What is a Gravel Bed River System?

An Invisible River: most of the water in the Snake River is not in the river — it’s in the gravel.

A gravel-bed river doesn’t just flow down the channel. It flows over and through the entire flood plain system, from valley wall to valley wall.

Melting snow and surface water flow down the channel; this is what we think of as a “river.” But underground, far more water is moving slowly through a labyrinthine network of cobble, gravel and sand that make up the entire valley bottom.

Due to the cold, clear baseline conditions in our lakes, rivers, and creeks, it doesn’t take a large increase in temperature, nutrient levels, or other contaminants to impact the dynamic gravel-bed river floodplain ecosystem. Another important component of where we live is our groundwater, which freely exchanges with surface waters through the porous cobble and gravel that comprise our valley floor.

An underground view of the Snake River shows its waters flow far beyond the river channel.

Interaction between surface water in the river and groundwater is fundamental to the health of the gravel-bed river ecosystem.

From Bugs to Bears, everyone relies on gravel-bed river ecosystems

Gravel-bed river floodplains like the Snake River ecosystem are among the most ecologically important habitats on the continent. Their subterranean habitat is the foundation of a food chain that creates biodiversity in the entire valley, by nourishing microbes and aquatic insects, and plant life such as willows, cottonwood, and aspen, which in turn sustain fish, birds and beavers, elk and caribou, and consequently wolves and grizzly bears.

Research has highlighted the importance of these gravel-bed rivers to an unexpectedly high proportion of the region’s aquatic, avian, and terrestrial species.
Although river floodplains themselves make up only roughly 3 percent of many river valleys, two-thirds of all species spend part of their lives in the floodplain.
Underground floodplains are the foundation of a healthy river “immune system”.

A large number of species rely heavily on the biodiversity generated by the gravel-bed river ecosystem of the Snake River, not just fish and other aquatic species.

Human activities contribute to the weakening of the immune systems of rivers like the Snake.

Although gravel-bed river floodplains play a large role in sustaining native plant and animal biodiversity, they have been disproportionately affected by human infrastructure and activities.

The impact of human development on top of our invisible rivers includes severe impacts to floodplain habitat diversity and productivity, restrict local and regional connectivity, and reduce the resilience of both aquatic and terrestrial species, including adaptation to climate change.
Human river valley developments such as homebuilding, dam construction, irrigation, and channelization may be slowly choking highly dynamic river systems — and the biodiversity that depends on them — to death.

Nutrient pollution greatly affects Invisible Rivers

How is Nutrient Pollution affecting the Snake River Watershed?

Nutrient pollution issues affecting our water quality affect the health of the entire floodplain immune system and alters the foundation of the ecosystem – microbes, aquatic insects, and riparian vegetation. The health of this foundation can have repercussions up the entire food chain within a gravel-bed river ecosystem.

Explore the Issues Map

List of Clean Water Act Section 404 Nationwide Permits

Section 404 of the Clean Water Act requires authorization from the Army Corps of Engineers for discharge of dredged or fill material into all waters of the U.S., including wetlands.

Comments on Snake River Mobile Home Park Permit No.WY0095320

August 19, 2024 Comments submitted on behalf of Protect Our Water Jackson Hole (POWJH) in response to the Wyoming Department of Environmental Quality’s (WDEQ) notice inviting comments on the pollution...

Comments on Class V Permit No. 2023-231

July 12, 2024 Comments submitted on behalf of Protect Our Water Jackson Hole (POWJH) in response to the Wyoming Department of Environmental Quality (WDEQ) public notice inviting comments on the...

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