Instantaneous Data Archive - IDA
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Discharge data past September 30, 2007 have been moved from IDA to the National Water Information System Web Interface (NWISWeb) . Historical instantaneous values for other parameters are now also available on NWISWeb and users are directed there, or to the related web services, for all data from October 1, 2007 through the present. IDA remains available for discharge data prior to October 1, 2007. Future plans are to move all remaining IDA data to NWISWeb sometime in 2013 at which time IDA will be discontinued. Please address any questions through the "Questions and Feedback" link above.
Since 1889 the United States Geological Survey has collected continuous discharge and other time-series data on the nations rivers and streams, with intervals commonly ranging from 5-60 minutes. Historically, these instantaneous data have been processed into various daily values, such as the daily maximum, minimum and/or mean. This was done primarily to provide concise values for publication in paper reports (prior to the advent of the computer age) or storage without significant memory usage (early in the computer age). In more recent years, and particularly since the USGS began making real-time instantaneous data available on NWISWeb in 1994, more attention has been given to historical instantaneous data and USGS offices have received increasing requests for these data. There have been several challenges associated with meeting those requests, among them are that:
In developing a system to make historical instantaneous data available, the USGS has attempted to balance the fact that it is not possible to completely quality assure historical instantaneous data at most site due to the time and resources required, with the fact that it would not be appropriate to simply show all available data and confuse the user with multiple data sets of ambiguous data quality. Thus the archive as been built around a process that compares the available instantaneous data to the published daily values. For each set of instantaneous data that exists for a given day, a new daily value is calculated and compared to the published daily value. The instantaneous data set that computes a value that most closely matches the published value is added to the archive for that day, along with an accuracy code explaining how closely it matched. Currently the archive is limited to comparing discharge data only against the published daily mean values. The possible classifications are as follows:
If the daily mean discharge calculated from the instantaneous values on a given day is greater than 10 percent different from the published daily mean, those instantaneous values are excluded from the archive. In addition, instantaneous data that corresponds to a daily mean value that was estimated are automatically excluded from the archive regardless of any comparison.
An additional classification is available at those limited sites where quality assurance of individual instantaneous data has been done. When this classification is used there is no comparison to the daily mean values.
It is important to note that, other than for classification code 9, the values available in the archive have not been individually reviewed and approved. They have been automatically compared against the published daily mean value and found to have no gross errors when used to compute a daily mean. Individual instantaneous values may still have significant error. For example a data spike might cause a given value to be off by several hundred percent, yet when combined with the other available values in the daily mean calculation the result might lead that spike to get added to the archive with an accuracy code of 2 or 3 because the impact on the daily mean is less than 5%. Users of the archive are thus strongly encouraged to review all data prior to use.
The USGS converted to electronic storage and computer processing of instantaneous time series data in the 1980's, however it was not until the late 1990's that computer storage was sufficient to hold long-term periods of instantaneous data. Recovery of historical data from backup tapes has been done in most locations, and thus stations available on this web site will typically have data starting in the late 1980s. Earlier data are archived on paper charts and must be processed manually. Populating this web site with instantaneous discharge data takes effort and resources that are being provided "as available." Because of this not all states and stations are available at this time; you should see the number of states and stations with data increase over time.