Jain_Dhruv_Tutorial2

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Name: Dhruv Jain Tutorial Section (Day/Time): D105 Tutorial #2: Using the Scientific Method to Investigate Streamflow and Flooding Adapted from http://www.hartnell.edu/tutorials/biology/scimethod.html and Kortz & Smay (2008) Instructions: Download this worksheet to your computer, and save the file as Your Last Name_First Name_Tutorial2 (e.g. Holland_Tara_Tutorial2). Type your answers directly onto this worksheet. Upload your completed worksheet to Canvas  Assignments  Tutorial 2 as a .pdf attachment. This tutorial is graded out of 25 marks. Point values are given in parentheses after each question Learning Goals:  List the steps of the scientific method, and explain how science works  Analyze hydrographs with respect to processes in the hydrologic cycle, especially precipitation, surface runoff, and infiltration  Apply the scientific method to generate and test hypotheses about environmental and human factors that influence flooding Resources on Canvas :  Video: How Science Works (10 min): https://youtu.be/JH0_xC7q9tU  Stream Hydrology primer  https://runoff.modelmywatershed.org/ Context: In this tutorial, you will apply the scientific method to an analysis of streamflow (discharge) graphs as related to the hydrologic cycle and human activity. Diagram of the Hydrologic (Water) Cycle Holland EVSC 100 2024 Tutorial 2

River Flow and Flooding The amount of water moving down a river at a given time and place is referred to as its discharge , or streamflow, and is measured as a volume of water per unit time, typically cubic meters per second (m 3 /s). The discharge at any given point in a river can be calculated as width (in m) times the average depth (in m) times average velocity (in m/s). The vast majority of rivers are known to exhibit considerable variability in flow over time because inputs, in the form of rain events, snowmelt, groundwater seepage, etc., vary over time. Some rivers respond quickly to rainfall runoff or snow melt, while others respond more slowly depending on the size of the watershed, steepness of the hillslopes, ability of the soils to (at least temporarily) absorb and retain water, and the amount of storage in lakes and wetlands. Floods are rare events in which a body of water temporarily covers land that is normally dry. River floods are typically caused by excessive rainfall and/or sudden melting of snow and ice. Most rivers overflow their banks with small floods about once every two years. Human activities such as development in the watershed and modifications of the river channel can change the frequency and severity of floods. Description of the Scientific Method One of the goals of science is to come up with explanations about how the natural world (all the things we see or experience) functions. It is important to note that there are also other important systems for understanding and explaining the world around us, such as Indigenous ways of knowing. Scientific explanations are based on patterns in nature that are objective (do not depend on faith, authority, or opinion), are testable (can be demonstrated with experiments), and are consistent (the same conditions produce the same results). The 4 Steps of the Scientific Method* To learn about the natural world, scientists use a four-step procedure called the scientific method. The four steps of the scientific method are listed below. Step 1: Observations & Questions Observe something in the natural world and ask a question about how it works. Step 2: Hypothesis Holland EVSC 100 2024 Tutorial 2

Make a hypothesis (an educated guess) that attempts to answer the question. A useful hypothesis is a testable statement. Step 3: Experiment Design and carry out an experiment that is capable of testing the hypothesis. In other words, the experiment must be designed so that it will produce results that either clearly support or clearly falsify (disprove) the hypothesis. It helps to use “If-Then” predictions based on your hypothesis. Step 4: Analyze Results and State Conclusions Reject the hypothesis if the results are not consistent with the hypothesis, or accept the hypothesis as possibly true if the results are consistent with the hypothesis. Notice that the hypothesis is not “proven to be true”, even if the results do support it. This is because there may be explanations other than the hypothesis for the experimental result. If the experimental results do not support the hypothesis, the hypothesis may be modified and additional experiments may be done to test the new or revised hypothesis. *Although we represent the scientific method as a somewhat linear process, it is important to recognize that science in reality is much more complex. The video on Canvas “How Science Works” will give you an idea of how the scientific method works “in real life”. Part 1: Rainfall Look at the cross section below showing the ground surface and water table (top level of where water is stored underground) during a short, powerful rainstorm. This diagram represents a watershed , which is the area from which rainfall flows into a stream, lake, or reservoir. For more background on how water reaches a stream, consult the Stream Hydrology primer on Canvas. Imagine that you are outside watching this storm happen. 1) Make an observation : (1) What two possible things will happen to Raindrop A when it hits the ground? Raindrop A may contribute to surface runoff and move downstream toward the stream when it hits the ground, or it may infiltrate into the ground and travel through the subsurface layers, ultimately going into the stream. 2) Draw or insert arrows showing the directions that surface water and ground water are flowing. (1) Holland EVSC 100 2024 Tutorial 2

