By Stephanie Lynn EBS CONTRIBUTOR
Runoff isn’t just for rafters. High water shapes streams and benefits all living things that depend on them.
The Gallatin is unimpeded during its journey from Yellowstone National Park to the headwaters of the Missouri River. Ungoverned by dams, this free-flowing river follows the natural ebb and flow of an alpine river system: swelling in the spring, declining throughout the summer and fall, and freezing in the winter. Each late May and early June, the rising waters play an important role in the life cycle of the river.
“Runoff primes the pump for stream ecological processes to occur,” said Jeff Dunn, project manager for Trout Unlimited. Peak flows reset riverbeds, propagate streamside plants, spur spawning for fish and amphibians, and supply water during the dry southwest Montana summer.
When the weather warms, melting snow flows downhill from the mountains to fill streams and rivers. Raging spring floods shift boulders and trees, which creates hiding places and habitat for fish. High water also flushes dirt out of gravel beds, which are used by trout to build their spawning redds and are a home for stream insects.
Spring flows regenerate streamside vegetation by transporting sediment, nutrients and seeds to riverbanks and floodplains. This influx of water carrying fertile matter promotes plant growth. Green, vegetated streambanks protect cold, clean water throughout the year by filtering runoff, using nutrients and shading water.
“Intact riparian vegetation is the key driver of healthy streambanks,” Dunn said. “Once plants are removed, you get excess sediment inputs to streams.”
Along with water temperature, runoff sets reproductive cues for fish and amphibians. Some species of trout, including native westslope cutthroat, know that it’s time to spawn when rivers begin to grow. During high water, cutthroat trout seek calmer water in tributaries to lay their eggs.
Finally, runoff expresses the water stored during the winter in the snowpack bank, providing the primary source of water all summer long. Paddlers, anglers, irrigators and wildlife enjoying the Gallatin River depend on how much, how fast, and how long snow melts in the mountains.
This year, snow-water equivalent—the amount of water stored in the snowpack—peaked in early May just above normal at about 115 percent of the average year, reported the Montana Natural Resource Conservation Service. As long as the Gallatin receives the anticipated spring rains, the watershed will have solid summer supply this year.
Despite the ecological value of runoff, high water occasionally threatens both humans and their homes. Gallatin County Emergency Management recommends on their website that riverside homeowners protect their properties from flooding by, “cleaning debris out of culverts and from under bridges; making sure there is a clear path for snow to melt away from buildings; and clearing snow piles away from doors, windows and other places that make it easy for melting snow to affect you.” Whitewater boaters should also take extra precautions when embarking on spring adventures.
That being said, there is no better time to protect water quality than during runoff, especially in Big Sky. Many streams begin in the mountains surrounding the community, and are critical to having clean, abundant water for all those downstream.
Big Sky community members can keep the Gallatin healthy during spring floods by picking up dog waste before precipitation events push it into waterways, maintaining a buffer of riparian plants near small streams at least fifteen to twenty feet wide, eliminating or limiting the use of fertilizer, and leaving woody debris in the channel.
Stephanie Lynn is the education and communications coordinator for the Gallatin River Task Force.