PROGRAMS AND PLANS--Guidelines for the Operation of a Crest-Stage Program In Reply Refer To: April 14, 1988 WGS-Mail Stop 415 OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 88.07 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 Water WRD Distribution: A, B, S, FO, PO This memorandum supersedes Surface Water Branch Technical Memorandum No. 74.17.