Flooding

Question 1

How is precipitation distributed?

Answer 1

Precipitation, or rain, snow, sleet, or hail, is not evenly distributed across the Earth. There are several factors that determine the distribution of precipitation, including:

1. Latitude - areas near the equator receive more precipitation than areas near the poles. This is because warm, moist air rises near the equator, cools, and releases moisture as precipitation.
2. Altitude - Precipitation increases with altitude, as air rises and cools, leading to the formation of clouds and precipitation.
3. Topography - The shape of the land can also influence the distribution of precipitation. For example, mountains can act as barriers, blocking moist air and leading to precipitation on the windward side, while the leeward side is much drier.
4. Air currents - Air currents, such as the prevailing winds, can also play a role in determining the distribution of precipitation. For example, coastal regions can receive more precipitation due to moist air being carried inland by prevailing winds.
5. Ocean currents - he distribution of precipitation is also influenced by ocean currents, which can transport warm, moist air from the ocean to the land, leading to increased precipitation in coastal regions.

Question 2

What causes floods?

Answer 2

1. Heavy Rainfall - Heavy and prolonged rainfall can overwhelm the capacity of rivers and streams to carry away water, leading to flooding.
2. Melting Snow - In areas with heavy snowfall, the rapid melting of snow can cause floods as the water runs into rivers and streams.
3. Dam or Levee Breaches - Dam or levee breaches can cause flooding by releasing large amounts of water in a short period of time. This can be due to structural failure, overtopping due to heavy rainfall, or human error.
4. Costal Storm Surges - Coastal floods can be caused by storm surges, which are ocean waves that are pushed inland by strong winds, such as those from hurricanes or tropical storms.
5. Urbanization - The urbanization of floodplains and the conversion of natural landscapes into pavement and buildings can increase the risk of flooding by reducing the amount of land available to absorb water.

Question 3

How does the water escape?

Answer 3

Water escapes either by forming new channels or through the floodplain

Question 4

What does a floodplain look like?

Answer 4

A floodplain may appear as a wide, flat plain that borders a river or stream. During dry periods, the floodplain may appear as grasslands or croplands, with little visible water. However, during times of high water, the floodplain can become covered with several feet of water, transforming it into a shallow lake or marsh.

Question 5

What are the types of floods?

Answer 5

1. River Floods - River floods occur when a river overflows its banks and inundates the surrounding land.
2. Flash Floods - are sudden and intense floods that occur within a few hours of heavy rainfall.
3. Coastal Floods - occur when seawater inundates coastal areas due to storm surges, high tides, or a combination of both
4. Urban Floods - occur when heavy rainfall or other precipitation accumulates on the pavement and roofs of cities and towns, causing flash flooding.
5. Reservoir Floods - occur when water is released from a dam or reservoir due to heavy rainfall, snowmelt, or other factors that increase the water level in the reservoir.
6. Ice Jam Floods - occur when ice accumulates in a river or stream, blocking the flow of water and causing the water level to rise. Ice jams can form when river ice breaks up in the spring and becomes lodged in narrow sections of the river channel, creating a dam-like effect.

Question 6

What causes downstream flooding?

Answer 6

Dam failure or mismanagement that is almost always preceded by heavy rainfall (Ex. Chicoutimi’s Flood or Oroville, California’s Sediment discharge)

Question 7

What are the environmental impacts of dams?

Answer 7

Positives:
1. Cheap electricity
2. Flood control
3. Reduction of draught fear

Negatives:
1. Dam fails
2. Habitat loss
3. Natural flooding loss
4. Natural sediment deposition loss
5. Impedes on aquatic biology
6. Erosion

Question 8

What is Dam Erosion?

Answer 8

Erosion caused by dams can occur both upstream and downstream of the dam structure. Upstream erosion is caused by the impoundment of water behind the dam, which can increase the velocity of the water and cause erosion of the riverbed and banks. Downstream erosion is caused by the release of water from the dam, which can also increase the velocity of the water and cause erosion of the riverbed and banks.

Question 9

What was the pre-history of the Aswan Dam?

Answer 9

Fossil groundwater mining in relation to the pre-history of the Aswan Dam refers to the extraction of ancient, non-renewable groundwater reserves in the region around the dam. The construction of the dam reduced the recharge of the groundwater aquifers in the region, leading to a decline in the availability of the groundwater, which has had significant impacts on the local population and the environment.

Question 10

Why was the Aswan Dam built?

Answer 10

1. Control Flooding
2. Water storage for irrigation
3. Hydroelectricity

Question 11

Why was Abu Simbel relocated?

