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WWRC 97-03
Evaluation of Flow Duration Analysis to Establish Winter Instream Flow Standards for Wyoming Trout Streams


The purpose of this project was to assess the use of hydrologic data and flow duration analysis in the establishment of winter instream flow standards for trout streams in Wyoming. Relations between measures of flow duration during winter and trout abundance or habitat features for trout in eight study streams in southeastern Wyoming could not be identified. Statistics describing winter flow duration frequencies for 31 streams across Wyoming were highly variable among streams. Variation in winter flows was highly related to elevation and the proportion of the drainage that was irrigated, but the ability to predict flow duration values for individual streams was low. Discharge data during winter were less accurate than during other times of the year due to common and extensive periods when daily flow records were estimated. Flow duration analysis by itself does not appear to have potential to establish winter instream flow standards for Wyoming trout streams. However, such analysis can be used to assess the frequency of achieving instream flows for trout that may be defined using other techniques.

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