What is a Shift-adjusted rating?
- Shift-adjusted rating:
- Stage-discharge relationships (ratings) are primarily
developed from a graphical analysis of multiple streamflow measurements.
Measurements are generally made on 8-week intervals. The frequency/interval of
streamflow measurements may change based on a variety of circumstances
including (but not limited to) flow conditions and rating definition. All
discharge measurements are compiled and maintained in the USGS NWIS database.
Each measurement is made according to established USGS guidelines and
undergoes quality assurance review. Some measurements indicate a change in the
rating, often due to a change in the streambed (for example, scour or
deposition) or growth of aquatic vegetation. Such changes, called "shifts,"
may indicate a short- or long-term change in the rating for the gage. When
indicated by a streamflow measurement, the shifts are applied mathematically
as temporary adjustments to a defined rating.
The tables being provided are shift-corrected. The indicated shift has been applied to the base rating.
The shift adjustments are applied to the rating as streamflow measurement data becomes available,
resulting in an adjusted rating. Some ratings may change as often as weekly, others may not change for months or years.