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Development of a Discharge-Stage Rating Curve for Strawberry Creek

Abstract

I developed a hydrological rating curve for Strawberry Creek on the University of California campus, so that estimated flow rates cold be calculated from stage records.  Since 2007, water stage levels have been automatically recorded every 15 minutes based on pressure transducers that are located on the North Fork, the South Fork and on the Main Stem just below the confluence.  I used current meters to collect flow measurements six times on the Main Stem, five times on the North Fork, and four times on the South Fork and used this data along with recorded stage data to develop a rating curve for each location.  The rating curves developed for the Main Stem, South Fork and North Fork are:  y = 9.5668x2.7479, y = 34.061x - 273.35 and y = 15.498x2 -19.768x + 6.2605, where y is streamflow in cubic feet per second (ft3/s) and x is stage in feet.  All these rating curves have very good overall correlations for the relationship between stage and flow (r2 greater than 0.92), and therefore are likely to provide reasonably accurate flow estimates for most all but the highest flow levels.  A considerable amount of uncertainty exists for the high flow estimates on the Main Stem and the North Fork.  This uncertainty may be due to limited data for high flows, error in flow measurements, unsteady flow conditions, extrapolation to higher flows rates than those measured, and/or stage shift where the pressure transducers are located.  The main sources of uncertainty are likely to be the unsteady flow conditions (due to rapid rate of change in flow) and potential stage shift due to erosion and/or deposition.  The rating curve equations are sufficient for rough estimates at high flows, but would be improved with additional data collection.

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