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Home > Spring Flood Risk “Frozen in Place”
Spring Flood Risk “Frozen in Place”
March 6, 2014
With stream flows, snowpack, and river ice all within a typical range, spring flood potential as of today could be considered normal for the time of year. However, continued frigid weather will hold all those risk factors in place, likely elevating flood potential in the next few weeks.
The Maine River Flow Advisory Commission, meeting today in Augusta, reviewed information on current hydrologic conditions across the state, as well as short-term weather forecasts.
Snowpack water content ranged from 3 to 6 inches in southern and coastal sections to 5 to 7 inches in northern and western Maine. These levels put water content in the middle range compared to historical averages across most of the state. Snow survey maps are available at http://maine.gov/rfac/rfac_snow.shtml
The National Weather Service noted that for the next two weeks, temperatures are expected to continue below normal. The cold weather will hold the current snow pack in place, and there will be a number of opportunities for additional snow to add to the total on the ground.
Despite the recent frigid temperatures, river ice is in the normal range in most areas of the State. This is because a spell of warm weather and rain in January eroded river ice significantly. However, the current cold temperatures will continue to hold ice in place, and ice may even thicken in the next few weeks. The US Coast Guard is working closely with the USGS, National Weather Service, MEMA and other operational partners to monitor river ice conditions and plan for potential ice-breaking on the Kennebec River.
Reservoir storages in the headwaters of Maine’s large rivers are being drawn down to prepare for spring rains runoff. River basin managers report that they are on track to achieve their drawdown targets.
The most important factor influencing flooding is rainfall, but even a normal snowpack adds risk. When water in the snowpack is released suddenly, by rainfall accompanied by warm temperatures, runoff amounts are increased dramatically.
Significant ice in rivers and streams presents an additional risk that cannot be forecast. Ice can jam, and water behind the jam can rise several feet in just a few minutes. When an ice jam lets go, water levels downstream rise suddenly.
The best case scenario is for days above freezing and cooler nights, to melt snow and ice gradually. However, with continued cold temperatures over the next two weeks, any melting will be minimal and snow and ice amounts may increase. The later that snow and ice persist into the spring, the greater risk they pose.
The annual meeting of the Commission represents the beginning of “flood season” in Maine, when all parties focus close attention to risk factors for flooding, and to temperature and precipitation forecasts. The following steps are recommended:
Commission members will stay in close communication throughout the spring season. They will likely meet again if the risk factors persist later into the spring, as currently it appears they will. Snow surveys will be conducted each week from now until the snow cover is gone.
The River Flow Advisory Commission meets annually in late winter to share information, examine potential for spring flooding and to renew operational protocols. The Commission is composed of state, federal and industry representatives with an interest in hydrologic issues.
The full report of the March 6 meeting will be available on the Internet at http://www.maine.gov/rfac by close of business on Friday.
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