example, I think X surface will have more water recharge because.) Hypothesis: If it rains, then. Experimental Variables Identify the variables and constants for your experimental trials.
Independent variable (what you will be changing?): Dependent variables (what will respond to the change?): Constant(s) (what parts of the experiment should you keep constant?): Procedure. Read the roles of team members before beginning your investigation. Conduct the investigation and record your data (results). Student 1:Measurer. Fill the graduated cylinder with 1000 ml of water and pour the water into the watering can. This will be repeated for each model. Student 2: Rain-maker. Beginning with the concrete model, pour the 1000 ml water slowly and evenly over the surface. Student 3: Water Collector 1. Collect the runoff water (top pipe) flowing from the model using one of the beakers. Student 4: Water Collector 2. Collect the recharge water (bottom pipe) flowing from the model using one of the beakers. Student 5: Recorder. Record runoff and recharge amounts in Table 2. Also, record what the water looks like (clean, dirty, etc.). *Change tasks and repeat the procedure with the other three models. Do as many trials as time permits.