Answer 11

Due to the construction of the Aswan Dam, the temples of Abu Simbel were in danger of being flooded by the rising waters of the lake. In order to save the temples, a massive international effort was launched in the 1960s to relocate them to a higher elevation, where they would be safe from the rising waters of the lake.

Question 12

How are hurricanes formed?

Answer 12

Hurricanes are formed from a type of tropical cyclone, which is a rotating system of clouds and thunderstorms that form over tropical or subtropical waters. This required conditions such as:

1. Warm water - a source of warm, moist air fuels their development. This air rises and cools, releasing heat and moisture into the atmosphere.
2. Converging winds - winds converge and force air to rise, which results in the formation of clouds and thunderstorms.
3. Low wind shear - helps to keep the storm organized and allows it to continue to grow.
4. Coriolis effect - the rotation of the Earth helps to steer the storm and gives it its characteristic rotating shape.

Question 13

How do Hurricanes cause floods?

Answer 13

1. Heavy Rainfall - Often brings heavy rainfall as they move over land, which can quickly lead to flash floods and river floods.
2. Storm Surge - The rise in sea level that occurs as the storm approaches the coast.
3. High Winds - The winds can knock down trees and power lines, creating blockages that can impede the flow of water and increase the risk of flooding.
4. Inland flooding - The wind can push water from the ocean or Gulf of Mexico into rivers and streams, causing them to overflow their banks and flood surrounding areas.

Question 14

What happened with Hurricane Katrina?

Answer 14

Hurricane Katrina was one of the deadliest and most destructive hurricanes to hit the United States. It struck the Gulf Coast region in August 2005, causing widespread devastation and loss of life.

Question 15

What are the types of hurricane strengths (Categories)?

Answer 15

Hurricane strength is classified using the Saffir-Simpson Hurricane Wind Scale, which is a 1-5 rating system based on the hurricane’s maximum sustained wind speed.

Category 1 (1.2m - 1.5m surge): Wind speeds of 74-95 mph. Category 1 hurricanes are considered to be the least dangerous, but can still cause some damage to buildings and trees, and cause power outages.

Category 2 (1.8m - 2.4m surge): Wind speeds of 96-110 mph. Category 2 hurricanes can cause significant damage to roofs, windows, and doors, and result in widespread power outages.

Category 3 (2.7m - 3.7m surge): Wind speeds of 111-129 mph. Category 3 hurricanes are considered to be major hurricanes, and can cause severe damage to buildings, uproot trees, and result in extended power outages.

Category 4 (4m - 5.5m surge): Wind speeds of 130-156 mph. Category 4 hurricanes are considered to be extremely dangerous, and can cause catastrophic damage to buildings, communities, and infrastructure.

Category 5 (>5.5m): Wind speeds greater than 156 mph. Category 5 hurricanes are the most powerful and dangerous, and can cause widespread destruction, including the complete destruction of some structures and communities.

Question 16

What is the El Nino Southern Oscillation (ENSO)?

Answer 16

A climate pattern that is characterized by variations in ocean temperature and air pressure in the tropical Pacific Ocean. The ENSO cycle involves the warming of the central and eastern Pacific Ocean (known as El Niño) and the cooling of the western Pacific Ocean (known as La Niña)

During El Nino years:
- Fishing of California increases
- Atlantic Hurricane Strength decreases
- Forest Fires is Southwest USA decreases
- Tornados in US decreases
- Citrus & Vegetable crops in US increases

Question 17

How will climate change influence hurricanes?

Answer 17

1. Increased intensity
2. Larger storms
3. Higher sea levels
4. Change in track
5. Increased rainfall

Question 18

What are the impacts of flooding?

Answer 18

Flow & Sediment Discharge impacts:
1. Engines
2. Electrical systems
3. Homes + mildew
4. Ecosystems - runoff contaminants & burial of benthic ecosystems
5. Fires

Mudslide / Debris destroy:
1. Bridge supports
2. Channel paths (erosion, shift of channels)

Question 19

How do we clean-up run-off pollution?

Answer 19

1. Phytoremediation - Plants have the ability to absorb and accumulate heavy metals, organic pollutants, and other contaminants through their roots and shoots. Once the contaminants have been taken up by the plants, they can be removed and disposed of properly, leaving the soil and water cleaner.
2. Pump & treat methods - can be effective in removing pollutants from contaminated groundwater, and it has been used to clean up many contaminated sites around the world

Question 20

What affects flooding velocity?

Answer 20

Discharge (Q) = Width(W) * Depth(D) * Velocity(V)

Question 21

What are fluvial features?

