[Note: this is an internal working document of a USGS-SFSU collaboration. Data, analysis and results herin should not be considered as final or accurate. Final results will be presented in print.]
Comparison of Two Rating Curves:
Full Gaussian-Bulge Fit (Including Kink and Offset) vs Simple Gaussian-Bulge Fit
( references |Delta Discharge |Rating Curves |Indexing software )

As a standard rating curve we choose the "Simple Gaussian Bulge" form, which has an upwards bulge on the "turning in" cycle, and a symmetrical downwards bulge on the "turning out" cycle. Here we compare this standard rating with the full Gaussian-Bulge fit, including an offset and a kink. The curves are shown below, and the effect on the calculation of the Delta Discharge.
Figure 1. The tms3 calibration data (black circles), the Simple Gaussian-Bulge model, and the Gaussian Model with Kink and Offset (plotted with p80717d.m). (Click in figure for blowup.) The addition of the kink and offset permit the model to follow the downwards curvature seen in the data. Figure 2. The average Delta Discharge, after application of the rating curve and filtering, is shown for the two rating curves (plotted with p80717c.m). The effect of the kink and offset is to decrease the discharge by about 22 m3/s. This is a substantial effect, comparable to the entire Delta Discharge during periods of lowest flow.