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3) Ask (and propose and answer to) a question : (1) Where will Raindrop A eventually end up? If Raindrop A hits the ground on the hill slope during the storm, it will eventually end up in the stream due to the steep slope of the surface. Part 2: Streamflow Analysis The graph below (called a hydrograph ) shows the level of water in the stream from Part 1. The black box indicates the duration of the short, powerful rainstorm. Rainwater reaches the stream by flowing along the ground surface (called runoff ) and/or by soaking into the ground (called infiltration ) and slowly traveling underground to the stream. 4) Observation : (1) Is the flood at its highest during the rain storm (highlight one)? Yes No The flood is not at its highest during the rainstorm. There is a distinct lag phase, indicating a delay between the onset of the rainstorm and the peak of the flood. Holland EVSC 100 2024 Tutorial 2

5) Question : (1) What causes the peak of the flood to occur after the peak of the rain? The peak of a flood occurs after the peak of the rain due to factors like infiltration into the soil, delayed surface runoff, and river routing. Infiltration takes time, and excess water needs to accumulate and flow to rivers. Additionally, river channels may require time for the water to travel downstream. The topography of the landscape such as the presence of buildings, roads, infrastructure also play a role, influencing the speed of water movement. Overall, these factors contribute to a lag time between the peak of rainfall and the peak of the flood. 6) Imagine a scenario where no water soaks into the ground but instead runs quickly off the surface all at once into the stream. Hypothesize how the following features of a flood would change ( highlight which answer you think is right), and explain how you came up with your answers. (3) a) The length of the lag time: longer shorter because… Shorter because without infiltration, water quickly runs off the surface into the stream, reducing the time it takes for the flood to peak. b) The height of the flood peak: higher lower because… Higher because without infiltration to slow down the flow, surface runoff would rapidly accumulate, leading to a more abrupt and elevated flood peak. c) The duration of the flood: longer shorter because… Shorter because with no infiltration, the absence of delayed contributions from underground flow would result in a more rapid rise and fall of water levels, shortening the overall flood duration. 7) If you wanted to test your hypotheses from above, how might you go about designing an experiment? (2) It is possible to design a small experimental setting in order to test the hypothesis. The experiment tries to imitate the effect of urbanization on water flow by using foam to construct a simulated river basin with plastic-laminated earth. The apparatus, when enclosed in a glass box, allows for regulated observation. A spray system and pipes are used to simulate rainfall. A stopwatch keeps track of the amount of time it takes for water to accumulate, and a marker on the glass is used to measure the height of streams and rivers. Through a practical demonstration of surface runoff and lag time, this approach offers valuable insights into how urbanization affects the dynamics of watersheds. Holland EVSC 100 2024 Tutorial 2

