PROGRAMS AND PLANS--Guidelines for the Operation of a Crest-Stage Program

In Reply Refer To:                               April 14, 1988
WGS-Mail Stop 415


Subject:  PROGRAMS AND PLANS--Guidelines for the Operation of a
                              Crest-Stage Program

Knowledge of the magnitude and frequency of flooding is required
for the design of transportation facilities such as bridges and
culverts, flood-control structures such as reservoirs and levees,
and for floodplain management and the establishment of flood-
insurance rates.  These flood-frequency analyses generally require
only the instantaneous annual peak discharge.  Many years ago, the
U.S. Geological Survey (USGS) recognized the cost-effectiveness of
us-ing crest-stage gages to collect instantaneous flood-peak data.
These partial-record stations can be operated for a small portion
of the cost of a continuous-flow station.  Even though these gages
are relatively simple to install and operate, the quality-
assurance procedures for computing annual peak discharges should
be comparable to those used at continuous-flow stations.  This
memo-randum restates and clarifies procedures for operating a
crest-stage program.

Existing crest-stage gages can be former flood-hydrograph sites
operated as part of the small-streams program, discontinued
continuous-flow gaging stations, or stations originally estab-
lished as crest-stage stations.  In all cases, the primary prob-
lem is in es-tablishing and maintaining a current stage-discharge
relation.  Suggestions for developing a sound stage-discharge re-
lation will be provided as well as suggestions for improving
documentation procedures and analyzing the crest-stage network.

Stage-discharge relations

1.  Develop the stage-discharge relation initially by making di-
rect or indirect high-water measurements, developing a theoret-
ical culvert rating, or using step-backwater techniques,
depend-ing on what is appropriate.

2.  Obtain direct or indirect measurements every couple of years
to verify the high-water range of the stage-discharge relation.
Identify the priority of making measurements at crest-stage
stations in the District flood plan.  Whenever possible, mea-
surements should be obtained for major flood events.

3.  Maintain and utilize upstream and down-stream gages if both
upstream and downstream water-surface elevations are required
to compute flow through the culvert.

At many culvert sites, the stage-discharge relations were de-
veloped during the days of the small-stream program.  In many
instances, these relations are being used today without mea-
surements or high-water marks to verify the relation or flow
condition.  Not only is it important to verify stage-discharge
relations by measurements, it also is important to obtain high-
water marks to verify the type of flow condition and utilize
elevations at upstream and downstream gages, if warranted.

4.  Plot the stage-discharge relation and all measurements above a
certain stage and identify the types of discharge measurements.

Documentation procedures

1.  Maintain a listing of direct and indirect measurements at each
station, and clearly identify the type of measurement.

2.  Number the stage-discharge relations, identify the periods of
applicability, and document how each stage-discharge relation
was developed.

3.  Maintain current station descriptions, run levels at intervals
identified in the quality-assurance plan, and provide all ap-
propriate field offices copies of pertinent information such as
stage-discharge relations, station descriptions, level sum-
maries, etc., so the station can be properly operated.

4.  Write a brief station analysis documenting how the annual peak
discharge was computed, identifying which stage-discharge rela-
tion was used, the type of flow condition, noting whether mea-
surements were made on the peak, describing how the dates of
the peaks were determined, etc.

5.  Update the Peak-Flow File promptly after the end of the water
year and qualify all annual peaks appropriately.  Maintain a
current listing of annual peaks and stages in the station
folder for review purposes.

6.  Maintain District quality-assurance procedures for reviewing
the crest-stage program, and document this review process.

Regional/Network Analysis

The recently developed generalized least squares regression proce-
dure provides a useful method for regionalizing streamflow charac-
teristics and for evaluating the stream-gaging network (see Office
of Surface Water Technical Memorandum 87.08 dated April 22, 1987).
In particular, this procedure is useful for evaluating the crest-
stage network and making modifications in the network to maxi-mize
regional flood information.  The following comments on this
procedure are pertinent.

1.  Analyze the crest-stage network whenever a regional flood
study is completed, approximately every 5 to 10 years.  An
analysis of the crest-stage network and those continuous-flow
stations used for regional information should be a part of
every proposed regional flood study.  Once the regional
analysis is complete, an evaluation of the network requires
minimal effort.

2.  Determine those existing crest-stage stations that contribute
most to reducing the prediction error of the regression equa-
tions.  Evaluate possible improvements in regional information
by establishing new stations using the generalized least
squares regression procedure.  Operate those stations that
maximize regional in-formation (i.e., mini-mize prediction
error) for a given oper-ating budget.  Since most crest-stage
stations are operated to define the flood hy-drology of a
region, the generalized least squares regression procedure
provides a mechanism for determining the best locations for
these stations.  An example of using generalized least squares
regression for network analysis in Kansas is given in Water-
Supply Paper 2303.

The successful operation of a crest-stage program requires a
variety of skills including knowledge of hydraulics, frequency
analysis, and regionalization techniques.  Adequate training in
all these areas should be obtained for those involved in the
operation of the crest-stage program.

                                       Charles W. Boning
                                       Acting Chief, Office of Surface

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

This memorandum supersedes Surface Water Branch Technical
Memorandum No. 74.17.