Flood "Control" (Construction Measures) - directed by U.S. Army Corps of Engineers. First we will introduce flood control methods involving construction measures. After that, BE PREPARED TO DISCUSS BENEFITS AND DRAWBACKS OF EACH CONSTRUCTION MEASURE.
1) Channelization - involves changing channel characteristics (straightening, deepening, widening, clearing debris of channel, or lining channel, e.g., with concrete). Example = Boneyard Creek in Campustown + Urbana (link #2) (see photos of kayak run on Boneyard Creek, trip #2) Allows more water to be funneled through river (faster flow).
2) Floodway (diversion channel) - transports
floodwaters away from populated areas. Example = Winnipeg,
Canada,
constructed 47 km (29 mile) floodway around city in 1968, which
<< flooding from Red River (floodway loops around
developed region + then dumps water back into river farther downstream)
(see photo).
3) Dam/Reservoir -
blocks flow of river + creates reservoir,
which can be filled during heavy rainfall; Examples = Hoover
Dam-
Colorado River, AZ/CA; Grand Coulee Dam -
Columbia River, WA;
Aswan Dam -
Nile River, Egypt; Three
Gorges Dam - Yangtse
River in China (largest
construction project
ever, see computer
image of completed dam). Detention basin
(Retention
pond/basin) - mini-reservoir for individual
developed area or community, e.g., Boneyard
Creek (link
#2, photo
#1 of "scenic" Boneyard Creek, photo #2).
4) Artificial levees - Human-made walls of sand + mud built along sides of channel to > height of riverbank (allows > flow without flooding) (photo #1, #2).
Which sediment type is better to prevent water from flowing through levee, sand or mud? Why?
Floodwalls = concrete river channel walls (more expensive, usually constructed near cities with large tax base + greater risk).
Pros + Cons of Construction Measures for Flood Control (from student responses)
| Flood Control Measure - Pros |
| Channelization |
| Floodway (diversion channel) |
| Dam/Reservoir |
| Artificial Levee |
| Flood Control Measure - Cons |
| Channelization |
| Floodway (diversion channel) |
| Dam/Reservoir |
| Artificial Levee |
| Flood Control Measure - Cons |
| Channelization |
| Floodway (diversion channel) |
| Dam/Reservoir |
| Artificial Levee |
Flood Mitigation (Public Policy)
1) Preserve wetlands (swamps) - excellent locations for rainwater infiltration into ground, rather than running off into river; ~50% of world's wetlands have been lost over past 200 years.
2) Public education - about risks of floods, floodplain, flood frequency, etc.
3) Mapping + zoning - determine areas of risk + restrict land use (allow only parks, golf courses, agriculture); most effective approach from environmental perspective. Zoning restrictions only apply to new construction.
4) Mandatory insurance - Require those who live on floodplain to have insurance (for homes + crops). Offered by Federal Emergency Management Agency (FEMA) since 1950s but not very popular.
5) Relocate - Give government aid for high-risk communities to move, e.g., Valmeyer, IL.
