Prediction of River Discharge at Ungaged Sites with Analysis of Uncertainty

Abstract

A technique is outlined for assigning uncertainty to the estimation of cumulative probability distribution functions (flow‐duration curves) for river discharge at ungaged sites. Data from existing stage‐discharge gaging stations are used to determine a best‐fit exponent for the adjustment of gaged data to a site within the watershed, and to estimate the uncertainty associated with said adjustment. Average annual discharge is shown to be a good indicator of the required adjustment and uncertainty of cumulative probability distribution functions, especially when applied to mean expected discharge through a water‐development project. The distribution of the actual values around the predicted is log‐normal, with a simple power relationship between discharge and drainage area describing the median values. In this paper, the application is to flow‐duration curves for the addition of hydropower capacity.