Upstream Flash Floods are caused by locally intense rainfall over a short period of time. They have steep gradient and usually have high and rapid runoff. They are narrow V-shaped channels, with no floodplains or levees. The waters rise quickly. There is a short lag time and high peak discharge. The damages it causes are from the force of the rapidly moving water and deposition of sediment. They flood rapidly, recedes quickly. Downstream is unaffected and covers a smaller area of land.Downstream Regional Floods are caused by large amounts of rainfall over an extended period of time over a large portion of the drainage basin. They have shallow gradient, and high infiltration. They have a wide, deep U-shaped channels with floodplains and levees and the water rises slowly. They have a long lag time and broad discharge curve. Flood damage mainly from extensive wetting and deposition of sediment. Great property damage because it covers a large area of land and flood waters remain high for long periods of time. They recedes slowly, and the floods affect tributariesName: ___Rebecca Gallanter_____Learning Unit 7: Flood Review QuestionsThis assignment is designed to assess your understanding of Unit 6 and includes some of the Questions forReview 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 three sentences. 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 80 percent of all deaths?The flooding of streams. 2. What aspects of weather cause a flood? (Be specific: not merely “more water.”)Precipitation is the main cause of flooding, and is exaggerated by how much rain falls over a given area, the duration of the rainfall, and the intensity of the rainfall.3. How is a drainage basin defined?The drainage basin is a cup of land bounded by areas of high relief. Precipitation that falls within the cup of land flows to the stream as runof over the surface or infiltrationand Base flow through the groundwater system4. Why does stream level rise within a few hours of a heavy rain, even though you see no water running of the slopes?The stream level could rise because the ground gets saturated with the excess moisture, and it swells, making it seem like it is higher5. How would you calculate the discharge of a stream?The discharge is calculated by looking at the total amount (volume) of water carried by the stream. is usually measured in cubic feet per second6. What is the definition of a flood? (Be specific: not merely more water)A flood is an overflowing of a lot of water beyond its normal confines, especially when it has to do with dry land.7. How do the characteristics of upstream and downstream floods difer?Upstream Flash Floods are caused by locally intense rainfall over a short period oftime. They have steep gradient and usually have high and rapid runof. They arenarrow V-shaped channels, with no floodplains or levees. The waters rise quickly.There is a short lag time and high peak discharge. The damages it causes are fromthe force of the rapidly moving water and deposition of sediment. They flood rapidly,recedes quickly. Downstream is unafected and covers a smaller area of land.Downstream Regional Floods are caused by large amounts of rainfall over anextended period of time over a large portion of the drainage basin. They have shallowgradient, and high infiltration. They have a wide, deep U-shaped channels withfloodplains and levees and the water rises slowly. They have a long lag time andbroad discharge curve. Flood damage mainly from extensive wetting and depositionof sediment. Great property damage because it covers a large area of land and floodwaters remain high for long periods of time. They recedes slowly, and the floods afecttributaries8. Why are upstream floods referred to as flash floods? What efect can flooding (an increase in discharge) have on stream flow in an upstream channel?Upstream floods rise rapidly and appear unexpectedly, which gives them their name “flash” making the point that they happen in the blink of an eye. Having such high velocity waters scours out new channels and can trigger landslides and debris flows.9. What changes imposed on a stream would likely lead to higher level floods with the same rainfall pattern?If the steam gradient changed, it could efect the height level of the floods that occurein a department 10. With urbanization of the drainage area, what changes can be expected in the height or extent of the 100-year floodplain?The national government has put together a few things to try to help to keep people and their homes safe during floods. They are raising the land level with fill, building walls and/or levees and using water-resistant building materials11. What information is represented by a hydrograph?The connection between precipitation and the efect it has on a streams12. How would a hydrograph for a stream change if major urban growth were to occur?The flood crest would be shown as being higher, and the lag time would be longer. After urban development, floods tend to peak earlier after a rainstorm, and have higher peak discharge! 13. People should not build homes on floodplains because of the danger of flooding. What are better uses for floodplains?Better uses for those floodplains would be as a place to let the excess water runof go after a storm, and it can act as a drainage basin14. If floodplains are such poor places to live, why are so many towns located on floodplains?Part of it could be ignorance. However, another factor is not every place that floods always flooded. Some places started flooding after a certain point. Also, In many places, floodplains are not adequately zoned15. What do we mean when we refer to a flood as the “10 year flood”.Whenever anyone says “__ year flood”, it usually means a flood for a stream that will, on average, cause a flood every certain number of years. So with the “10 year flood”, on average there would be a big flood every 10 years16. 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
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