PROGRAMS AND PLANS - Guidelines on Entering Synthesized Flow Data Into The Streamflow and Basin Characteristics Computer File

In Reply Refer To:                                   Code 4351 4016
Mail Stop 415                                        SW Branch

                                                     January 17, 1978


Subject:  PROGRAMS AND PLANS - Guidelines on Entering Synthesized Flow Data
                               Into The Streamflow and Basin Characteristics
                               Computer File

The purpose of this memorandum is to provide guidance on entering into
the Streamflow and Basin Characteristics computer file data that are based
on synthesized flow records.  One of the objectives of this file is to pro-
vide a data base that can be used as input for regional studies or statistical
analyses.  To meet this objective, the file should contain the "best"
estimate of flow characteristics that are based on observed flow records
for the site and possibly from such non-flow information as climatic records.
The flow characteristics should not be adjusted by comparison with nearby
flow records or weighting with regional estimates (WRC Bulletin 17, p. 18-19).

It is desirable to identify those data contained in the file that are
derived from non-observed record.  All districts should, as soon as possible,
identify those data currently contained in the file that are based on syn-
thesized record.  This identifier can be entered into the file by adding
to a single type 0 or 1 card for each station an appropriate code as
detailed on the enclosed change to Program E772 - update program.

Currently, the file should contain data only for unregulated (or based
on period of unregulated flow), non-urban, natural-flow stations.  The ap-
propriate basin and streamflow characteristics should be entered, as 10 or
more years of observed record or as synthesized record becomes available.
Of particular concern at present are the numerous peak-flow characteristics
based on synthetic records; however, other synthetic streamflow data (low-
mean, and flood-volume) should be entered and identified if available.
Data for urban sites should not be entered into the Streamflow and Basin
Characteristics file at this time.

Discharge characteristics for synthetic record sites should be obtained by
weighting the frequency data from the observed record with that from the
synthesized record.  Several procedures, ranging from simply averaging the
curves to a soon-to-be published procedure proposed by Bob Lichty, have
been used to combine the frequency values.  No decision has been reached
as to which of these methods is preferable, and a subjective decision may


be required to determine which frequency data will best meet the objective
of the file.  All appropriate statistics should be entered in addition
to the flood-frequency discharges.  The mean, standard deviation and skew
values of combined frequency curves may be computed as shown in Appendix 4,
WRC Bulletin 17 and on the enclosed explanation.

Districts are encouraged to submit, by memorandum to the Surface Water
Branch, suggestions or comments regarding uses or potential uses, by dis-
tricts or others, of data contained in the Streamflow and Basin Character-
istics File.  Provision may be made in the future to include data from urban
sites.  It would be helpful to know which streamflow and basin variables
the districts consider should be included for these sites.

                                    D. M. Thomas, Acting Chief
                                    Surface Water Branch


WRD Distribution:  A, FO