WSP02699 - Laserfiche WebLink

Home Browse Search

000591 quently in response to changing conditions. Accuracy goals at a given site depend on the requirements of a particular management system, and can be met by intensive observations or by more sophisticated instrumentation as needed. Data for Planning and Design of Water Projects The goal for this type of data is to define with appropriate accuracy the statistical flow characteristics for all streams in Kansas. This includes not only all streams with natural flow, but also those streams that are affected by regulation and diversion. Accuracy goals in this report are defined in terms of accuracy of statistical characteristics of streamflow, rather than accuracy of basic data such as individual discharge measurements or daily flows. Except for a few stations with unusual problems, accuracy of the basic data Is ade- quate for use in determining statistical characteristics; accuracy of statistical characteristics is limited almost exclusively by the length of streamflow record. The principal measure of the accuracy with which a particular stream- flow characteristic can be determined is the standard error, expressed in this report as a percentage of the estimated value of the characteristic. For flow characteristics (except standard deviations of annual and monthly flows) calculated from streamflow records at a particular site, the standard error can be calculated from a theoretical relation of standard error to variability index (standard deviation of the logarithms of the data) and number of years of record. For standard deviations of annual and monthly flows, the standard errors, In percent, can be calculated only from the number of years of record. In general, the longer the record, the more reliable are the estimates of probable future occurrences. However, even with a long record, 50 to 100 years', It is not possible to determine flow characteristics with great precision. The standard error of a streamflow characteristic decreases with years of available record, but at a decreasing rate as shown In table 2. For both natural and regulated principal :streams, the Importance and multiple uses of data justify high accuracy so the proposed goal Is an accuracy equivalent to that obtained from 25 years of record. For the remaining streams, accuracy equivalent to that obtained from 10 years of record is proposed as the goal. These goals apply to streams wIth natural flow and to streams affected by regulation and diversion. For the latter case the flow characteristics to be defined are those that reflect present condi- tions of development. Long-Term Streamflow Data The goal for this type of data is to operate Indefinitely a small net- work of stations for streams that are expected to remain relatively free 15