PROGRAMS & PLANS--Low-Flow Frequency Estimates

In Reply Refer To:                                           June 17, 1985
WGS-Mail Stop 415


Subject:  PROGRAMS & PLANS--Low-Flow Frequency Estimates

Attached is a copy of the Open-File Report 85-95 "Low-Flow Frequency Estimation
Using Base-Flow Measurements" by J. R. Stedinger and W. O. Thomas, Jr.  The
paper has been submitted to the American Society of Civil Engineers (ASCE),
Journal of Water Resources Planning and Management.  Due to the importance
of the report and the uncertainty of publication by ASCE, we are furnishing
a copy of the open-file report.

Experience has indicated that estimates of the d-day and T-year low flow
cannot be accurately estimated by regression on drainage-basin characteristics.
An alternative is the use of base-flow measurements at the ungaged site and
concurrent daily flows at a nearby gaged site to establish a regression
relationship between low flow at the two locations.  A new estimator of the
d-day T-year low flow is proposed.  When applied to an actual data set, the
new estimator appears to be unbiased and to have the minimum mean square error
among the five estimators considered.

The method appears to be promising but was tested on a limited data set.
We suggest that you try the method at your convenience and when the need
arises.  Contact Ed Gilroy or the Regional Surface Water Specialists if
you have any questions.  Please relay comments concerning your experiences
with the method to the Surface Water Branch through the Regional Surface
Water Specialists.

                                           Verne R. Schneider
                                           Acting Chief, Surface Water Branch


WRD Distribution:  A, FO, SL

This memorandum does not supersede any previous SWB memorandum.