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Propagation of Uncertainty in Streamflow to Water Quality Estimates
Citation:
Gupta, A., G. Mallya, M. Hantush, AND R. Govindaraju. Propagation of Uncertainty in Streamflow to Water Quality Estimates. World Environmental and Water Resources Congress 2019, Pittsburgh, PA, May 19 - 23, 2019.
Impact/Purpose:
We will present a method that estimates uncertainty due to measurement, parametric and structural errors in estimated streamflow at unmeasured locations and propagates this uncertainty to a reconstructed WQ parameter. Subsequently, we will evaluate the effect of uncertainty in streamflow on TMDL analysis.
Description:
Traditionally, load estimator (LOADEST) equations are used to reconstruct water-quality (WQ) parameters using streamflow as predictors. Often, streamflow and WQ data are available at different locations in a watershed. Therefore, for the reconstruction of WQ data, streamflow is estimated at the WQ station using a hydrologic model, which is calibrated against streamflow at other locations. Streamflow values that are estimated using this method may deviate significantly from the true streamflow values, which will bias the estimation of WQ parameters and subsequently affect the TMDL analysis. It is recognized that WQ data estimated using LOADEST incur model-errors because LOADEST estimates do not represent the true relationship between streamflow and a WQ parameter. Recently, methods to quantify model-errors have been proposed in the literature; however, these methods implicitly assume that the input streamflow data is error-free. The effect of neglecting uncertainty in streamflow data on WQ parameter estimation has not been examined by previous researchers. We will present a method that estimates uncertainty due to measurement, parametric and structural errors in estimated streamflow at unmeasured locations and propagates this uncertainty to a reconstructed WQ parameter. Subsequently, we will evaluate the effect of uncertainty in streamflow on TMDL analysis. EPA Disclaimer: The findings and conclusions in this abstract have not been formally disseminated by the U.S. EPA and should not be construed to represent any agency determination or policy.