Final Selection of the Discharge Station Records to be Included in the Hydro-Climatic Data Network (HCDN)

In Reply Refer To:                               August 9, 1989
WGS-Mail Stop 415




Subject:  PROGRAMS AND PLANS--Final Selection of the Discharge
                              Station Records to be Included in
                              the Hydro-Climatic Data Network

The Office of Surface Water (OSW) expresses its thanks to the
Districts for their response to Technical Memorandum No. 88.05,
requesting assistance in defining a list of discharge records
suitable for climatological analysis as part of the
U.S. Geological Survey (USGS) Hydro-Climatic Data Network.  All of
the responses have been consolidated and either Jim Slack or
Jurate Landwehr has talked to each District about their choices.
A list of the stations suggested for each State is being
transmitted separately to each District and State Office Chief and
to previously designated District contacts.  They should review
this list and make ANY corrections, additions, and deletions which
are necessary to make the list consistent with the criteria
restated below.

The purpose of establishing this list is to provide a single,
division-wide compilation of discharge stations having periods of
record for which the monthly and annual streamflow values are
suitable for climatological analysis.  From the comments of the 60
or so District and Regional staff members who have helped assemble
this list, it was discovered that there was a much wider interpre-
tation than was expected of the suggested criteria for selecting
stations given in OSW Technical Memorandum 88.05.  Also, several
of you have raised important questions and issues which were not
fully addressed or even foreseen.  As a result, the present list
should have a final review for conformance and national unifor-
mity.  There are likely some stations or periods of record on the
list which should not be there.  Likewise, there may be suitable
stations and periods of record which are missing, and some
selections need better annotation.

The accuracy of this list is critical--there is great interest in
using the USGS data in climate change studies throughout the
hydrologic community.  This list will form the basis of a report
which we expect will receive worldwide circulation, for example,
through our current participation in an experiment for the World
Meteorological Organization.  We have already received numerous
requests for the list, or parts of the list, from outside the
agency, both from other Federal agencies and from the academic
community.  However, in the interest of accuracy and to avoid
favoritism in distributing USGS data, we are not honoring any of
these requests until the list is finalized in a Survey report.  We
request that you refrain from distributing the list in whole or in
part until then as well.

By separate memo, we are providing our contacts in each district
with further specific instructions for preparing the revised list,
plus other supporting material to assist in the review.  Please
ensure that great care is taken to review this list bearing in
mind the potential embarrassment of having included unsuitable
periods of record or having missed key stations.  THE RESPONSIBIL-
There will be no higher level technical screening of the
individual records which the District chooses.

Below is a clarification and expansion of the selection criteria
of OSW Technical Memorandum 88.05.  Please remember there may be
exceptions to any of these criteria.  We need to document such
exemptions on a station-by-station basis by means of an
explanatory comment in the list.

    Criterion of record length:  At least 20 years of suitable
record.  If a station has been operated for 50 years and only the
first 20 years are free of defects discussed below, then only that
20 years should be selected.  If, however, a shorter record is all
that is available to fill a gap in geographic or climatic repre-
sentation, it is acceptable.  A specific example is the inclusion
of short records from islands in the Pacific because that is all
that is available for that geographic region.

    Criterion of data quality:  A rating of "good" or "excellent"
on nearly all of the annual daily discharge records.  A few days
in some years rated "poor" or "fair" because of estimated record
or similar considerations would not necessarily disqualify a sta-
tion, nor would a few years rated "poor" or "fair" out of many
rated "good" or "excellent."

    Criterion of coverage:  Broad geographic and diverse climatic
representation across the country.  We prefer to have too many
stations rather than too few.  It is always more desirable for the
individual users to have the option of paring down the list
according to whatever density or accounting criteria they choose
than to be supplied with an insufficient number of stations.  Thus
we now consider the suggestion of one or two stations in each
accounting unit or areal rectangle as, at best, a desirable mini-
mum.  ALL stations and periods of record which fit the other
criteria should be included in the list.  (We are currently
expecting a network of about 1000 stations.)
    Criterion of natural conditions:  Minimal anthropogenic
effects such as diversion, augmentation, land-use changes, or
regulation of the stream discharge or reduction of base flow due
to extreme ground-water pumping.  This is the most difficult
criterion.  The objective is to include a discharge station if the
anthropogenic effects are not felt to mask the effects of climate
variation in the monthly and annual values.

    a.  Stations subject to regulations by dams are generally not
acceptable.  However, as an example, a low-head hydropower dam
which has only a transient effect on high or low flows, but not on
the monthly values, is acceptable.  This effect should be noted.

