USDA-ARS: USDA HWQ4: Estimating Uncertainty in Measured Discharge and Water Quality Data
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Official Method Name
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A Software Tool for Estimating Uncertainty in Measured Discharge and Water Quality Data: Development and Published Results |
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Current Revision
| 2009 |
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Media
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WATER |
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Instrumentation
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Not Applicable |
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Method Subcategory
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General |
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Method Source
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Citation
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Brief Method Summary
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This method consists of two aspects. One, it presents cumulative uncertainty results for actual measured storm water quality data (flow, N, P, sediment). For storm events, the uncertainty was typically least for discharge (7 to 23%), greater for sediment (16 to 27%) and dissolved N and P (14 to 31%)loads, and greater yet for total N and P (18 to 36%) loads. These results are presented to provide reasonable uncertainty estimates in situations where project-specific uncertainty information is not available. Two, it presents a software tool called DUET-H/WQ (Data Uncertainty Estimation Tool for Hydrology and Water Quality). DUET-H/WQ lists published uncertainty information for data collection procedures (discharge measurement, sample collection, sample preservation/storage, laboratory analysis, and data processing and management). The tool assists users in assigning appropriate data-specific uncertainty estimates and then calculates the uncertainty for individual discharge, concentration, and load values. |
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Scope and Application
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DUET-H/WQ was developed from a framework for quantifying the uncertainty in measured discharge and sediment, N, and P load and concentration data collected at the field and small watershed scale (NEMI Method - USDA HWQ1). The framework consists of: 1) establishment of categories within which to classify monitoring procedures and 2) presentation of an accepted method for estimating cumulative uncertainty in individual measured values resulting from component uncertainties within procedural categories. DUET-H/WQ was designed to be a user-friendly application and enhancement of the uncertainty estimation framework. |
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Applicable Concentration Range
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Interferences
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Both DUET-H/WQ and its framework-basis (NEMI Method -USDA HWQ1) utilize the root mean square error propagation methodology to provide uncertainty estimates instead of more rigorous approaches requiring detailed statistical information, which is rarely available. In applying DUET-H/WQ, several important issues (e.g. user subjectivity and temporal/spatial variability) should be kept in mind. The process by which users determine a reasonable uncertainty estimate for each procedure is quite subjective because of the considerable variability of published uncertainty information as affected by study design, collection methods, and monitoring conditions. In the face of this subjectivity, users should strive to make the most accurate uncertainty estimate possible for each data collection procedure. The benefits of uncertainty estimates corresponding to measured data cannot be fully achieved if uncertainty is purposefully under-estimated in an attempt to make data appear to be ``better¿¿ or less uncertain. DUET-H/WQ does not include all sources of uncertainty (e.g. uncertainty contributed by spatial and temporal variability). Such uncertainty sources were excluded to maintain a focus on uncertainty estimation for individual measured values. DUET-H/WQ does, however, provide necessary inputs, specifically measurement uncertainty, for comprehensive uncertainty analyses conducted with watershed models or other geospatial-statistical tools. |
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Quality Control Requirements
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Sample Handling
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Maximum Holding Time
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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