Channel-Morphology Data for the Tongue River and Selected Tributaries, Southeastern Montana, 2001-02

Coal-bed methane exploration and production have begun within the Tongue River
watershed in southeastern Montana. The development of coal-bed methane requires
production of large volumes of ground water, some of which may be discharged to
streams, potentially increasing stream discharge and sediment load. Changes in
stream discharge or sediment load may result in changes to channel morphology
through changes in erosion and vegetation. These changes might be subtle and
difficult to detect without baseline data that indicate stream-channel
conditions before extensive coal-bed methane development began. In order to
provide this baseline channel-morphology data, the U.S. Geological Survey, in
cooperation with the Bureau of Land Management, collected channel-morphology
data in 2001-02 to document baseline conditions for several reaches along the
Tongue River and selected tributaries.

This report presents channel-morphology data for five sites on the mainstem
Tongue River and four sites on its tributaries. Bankfull, water-surface, and
thalweg elevations, channel sections, and streambed-particle sizes were
measured along reaches near streamflow-gaging stations. At each site, the
channel was classified using methods described by Rosgen. For six sites,
bankfull discharge was determined from the stage- discharge relation at the
gage for the stage corresponding to the bankfull elevation. For three sites,
the step-backwater computer model HEC-RAS was used to estimate bankfull
discharge. Recurrence intervals for the bankfull discharge also were estimated
for eight of the nine sites. Channel-morphology data for each site are
presented in maps, tables, graphs, and photographs.

[Summary provided by the USGS.]