Madison River ice gorging causes flooding
ENNIS – Walk across the Highway 287 bridge over Odell Creek south of town and you will see a rather scary sight, a huge slug of water roaring under the bridge, mere inches away from cresting the concrete edge of the bridge.
This increase in flow is the result of ice gorging, a natural phenomenon that takes place after a string of bitter cold days; when ice forms on a river, collects, builds up, then creates icy dams that divert the normal flow of water into either new channels or a pond, flooding low-lying areas.
The ice gorge on the Madison River, for example, has been building for the last several weeks. Currently, it has backed up water, flooding the southern and eastern meadows around town; including the Valley Garden and Ennis Fishing Access Sites (FAS). These FAS have been closed for the last several weeks as the Madison’s ice gorge has grown.
And Ennis is not the only place contending with ice gorging. Similar issues are taking place on the Jefferson and Rosebud rivers.
According to Martin Holtmyer, Montana Fish, Wildlife and Parks’ Region 3 FAS foreman, ice gorges are a natural occurrence that take place most winters and Fish, Wildlife and Parks (FWP) just “deals with it.”
Holtmyer said ice gorges and jams redirect the flow of water, and FWP closes FAS – not that many trout anglers are out fishing when it’s sub-zero weather – because it is a safety issue for people to be in those areas.
Valley Garden and Ennis were closed earlier this month. due to “flooding and other dangerous conditions”
Holtmyer said FWP tries to be proactive when it comes to dealing with ice gorging: FWP removes all picnic tables and fencing that might be impacted by gorging, but the primary problem is road work: When gorging channels water towards alternative channels, the water can tear out roads. What work needs to be done depends on the damage wrought. Typically FWP cleans up trees and other debris washed into FAS by gorging.
However, Holtmyer noted that two winters ago (2016-17) water moved by ice gorging created a substantial hole at the entrance to the Ennis FAS. “It got ugly,” he said.
Historically, ice gorges can occur from Ennis Lake upstream to Varney Bridge, although the jams have occasionally gone further south in severe winters.
Jefferson, other rivers
According to Twin Bridges Maintenance Supervisor Sam Novich, on Monday, February 25, the Big Hole and Beaverhead rivers were “flowing right where they were all winter.”
Downstream, where the junction of these rivers form the Jefferson River, according to Holtmyer, ice jams were forming and creating problems at FWP’s fishing access sites.
However, Lori Ryan, state Department of Transportation (MDOT) spokesperson, said that the MDOT’s section man had monitored the Jefferson River on Monday, February 25 – “We’re always monitoring the river,” she said – and there were no problems, no gorging.
Further east, in Stillwater County Ice gorging and ice jams on West Rosebud Creek have caused water to channel through the entire Rosebud Isle FAS. The creek water is freezing, and causing dangerous conditions, including flooded areas throughout the site.
No end in site
When will the gorging end?
“I wish I knew,” Holtmyer said, “It all depends on the thaw cycle and the weather. Whenever it moderates, that’s when it will end.” He anticipated that the thaw might come in mid-March.
The flooding caused by ice jams and gorging is a fact of life along many rivers and streams, according to the Montana Department of Natural Resources and Conservation.
DNRC reminds residents that February and March have the greatest potential for ice jams, and conditions can change rapidly.
“Montana experiences the highest number of reported ice jams in the continental US, with most occurring in February and March” said DNRC Director John Tubbs. “Flooding can happen in any community and it can happen quickly. Residents in flood-prone areas should take steps to safeguard their families and property.”
Arin Peters, Senior Service Hydrologist with the National Weather Service Great Falls, has advised that the thick ice associated with ice jams forms when temperatures are consistently low for extended periods of time.
Worby McNamee, a DNRC floodplain specialist, said it’s important that residents living near a river or stream develop a flood evacuation plan and consider the following steps:
• Purchase flood insurance. In most cases flood insurance must be purchased 30 days before a flooding event.
• Keep extra drinking water on hand. Flooding can compromise local water systems.
• Shovel or plow snow away from homes and structures.
• Be ready to transport valuables or, where practical, elevate them.
The Montana All-Hazards Weather Monitor web site offers up-to-date information on stream flows and potential flood conditions: http://www.wrh.noaa.gov/byz/state/current.php?wfo=tfx
To learn more about the National Flood Insurance Program, visit www.floodsmart.gov.
More than 80 percent of ice jams and associated flooding in Montana take place between January and March, with the highest number occurring in March.
The greatest number of ice jams ever recorded in a single season was 75 in 1996.
For more information contact the Bozeman FWP office at 994-4042.