8) Let’s say that a city with concrete parking lots and roads is built in a previously undeveloped watershed (see figure above). Hypothesize how the presence of the city would affect the amount of water soaking into the ground vs. running off the surface. Explain your reasoning. (2) It is anticipated that the presence of a concrete-surfaced metropolis will lessen the amount of water seeping into the ground (infiltration). Because impermeable concrete prevents infiltration, more rainfall runs off the surface, leading to an increase in abrupt discharge. Increased surface runoff results from this, changing the watershed's natural water balance One way that you can test your hypothesis is to use a model. Go to https://runoff.modelmywatershed.org/ , which presents a simple watershed model where you can explore how changes in rainfall, ground surface, and ground texture can change where water goes. This model looks at both infiltration and runoff, as well as evapotranspiration . Let’s assume that our original catchment area was forested land, with a moderate infiltration soil type. Select these land cover settings on the model . Set the amount of precipitation for the storm event to 5.0 cm by sliding the green circle to the middle of the precipitation scale. With these settings: 9) How much water from the storm infiltrates into the soil? (1) 4.4 cm of water from the storm infiltrates into the soil. 10) How much water from the storm runs off the surface? (1) 0 cm of water from the storm runs off the surface. Change the amount of precipitation to 21 cm , which would represent a very intense storm event. 11) How does this change the amount of infiltration vs. runoff? Explain why you think this is the case. (2) With an increased precipitation of 21 cm, the infiltration has risen to 12.9 cm, and runoff has increased to 7.5 cm. This shift implies that the soil reaches its saturation point faster as the storm strength increases. There is less capacity for the soil to hold onto water, which increases surface runoff. More precipitation causes the soil's infiltration capacity to be exceeded, which increases the amount of water that runs off the surface. Holland EVSC 100 2024 Tutorial 2

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Now that you have seen how water would move in a forested catchment, let’s test your hypothesis from #8 about how the presence of a city would affect the water flow. Change the land cover to “Developed-med”, and keep the intense rainstorm event at 21 cm. 12) How much water from the storm infiltrates into the soil? (1) 17.3 cm of water from the storm infiltrates into the soil. 13) How much water from the storm runs off the surface? (1) 3.6 cm of water from the storm runs off the surface. 14) Quantify (give in numbers) the difference between the flow of water (infiltration vs. runoff) after the intense rainstorm in the forested catchment vs. the catchment with the city. Does this result support your hypothesis? (2) Following a heavy downpour, the catchment with the city shows 3.6 cm of water infiltration into the soil, whereas the catchment with the forests shows 17.3 cm. This indicates a 13.7 cm difference, underscoring the fact that urbanization reduces the soil's ability to retain water compared to a natural forest. Furthermore, the urban catchment receives 17.3 cm of runoff, while the forested catchment receives 7.5 cm, indicating a 9.8-centimeter discrepancy. These measured differences provide compelling evidence for the hypothesis that, as compared to a naturally occurring, forested catchment, the existence of a city with concrete surfaces decreases infiltration and increases surface runoff. 15) Now let’s apply your findings from the watershed model to our flooding scenario. Hypothesize how building a city in a previous undeveloped area would affect (if at all) the following features of a flood ( highlight one) and explain your reasoning with reference to the model findings: (3) a) The length of the lag time: longer not affected shorter Briefly explain: Urbanization, as observed in the model, decreases infiltration capacity due to increased impervious surfaces in a city. This results in faster surface runoff, leading to a shorter lag time before water reaches rivers or streams. b) The height of the flood peak: higher not affected lower Briefly explain: The model findings indicate that urbanization reduces soil infiltration and enhances surface runoff. With less water being absorbed by the soil and more flowing over impermeable surfaces, the volume of water entering water bodies during a storm is greater, contributing to a higher flood peak. c) The duration of the flood: longer not affected shorter Briefly explain: Urbanization's impact on lag time and runoff translates into a more rapid drainage response in the city. Consequently, the duration of the flood event is expected to be shorter compared to a scenario in a less developed, forested catchment. 16) On the diagrams below, the solid line is a flood curve for a rainstorm in a rural area. Which new curve (dashed line) best represents how the curve would change if a city was built in the area? (1) Diagram B's dashed line is thought to most accurately depict how the development of a metropolis in the region has altered the flood curve. The dashed line represents the impact of urbanization, showing increased surface runoff, with a sharp peak and swift drop. This pattern is in line with what would be predicted given the greater Holland EVSC 100 2024 Tutorial 2

impervious surfaces found in metropolitan areas, which would cause the flood peak to climb and recede more quickly. 17) Based on your findings in this tutorial, what is a further question you would be interested in asking about the relationship between the water cycle and water movement in a watershed? There is no right answer here – this is your chance to start thinking with scientific curiosity . (1) A further question that arises from the findings in this tutorial is: How do the micro-scale features of vegetation, such as the structure and diversity of plant communities, influence the partitioning of rainfall into infiltration and runoff within a watershed? Holland EVSC 100 2024 Tutorial 2

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