Approaches to estimate uncertainty in longitudinal channel water balances

Document Type

Article

Journal/Book Title/Conference

Hydrology and Earth System Sciences

Volume

15

Publication Date

2011

First Page

1547

Last Page

1561

Abstract

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.

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