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Streamflow Record Augmentation and Record Extension

For questions and comments, contact email: h2osoft@usgs.gov.

Streamflow record augmentation and record extension refer to methods used to enhance limited information at a site of interest by using data at a nearby streamgage with a longer period of record. Generally, streamflow record augmentation refers to methods for improving the estimate of a streamflow statistic, while streamflow record extension refers to actually filling in daily data for periods without an at-site record.

Technical Policy Memos

Programs and Scripts

SREF: Streamflow Record Extension Facilitator. SREF is included in a suite of programs developed by Greg Granato. SREF can be used for either record augmentation or record extension.

FAQ

• How should streamflow record augmentation be handled when estimating N-day statistics?
  

  Generally, the data used to fit the relationship between the short record site and the index station should be in a similar range of flow as the statistic of interest. For example, to improve estimates of the 7Q10, only low flows should be used to fit a MOVE.1 line. Some issues in conducting this type of analysis are discussed in this memo to S. Carolina (word document).

  Using only low flow data for augmentation of low flow statistics can help to prevent bias in the results, as discussed in:
  Eng and others (2011) Causes of systematic over- or underestimation of low streamflows by use of index-streamgage approaches in the United States, Hydrological Processes, DOI: 10.1002/hyp.7976

  Using streamflow stations nationwide, Eng and others (2011) found that MOVE.1 and baseflow correlation tend to overestimate the Q_7,10. This bias can be reduced by using only flows less than the 90% flow duration to develop the linear relation between index site and partial record site. In the western U.S. where there is a prolonged dry period, using flows up to the 80% flow duration was preferred. Eng and others also found that the treatment of zero flows when using these methods is likely to have a large effect on their accuracy. A large bias in these methods was found for stations where the flow approaches zero when the pool of index stations did not include any with intermittent flow. As a side note, Eng and others also found that selecting an index station on the basis of highest correlation or most similar basin characteristics yielded roughly equivalent results.