Approaches to estimate uncertainty in longitudinal channel water balances

The effects of uncertainty in field measurements on estimated longitudinal channel water balances are a poorly understood aspect of hydrology A mountain stream study reach in northern Utah with spatially variable groundwater exchange was used to explore a detailed uncertainty analysis approach to estimate the error in water balances Net changes in stream flow were first estimated for both a 515 m and a 560 m reach using two discharge measurement methods (1) rating curves and (2) dilution gauging with Instantaneous tracer experiments Errors in estimates were quantified using 95% Joint confidence regions for rating curves and a first-order error analysis for dilution gauging With the mean errors in rating curve predictions and dilution gauging estimated to be +/- 8 2% and +/- 8 4% respectively neither method was found to definitively detect net changes in stream flow at this scale Using dilution gauging net channel water balances were then estimated for a collection of 56-229 m sub-reaches within the two original study reaches When considering the +/- 8 1% error (defined as 95% prediction intervals) in these estimates at this scale significant net changes were observed in only half of the sub-reaches Gross gains and losses that contribute to these net changes were estimated and a first-order error analysis was additionally performed Half of the sub-reaches had significant gross gains and losses concurrently occurring that did not have significant net changes The uncertainty analyses proved imperative to appropriately interpret results (C) 2010 Elsevier B V All rights reserved