FloodingGoods and Bads, Natural and Man-made

Types of Floods

• Flash-floods (quick to come and quick to go – don’t know they are coming)

• Rapid-onset floods (slightly slower to come and last a bit longer – know they are coming but not much time to do anything about it except avoid)

• Slow-onset floods (know they are coming before hand, but usually last longer as well - can plan ahead and work to alleviate issues)

What Causes Flooding?

Look at natural and human causes.

Natural

• volume, distribution, intensity and duration of rainfall over a catchment• snowmelt/ice melt and corresponding runoff• the capacity of the stream or river network to handle runoff• blockages in the stream and river network• catchment and weather conditions prior to a rainfall event• ground cover in area of rainfall• topography• tidal influences

Human• Limitations to drainage caused by human infrastructure or change (eg.

roads, bridges, parking lots, cityscapes, farming)• Changes to stream or river networks• Climate change (the increasing intensity of storms)• Deforestation

Positives and Negatives of Flooding?

Positives

• Nutrients brought to soil• Wetlands can be re-filled and renewed• Seeds are carried from one place to another• Groundwater and soil water can be replenished

Negatives

• Huge economic costs (both urban and rural)• Crops ruined and livestock killed or displaced• Human infrastructure destroyed

• Invasive species• Spread of toxic substances • From one waterway to others• From land into water

• Animal and human life can be taken• Changes landscapes (erosion etc.)

Example: Winnipeg, Manitoba, Canada

Nelson River Basin (catchment) Red River Drainage Basin (catchment)

2011 Flood: Winnipeg, Manitoba, Canada

Winnipeg Solutions: Amphibex Machines

Amphibex Machine breaking up ice on river near Manitoba

Winnipeg Solutions: The Floodway

Ways to Minimize Flood Risks?

• Walls, levees, dams, etc.• Spillways (to take floods around problematic areas)• Keeping drainage infrastructure in good working order• Good town planning• Vegetation projects

Prep: Case Study

• Find a case study and build a visual and written river based case study briefly covering:

1. Flood event (with maps and pictures)2. Cause for floods3. Damage caused by flood/benefits to area (if any)4. Ways they try to minimize flooding in area or will try to minimize

flooding in area in future