The basic steps for building reaches are:
1. Convert RF3 to R3 double prime. This batch operation processed Reach File version 3 to delete duplicate reaches, reassign reaches to the correct cataloging unit, validate geographic names assigned to reaches against data from the Geographic Names Information System (December 1996 extract), apply updates supplied by the States of California and Arizona, redelineate reaches based on the standards used for the National Hydrography Dataset, and identify inflow/outflow points where transport reaches entered and exited water bodies.
2. Create artificial paths. Using waterbodies from the features data and inflow/outflow points extracted from RF3 double prime, this process automatically generated the lines used to delineate artificial paths within water bodies using the ARC/INFO GRID routine.
3. Blind pass. This batch step conflated RF3 double prime reaches, and transferred reach information (reach code, reach date, name, stream level, and flow relationships) to the features. It also integrated the artificial paths generated in the previous step with the other features, built reaches on the artificial paths, and assigned geographic names to water bodies (February 1995 extract).
4. Quadrangle-based visual pass. During this interactive step, analysts ensured that the data developed in the previous batch processes conformed to reach delineation rules and that reaches were assigned to the appropriate cataloging unit. Batch procedures identified and developed a list of possible errors. Using the list, software presented each case to analysts to make appropriate edits to the data. Analysts recorded notes where repairs could not be made; these notes are encoded in the digital update units associated with reaches.
5. Build superquads. After the quadrangle-based visual pass was complete, all quadrangles that cover all or part of each cataloging unit were paneled into a superquad. In this batch process, reaches that cross quad boundaries were corrected to conform to reach delineation rules.
6. Cataloging unit-based visual pass. Like the quadrangle-based visual pass, analysts ensured that reaches conformed to reach delineation rules. Batch procedures identified and developed a list of possible errors. The analysts examined each error, and corrected the data.
7. Central quality assurance/quality control. This step (1) confirmed that integrity checks were performed successfully during the visual pass activity, and (2) assessed statistics gathered during the earlier processes to determine if additional review was needed. A check of data from the cataloging unit-based visual pass was run in batch; any data that did not pass the procedure were reviewed interactively. If substantive changes were required, the data were reprocessed using procedures (as required) described in previous steps. The edited data then were rechecked using the central quality assurance/quality control process.
8. Data preparation and database load. This batch procedure performs final processing to the data emerging from the quality assurance/quality control step. Some of the activities include assigning the final reach codes, building waterbody reaches, adding final artificial paths in water bodies, and implementing any recent changes in standards for the National Hydrography Dataset. The encoding of geographic names was synchronized between the National Hydrography Dataset and the Geographic Names Information System using the March 1999 geographic names extract. Following this procedure, reaches, features, characteristics, geographic names, and relations were loaded into the database that holds the National Hydrography Dataset.
9. Flow relation correction and validation. Using an extract from the database, a batch procedure checked flow relations for consistency and generated a list of possible errors. Software presented each case to analysts to make appropriate edits to the data. Corrections were made to the flow relations and, occasionally, to the delineation of reaches. Changes were posted to the database. 10. Extract distribution copies of data. Data for a cataloging unit were extracted from the database, and converted into an ARC/INFO workspace containing coverages and other files related to the National Hydrography Dataset. Data available in the Spatial Data Transfer Standard format were developed from the workspaces. The workspaces, and the Spatial DataTransfer Standard-formatted files, were made available to the public.