Northern Prairie Wildlife Research Center
|A CONFLUENCE IS AN AREA WHERE TWO RIVERS JOIN TO BECOME ONE. NORTH DAKOTA'S "CONFLUENCE" IS DEFINED AS THE AREA WHERE THE MISSOURI RIVER AND ITS LARGEST TRIBUTARY, THE YELLOWSTONE RIVER, MERGE.|
|This Confluence is unique in many ways, one of which is that the Yellowstone
is the larger river of the two at this point. The average annual flow
of the Yellowstone River, as gauged at Sidney, Montana, is approximately
13,000 cubic feet per second, compared to the Missouri River's average
annual flow at Culbertson, Montana of approximately 11,000 cfs.
Both rivers historically were turbid during high flow periods. Their channels were braided, with numerous side channels and chutes, lush islands with dense willow and cottonwood stands, and innumerable scoured sandbars. Both rivers historically exhibited predictable annual spring flood pulses as a result of snow melt and early rainfall, followed by generally declining flows throughout summer and fall.
Some of their floods were spectacular, with combined river flows at the Confluence occasionally exceeding 100,000 cfs. Ice jams in the lower Yellowstone and in the Missouri below the Confluence have historically caused some of the highest flood events. During high flows, the rivers frequently exhibited wholesale channel movements within the floodplain.
The Missouri River's water below Fort Peck Dam is in stark contrast with the sediment-loaded flows of the Yellowstone where the two rivers merge near the Montana border west of Williston.
Prior to white settlement, the Confluence area and much of the lower Yellowstone River Valley was a large, wooded floodplain. Above the floodplain a vast prairie stretched for miles, with only an occasional range of hills and woody ravines to break up the skyline. The Confluence area was a favored hunting grounds for numerous Native American tribes, who came from all directions to partake of its bountiful fish and wildlife resources. Early explorers of the region were quick to note the abundance of wildlife in the area, especially vast numbers of elk and bison.
Since both rivers were navigable above the Confluence for at least several months each year, a growing number of crafts of all description used the rivers to access far-flung regions of what would eventually become Montana. A few shrewd entrepreneurs also noted that the Confluence would be an advantageous site at which to establish a trading post. They reasoned that a post would not only capture trade with numerous tribes, but also with early European interlopers who used the two rivers to access and exploit wildlife resources, especially beaver, hundreds of miles upstream.
Fort Union Trading Post, founded in 1829 at the Confluence, was by far the grandest of an extensive network of fur posts erected on the upper Missouri and Yellowstone rivers.
In the late 1800s, homesteaders converged on the Confluence area to farm the productive floodplain. Some of the first irrigation development in North Dakota was in the lower Yellowstone River Valley at the turn of the last century.
During the initial settlement period, over harvest of many wildlife species and clearing of vast stands of riparian timber to make way for agricultural production greatly affected the Confluence area's wildlife populations. Although deer and beaver are again abundant, along with seasonally high populations of Canada geese and other waterfowl, elk, bison, and grizzly bear are gone.
Early settlers had far less impact on the rivers themselves, however. Both rivers remained virtually unaltered, with large and rapid swings in flows, silt loads and water temperature. Both rivers frequently flooded.
Joel Schriver and Tom Crutchfield hold an endangered pallid sturgeon netted in the Confluence area.
| Because early settlers knew that high flows would easily
damage or destroy any structures foolishly built within the floodplain,
they built their houses and ranch buildings above the active floodplain.
Many warmwater fish species evolved in the waters of the lower Yellowstone and Missouri rivers. Paddlefish, pallid and shovelnose sturgeon, sicklefin, sturgeon and flathead chubs, blue sucker, sauger, and other native species thrived in the unique environment created by these two large, turbid rivers.
The impoundment of the Missouri River by Fort Peck Dam in the late 1930s greatly altered the flow and water quality characteristics of the Missouri River downstream. The Missouri River's flows below Fort Peck are now regulated, with greatly reduced peak flood flows and generally higher than pre-impoundment base flows. Unfortunately, tributary inflows between Fort Peck and the Confluence are generally far too small to have much of an impact on the Missouri's flow characteristics.
Fort Peck's releases are much clearer and cooler than pre-impoundment flows, but the water temperature does gradually increase downstream and becomes nearly ambient at the Confluence. Because of great changes in habitat, the Missouri River above the Confluence retains little of its former value for many native fish species.
Impoundment and channelization have similarly altered most of the 2,300 miles of the Missouri River System. Only small segments of the Missouri River now exhibit flows that even somewhat resemble natural flow characteristics.
Because of modifications throughout the Missouri River System, many native fish species are suffering. The pallid sturgeon is the only upper Missouri River System fish listed as "endangered" under the Endangered Species Act. Several other species, however, have been considered or petitioned for listing under the ESA, including paddlefish, blue sucker, sicklefin chub, sturgeon chub, and flathead chub.
Fortunately, the Yellowstone River, the longest undammed river in the contiguous United States, retains most of its natural habitat characteristics and flows. Its flows define the riverine habitat of the Confluence and the Missouri River downstream to the headwaters of Lake Sakakawea. The Yellowstone River serves as a refuge for many of the Missouri River System's native fish species.
Several fisheries research projects in recent years have documented the Confluence area's vital habitat conditions. Seasonally high flows of turbid water appear to be critically important for species that have unique adaptations for living in turbid water.
Several species of fish apparently "stage" at the Confluence area in spring and early summer, waiting for warmer and higher flows to trigger upstream spawning migrations. High spring and early summer flows are necessary to trigger spawning movements of paddlefish and pallid and shovelnose sturgeon. Good paddlefish reproduction, primarily in the lower Yellowstone River, has been documented almost every year in the past several years when the Yellowstone has often flowed higher than normal.
Blue sucker, another fish in decline in many parts of its range, has successfully reproduced at the Confluence area. All three chub species listed above, which have declined significantly in many parts of their range, are fairly abundant and reproduce in the Confluence area.
The Confluence area is also important to several sport fish species and area anglers. It is by far the best site in North Dakota to snag paddlefish. Since turbid water has little effect on the foraging ability of channel catfish, good fishing for this species is available throughout the open water season. Walleye and sauger are generally present only at times when the water clears, meaning that good angling for these species is usually found only during low-flow periods in spring and fall.
The Confluence will remain a critically important area for many Missouri River System native fish only as long as its unique habitat conditions remain intact. Fortunately, many Montanans, and especially the Montana Department of Fish, Wildlife and Parks, have long recognized the need to maintain adequate flows in the Yellowstone River. Through the water appropriation process, Montana has protected more than one-half of the river's historic flows through an instream water right for fish, wildlife and nonconsumptive purposes.
This amount of water may not be enough to sustain the long-term ecological integrity of the Yellowstone River, however. Unfortunately, by the mid-1970s water depletions and diversions had decreased the Yellowstone River's flows by approximately 24 percent from historical levels, and additional depletions have been allowed since that time.
An increase in Fort Peck releases during late spring and early summer, an alternative under consideration by the Corps of Engineers as part of its master manual review process, could have some merit in restoring some former warmwater habitat in the Missouri River below Fort Peck.
Oil industry activities, bank stabilization, irrigation withdrawals and return flows, and a host of other developments must be carefully regulated and monitored in order to limit the negative impacts of these activities to the largest extent possible. Land acquisition and/or easement efforts should be pursued in order to limit shoreline development in the immediate Confluence area. Above all else, careful consideration of the area's unique and important values is necessary to any projects that would significantly impact the area.
*Fred Ryckman is a fisheries biologist at the Department's Williston district office.