Interrogation Site Location Changes
We have made changes to how interrogation site location is reported, at the direction of the PTSC, to better accommodate interrogation sites getting moved to new locations.
A handful of interrogation sites have been moved to new locations that provide better detection opportunities or protection against damage from high flows. Interrogation sites are only allowed to move up- or downstream in the same stream. If a site moves to a different stream the original site is decommissioned and a new interrogation site is added for the new stream location. If a site moves less than 1 kilometer, the latitude/longitude coordinate values change, but the RKM stays the same.
Up to now we have treated changes to these locations values as a type 1 slowly changing dimension, which meant that we overwrote the old location values with the new location values. Going forward we will treat these values as type 2 slowly changing dimension, which means that the location history will be available and reported with the observation data.
For example, the interrogation site on the lower Methow River (LMR) moved from its original location with RKM 843.003 to a new location on August 18, 2017, 5km upstream with RKM of 843.008. Now that we have made this change, an interrogation report with the Site RKM attribute will show 843.003 for all observations before August 18, 2017 (highlighted in yellow below), and 843.008 for all observations after that date (highlighted in blue).
The PTAGIS sites map and interrogation site metadata page will show the most current location, but the site description will provide general information about when and how far the site moved from its original location.