Emergent Sandbar Habitat

By Kelly Crane
U.S. Army Corps of Engineers

The Missouri River looks very different today than it did before construction of six dams from Fort Peck, MT. to Yankton, SD.

Before the dams, there were no reservoirs to contain the spring influx of water from mountain snowmelt and plains runoff and the Missouri River would routinely wander out of its many meandering side channels, flowing through the plains, collecting and depositing sediment.

Sandbars were routinely washed away in some places and created in others.  During the forming and reforming of these sandbars, much of the vegetation that grew on the bars from the year before was scoured away.

These newly created or scoured sandbars are thought to be desirable habitat for two species of birds, least terns and piping plovers. Both use the same habitat even though their feeding habits are different. Least terns eat small fish in shallow water surrounding the sandbars, while piping plovers forage along the shoreline for a variety of invertebrates.

After the dams were built, the annual grand scale sediment collecting and depositing cycle no longer occurred naturally.  Flood or high water events such as in 1997 put large amounts of water and sediment into the Missouri River System because of near-record mountain and plains snowmelt and heavy spring rains.

Reservoirs swelled to near capacity and water was released---mimicking some of the pre-dam historic high flows.  Hundreds of acres of new sandbars were created. Abundant habitat was available for a few years after the 1997 flood, but since then available habitat for terns and plovers has declined.

In November 2000 the U. S. Fish and Wildlife Service issued a biological opinion (BiOp) addressing interior least tern and piping plover habitat along with other threatened or endangered species that have been adversely affected because of operation of the Missouri River mainstem system.

One BiOp recommendation was a habitat creation goal for each stretch of the river as well as for Lewis and Clark Reservoir just above Gavins Point Dam.

The river stretches, roughly stated, are below Fort Peck Dam, below Garrison Dam, below Fort Randall Dam, and below Gavins Point Dam.

Terns seem to prefer sandbars in the river stretches rather than reservoir shorelines, while plovers will use reservoir shorelines or sandbars in the river.

Responding to BiOp recommendations that upwards of 12,000 acres be available for use by terns and plovers by 2015, the Corps began creating what Missouri River flows no longer can.

While the task sounds daunting, some of the habitat already exists. Aerial photos taken in June are being analyzed to determine how much habitat is currently available. The Corps’ responsibility is to determine how much habitat currently exists compared to how much is recommended by the BiOp, and to create the rest.

Mechanical habitat creation can be done by several different methods.  Redistributing sediment might be a better descriptive term for what actually happens during sandbar creation. In the river stretches and in Lewis & Clark Reservoir, there is plenty of deposited sediment---though most of it doesn’t stick out of the water.

Using dredges, bulldozers, backhoes and scrapers, the sand and sediment is piled onto a shallowly submerged sandbar to create one above water so the birds can use it.

Another way to create habitat is by removing vegetation from existing sandbars since both species of birds seem to prefer sparsely vegetated sandbars. When plant growth hinders their ability to see predators, the birds will not use the sandbar. Killing the vegetation with herbicides, then clearing the dead vegetation away is thought to be effective in creating barren sandbars.

But creating habitat is no guarantee the birds will use it, however.

Monitoring created habitat is crucial to understanding what methods are effective for the birds. The U. S. Geological Society’s Northern Prairie Research Center in Jamestown, ND is leading an interagency team that is currently creating a monitoring plan for all methodologies.

Over the past two years, the Corps has created more than 800 acres of emergent sandbar habitat.  Most of this was created by vegetation removal and close to 150 acres was created by dredging and other mechanical equipment.

The Corps, U. S. Fish and Wildlife Service, state game and fish departments, National Park Service, and U. S. Geological Service are working together as an interagency team to determine habitat creation priorities on the Missouri River.