An extremely simple definition of flooding is “too much water in a new place” but a more technical description is when water has overflown into an area that is normally dry. In Alberta there exists a potential for flooding along all rivers and streams and there is also potential for flooding from rising groundwater levels or an abundance of stormwater. When floods occur there is the potential for property damage, hardship to people, and loss of life. However, flooding is also a natural hydrological process required by some plants and animals to thrive.
Types of Floods
There are three types of flooding of which have the potential to impact Albertans. They are Fluvial Flooding, Pluvial Flooding, and Groundwater Flooding.
Fluvial (Riverine) Flooding
Fluvial flooding occurs when surface runoff washes into a river causing the water to breach the river’s banks. The water then overflows into the surrounding area.
There are numerous contributing factors to fluvial flooding. They include:
- Rainfall conditions, such as intensity, amount, and distribution; and
- Ground conditions, such as amount of soil moisture, seasonal variations in vegetation, depth of snow cover, imperviousness due to urbanization.
In addition to regular fluvial flooding, there are some special subtypes of fluvial flooding that are defined by how the water breaches its banks, or the time it takes for the flood to occur. They include:
Flash Flooding – Rapid flooding caused by combination of intense rainfall and fast runoff. Flash flooding generally occurs in less than 6 hours and is therefore difficult to predict.
Ice Jam Flooding – When an ice jam forms on the river, the flow of water behind it backs up until the jam breaks, causing a rush of water downstream.
Alluvial Flooding – Alluvial fans are naturally occurring deposits of unconsolidated sediment that have accumulated at the mouth of a mountain canyon. As sediment comes downstream it accumulates until the riverbed rises high enough that water spills over the banks and begins to create a new path for the river in a lower area. The process is then repeated in a new area. This process causes the alluvial fan river to move either gradually over time or rapidly during flash flooding .
Dam Break Floods – Improper care of dams or the accumulation of water that is higher than the maximum holding threshold can contribute to a dam break. A dam break will cause overflowing of the river downstream due to the suddenly released volume of water. This is also called catastrophic flooding.
Pluvial flooding is when rainfall or snowmelt is not absorbed into the ground forcing the water to flow overland. The area will remain flooded until water has drained away through stormwater systems or waterways. In instances where there is no drainage system, such as the prairie pothole region, the water ponds remain until the excess water evaporates, sublimates or transpires.
Factors that contribute to pluvial flooding include:
- Rainfall conditions, such as the severity of rainfall;
- Ground and soil conditions, such as, soil type, amount of soil moisture, seasonal variations in vegetation, depth of snow cover, imperviousness due to urbanization;
- Sewer infrastructure, such as overland stormwater flow conveyance capacity, the state of the sewer infrastructure; and
- Lot level actions by property owners.
|Figure 1 – Imperviousness due to urbanization’s effect on flooding.|
The predominate subtype of pluvial flooding is stormwater flooding, which is sometimes called urban flooding. Although urban areas may be flooded when riverine flooding occurs, urban flooding is often used to refer to pluvial flooding in urban areas.
Urban flooding occurs when the runoff from a heavy downpour of rain overwhelms the drainage system. The excess water cannot be absorbed by the ground or contained within drainage systems. This results in water flowing overland into nearby lakes and streams or creating temporary pools in low(er) lying areas.
Groundwater flooding occurs when the water table rises up through permeable sediments to the ground surface or basements. Groundwater flooding can occur weeks or months after a large rain event, and may not be linked to any specific rainfall even.
- Do not litter waste, plastic bags, plastic bottles in drains
- Try to be at home if high tide and heavy rains occur simultaneously
- Listen to weather forecast at All India Radio, Doordarshan. Also, messages by Municipal bodies from time to time and act accordingly.
- Evacuate low lying areas and shift to safer places.
- Make sure that each person has lantern, torch, some edibles, drinking water, dry clothes and necessary documents while evacuating or shifting.
- Make sure that each family member has identity card.
- Put all valuables at a higher place in the house.
In the Flood Situation
- Obey orders by government and shift to a safer place.
- Be at safe place and they try to collect correct information.
- Switch of electrical supply and don’t touch open wires.
- Don’t get carried away by rumors and don not spread rumors.
- Switch off electrical and gas appliances, and turn off services off at the mains.
- Carry your emergency kit and let your friends and family know where you are going.
- Avoid contact with flood water it may be contaminated with sewage,oil,chemicals or other substances.
- If you have to walk in standing water, use a pole or stick to ensure that you do not step into deep water, open manholes or ditches.
- Stay away from power lines electrical current can travel through water, Report power lines that are down to the power company.
- Look before you step-after a flood, the ground and floors are covered with debris, which may include broken bottles, sharp objects, nails etc.Floors and stairs covered with mud and debris can be slippery.
- Listen to the radio or television for updates and information.
- If the ceiling is wet shut off electricity. Place a bucket underneath the spot and poke a small hole into the ceiling to relieve the pressure.
- Use buckets,clean towels and mops to remove as much of the water from the afflicted rooms as possible.
- Place sheets of aluminium foil between furniture wet carpet.
- Don’t walk through flowing water – currents can be deceptive, and shallow, fast moving water can knock you off your feet.
- Don’t swim through fast flowing water – you may get swept away or struck by an object in the water.
- Don’t drive through a flooded area – You may not be able to see abrupt drop – offs and only half a meter of flood water can carry a car away. Driving through flood water can also cause additional damage to nearby property.
- Don’t eat any food that has come into contact with flood water.
- Don’t reconnect your power supply until a qualified engineer has checked it. Be alert for gas leaks – do not smoke or use candles, lanterns, or open flames.
- Don’t scrub or brush mud and other deposits from materials, This may cause further damage.
- Never turn on ceiling fixtures if ceiling is wet. Stay away from ceilings those are sagging.
- Never use TVs, VCRS, CRT terminals or other electrical equipment while standing on wet floors, especially concrete.
- Don’t attempt to remove standing water using your vacuum cleaner.
- Don’t remove standing water in a basement too fast. If the pressure is relieved too quickly it may put undue stress on the walls.