Fluvial ecosystems exhibit a wide range of natural variability in the quantity, quality, timing, and temporal variability of river flow. How much water does a river need, and what is the importance of natural variation? To answer these questions, an understanding of flow and its far-reaching consequences for the physical, chemical, and biological condition of rivers is essential. This chapter shows how a basic appreciation of the water cycle is critical to understanding the magnitude and timing of streamflow, and discusses how natural variation in flow often has been altered by human actions. Increasingly today, the tools of hydrologic analysis are being combined with other elements of river science to ensure that “environmental flows” are sufficient to protect and restore stream ecosystems.
KeywordsBase Flow Overland Flow Impervious Surface Environmental Flow Recurrence Interval
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