RECORDS--Policy on the Publication of Estimated Flows In Reply Refer To: WGS-Mail Stop 415 March 8, 1990 OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 90.11 Subject: RECORDS--Policy on the Publication of Estimated Flows Flow records on some streams are poor at times because of channel and flow conditions or because of monitoring problems. The U.S. Geological Survey is sometimes asked to obtain flow records on streams that are very difficult and/or very expensive to gage. Flows can be estimated for some of these sites as accurately, at times, from flow routing or regression procedures or, possibly in some cases, from precipitation-runoff modeling, as from a flow record collected at the site. This policy statement provides guidelines for the publication of estimated flows. In situations where there is missing or unreliable record and these periods of record must be estimated, methods such as flow routing or regression analysis may be used to estimate the flow during these periods. Although periods of routed or modeled flows used to fill missing periods can be published in an annual data report and stored in WATSTORE, long periods computed for special projects should not be. The estimated record, however, must be clearly identified and qualified, as noted in the "WRD Data Reports Publication Guide," if it is considered to be of a differ- ent accuracy than the monitored flow record. Flow records estimated from precipitation-runoff models may be of statistical value but may not be an adequate representation of daily or peak flows at a site because of the uncertainty that the precipitation record is representative for a given day or storm event. Therefore, flows estimated from precipitation-runoff models should not be published in the annual data reports or stored in WATSTORE. Flows estimated from flow routing or regression models or from precipitation-runoff models may be published in other reports provided that it is clearly identified that the records were obtained from a model and are not from monitored data at that site. The methods and assumptions for the modeled flows also should be clearly described. Flow records computed from a hydraulic routing model such as BRANCH, where stage data are obtained at the gage site and at a site either upstream or down- stream from the primary gage, can be published in the annual data report. Records published in the annual data reports should be based on one or more types of measured correlative data of the stream, such as stage or velocity, at the site. Estimates of missing record should be made using the most accurate method available and then should be qualified as appropriate. Flow records published in the annual data reports and stored in WATSTORE should represent the best possible flow record at the site indicated. These records are sometimes used in court and are also used for a variety of other water-related decisions. The records must be computed in such a way that the U.S. Geological Survey can support published discharges and computational procedures in court or in dealings with other agencies and the public. Charles W. Boning Chief, Office of Surface Water WRD Distribution: A, B, S, FO, PO This WRD Memorandum does not supersede any previous WRD Memorandum.