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<br />Instrumentation <br /> <br />Each of the 17 stations consisted of stage (flood-hydrograph) and rainfall <br />recorders, both located at the downstream limit of the study watershed. Stage. <br />recorded in hundredths of feet, was measured inside a 4-inch stilling-well pipe by <br />a small float connected directly to a digital recorder; runoff entered the pipe <br />through numerous 1/ 4-inch holes drilled at several levels in the pipe. Rainfall, <br />recorded in hundredths of an inch, was measured inside a 3-inch pipe by a small <br />float connected directly to a digital recorder; rainfall entered the pipe from a <br />5-inch by 10-inch rectangular collector located on top of the shelter. The digital <br />recorders punched all data on 16-channel paper tape at 5-minute time intervals. <br />A single cam-type timer was used to activate both rain. and stage recorders, thus <br />assuring time-synchronous data. <br /> <br />Theoretical Stage-Discharge Relations <br /> <br />Recorded stage data was converted to discharge through use of theoretical <br />stage-discharge relations. For most stations, these relations were determined by <br />step-backwater analyses as described by Bailey and Ray (1966). Because <br />changes in channel configuration may affect this type of theoretical relation, sites <br />were resurveyed and step-backwater analyses were revised throughout the study <br />following major flood events or evident channel changes. The stage-discharge <br />relation for station 0715480'0 was determined by culvert analysis as described by <br />Bodhaine (1968). The basis of the stage-discharge relation for each station is <br />given in table 1. <br /> <br />In addition to the theoretical stage-discharge relations developed for each <br />site, indirect determinations of peak discharge were obtained during the study to <br />provide additional stage-discharge information for significant flood events. A <br />total of 12 such determinations was made at 11 of the 17 study sites. <br /> <br />STATION FLOOD-FREQUENCY ANALYSIS <br /> <br />When annual flood information is available at a site, a relation can be devel- <br />oped between flood magnitude, expressed in terms of either peak discharge (cubic <br />feet per second) or runoff volume (acre-feet), and frequency of occurrence, <br />expressed in terms of recurrence interval. Recurrence interval is the average <br />interval of time, usually in years, within which the given flood will be equaled or <br />exceeded once (Chow, 1964). A uniform technique by which this relationship is <br />developed has been established by the U. S. Water Resources Council (1977). <br />These guidelines are generally accepted by Federal and State agencies and were <br />used to develop the flood-frequency relations presented in this report. The <br />following guidelines are noteworthy: <br /> <br />1. The log-Pearson Type III distribution, applied to the annual flood <br />series, should be used. <br /> <br />2. A generalized skew coefficient is recommended for analysis of short <br />records, while a weighted skew coefficient is recommended for <br />longer records. <br /> <br />5 <br />