GEOL 118 Final Eam Format similar to eams 1 and 2 Covers Lectures #27 40 (Global Climate Change I - Meteorite Impacts III) 8:00 AM, Thursday, May 11 th Location HERE Bring Photo ID Optional Question/Answer Session Location and time TBA Official University of Illinois policy will be followed for requests for a conflict final eam time. Specifically, you must have a verifiable official University ecuse such as three final eams in 24-hour period to schedule a conflict final eam for GEOL 118. If you have another final eam scheduled for the same time, then it is probably a combined section (or conflict) final eam and you must take a conflict eam in that course in accordance with Student Code.
#36 Floods III - Pros and Cons of Construction Measures for Flood Control
Flood Control US and other countries have enormous "investment" in flood-prone areas (heavily inhabited and developed), which needs to be protected. People have epended many resources to "control" flooding. Trends in flood damage and cost of flood control measures, 1928-2006
Flood Control - Construction Measures Four major flood control measures involving construction are: channelization, floodways, dams, artificial levees. Fortified by a levee, a house near Vicksburg, MS survives Yazoo River flood in May 2011
Flood Control - Channelization Channelization involves changing channel characteristics including straightening, deepening, or widening channel, or clearing debris from the channel, or lining channel with concrete. Goal is to allow more water to be pass through river with faster flow or greater discharge. Sometimes channelization intended for both flood control and meander erosion control, important for urban rivers.
Flood Control - Channelization of Boneyard Creek Boneyard Creek, which runs through Champaign-Urbana, had its channel enlarged, which helped to reduce flooding. Channelized Boneyard Creek at Bardeen (Engineering) Quad
Flood Control - Floodway (Diversion Channel) transports floodwaters away from populated areas Eample = Winnipeg, Canada, built ~30 mile floodway around city in 1968, which greatly reduced flooding from Red River (floodway loops around developed region, dumps water back into river farther downstream) Red River floodway
Flood Control - Dams/Reservoirs A dam blocks flow of river and creates reservoir behind it, useful for flood control because reservoir can be filled during high rainfall periods. Reservoirs usually not intended to retain all rainwater during flood; help to control rate of stream flow, like large valve. Fanshawe Dam and Reservoir, England
Flood Control - Retention Pond Retention pond (detention basin) is reservoir on smaller scale for individual towns or neighborhoods. Another solution to frequent flooding of Boneyard Creek was construction of two retention ponds in area bounded by University Ave., Green St., Second St., Neil St. Boneyard Creek detention basins
Flood Control - Artificial Levees Artificial levees are human-made walls of sand and mud built along sides of channel to raise height of riverbank, allowing greater flow without flooding. To prevent water seepage through levee (weakens it), which is better - sand or mud? mud levee allows less water seepage through because mud is much less permeable than sand artificial levee (grassy area) along Mississippi River
Clicker Question The levee below stops floodwaters from going into the floodplain. How does this affect the height of floodwaters downstream from this area, compared to before the levee eisted? A. Tends to make the flooding worse. B. Tends to make the flooding less severe. C. Does not affect downstream areas.
Flood Control - Floodwalls Floodwalls = concrete levees; much more epensive than sediment levees, most commonly constructed near cities, with high ta revenue Floodwall along Mississippi River near St. Louis
Flood Control (Construction) Measures-Benefits, Drawbacks Channelization, Floodway, Dam/Reservoir, Artificial Levee What are the benefits to society (pros) associated with the above measures? What are the drawbacks to society (cons) associated with the above measures?
Flood Control (Construction) Measures - Benefits Benefits Flood Control Measure Reduce Flooding (Decrease Damage, Deaths) Meander, Erosion Control Hydroelectricity, Water Supply, Recreation Channelization Floodway Dam/Reservoir Levee
Flood Control - Dams/Reservoirs Other benefits to dams and reservoirs include hydroelectricity, water supply, recreation Hoover Dam along Colorado River
Flood Control (Construction) Measures - Drawbacks Flood Control Measure Epensive Limited Lifespan Can Be Futile (+ catastrophic failure) Channelization Floodway Dam/Reservoir Levee
Flood Control Measure Channelization Floodway Dam/Reservoir Levee False Sense of Security Flood Control (Construction) Measures - Drawbacks
Flood Control (Construction) Measures - Drawbacks Drawbacks Flood Control Measure Transfers Problem Elsewhere Can Worsen Erosion Problems Loss of Beauty Channelization Floodway Dam/Reservoir Levee
Flood Control - Channelization Kissimmee River, FLchannelized/straightened in 1960s, restored in 1980s
Flood Control - Channelization Concrete-lined Los Angeles River
Flood Control - Channelization of Boneyard Creek Boneyard Creek, which runs through Champaign-Urbana, had its channel enlarged, which helped to reduce flooding. Boneyard Creek-unscenic section Boneyard Creek-scenic section Crazy guy kayaking Boneyard
Flood Control (Construction) Measures - Drawbacks Drawbacks Flood Control Measure Habitat Loss (Negative Impact on Ecosystem) Lose flooding benefits (fertile soil, water) Impacts of Dams/Reservoirs Channelization Floodway Dam/Reservoir Levee
Drawbacks of Dams/Reservoirs One drawback is the creation of a standing water body, which causes deposition of sediment in the reservoir and erosion downstream due to lack of sediment load. Effect of Dam Construction Deposition Dam Erosion Initial profile There also is an impact on ecosystem due to change from river to lake ecosystem (endangered Yangtze River dolphin) can also hinder migration of fish such as salmon
Drawbacks of Dams/Reservoirs Other drawbacks to dams and reservoirs are land lost and people displaced due to creation of large reservoirs, e.g., Three Gorges Dam, China, and loss of scenic beauty Three Gorges Dam, China Lake Mead, associated with Hoover Dam
Putting it all together. Make a quick list of the positive and negative impact of a large dam project.
Opinion Question In your opinion, do dams like the Three Gorges Dam have an overall positive impact? A. Yes, positive impact. More positive effects than negative. B. No, overall negative impact. More negative effects than positive. C. Neutral- some positive, some negative, roughly equal.