Tropical Storm Irene pummeled Vermont on August 28, 2011, causing dramatic flooding and widespread damage to roads, bridges, buildings, homes and property in over half the state. Not since the great flood of 1927 had Vermont seen such widespread and extreme flooding. Yet, Vermont has seen more frequent flooding on a more localized basis, including in 1973 and several other times since 2011.
A year after Irene, what happened to so many Vermonters in so many towns is well known. But what happened to our fish as the rivers churned? Unlike the readily visible changes that occurred in many rivers, what happened in the living underwater world cannot be readily seen. Let’s take a look... with a focus on our treasured trout populations.
Trout need good habitat -- what does good habitat look like?
Good habitat has a mix of large boulders, fallen trees, cobbles, gravels and forested shoreline. There is a mix of fast and slow currents, of deep and shallow areas.
Healthy habitat = healthy fish populations
Poor habitat looks a lot different. This stream has been straightened and widened with the large rocks and trees removed, resulting in a featureless stream channel with poor aquatic habitat value.
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What happened to the trout after Irene?
Department surveys in the Mad and Dog River watersheds showed that trout numbers declined to 33-58% of pre-flood levels.
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Will fish populations recover?
Fish have survived floods and droughts for thousands of years, and are well adapted to survive and recover relatively quickly. A devastating flood reduced trout numbers in Clay Brook in 1998 but they rebounded within a few years. While significant changes to the physical habitat occurred following the flood, the overall quality of the habitat remained in tact.
However, where the habitat no longer exists, recovery will take many years, if not decades. Unfortunately, much damage was done to our streams by our own activities after the waters receded. The Rivers Program of the Department of Environmental Conservation, estimates that 40% of the river repairs done after Irene may actually have increased our vulnerability to damages during future floods.
Department biologists are surveying Vermont’s streams, but it’s too early to quantify the effects of the storm.
Floods play a positive role in renewing fish habitat.
As damaging as floods can sometimes be, they also are part of a natural process by which a river renews and maintains itself over the long term. Floods recruit large trees, refresh gravel deposits, and cause localized scour, resulting in high quality habitat conditions. The fallen trees shown in the photo promote pool formation and excellent hiding places for fish.
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Will we do better next time?
The floods of 2011 won’t be the last, so we need to learn from our mistakes and better prepare for the next time. Irene showed us that we can’t control rivers and that we need to learn to live in harmony, recognizing the amount of room a river needs. Preventing flood damage and protecting our rivers go had in hand. Our understanding of the science of how rivers behave has advanced a great deal in recent years, and we are well-positioned to chart a better path forward. Let’s work together at both the state and community levels to effectively reduce the potential for future flood damage in a way that respects and conserves our natural resources.
Fortunately, Vermont still has abundant opportunities for great wild trout fishing. While some rivers were damaged, most were not. Biologists are surveying trout populations this summer, and early reports indicate that healthy wild trout populations are still present in quite a few locations.
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Flood Impacts to Wild Trout Populations in Vermont. 2011. Vermont Fish and Wildlife Department.
While the large scale movement of streambed material and debris, displacement effects fish populations in the short term; they will quickly rebound when quality aquatic habitat remains intact.
- Impacts to Stream Habitat and Wild Trout Populations in Vermont
Following Tropical Storm Irene. 2012. Vermont Fish and Wildlife Department.
Where aquatic habitat has been severely altered through streambed and natural wood mining, channel widening and straightening, complex habitat features will need to re-establish before improvements in fish and aquatic populations can be expected.
- Vermont's Wild Brook Trout A Hidden Treasure. The Fish & Wildlife Department website explaining the habitat needs of brook trout.
- What makes a good brook trout stream? 2012. Vermont Fish and Wildlife Department.
A short paper that explains the temperature, water chemistry and physical habitat requirements of brook trout and how these factors affect brook trout abundance.
- Living in Harmony with Streams: A Citizen's Handbook to How Streams Work. 2012. Prepared by Friends of the Winooski River, White River Natural Resources Conservation District and Winooski Natural Resources Conservation District.
A handbook about how streams work, the effects of human activities, protecting river corridors, and undertaking stream restoration projects.
- Irene's Impact On Trout: An Outdoor Journal Special. In a live broadcast that aired May 3, 2012, Lawrence Pyne of Vermont Public Television talks with Fish and Wildlife Department representatives about the health of Vermont’s trout streams after Tropical Storm Irene.
- Department of Environmental Conservation’s River Management Section Website.
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