Name: ______Caleigh Kehoe______ Learning Unit 7: Flood Review Ques=ons This assignment is designed to assess your understanding of Unit 6 and includes some of the Ques=ons for Review at the end of Chapters 10, 15 and 14 from your text plus a few addi=onal ques=ons. Each ques=on 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 evalua=on 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? Of all of the common natural hazards, floods cause more than 80 percent of all deaths. 2. What aspects of weather cause a flood? (Be specific: not merely “more water.”) Intense or prolonged rain, rapid runoff (as in short basins with no tributaries, that is, first-order streams), bedrock channels can all cause a flood. 3. How is a drainage basin defined? Drainage basin is the area upslope from a point in a valley that drains water to that point. It is the area where all precipita=on into a stream or a set of streams will go. 4. Why does stream level rise within a few hours of a heavy rain, even though you see no water running off the slopes? Even though you see no water, the water gets absorbed into the ground and raises the water table. This causes more water to flow into the stream more quickly it usually does and with a higher volume. 5. How would you calculate the discharge of a stream? To find the discharge of a stream, mul=ply the velocity of the water by the width of the stream by the depth of water. 6. What is the defini=on of a flood? (Be specific: not merely more water) A flood is a stream flow high enough to overtop the natural or ar=ficial banks of a stream. 7. How do the characteris=cs of upstream and downstream floods differ? Upstream (flash) floods are caused by really intense rainfall that happens in a small area over a short period of =me, occur in the upper part of the drainage basin, and have ahigh and rapid runoff. Downstream floods are caused by prolonged periods of rain that saturate the area and occur in the lower part of the drainage basin. They have a long lag =me and recede slowly, so the damages caused by satura=on and deposi=ng of sediments. 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? They are referred to as flash floods, because they can happen quickly and with a liele warning. Due to an increase in discharge the water level will rise quickly and gain velocity. 9. What changes imposed on a stream would likely lead to higher level floods with the same rainfall paeern? Some changes are urbaniza=on, deforesta=on, mining, or over-grazing. 10.With urbaniza=on of the drainage area, what changes can be expected in the height or extent of the 100-year floodplain? An increase in height can almost always be expected and it can increase the probability that a flood will occur. This means that instead of being once in every hundred years, it would be lower, like once in ever figy years, if there was a lot of urbaniza=on. 11.What informa=on is represented by a hydrograph? A hydrography represents the rela=onship between precipita=on and the impact that it has on the discharge of a stream. 12.How would a hydrograph for a stream change if major urban growth were to occur? If major urbaniza=on were to occur the flood peak would be earlier due to increased run-off and decreased infiltra=on. There would be an increase in the flood crest, lag =me, and peak discharge. 13.People should not build homes on floodplains because of the danger of flooding. What are beeer uses for floodplains? A beeer use for floodplains to use them for parks, golf courses, and plainfields. 14.If floodplains are such poor places to live, why are so many towns located on floodplains? Floodplains became populated because the land is cheap, the soil is fer=le, and there scenic views. Due to ignorance, people feel that if there was a flood in the past, then it’s over and cannot be repeated. Another possibility can be the towns were set up and over =me the land changes into a floodplain.15.What do we mean when we refer to a flood as the “10 year flood”. A “10 year flood” means that a flood of that magnitude should occur every 10 years. 16.What is the simple formula for calcula=ng 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. The formule is T=(n+1)/m where n is the number of years in flood record. Where m is the rank of the flood in ques=on. In the largest flood, m=1 so T1999= (69+1)/1 = (70/1)= 70. This is a 70-year flood. 17.If the 70-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. Now “n” would equal 73 because it is 4 years later, but “m” would now change to 2 because it is the second ranked flood. T1999= (73+1)/2 =74/2 = 37-year flood 18.If a 100-year floodplain was flooded in 2003, in how many years should we expect the next 100-year flood? If a 100-year floodplain was flooded in 2003, indicates that one happens every 100-year on average; so the next one will happen by 2103, but another flood could happen at any =me. 19.Why is the specified 100-year floodplain size or 100-year flood height not a very reliable indicator for future large floods? The 100-year flood height is not very reliable, because the indicators of the flood height, such as debris (twigs, logs, silt, etc.) are not preserved long ager the flood, and drigwood will probably end up well below the maximum water level. Floods can also leave behind drig lines, but they are washed away with the next incoming rainfall in the future. The 100-year floodplain size is not reliable because it is based on a few number of events over a short and incomplete period of flood record. It does not consider any changes in the floodplain over =me (naturally or due to urbaniza=on), so the boundaries are really just an es=mate. 20.What are the limita=ons
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