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Streamflow Analysis

Streamflow Analysis. Module 8.7. Frequency Analysis – Why?. Common dialog to describe events Quantify extreme events Flood flow return periods Engineering design Watershed planning Zoning Geomorphic processes Water resources management

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Streamflow Analysis

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  1. Streamflow Analysis Module 8.7

  2. Frequency Analysis – Why? • Common dialog to describe events • Quantify extreme events • Flood flow return periods • Engineering design • Watershed planning • Zoning • Geomorphic processes • Water resources management • What is the probability of a given flow being available?

  3. How is Flow Variability Quantified? 2 Methods: • Recurrence interval / Flow probability • General technique to describe the probability of an event occurring • Frequently used for flood peaks • Just like we did for precipitation • Flow duration • Indicates the amount of time a given flow is equaled or exceeded • Describes availability of water resources

  4. Frequency Analysis How’s it done? • Rank (sort) events • Calculate return interval (Tr) • Calculate probability (p) Example: Maximum hourly rainfall per year

  5. Frequency Analysis How’s it done? • Rank (sort) events • Calculate return interval (Tr) • Calculate probability (p) • Plot event vs. recurrence interval 1. 2. 3.

  6. Flood Frequency Plot Viessman Fig. 3.9 Source: Viessman & Lewis, Introduction to Hydrology

  7. Flow Duration Analysis Variant of Flow Frequency Analysis • Probability presented as:percent of time a given flow is equaled or exceeded • Often constructed for a complete series of flows • e.g. daily average streamflow

  8. Viessman Fig. 3.14 Flow Duration Curve James River at Cartersville, VA Source: Viessman & Lewis, Introduction to Hydrology

  9. Discharge (cfs) 0 100 Percent of time flow exceededExceedance probability Conceptual Example Which system has greater flow variability?

  10. Relation of Flow Variability to Riparian Zones

  11. Metolius River

  12. Siletz River How do disturbance regimes differ?

  13. Runoff Distribution

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