Determination of low-flow characteristics for Texas streams

Predictive equations for the harmonic mean flow; the 7-day, 2-year low-few (7Q2); and the 7-day, 10-year low-flow (7Q10) of ungauged Texas streams are developed using multiple regression analysis based on meteorological and physiographic data from 63 gauged streams, Harmonic mean, 7Q2, and 7Q10 values from the data range from 0.0001 to 1.6448 m(3)/s (0.004 to 58.12 cfs), 0 to 0.566 m(3x)/s, (0 to 20cfs), and 0 to 0.425 m(3)/s (0 to 15 cfs), respectively. Gamma-produced 7Q2 and 7Q10 estimates yielded more statistically reliable equations than either the log-Pearson Type III or mixed-log-Pearson Type III produced estimates. The basin parameters considered include contributing drainage area, channel length and slope, basin shape factor, mean annual precipitation, predominant hydrologic soil group, and the 2-year 24-h precipitation. The regression equation for the harmonic mean included channel slope, mean annual precipitation, and drainage area and had a higher adjusted R-2 than the 7Q2 and 7Q10 equations. A regional regression analysis yielded higher adjusted R-2 For the harmonic mean than the statewide equation, implying that regional equations are more appropriate than statewide equations for Texas.