Winter Flooding Risks
Flooding from Snow and Rain Mix
Many of the worst Winter floods in the US are caused by a combination of heavy rains and melting snow. These events are tough to forecast, but they will become more common as the planet warms and more winter precipitation falls as rain rather than snow. Rain falling on already accumulated snow is how most of the largest floods on record in the Western US are caused. Moisture in the air actually condenses on the cold snow, similar to when water droplets form on a cold drink. The energy released from the condensation is then absorbed by the snow. Another way that the snow can melt is from the warmer air that accompanies rain, blowing across the surface of the snow. Because the ground is hard and frozen, the excess water cannot be reabsorbed. The water then runs off the surface and flows into lakes, streams, and rivers, causing excess water to spill over their banks.
Other Flooding Risks
Long cold spells can cause the surface of rivers to freeze and since the ice covering the river is lighter than water, it will tend to float. Under pressure, the ice will often break into huge slabs that move downstream and cause an ice jam at man-made and natural obstructions. When the flow of a river is blocked by an ice jam, the water can overflow the river banks, resulting in severe flooding. As the water rises, the excess pressure can break the jam and release a sudden surge of water and ice down the river. While ice jams often form in the same spots year after year, it is nearly impossible to predict exactly when or where a jam will form, or when one will break. Some ice jams will stay put for most of the Winter season. Winter storms generate high winds that can cause widespread tidal flooding and severe beach erosion along coastal areas. In the Great Lakes for example, winter storms can bring strong winds that push water levels up at one end of the lake, causing a storm surge. As the water levels return to normal, a pendulum effect takes place causing high water levels on alternating sides of the lake until a balance returns.
Expensive Damage from Flooding
While the entire US is at risk for Winter flooding, some areas are more likely to experience Winter flooding than others. Cities on rivers that begin in the mountains, such as Sacramento, California and Centralia, Washington are more likely to experience flooding from rain on snow. Melting snow exacerbated flooding in the 1997 New Year's Day flood in Northern California. The flood broke levees and caused millions of dollars in damage. The 2009 flood in the Snoqualmie basin of Washington and the Calgary flood in Summer of 2013 were both huge rain-on-snow events.
By recreating the 10 worst rain-on-snow flooding events on the West coast, in the Snoqualmie basin, San Joaquin basin and the East North Fork of the Feather River basin, researchers have developed a model for guaging the risk of incoming storms. The research determined three key factors affecting the risk, which includes the shape of the basin, the elevation of the rain-to-snow transition before and during the storm, and the amount of tree cover. It was found that trees actually reduce the risk of flooding becuase they slow the storm's winds.
For more informaiton on this study, please visit: http://www.futurity.org/rain-snow-flooding-828282/.
Residents and business owners need to prepare in advance for these Winter flooding situations. If you know anyone in coastal areas or river basin areas, tell them about BIG BAGS USA®. Our large polypropelene sandbags are the perfect solution for controlling the excess water associated with Winter storms. BIG BAGS USA® is meeting flood mitigation & flood preparedness needs across the United States. Contact us today at 800-337-0537 for more information on how we can help you be prepared for the worst when it comes to Winter flooding!
Sources:
http://fox43.com/2014/11/13/winter-weather-awareness-flooding/
http://www.futurity.org/rain-snow-flooding-828282/
https://www.floodsmart.gov/toolkits/flood/downloads/WinterFlooding-OT2007.pdf
If you have an immediate need for our systems, or have any questions for us, please Call us Toll Free at 1-800-337-0537 or visit www.BigBagsUSA.com.
If you have an immediate need for our systems, or have any questions for us, please Call us Toll Free at 1-800-337-0537 or visit www.BigBagsUSA.com.
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