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Determination of Channel-Morphology Characteristics, Bankfull Discharge, and Various Design-Peak Discharges in Western Montana

Sean M. Lawlor

U.S. Geological Survey
Scientific Investigations Report 2004-5263

In cooperation with  Montana Department of Transportation, and the
U.S. Department of Agriculture-Forest Service
     Lolo National Forest


Stream-restoration projects using natural stream designs typically are based on channel configurations that can accommodate a wide range of streamflow and sediment-transport conditions without excessive erosion or deposition. Bankfull discharge is an index of streamflow considered to be closely related to channel shape, size, and slope (channel morphology). Because of the need for more information about the relation between channel morphology and bankfull discharge, the U.S. Geological Survey (USGS), in cooperation with the Montana Department of Transportation and the U.S. Department of Agriculture-Lolo National Forest, conducted a study to collect channel-morphology and bankfull-discharge data at gaged sites and use these data to improve current (2004) methods of estimation of bankfull discharge and various design-peak discharges at ungaged sites. This report presents channel-morphology characteristics, bankfull discharge, and various design-peak discharges for 41 sites in western Montana.

Channel shape, size, and slope and bankfull discharge were determined at 41 active or discontinued USGS streamflow-gaging sites in western Montana. The recurrence interval for the bankfull discharge for this study ranged from 1.0 to 4.4 years with a median value of 1.5 years.

The relations between channel-morphology characteristics and various design-peak discharges were examined using regression analysis. The analyses showed that the only characteristics that were significant for all peak discharges were either bankfull width or bankfull cross-sectional area.

Bankfull discharge at ungaged sites in most of the study area can be estimated by application of a multiplier after determining the 2-year peak discharge at the ungaged site. The multiplier, which is the ratio of bankfull discharge to the 2-year peak discharge determined at the 41 sites, ranged from 0.21 to 3.7 with a median value of 0.84.

Regression relations between bankfull discharge and drainage area and between bankfull width and drainage area were examined for three ranges of mean annual precipitation. The results of the regression analyses indicated that both drainage area and mean annual precipitation were significantly related (p values less than 0.05) to bankfull discharge.


    Purpose and scope
    Description of the Study Area
Determination of Channel-Morphology Characteristics
Determination of Bankfull Discharge at Gaged Sites
Determination of Various Design-Peak Discharges at Ungaged Sites
   Regression Relations between Various Design-Peak Discharges and Channel Morphology
   Use of Existing Flood-Frequency Equations
Regression Relations between Channel Morphology and Drainage Area and Bankfull
     Discharge and Drainage area
References Cited


  1. Map showing location of the study area, measurement sites, and two flood regions.
  2. Schematic diagram showing typical channel reach and cross section for measurement of channel features.
  3. Photographs showing site and cross-section locations on South Crow Creek and Mill Creek, western Montana.
  4. Graph showing longitudinal profiles for Boulder Creek at Maxville and Eightmile Creek near Florence, Montana.
  5. Boxplot showing variation in recurrence interval of bankfull discharge at 41 selected sites, western Montana.
  6. Boxplot showing variation of ratio of bankfull discharge to the 2-year design-peak discharge at 41 selected sites, western Montana.
  7. Graphs showing regional relations of bankfull-channel dimensions and bankfull discharge to drainage area for different ranges of mean annual precipitation.


  1. Channel-morphology characteristics and design-peak-discharge data for selected streamflow-gaging stations, western Montana.
  2. Basin and climatic characteristics for selected streamflow-gaging stations, western Montana.
  3. Three sets of regression equations for estimation of design-peak discharge in western Montana.

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