Flooding events are the most frequent and costly natural hazards that humans encounter. At any given time, there are numerous locations on Earth experiencing flooding as a result of heavy precipitation, hurricane storm surges, or even tsunamis triggered by geologic events. Visit the NASA Earth Observatory website to view current flooding events. Since flooding events are often unpredictable, there may be few floods on the current map. However, you are encouraged to search the most recent months of data by clicking the links in the bottom right of the map.
Things an Experienced Geographer Would Consider While Exploring the Map:
Where are flood events occurring? Are there patterns or trends in their occurrence?
What natural events are causing the flooding in these places? What features create the unique spatial significance?
How is the flooding affecting people? How are people affecting the flooding? What interrelationships exist?
How would you feel if this were happening in your community? What geographic perspectives exist?
ACTION
Part 1: Causes of Flooding
Flooding is most often a natural process that occurs anywhere an excess of water accumulates. However, floods can also have human origins. For instance, human activities, such as dams, create controlled flooding situations. However, the most dangerous floods are created by natural and unpredictable circumstances. There are no complexities involved other than identifying the source of the excess water. Floodwaters can be created as a result of a few situations, each with their own unique spatial significance.
Sustained heavy rainfall: Weather systems passing over a region can drop more precipitation than the ground is able to soak up. This excess water flows overland to lakes and rivers where it can cause flooding. All regions have unique underlying geology that determines how quickly and how much water can be infiltrated into the ground. For instance, areas with clay soil or a solid bedrock surface do not soak up water well, whereas areas with deep, sandy, or heavily vegetated surfaces are readily able to absorb water.
Rapid snowmelt: In colder regions where snow accumulates throughout the winter, periods of warm temperatures can melt a season's worth of snow in a short time. Drainage basins(definition:A drainage basin or catchment basin is an extent or an area of land wherer all surface water from rain, melting snow, or ice converges to a single point at a lower elevation, usually the exit of the basin.) receive more water than can be handled, causing lower elevation rivers and lakes to flood as they receive the melted snow from the entire region. This situation is most likely to happen in mountainous regions or northern latitudes like Canada during the spring.
Storm surges from hurricanes: The centre of a hurricane (the eye of the storm) has an extremely low atmospheric pressure. At all times, the atmosphere pushes down on ocean water. However, in the eye of a hurricane this pressure is so low that the ocean water is free of the downward force. It can therefore rise several metres, causing flooding in coastal areas.
Tsunamis: Activity 2 taught us how tsunamis form. As a tsunami approaches shallow water, its energy creates a tidal wave that can inundate coastal regions.
Controlled human activity: All around the world, dams have been created that purposefully restrict the flow of rivers. Dam creation results in a reservoir that slowly increases water levels above the dam. Though controlled and expected, there are often many public impacts, such as relocation of people or alterations to the environment. This graphic shows how the creation of a dam led to the flooding of agricultural land in Saskatchewan. Controlled flooding is actually more common than you might think. It has been undertaken hundreds of times in Canada for the creation of hydroelectric generating stations. One little known example occurred during the creation of the St. Lawrence Seaway. Learn more about the nine communities flooded to build this seaway.
Uncontrolled human activity: Sometimes, despite our best efforts, dams created by humans breach and release a torrent of water stored in their reservoirs. Click here to see an image of the Mount Polley mining disaster that spilled toxic effluent into BC waterways in August of 2014.
Whether caused by nature or humans, flooding poses a significant risk to people and property. In addition, Numbers 3 and 4 in the above list are perfect interrelationship examples as the events of one natural hazard can then influence the occurrence of another hazard. Keep these six situations in mind as you complete the study of the 2013 Calgary Flood later in this activity.
Part 2: Influence of Water and Flooding on the Landscape
In Unit 2 Activity 1 you learned that earthquakes and plate tectonics are able to create towering mountain ranges or deep ocean trenches over the course of millions of years. The long term erosive actions of water also create magnificent landscapes, sometimes over the course of only a few years. The power of water is no better seen than by looking at a few of the landscapes it has created. Use the slideshow to learn about landforms created by water.
The Colorado River has carved this epic river valley (definition:canyon)over millions of years.
David Scott, 2012
Alberta Badlands
They were created 14000 years ago when a natural dam holding back glacial meltwater burst. A flood of epic proportions ensued, creating a landscape feature called channeled scablands/badlands(definition:barren landscapes of interconnected eroded river channels created during large releases of water.) in a matter of years. The same events have happened all over the world and are even a leading hypothesis in the explanation of the historical accounts of biblical floods.
All rivers have a main channel(definition:the normal course of a river's flow marked by riverbanks) where water typically flows, but all rivers also create a larger feature known as a floodplain where occasionally high waters spill over the river banks and flood the adjacent area. Over geologic time (millions of years) this periodic flooding deposits sediment on the floodplain creating a flat, easily observable landform, which is often excellent for agriculture.
NASA image created by Jesse Allen, using data provided by the University of Maryland’s Global Land Cover Facility
The Mississippi Delta
Deltas are fan shaped landforms created where rivers meet bodies of water. The fast moving river water slows down and deposits sediment, creating an intricate network of channels that extend out into the water. Deltas are particularly susceptible to flooding as they are low lying, must direct the entire flow of the river, and usually meet oceans where hurricane storm surges pose additional threats.
Now that we understand the causes of floods and some terms and landforms associated with them, we will use the concept of geographic perspectives to study a famous Canadian flood. To begin, use the slider to interpret satellite imagery of the flood from before and during this event. Remember that you practiced interpreting timelapse imagery in Unit 1 Activity 2.
To access the Arc GIS application to explore the Calgary Flood of 2013 you will need to create a trial account on the Arc GIS site.
Calgary Flood Case Study
Explore the story map below and complete the Calgary Flood Case Study: Student Questions. The activity requires you to think from the perspective of someone else, which is sometimes hard to do. For some tips on how to think from someone else's perspective read the following article.
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CONSOLIDATION
The Calgary flood is a great place to dig deeper into the study of geographic perspectives. As you discovered earlier in the lesson, the Calgary Zoo was hit hard by the flood, as it is located on the river bank and a small island within the river. Knowing this surficial information is important. However, to better understand the flood’s impact on all people (and animals) connected to the zoo, you will read this article Flood at the Zoo: The Inside Story.
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Flood at the Zoo
When we read, we often pay attention to specific pieces of information based on our own perspectives and interests. Once you have read this article, imagine the information that other individuals and stakeholders would find most important and significant based on their perspective. Complete this chart as a way of organizing information from the article.
Calgary Flood Case Study
Learning Goals and Success Criteria
Learning Skills and Work Habits