Ashlan Rogers
A01531295
Assignment 10 1. List the 4 key variables that describe how streams work. The four key variables that describe how streams work are discharge, gradient, available sediment, and channel sinuosity. 2. A) Describe what happens to a stream if it has too much discharge. When there’s an increase in discharge, it causes an increase in velocity and energy the stream has. This increases erosion of the stream bottom or increases sinuosity of the channel by eroding the stream banks.
B) What happens if a stream has too much sediment load? It causes sediment deposition on stream bottom creating a braided stream. 3. A) What expected flood size does FEMA use to establish its regulatory requirements? FEMA uses the 100 year flood for building regulations.
B) In any given year, what is the probability that a 100 year flood will occur? There is a 1% chance each year that this level of flood could occur. Maps are available with 100 year flood outlines. 50 year flood = 2% chance. 4. What are 6 ways that killer floods can occur? 1) Precipitation is above normal in drainage basin, 2) sudden snow/ice melts, 3) landslides, 4) modifications, fire and urbanization = more runoff 5) Dam failure, 6) geography of stream basin/area. 5. A) Are the canyons of Utah susceptible to flash floods? Why or why not? Yes because steep topography helps thunderstorms build and then provide the rugged valleys that channelize the killer floods. Utah canyons are very steep so it is very possible.
B) How deep does water have to be to possibly be fatal to people who try to drive through flood waters? 2 ft deep. 6. A) How do regional floods differ from flash floods? They differ because regional floods occur in large river valleys with low topography whereas flash floods happen in tall steep places.
B) Why was the Mississippi River flood of 1993 so big? Because it went through all of the different flood stages and water levels began in April and continued through August. Some towns had more than 160 consecutive days of flooding. 7. A) List all the 4 ways that levees can fail. 1) waves 2) overtopping water 3) slumping 4) piping
B) How can dams offer some flood control? Do they? Why or why not? Dams do not provide flood control because they are usually too full. They can fail. 8. List the pros and cons of building more levees. A con is that some people say levees cost more than the value of the buildings they are protecting. A pro is that the increased carrying capacity of a river allows more years of high-water flow to occur without flooding. 9. What are 5 other ways that flood damage can be mitigated? 1) sandbagging 2) forecasting 3) zoning and land use 4) insurance 5) presidential disaster declarations 10. A) What exactly is a hydrograph? A hydrograph plots the volume of water or stream depth versus time, recording the passage of water volumes flowing down-stream.
B) How does urbanization affect hydrographs? In urbanized areas, humans cover much of the ground with houses and everything.. Covering the ground with an impervious seal prevents rainwater from soaking into the ground and causes rainwater to flow rapidly across the surface, thus reaching the stream ever more quickly. 11. A) How is an existing stream changed by channelization to allow water to flow easier through the channel? Clearing the channel of trees, debris and large boulders to reduce channel roughness and then increasing the channel capacity by digging it deeper, wider and straighter.
B) Would you want to live along a channelized stream? Why or why not? I would not just because they clear trees and everything and I want to live in a place that has lots of trees and is beautiful… I can’t imagine a channel being a pretty place to live. 12. What is a problem associated with the channelized San Diego River in Tijuana, Mexico and the un-channelized San Diego River as it enters San Diego California? Tijuana channels and San Diego doesn’t. Water spreads out once in San Diego and causes flooding. 13. What caused the flood that created the channeled scablands in Washington? Immense floods eroded channels and stripped the overlying sediments off an area.
Thought Question 1. Millions in the United States live on floodplains. Do you feel that taxpayers (the federal government) should offer disaster relief to victims of floods? Should people, who’s homes have been destroyed by floods, be allowed to rebuild in the floodplain? I don’t know, this is such a hard question! I have a lot of issues with a lot of things that our tax money goes to and I feel that if you choose to live in a place where you’re in danger of floods, then that’s your choice. But I do think there should be some disaster relief offered because that situation is just totally unfortunate.