The concentrations of many constituents are affected by streamflow.
Typically, adjustment of the concentration data to account for varying
streamflow is needed before further analysis to evaluate differences
in concentration is done. The effects of streamflow can pose a problem
when evaluating changes in specific conductance and dissolved solids
because of the inherent inverse relation between these variables
and streamflow. The use of flow-adjusted concentrations by the residuals
method provides a way to remove the source of much of the variance
due to the influence of streamflow. Residuals analysis regresses
the measured value on some function of streamflow and uses the residuals
from the regression (the observed measurement minus the predicted
value) as flow-adjusted values. The residual method works well if
a functional form of the measured value to streamflow regression
produces a reasonable fit. To estimate daily specific-conductance
values from streamflow, instantaneous specific-conductance data and
continuous daily streamflow data were input into a multi-parameter
regression model. Regression equations for the model can be found
in Table
3 of the USGS
Scientific-Investigations Report 2004-5024. See the report for
a more detailed explanation of flow-adjusted concentrations.
U.S. Department of the Interior
U.S. Geological Survey
Water Resources of Colorado
Contact: webmaster_co@usgs.gov
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Last Modified:
May 4, 2004