Name Rebecca Gallanter Learning Unit 7 Flood Review Questions This assignment is designed to assess your understanding of Unit 6 and 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 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 infiltration and Base flow through the groundwater system 4 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 higher 5 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 second 6 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 of time They have steep gradient and usually have high and rapid runof 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 unafected 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 afect tributaries 8 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 occure in 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 materials 11 What information is represented by a hydrograph The connection between precipitation and the efect it has on a streams 12 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 basin 14 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 zoned 15 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 years 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 The simple formula is T N 1 M A numeral example would be 140 1 4 35 years 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 100 1 2 50 18 If a 100 year floodplain was flooded in 2003 in how many years should we expect the next 100 year flood By referring to them as 100 year floods it is giving the impression that those floods do not occur very often So one would assume that on average they would occur every 100 years however there could be two follow each other in two years in a row 19 Why is the specified 100 year floodplain size or 100 year flood height not a very reliable indicator for future large floods They are not reliable because the geography can change based of a bunch of diferent factors such as urbanization or reconfiguring of an area to make it less likely to flood So having the specified 100 year floodplain size or 100 year flood height could change between when the next two floods occur 20 What are the limitations for building on a designated floodplain The limitations are raising the land level with fill building
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