Teacher guide Flash

Teacher guide Flash floods Flooding There are many factors that affect the likelihood and severity of flooding, including the amount of rainfall, the intensity of rainfall, topography, soil conditions and ground cover. In this project, students will look at soil conditions and ground cover, and explore whether changes can be made to the local environment to reduce flood risk. Soil and rock type can have a big influence on what happens when it rains. For example, impermeable soils and rocks such as clay or shale do not allow water to infiltrate, and this forces water to run off, increasing flood risk, whereas permeable rocks allow water to infiltrate into them. Vegetation can also affect the likelihood of flooding. By intercepting and slowing precipitation hitting the ground, vegetation substantially reduces the volume and rate of stormwater runoff. This helps to protect soil from erosion and reduces flash flooding. In this project, students will design and run a series of experiments, including a channel, to investigate the relationship between flood velocity and the rate of erosion. Prompts Ideas for what to test inside the channel. If students are stuck, suggest some ideas such as: • Fill the channel with different types of soil, e.g. silt, sand and clay. • Fill the channel with different types of stone or rock. • Fill the channel with small plants. • Pour water through a second time, or even third, to see what happens when there is already some water absorbed in the ground. How will you measure erosion? Encourage students to think about what observations and measurements they can make to quantify the differences between their experiments. For example, they might like to time how long it takes for water to stop dripping out of the end of their channel. They might also like to measure the volume of water that they collect at the end of their channel and compare this to the amount they poured in, to see how much water has been absorbed by the contents of their channel. How will you make sure your experiment is fair? Encourage students to think about using the same volume of water, and how they will control the rate at which they initially pour the water into the channel, using the same volume of filling, taking care to spread the filling similarly through the channel, and so on. How do the width and slope of your channel affect the speed of water? Students could build a second model with a different width and slope to compare. What if the width of the channel changes part way down the slope? Encourage students to look at the depth of the water as well as the speed. If your model was a river would it be at risk of overflowing its banks? 22

Student brief Flash floods Flooding (Physics, flooding, climate change, environment) Have you ever wondered how fast a flash flood is? Imagine you are a town planner. You are thinking about building a new school at the bottom of a hill in your town. You are worried about the risk of flooding and want to know whether there is anything you can do on the slope or around the school grounds to reduce the risk of flooding. Getting started Using a channel for the water to travel down, set up your experiment. Your channel will need to be open at the top (i.e. not a closed tube), so that you can easily set up different ‘soil conditions’ and ‘ground cover’. Set up your channel at a slight slope, and make sure to put a bucket or tray at the bottom of the channel to catch any water or other materials as they flow out. Decide what measurements and observations you will make for each test. You might like to start by pouring the water with nothing in the channel. Things to think about • What different things will you fill your channel with? You might like to make some predictions about what materials will perform best in terms of slowing or absorbing the water. • What measurements will you take? How will you record your results? • Is it just the amount of water that matters? Try testing pouring the water at different speeds – what difference does it make? • How do the width and slope of your channel affect the speed of water? What if the width and slope of the channel changes part way down the slope? Useful resources • What difference could natural flood management techniques make? https://www.ceh.ac.uk/news-andmedia/blogs/what-difference-could-natural-floodmanagement-techniques-make • Urban Flood Risk Reduction by Increasing Green Areas for Adaptation to Climate Change https://www.sciencedirect.com/science/article/pii/S 1877705816330570 • Types of flooding https://floodguidance.co.uk/what-isresilience/types-flooding • Stream Flow and Sediment Transport http://www.columbia.edu/~vjd1/streams_basic.htm • River Processes https://geographyas.info/rivers/river-processes/ Health and safety To avoid any accidents, make sure you stick to the following health and safety guidelines before getting started: • Find out if any of the materials, equipment or methods are hazardous using http://science.cleapss.org.uk/Resources/Student- Safety-Sheets/ to assess the risks. (Think about what could go wrong and how serious it might be.) • Decide what you need to do to reduce any risks (such as wearing personal protective equipment, knowing how to deal with emergencies and so on). • Make sure there is plenty of space to work. • Clear up slip or trip hazards promptly. • Make sure your teacher agrees with your plan and risk assessment. 23