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WSUT SOE 101 - Assignment 10 -- Stream Erosion_2019

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SOE 101: Introduction to Geology Assignment 10: Factories, Farming, and Floods Name: _____________________________ Read: Chapter 14 in Essentials of Geology; access to the internet; colored pencils (red and blue) HERE’S THE SCENARIO: You found property on which to build your factory. However, the local farmers are concerned that the nearby stream (Cougar Run) will experience increased flooding and erosion of their valuable farmland due to construction of your facility. These farmers are particularly sensitive to the erosion of their soil because it produces the best potatoes in the state. They are also worried about contamination of their groundwater from industrial runoff as groundwater is vital for irrigating their crops. How will your new business impact the local farming community? 1. Complete the Guided Learning Activities “River Processes and Flooding” AND “Groundwater” available on Blackboard. 2. Cougar Run flows from the west to the east (see figure below showing the location of the river, your factory, a factory built in 2004, local farms (A-F), and water wells). Based on the shape of the stream channel, indicate on the figure where you would expect significant erosion or deposition to occur? Which landowner (A-F) could experience the worst erosion damages to their property?Assignment #10– Page | 2 3. A geologic cross-section of Cougar Run (shown below) shows that the stream channel bedrock is limestone. The limestone is overlain by pebble-sized sediments, which itself is topped with a layer of rich soil with a mix of sand and silt. The typical water depth is 7.5 meters and the channel width is 15 meters. • What is area of the stream channel that is occupied by water as shown in the cross-section? Show your work. {Don’t forget the units…} • What is area of the stream channel that isn’t currently occupied by the water? Show your work. {Don’t forget the units…} • What is the total area of the stream channel below the soil layer? Show your work. {Don’t forget the units…} 5. To erode the fertile soil, the stream must be traveling fast enough to pick up the sand/silt and transport it downstream. Practice using the “velocity vs. particle size” graph found on Blackboard by filling in the blanks below. If asked for velocity, report your answer in meters per second (m/s). • Sand particles that are ___________ mm will be eroded when water travels at 30 cm/s. • Deposition starts to occur at ___________ cm/s or ________________ m/s for particles 0.01 mm in size. • To pick up (erode) and transport larger particles, much higher velocities are needed. To move cobbles that are 200 mm (or 20 cm in size), water velocities must be at least ______________cm/s or ______________ m/s. • Pebbles (50 mm) being transported will begin to be deposited when water velocity drops below ________________ cm/s or __________________ m/s. 6. Thankfully, the soil layer is underlain and protected by a thick pebble layer (20 mm in size). What velocity is required to erode 20-mm pebbles? Using the cross-sectional area (m2) for the Cougar Run stream channel that you calculated above and the velocity of the water required to erode 20-mm pebbles, calculate the stream discharge. Report your answer in m3/s and to the nearest tenth (e.g., 10.2). 7. Will the erosion velocity that can erode 20-mm pebbles be sufficient to erode the soil layer?Assignment #10– Page | 3 8. The local farmers are convinced that industrial development in 2004 (west of your factory) led to increased rates of flooding/erosion of their land. To determine if the industrial development could increase erosion/flooding, you compare flooding trends before and after construction by evaluating the stream discharge data of Cougar Run (see table). Using the provided stream discharge data and your calculated stream discharge needed to erode the 20-mm pebble layer, answer the following: • How many times was the pebble layer (and the soil) eroded by Cougar Run prior to the factory development in 2004 (e.g., between 1919 and 2004)? List the years in which it occurred. • How many times was the pebble layer eroded by Cougar Run in the years after 2004 (e.g., between 2004 and 2019)? List the years in which it occurred. • Based on your analysis, has the development of the large factory in 2004 increased flooding and erosion in Cougar Run? Why or why not? 9. The runoff into the stream from some factories in the industrial park has been shown to be quite acidic. • Will this acidic runoff cause an erosion problem? Why or why not? • Could this industrial runoff infiltrate the groundwater? Explain. 10. You decide to implement engineering designs to reduce runoff from your factory. What engineering designs could be implemented to reduce runoff from the industrial park and factory? In your answer, describe 3 methods and how each reduces/mediates runoff into Cougar Run. {HINT: there is information on the Blackboard website.} • • • top 20 discharges for Cougar Run Years: 1919-2019 Year Discharge (m3/s) 2010 575.6 1983 545.6 1953 514.6 1923 501.7 2006 489.3 2013 430.8 2017 412.2 1972 407.5 1957 400.2 2011 398.3 1939 377.6 2005 367.4 1961 366.7 1942 354.5 2009 341.4 1936 321.6 1919 310.8 2007 307.6 2015 296.8 1969


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