Regional Regression Equations

Region Regression Equations by State

Washington

Low Flow (Qlow): To find the low flow regional regression equation, use this document from USGS.

1. Equation 11 (p. 32) is the correct low flow equation.
2. Reformatted to fit sqlBRAT’s terminology, it becomes 8.48*.0001*((DRNAREA**1.17)*(PRECIP**1.23))
3. Put the regression equation into the appropriate area on the Google Sheet that represents your watershed.

High Flow (Q2): To find the high flow regional regression equation, use this document from USGS.

1. Use Figure 16 (p. 29) to identify what regression region your watershed is in.
2. Use Table 6 (p. 36) to find the regression equation for your region. This will be in the 3rd column, titled Form of the regression equation
3. Replace all of the constants and coefficients in the equation with the values from the table. We recommend an exceedance probability of 0.5.
4. Replace the variables A, P, and CAN with the correct terminology used in sqlBRAT. A becomes DRNAREA, P becomes PRECIP, and CAN becomes CANOPY_PCT.
5. Reformat the rest of the equation so that sqlBRAT can understand it. Make sure that parenthesis are in the correct place, exponents become **, and multiplication becomes *.
6. Put the regression equation into the appropriate area on the Google Sheet that represents your watershed.