J.E. Kiang | USGS Science

USGS2012

Quantifying uncertainty in discharge measurements: A new approach

The accuracy of discharge measurements using velocity meters and the velocity-area method is typically assessed based on empirical studies that may not correspond to conditions encountered in practice. In this paper, a statistical approach for assessing uncertainty based on interpolated variance estimation (IVE) is introduced. The IVE method quantifies all sources of random uncertainty in the measured data. This paper presents results employing data from sites where substantial over-sampling allowed for the comparison of IVE-estimated uncertainty and observed variability among repeated measurements. These results suggest that the IVE approach can provide approximate estimates of measurement uncertainty. The use of IVE to estimate the uncertainty of a discharge measurement would provide the hydrographer an immediate determination of uncertainty and help determine whether there is a need for additional sampling in problematic river cross sections. ?? 2009 ASCE.

Conference Paper↗

USGS2011

Causes of systematic over- or underestimation of low streamflows by use of index-streamgage approaches in the United States

Low-flow characteristics can be estimated by multiple linear regressions or the index-streamgage approach. The latter transfers streamflow information from a hydrologically similar, continuously gaged basin ('index streamgage') to one with a very limited streamflow record, but often results in biased estimates. The application of the index-streamgage approach can be generalized into three steps: (1) selection of streamflow information of interest, (2) definition of hydrologic similarity and selection of index streamgage, and (3) application of an information-transfer approach. Here, we explore the effects of (1) the range of streamflow values, (2) the areal density of streamgages, and (3) index-streamgage selection criteria on the bias of three information-transfer approaches on estimates of the 7-day, 10-year minimum streamflow (Q 7, 10 ). The three information-transfer approaches considered are maintenance of variance extension, base-flow correlation, and ratio of measured to concurrent gaged streamflow (Q-ratio invariance). Our results for 1120 streamgages throughout the United States suggest that only a small portion of the total bias in estimated streamflow values is explained by the areal density of the streamgages and the hydrologic similarity between the two basins. However, restricting the range of streamflow values used in the index-streamgage approach reduces the bias of estimated Q 7, 10 values substantially. Importantly, estimated Q 7, 10 values are heavily biased when the observed Q 7, 10 values are near zero. Results of the analysis also showed that Q 7, 10 estimates from two of the three index-streamgage approaches have lower root-mean-square error values than estimates derived from multiple regressions for the large regions considered in this study.

Hydrological Processes↗

USGS2004

Water loss in the Potomac River basin during droughts

The water loss phenomena in the Washington DC metropoliton area's (WMA) Potomac River water supply basin during droughts was analyzed. Gage errors, permitted withdrawals, evaporation, and transpiration by trees along the river were investigated to account for loss. The Interstate Commission on the Potomac River Basin (ICPRB) calculated potential gage error and examined permits to determine permitted levels of consumption withdrawals from the Potomac. The result of a single slug test indicated that the soil transmissivity may not be adequate to allow passage of enough water to account for all of the calculated water loss.

Conference Paper↗