Answer 21

Fluvial features are physical characteristics of a river or stream that are created by the movement of water. These include:

1. Riffles - shallow areas in a stream where the water flows rapidly over a bed of rocks or gravel.
2. Pools - deep areas in a stream where the water flows more slowly and often supports aquatic life.
3. Meanders - curved sections of a stream channel that result from the erosive and depositional actions of flowing water.
4. Oxbow Lakes - a crescent-shaped lake that forms when a meandering river erodes the outer banks of a bend and deposits sediment on the inner banks, causing the river channel to shift. Over time, the river may abandon its old channel and flow along a new course, leaving behind a lake.
5. Deltas - a deposit of sediment at the mouth of a river where it enters a larger body of water, such as a lake or ocean.

Question 22

How does topography affect river channels?

Answer 22

1. Slope - The slope of the land determines the speed and energy of the river flow, which in turn affects the river’s ability to erode or deposit sediment. Steep slopes produce fast-moving, energetic rivers that are capable of eroding and carving deep channels, while gentle slopes produce slower-moving, less energetic rivers that tend to deposit sediment and form wide, shallow channels.
2. Drainage Basin - The shape of the drainage basin, or the area of land that drains into a river, influences the way that water moves through the landscape and affects the river’s velocity, direction, and discharge.
3. Rocks and Soil Types - The types of rocks and soils in the landscape determine the resistance of the river channel to erosion and sedimentation. Harder rocks, such as granite, are more resistant to erosion than softer rocks, such as shale. Soils with high clay content are also less susceptible to erosion than those with low clay content.
4. Land Use: Human activities, such as deforestation, urbanization, and agriculture, can alter the topography of the landscape and affect the behavior of river channels. For example, removing vegetation from the riverbank can increase erosion, while building structures such as dams can change the river’s flow patterns and alter the formation of fluvial features.

Question 23

What are the two types of levees?

Answer 23

1. Natural Levees - Flood sediment deposition
2. Artificial Levees - Built elevated flooding blocking

Question 24

How do levees work?

Answer 24

They work by preventing water from overflowing the banks of a river or from encroaching on low-lying coastal areas. The basic principle behind levees is that they provide a raised barrier that physically holds back the water, diverting it along its normal course.

Question 25

Why do levees create a false sense of safety?

Answer 25

The existence of a levee can make people feel more secure and less likely to take other measures to prepare for a flood event. This can lead to complacency and a lack of preparedness, which can have serious consequences if a levee fails or is overtopped by a flood.

Question 26

How do you read a hydrograph?

Answer 26

A hydrograph is a graph that shows the variation of water discharge (also known as streamflow) in a river over time.

Question 27

Why might there be a difference in discharge?

Answer 27

1. Precipitation
2. Runoff
3. Evapotranspiration
4. Infiltration
5. Seasonal Changes
6. Human Activities

Question 28

How does urbanization affect flooding?

Answer 28

1. Water meets and impervious surface
2. Runoff is mostly captured in sewers
3. Changes in: terrain, slopes, vegetation, soil types

Question 29

Why is it important to know the flood frequency?

Answer 29

1. Designing dams
2. Bridge clearance
3. Size of storm drains
4. Insurance pricing
5. Floodplain proofing/management

Question 30

What was the frequency of the “Vancouver 2021”-like flood?

Answer 30

500-year event

Question 31

How was the Vancouver 2021 flood deemed to be a 500-year event?

Answer 31

A 500-year flood is one that has a 0.2% chance of occurring in any given year. They analyzed the long-term records of stream flow and precipitation in the area to estimate the maximum discharge that can be expected in a given year. They then compare this maximum discharge to the observed discharge during the flood event in question to determine if it is outside the normal range of expected values. If the observed discharge is significantly larger than what would be expected in a typical year, it may be considered a 500-year event.

Question 32

What are the different flood mitigation strategies?

Answer 32

1. Floodplain management - This involves managing land use and development in flood-prone areas to minimize the potential for damage and reduce the risk to human life and property.
2. Flood-proofing - This involves making changes to buildings and infrastructure to make them more resistant to flood damage.
3. Dams and levees - Dams can be used to regulate the flow of water and reduce the risk of downstream flooding.
4. Channelization - This involves modifying the shape and flow of rivers and streams to increase their capacity and reduce the risk of flooding.
5. Flood forecasting and warning systems - Early warning systems can provide critical information to help communities prepare for and respond to flood events.
6. Emergency planning and response -Effective emergency planning and response can minimize the impact of flood events and protect human life and property.