Exploring Watersheds and Runoff with Physical and Computational Models
Engage in hands-on activities using physical models like a big tarp to simulate rainfall on landscapes and explore the movement of water. Dive into discussions about the pros and cons of using physical models for studying water flow. Discover the introduction to computational models and discretization for a deeper understanding of watersheds and runoff.
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COMPHYDRO BALTIMORE Lesson 3 - FLOORLANDIA: Topography, Runoff and Watersheds Activity Description 1 Big Tarp: Physical Model of Rain on a Landscape 2 Big Tarp: Thinking about Physical Models 3 Flow on Floorlandia: Watersheds 4 Flow on Floorlandia: Hydrographs 5 NetLogo Floorlandia: computer simulation models 1
Lesson 3 - Activity 1 Big Tarp: Physical Models Pairs of students receive the Lesson 1 Activity 1 - Student Pages (on clipboard) Create an imaginary landscape with topography using a tarp outside or in a basin Simulate precipitation on the landscape with spray bottles Use the Student Pages to guide exploration of the model and complete the worksheet 2
Lesson 3 - Activity 2 Big Tarp: Thinking about Physical Models Brainstorm with your partner What other physical models do you know about? What are the pro s and con s of using a physical model like Big Tarp to study the movement of water across a landscape. Record your ideas on the Student Pages for Activity 2. Collect students ideas about the pro s and con s in two columns on the board, flipchart or directly in the blank powerpoint slide that follows. 3
Lesson 3 - Activity 2 Big Tarp: Thinking about Physical Models Pros Cons 4
Lesson 3 - Activity 2 Big Tarp: Thinking about Physical Models Possible student ideas Pros Small scale Visual Real materials Easily replicable Condense time Cons Scale challenges Not realistic Can be hard to do multiple trials 5
Lesson 3 - Activity 2 Introduction to Computational Models 6
Lesson 3 - Activity 2 Discretization 7
Lesson 3 - Activity 2 Discretization finer scale grid 8
Lesson 3 - Activity 2 Introduction to Computational Models 1. Discretize a. break landscape into cells b. decide on time-step 9
Lesson 3 - Activity 2 Parameterization & Algorithms 10
Lesson 3 - Activity 2 Parameterization & Algorithms 2. Paramaterize a. What information needs to assigned to each cell for driving variables that will determine how water will move across the landscape / model? 3. Set rules or algorithms a. establish rules for water movement for each cell 11
Lesson 3 - Activity 2 Parameterization & Algorithms We already did these steps: 1. Identify area that you are confident will encompass the entire watershed. 2. Discretize the area into equal sized cells. Now 3. Determine the (average? Weighted average?) elevation of each cell 4. Establish rules for how water moves across our simulated landscape 12
Lesson 3 - Activity 2 Summary of Computational Modeling 1. Discretize a. break landscape into cells b. decide on time-step 2. Paramaterize a. assign values for driving variables to each cell 3. Set rules or algorithms a. establish rules for water movement for each cell 4. Deal with boundaries a. Determine what the rules are at boundaries 13
Lesson 3 - Activity 3 Setting up a Computational Model Floorlandia: Optional Floor Version Class stands around the outside of the Floorlandia grid of elevations Examine the topography of the model and find key features: Rain on Floorlandia, with each student representing a raindrop and moving with each time-step Discuss basic rules for how water will move in the model Walk through the model following the rules Continue until all have reached the edge or off the grid Discuss pattern of water movement in Floorlandia 14
Lesson 3 - Activity 3 Setting up a Computational Model Floorlandia: Tabletop Version Pairs of students receive Floorlandia grid of elevations Part 1 Lay of the land Part 2 Setting rules for how water will move Part 3 Model water flow paths Part 4 Delineate watersheds Part 5 About watersheds 15
Discussion of how this exercise is a model of a system Remember that a model is a simplified representation of a system And that systems are defined by some common elements What are the elements of a system? 18
How does this exercise model a system? A system Is a whole thing Consists of interacting parts Is organized for a function Has rules regarding how the parts interact Has boundaries Emergent Properties (properties as a whole that can t be reproduced by its parts alone) 19
What is the whole thing? A watershed 21
What are the interacting parts? Grid cells Particles of water Elevation Values 23
What is the function? Understanding and predicting the movement of water in a surface system or watershed 25
What are the rules? (within area of model called the model domain) A turn is one unit of time or time step. Water moves in direction toward adjacent cell with largest elevation difference. Stop when you can t go any further within the table by following the rules above. 27
What are the boundaries? The edge of the grid of cells In this example, water flows off the model at the lowest elevation. We recorded the number of beads per time step that came off the model on our data sheet for each watershed. 29
What are any emergent properties? Particles of water always move from an area of high elevation to low elevation within model domain (grid space) 31
Lesson 3 - Activity 4 Floorlandia: Hydrographs Form pairs and use the expert Floorlandia model Simulate the path of a rain drop starting at a high point in the central watershed and determine how many time steps it takes to the discharge point. Determine the number of time steps a simulated rain adding one drop to reach the discharge point from each cell. 32
Lesson 3 - Activity 4 Floorlandia: Hydrographs - Tips The number of steps away from the outlet each droplet (cell) is will equal the number of time steps that droplet takes to leave the watershed Count the number of arrows between each cell and the outlet and tally these Since the watershed was dry at time zero (before the rain was added), make sure to include a time zero in your results. Since the watershed empties completely according to our rules, make sure to include a final time step with zero droplets (the stream dries up!). 33
Lesson 3 - Activity 5 A Simple Computer Model of the Surface Water System Floorlandia moved a particle through a grid. This is a model, but not a computer model. How could you turn Floorlandia into into a computer model? 34
Boundaries Computer models must designate a system space that is constrained by boundaries. 36
Discretization Discretization involves dividing a system space into smaller parts (in this case cells). 37
Parameterization In a computer model a parameter is a variable that we can assign a value to. Parameters are included in the rules for how the model works. By changing parameter values we can change what happens in the model. Potential energy is an example of a parameter in this model. 38