    b.  Stations subject to diversion or transfer for any use are
generally not acceptable.  However, if the diversion has existed
essentially unchanged for the entire period of record, the station
may be acceptable.  For example, a station in, say, the Nevada
desert may be subject to diversions for irrigation but the prac-
tice has remained unchanged over the entire period of record.  So,
while the diversions exist, and do affect the actual values, the
process by which they alter the record is, in a sense, unchanging
and does not significantly confound the influence of climate on
the record.  These considerations should be noted.

    c.  A station in a basin which has undergone a substantial
change in usage, say forest to agriculture or urban, is probably
not suitable even if the change was gradual.  If such a station is
included, such change should be noted.

PLEASE NOTE:  Even though it will be stressed in the report that
the selected periods have been qualified so that at least the
monthly averages meet our criteria, users of this data set may
wish to do analyses on a shorter time step, possibly daily.
Please indicate any conditions which would make the discharge
records unsuitable for analysis at less than a monthly resolution.

    Criterion of basin size:  There was a typographical error in
this criterion in OSW Technical Memorandum 88.05.  The range
listed should have been 100 to 10,000 square miles.  In practice--
given the exception granted for the "Big Five" rivers, the excep-
tion granted for the Benchmark stations, and the exceptions
granted to achieve the desired coverage--this criterion has little
meaning and should be ignored.

    Inclusion of formerly suitable stations:  If a station is not
presently suitable because of regulation, diversion, augmentation,
or because it has been discontinued but had a period of record
which on its own is suitable, the suitable period should be
listed.  Likewise, the fact that a station might soon be discon-
tinued or become regulated is not cause to exclude it.  We are
making no statement about the suitability of records for water
year 1989 or later.  The heart of this effort is to identify

existing periods of record suitable for climate analysis.  Ques-
tions of funding to continue or re-establish any station are not
germane to this study.

    Exclusion of constructed records:  Records that are con-
structed (e.g., the Four Rivers Index of the Sacramento Basin) or
re-constructed (e.g., the "natural flow" for the Colorado River at
Lee's Ferry) from other sites or information on diversions, aug-
mentation, pumping, regulation, etc. are generally not suitable.
While such records may be indicative of current conditions, we
wish to avoid the question of whether the computational algorithm
might disguise the effects of climate.  We do not mean to exclude
stations for which the effect of diversions, etc., are easily and
routinely corrected.  A comment to this effect should be included
for these records.

    Explanation of Benchmark and Current Conditions stations:  One
impetus for this study was the desire to reconcile the differences
between several lists of "indicator" stations that have been used
within the Water Resources Division.  These lists were described
at the end of OSW Technical Memorandum 88.05.  We want to clarify
in the report why a Benchmark or Current Conditions station not in
the final list is not suitable for climate analysis.  Most reasons
are straightforward.  For example, Crater Lake, Oregon, is a
Benchmark station but is not a discharge station.  Similarly, the
Sacramento River at Verona, California, is a Current Conditions
station but is highly regulated.  We ask you to provide any such
reasons why all or part of the record at these sites should not be
included in the HCDN.

    Reconciliation of the National Water Summary (NWS) stations:
Since we began this project, one other consideration has arisen.
The original compilation was provided to the Office of Long Range
Planning and Assessment as a help in getting the State reports for
the 1988-89 National Water Summary started.  The NWS had its own
objectives and criterion.  Some stations which were not in our
original list nor were suggested to us for inclusion in the HCDN
by the District in commenting on the original list have been used
for the NWS study.  Please reconsider the suitability of any
station that was in the NWS study but does not appear on the HCDN
list.  In particular, we have noted each drought index station
that was used in the NWS work but was not selected by the District
for the Hydro-Climatic Data Network with the notation "NWS*" in
the "Last usable Water Year column".  Please comment on the suit-
ability of these and any other NWS stations--in particular, the
flood index stations if they differ from the drought index
stations--for inclusion in the HCDN list.

Please return your comments, preferably by EDOC, to JRSLACK (WR
and CR) or JMLANDWEHR (SR and NR) no later than September 1, 1989.
An official report on the results should be available by December
1989 at which time the list will be available for distribution.

Again, OSW wishes to thank those in the Districts that have par-
ticipated in this project.  Their efforts will help make this
network an important scientific tool.

                                  Charles W. Boning
                                  Chief, Office of Surface

WRD Distribution:  A, B, S, FO, PO

Copy to:  Jim Slack, WRD, Menlo Park, California
          Jurate Landwehr, WRD, Reston, Virginia