Module #16 - Fluvial Actions (Rivers and Lakes)

Please remember to record all definitions and content in your virtual notebook. Definitions can be found by clicking on highlighted words.

Rivers go through periods of development, just like humans do. Rivers start out young, with a lot of vertical erosion. The shape of its valley tends to be V-shaped, with many rapids and falls. The channel of a youthful river tends to be straighter, with a steep gradient (slope). Because these rivers flow rapidly, they can transport huge amounts of sediment. Young rivers tend to be found in mountainous and highland areas, where the ground has recently uplifted. Gradually, as the youthful stream cuts into the ground, less energy is used in cutting vertically and more energy is transferred laterally or sideways. When more sideways erosion occurs, the river enters maturity, and the river begins to meander, widening the valley floor. The meandering river now erodes on its outer banks and deposits material on its inner banks.

Permission granted by Bruce Railsback, Professor, Department of Geology

In maturity, the river current slows down and the channel begins to widen. Fewer rapids and waterfalls occur and many large tributaries enter the main river channel. Finally, rivers become old when they begin to deposit more sediment than they transport. Old rivers have very wide flood plains, are slow moving, and tend to be muddy. Sediments deposited in the stream channel build levees that contain the water. When water levels rise on rivers with levees, the water breaks through the natural banks and fills the flood plain with silty water. This flooding provides natural fertilizer to flood plains, creating excellent farming land. Most of the world's best farmland has been the result of old age rivers flooding over their banks. The Nile, Ganges and Indus rivers are all famous rivers that supported great agricultural societies. Old age rivers continue to erode sideways, eventually forming meaders that cutoff from the river channel. When these meanders completely cut off from the main channel, they created isolated lakes called oxbow lakes.

Permission granted by Bruce Railsback, Professor, Department of Geology

Part 2: Blog Posting

Log in to the LMS. Complete a post under Module #16 answering the following question:

1. Choose one natural disaster that involved severe flooding (other than the Red River flood in 1997). Here is a link to some major floods in the past 50 years worldwide. Major Floods in Canada. Floods can occur due to a number of causes including hurricanes / typhoons / cyclones, snow / ice melt, intense rainfall, etc.

Task: Write a 50-100 word summary of the flood Including the geographic region, the major causes of the flood and the environmental, economic impacts, the features of the system, wildlife, hydrology, etc. Include a link to a photograph, map of location and a youtube video if possible. Include all sources at the bottom of our post.

Part 3: Assignment: Red River Flooding in Manitoba

Many areas in Canada face flooding from rivers. In Ontario, Conservation Authorities were formed many decades ago to prevent people from damaging watersheds and increasing the flooding threat. Conservation Authorities protect and manage water resources so people don’t build on flood plains, natural areas are protected to prevent future flooding, and to educate the public about our valuable water resources. Despite the work of Conservation Authorities and governments, flooding is still a major problem through out Canada.

CASE STUDY: MANITOBA’S "FLOOD OF THE CENTURY" (SPRING 1997)

• the Red River flows 700 km northward to Lake Winnipeg

• Winnipeg is at the confluence (where two rivers meet) of the Red and Assiniboine Rivers

• in 1950 100,000 people were flooded out of Winnipeg with 12% of the city underwater

• Manitoba decided to build a massive earth channel that taps the Red River, nicknamed the Red River Floodway. It taps the Red River just south of the city and goes east of Winnipeg then rejoins the Red River 20 km north of the city.

• the Red River Floodway took 6 years to build, cost 63 million dollars, is 47 km long, over 100 m wide, moved 30 % more earth than the building of the St. Lawrence Seaway

• it is estimated to have saved $ 2 billion dollars (6 times the cost of building it), used 18 times since it was built

• huge gates which can be opened, normally can divert 45 % of Red River (60,000 cubic feet per second [c.f.s.]) but can be pushed to 100, 000 c.f.s.

• in 1997 as the water flowed north, created a 2000 km2 lake dubbed the “ Red Sea”. This backflow (over 7000 c.f.s. more than the Red’s capacity) would have skirted the floodway to the West of Winnipeg so the Brunkild dike had to be constructed in 3 days (should have taken one month). It is a 40 km earthen dike which had to be built at night by the military (using flares).

• every town in Manitoba saved due to permanent ring dikes around small towns (eg. Morris, St. Jean Baptiste) and extra sandbagging done at the last minute.

• “ Red Sea” was contaminated by fertilizers, pesticides, and animal carcasses. Over 100,000 cattle moved, rest shot.

• 6.5 million sandbags used, 7000 troops, 85, 000 people evacuated on both sides of the border, 26,000 in Manitoba

• Red River crested 24.5 feet above normal

Stats Canada: Red River Flooding Site (1997)

City of Winnipeg: 1997 Flood Facts and Statistics

Assignment (answer in google docs and share with Mr. Durk)

Write a one page letter (double spaced) to a Minister in the House of Commons or mayor (choose one that this topic would be relevant to, it could be the ) addressing your concerns over the issues of flooding, flood control (dams) and the building on floodplains in their city / riding. Use relevant statistics in your letter to supplement your argument and concerns.

Resources

1. Conservation Ontario

2. The Atlas of Canada - Major Floods