Unmeasured Residuals in Sediment Budgets: A Cautionary Note

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Abstract
In studies that develop sediment budgets, one or more terms (constituting up to 94% of the total budget) have been obtained by subtraction. These unmeasured residual terms incorporate not only the sediment budget components attributed to them, but also the net sum of all errors in measured components. Thus, budgets may appear to balance only because errors are hidden in the residual term. The nature of sediment measurements is such that some error is virtually certain, and in sediment budget studies where all terms have been quantified, imbalances range as high as 104% of total basin yield. Despite these potential problems, the process of constructing the budget is still informative (even when terms are obtained as residuals), because it requires sediment sources and transport pathways to be identified and quantified. However, terms obtained by subtraction should be clearly identified as such, and where possible, error analysis of all terms should be included.