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.
