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 le 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 oods cause more than 80 percent of all deaths 2 What aspects of weather cause a ood Be speci c not merely more water Intense or prolonged rain rapid runo as in short basins with no tributaries that is rst order streams bedrock channels can all cause a ood 3 How is a drainage basin de ned 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 o 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 ow into the stream more quickly it usually does and with a higher volume 5 How would you calculate the discharge of a stream To nd 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 de ni on of a ood Be speci c not merely more water A ood is a stream ow high enough to overtop the natural or ar cial banks of a stream 7 How do the characteris cs of upstream and downstream oods di er Upstream ash oods 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 a high and rapid runo Downstream oods 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 oods referred to as ash oods What e ect can ooding an increase in discharge have on stream ow in an upstream channel They are referred to as ash oods 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 oods 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 oodplain An increase in height can almost always be expected and it can increase the probability that a ood will occur This means that instead of being once in every hundred years it would be lower like once in ever gy 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 ood peak would be earlier due to increased run o and decreased in ltra on There would be an increase in the ood crest lag me and peak discharge 13 People should not build homes on oodplains because of the danger of ooding What are beeer uses for oodplains A beeer use for oodplains to use them for parks golf courses and plain elds 14 If oodplains are such poor places to live why are so many towns located on oodplains 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 ood 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 oodplain 15 What do we mean when we refer to a ood as the 10 year ood A 10 year ood means that a ood 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 ood on a stream in 1999 if there are sixty nine years of record Give a numerical example based on the largest ood The formule is T n 1 m where n is the number of years in ood record Where m is the rank of the ood in ques on In the largest ood m 1 so T1999 69 1 1 70 1 70 This is a 70 year ood 17 If the 70 year oodplain was ooded in 1999 and there is a slightly larger ood 4 years later in 2003 what if any change is there in the recurrence interval for the 1999 ood Be numerically speci c Now n would equal 73 because it is 4 years later but m would now change to 2 because it is the second ranked ood T1999 73 1 2 74 2 37 year ood 18 If a 100 year oodplain was ooded in 2003 in how many years should we expect the next 100 year ood If a 100 year oodplain was ooded in 2003 indicates that one happens every 100 year on average so the next one will happen by 2103 but another ood could happen at any me 19 Why is the speci ed 100 year oodplain size or 100 year ood height not a very reliable indicator for future large oods The 100 year ood height is not very reliable because the indicators of the ood height such as debris twigs logs silt etc are not preserved long ager the ood 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 oodplain size is not reliable because it is based on a few number of events over a short and incomplete period of ood record It does not consider any changes in the oodplain over me naturally or due to urbaniza on so the boundaries are really just an es mate 20 What are the limita ons for building on a designated …
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