Streamflow characteristics of small tributaries of Rock Creek, Milk River basin, Montana, base period water years 1983-87

Five streamflow-gaging stations four on small tributary streams and one on Rock Creek were installed in the Rock Creek basin north of the Milk River near Hinsdale, Montana.Streamflow was monitored at these gaging stations and at an existing gaging station upstream on Rock Creek from May 1983 through September 1987.On the basis of 9 years of record at the existing gaging station, annual mean streamflow in the study area was substantially less than the long-term (1979-87) mean annual streamflow (17 cubic feet per second) during water years 1983-85 and was greater than the mean annual streamflow during water years 1986-87.. Annual mean streamflow for 1983-87 ranged from 2.8 to 57 cubic feet per second in the mainstem and from zero to 0.60 cubic foot per second in the tributaries.Monthly mean streamflow at the six gaged sites ranged from zero to 528 cubic feet per second.Although monthly runoff trends of the four tributary streams were similar to those of Rock Creek, monthly mean flows of the four tributary streams were small, ranging from zero to 5.3 cubic feet per second.Daily mean streamflow data for the six gaged sites indicate similar patterns during periods of large runoff, but substantial individual variations during periods of lesser runoff.During periods of little area-wide runoff, the small streams may have daily mean flow that is several times larger than that at the two Rock Creek sites.Daily mean streamflows of Rock Creek were often less at the downstream site than at the upstream site.Thus, daily mean streamflow in the tributaries appears to be closely related to daily mean streamflow in mainstem Rock Creek only during periods of substantial area-wide runoff.Streamflow in the tributaries resulting from local storms or local snowmelt may not contribute to streamflow in the mainstem.On the basis of this study, daily mean to be closely related to daily mean streamflow during periods of substantial area-wide runoff, taries resulting from local storms or local flow in the mainstem.