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Science

Logan River’s Evolving Geomorphology

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Logan River’s geomorphology, or landform, has changed very little over the past 150 years in the mountain canyons.  But where the river leaves the mountains and drops down onto Cache Valley’s floor, its geomorphology has changed dramatically.

A river’s geomorphology is how it interacts with its environment, how it changes 

  and moves over time, how it picks up sediment and debris when its flowing fast then releases the sediments downstream where the river slows and spreads over open-flat landscapes. 

The route of Logan River is noteworthy.  Peter Wilcock, department head of Watershed Sciences in the Quinney College of Natural Resources explains,  Logan River cuts through a large amount of the Bear River mountain range [in northeastern Utah and southeastern Idaho] and is by far the biggest drainage from the range.

The river’s size has made a mark on the mountain.  When all the tributaries and springs come together, the result is the fast-flowing river with great force for erosion.  If you compare Logan Canyon with other canyons coming out of the Bear River Range such as Green Canyon or Providence Canyon you can see Logan Canyon is close to 600 feet lower than all the other canyons.   The volume and force of Logan River cut through the beach material that ancient Lake Bonneville left behind, the other drainages have been too small to cut through the ancient short line.

In the early 1800s, the lower part of Logan River flowed freely, meandering and spreading across the Cache Valley floor.  As it entered the valley, the river would form into an alluvial fan spreading like fingers over the valley floor and meeting the natural functions of a river to transport water, sediments and nutrients.

As each decade passed an increasing number of buildings, roads and complex infrastructures were built to keep up with the growing population.  And to protect this infrastructure, people attempted to restrict the movements of the river. In many places, the river was straightened or channelized even as its water was re-routed for irrigation. 

The dams placed along the river and at the mouth of Logan Canyon slowed the river before it reached the valley floor.  As a result, a large percentage of the sediments which would have dropped on the valley floor, are now captured behind the river’s dams and fill the reservoirs. 

Frank Howe, chairman of the Logan River Task Force, explains how this impacts the river’s geomorphology, “Water released from the dams is free of deposits; the river is now “hungry” -  hungry for new sediments. It’s now capable of picking up large amounts of sediments which causes erosion problems miles below the dams.”

The Logan River Task Force, consisting of representatives from Utah State University, Logan City, Cache County, State and Federal Agencies, six non-profit organizations, corporations and interested citizens came together to find solutions to the erosion problem and other river issues. To address these issues, they prepared a “long-term plan for the Logan River to balance ecological and social values and capture what Cache Valley community wants the river to become. “

Rivers, by nature, are dynamic. They move back and forth especially where the slope is gentle.  Over time, this meandering movement delivers fine sediments, across the river’s floodplains creating rich soils diverse in vegetation and wildlife.  By changing the river’s geomorphology, we’ve altered the rivers dynamics, as well as how and where it delivers sediments.

Fortunately, parts of the Logan River’s geomorphology can be restored.  River restoration will be the topic of our fourth and final segment for the Logan River series on Wild About Utah.