Name: Nillamie Rivera Learning Unit 7: Flood Review Questions This assignment is designed to assess your understanding of Unit 6and includes some of the Questions for Review at the end of Chapters 10, 15 and 14 from your text plus a few additional questions. Each question can be answered in one to two sentences. Please limit yourself to a maximum of threesentences. Access the assignment, complete it with ANSWERS IN A DIFFERENT COLOR FONT as a separate file, and send it back for evaluation and grading through the assignment tab by or before the due date. 1. Of all of the common natural hazards, which causes more than 80percent of all deaths? Floods cause more than 80 percent of all deaths. 2. What aspects of weather cause a flood? (Be specific: not merely “more water.”) Flooding is caused by conditions that lead to intense raining or melting of ice. 3. How is a drainage basin defined? A drainage basin is the area from which all of the precipitation flows to either one stream or a set of streams. 4. Why does stream level rise within a few hours of a heavy rain, even though you see no water running off the slopes? Water going down the ground causes the water table to raise, resulting in rapid outflowfrom groundwater into the streams located down slope. 5. How would you calculate the discharge of a stream? To calculate the discharge of a stream you would multiply the area of water in a channel cross section by the average velocity of water in that cross section. [Discharge(Q)= velocity (v) x cross-sectional area (A= average width x average depth)6. What is the definition of a flood? (Be specific: not merely more water) A flood is an overflow of water, on a part of land that is usually dry. 7. How do the characteristics of upstream and downstream floods differ? Downstream floods are caused by long storms that produce increased runoff. Downstream floods tend to saturate the solid. Short, but intense rainstorms are what causes a Upstream flood. 8. Why are upstream floods referred to as flash floods? What effect can flooding (an increase in discharge) have on stream flow in an upstream channel? Flash floods are caused by intense short timed rainfalls which cover up to two tributaries. Due to this, flood waters rise up rapidly. While discharge and velocity increases the water force is able to transport large debris. 9. What changes imposed on a stream would likely lead to higher level floods with the same rainfall pattern? Increased urbanization would likely lead to higher level floods with the same rainfall pattern. 10. With urbanization of the drainage area, what changes can be expected in the height or extent of the 100-year floodplain? The height of the 100 year floodplain could be expected to be greater/larger area. 11. What information is represented by a hydrograph? A hydrograph represents the geography of discharge, velocity, and other prosperities of water flow. 12. How would a hydrograph for a stream change if major urban growth were to occur? Changes if major urban growth were to occur include paved streets and decreased infiltration. 13. People should not build homes on floodplains because of the dangerof flooding. What are better uses for floodplains? Agricultural parks and golf courses are better uses for flood plains. 14. If floodplains are such poor places to live, why are so many towns located on floodplains? Many towns are located on flood plains because many cities were built near rivers in the past. In the past it was beneficial to live in these areas because transportation was more affordable, but now people are just at flood risk.15. What do we mean when we refer to a flood as the “10 year flood”. When a flood is referred to as the 10 year flood it means that is the flood with the highest discharge in the past decade. 16. What is the simple formula for calculating the recurrence interval (T) for a certain size flood on a stream in 1999 if there are sixty-nine years of record? Give a numerical example based on the largest flood. 17. If a 100-year floodplain was flooded in 1999, and there is a slightly larger flood 4 years later in 2003, what if any, change is there in the recurrence interval for the 1999 flood? Be numerically specific. RI n 1 m n number of years in flood record m rank of the flood 18. If a 100-year floodplain was flooded in 2003, in how many years should we expect the next 100-year flood? It could be anytime, in 100 years or maybe even 10 years. 19. Why is the specified 100-year floodplain size or 100-year flood height not a very reliable indicator for future large floods? It is basedon a sample of floods that is not reliable enough to be accurate. 20. What are the limitations for building on a designated floodplain? The lowest floor of a building on a designated floodplain must be 2 feet above the 100 year flood level. 21. What are natural levees and where do they form? Natural levees arebuilt up mud on either side of a stream or river. 22. Aside from protecting the adjacent stream bank, what effects do levees have on a stream? Levees cause the flood level to raise and italso increases the water velocity near the levee, it then causes a flood. 23. What processes can lead to the failure of a river levee? Overtopping, erosion, and structural failures, are all factors that can lead to the failure of a river levee.24. What constitutes channelization and what is it intended to do?Channelization is constituted by straightening, lining, widening, or deepening of existing streams. Channelization works to prevent floods. 25. What is avulsion?Avulsion is the rapid abandonment of a river channel and the creation of a new river