Science of Natural Disasters: RIVERS& FLOODS! 27 April 2016 Rebecca Clotts Department of Geology, University of St Thomas Flood in St Paul, 2014, Star Tribune 1
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What is a watershed? 3
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What is a drainage network? (a) Dendritic (b) Rectangular (c) Trellis (d) Radial 8
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What is a river profile? 11
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What is a river profile? How does the channel shape change? How does the discharge change? 13
The work of rivers Work of water River Erosion, Transport, & Deposition Watch the animation: http://www.classzone.com/books/earth_scien ce/terc/content/visualizations/es0604/es0604 page01.cfm?chapter_no=visualization Where are the biggest particles deposited? Smallest? What controls where each is deposited? 14
River Types Permanent Ephemeral 15
16 River Channel Types
What kind of river? Platte River 17
What kind of river? Mississippi River 18
What kind of river? Minnehaha Creek 19
Meandering Rivers 20
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Formation of an Oxbow Lake 23
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Meandering Rivers Minnesota River & Rush River Confluence 28
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What is a Flood? Over Bank Bank Full 30
What is flooding? Flood Monitoring: http://water.weather.gov/ahps/ 31
What causes Flooding? 32
How are Floods measured? Dischargeis the volume of water that passes through a given cross section per unit time, usually measured in cfs or cms 33
How are Floods measured? Stage 34
How are Floods measured? River Stage River Discharge 35
How are Floods measured? http://water.weather.gov/ahps2/hydrograph.php?wfo=mpx&gage=mham5 36
How are Floods measured? http://water.weather.gov/ahps2/hydrograph.php?wfo=mpx&gage=stpm5&view=1,1,1,1,1,1,1,1&toggles=10,7,8,2,9,15,6&type=2 37
What is LAG TIME?
Flood Prediction? Recurrence Interval RI = N + 1 m
ST. CROIX RIVER AT ST. CROIX FALLS, WI Year Maximum Discharge (cfs) 1998 3,746 1999 4,469 2000 3,432 2001 6,120 2002 5,510 2003 5,436 2004 4,380 2005 4,390 2006 4,312 2007 2,777 http://waterdata.usgs.gov/nwis/rt N + 1 RI = m N = # of years of records N = M = rank of discharge Which year is 1? 40
Flood Prediction? Flood Frequency 41
What are the types of floods? Flash Floods
What are the types of floods? Seasonal Floods
What are the effects of floods? Transport of large particles or objects Erosion Water damage to structures Deposition of mud Crop loss Concentration of garbage, debris, pollutants LINK, photo link Drowning NWS PSA Turn Around Don t Drown (0:53): http://www.nws.noaa.gov/os/water/tadd/ 45
Are there flood benefits? Fertile Land Floods flush channels of accumulate debris important to the aquatic ecosystem Flooding builds up sediment on the surrounding land 46
What factors influence flood severity? Amount of rainfall/snowmelt Infiltration Extent of soil saturation Vegetation cover Soil Types (depends on climate) Frozen ground Human Construction Rainfall Distribution 47
What factors influence flood severity? Rainfall distribution 48
Flood Mitigation Mapping Floods 50
Flood Mitigation Reduction of Vulnerability Floodplain zoning Floodplain Building codes Floodplain Buyouts 51
Flood Mitigation Engineering approach Channel modification Dams Retention Ponds Levees, Dikes, and Floodwalls Floodways LINK http://www.fmdiversion.com/ Website Modeling: https://ees.as.uky.edu/sites/default/files/elearning/module12swf.swf 52
Humans & Floods Levees and Flood walls 53
Humans & Floods -Channelization 54
Humans & Floods -Channelization 55
http://skagitcoop.org/wp-content/uploads/illabot-report_final_draft2.pdf 56
Increase in flood plain adjacent to the channel Decrease in width of the channel Change in the natural character of the channel 57
http://skagitcoop.org/programs/restoration/illabot-creek/ 58
Humans & Floods -Urbanization red = vegetation blue = water pale blue = shallow or sediment-laden water gray = buildings and paved surfaces 59
Humans & Floods -Urbanization 60
Humans & Floods Loss of Wetlands Wetlands help absorb excess water from precipitation and spring melt Naturally store water during heavy rains Slow runoff going into a stream Reduce flooding peaks 61
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Humans & Floods -Dams 63
Humans & Floods Soft solutions Video: 2:18 minutes: http://www.pbs.org/wgbh/nova/tech/judo-nature.html 64
What are some problems with rivers? Flooding is the #1 disaster in the US 30 year averages 82 fatalities / year Nearly >$8 billion / year http://www.nbcnews.com/science/increased-flooding-maycost-world-1-trillion-2050-6c10937608 http://www.nws.noaa.gov/hic/ 65
What are some problems with rivers? Water Quality / Pollution MN Drinking water: http://www.epa.gov/waters/ http://www.cnn.com/2014/08/05/tech/gulf-of-mexico-dead-zone/ http://oceantoday.noaa.gov/happnowdeadzone/ 66
What are some problems with rivers? Overuse 67
Flood Resources US Rivers in trouble from overuse http://www.smithsonianmag.com/video/clim ate-change-and-the-colorado-river.html 68
What are some problems with rivers? Avulsion River channel is abruptly abandoned in favor of a new channel 69
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Flood Resources: Are YOU at RISK? Check out: http://www.floodsmart.gov 71