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Determining Average Irrigation Need

Determining Average Irrigation Need. Review Hearing Officer conclusions regarding supply needed to prevent material injury Selecting year to use as baseline supply Overview of adjustment technique to account for differing climatic conditions from baseline. IDWR – Spring 2009.

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Determining Average Irrigation Need

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  1. Determining Average Irrigation Need • Review Hearing Officer conclusions regarding supply needed to prevent material injury • Selecting year to use as baseline supply • Overview of adjustment technique to account for differing climatic conditions from baseline IDWR – Spring 2009

  2. Hearing Officer Conclusion • The minimum full supply established in the May 2, 2005, Order is inadequate to predict the water needs of SWC on an annual basis. Recommended Order at 50 • It is based on a decade old year that does not reflect current efficiencies such as the increased use of sprinkler irrigation and computer monitoring or changes in the amount of land irrigated. Recommended Order at 49 • ...it is time for the Department to move to further analysis to meet the goal of the minimum full supply but with the benefit of the extended information and analysis offered by the parties and available to its own staff. Recommended Order at 51

  3. Hearing Officer Conclusion • The parties have attempted to establish water budgets that reflect the needs of SWC members using sophisticated analytical techniques, but the parties' analyses are too far apart to reconcile. Recommended Order at 49 • (…conclusions in SWC's expert testimony are closer to being acceptable…) Recommended Order at 50

  4. Delivery Losses Water Budget Schematic Canal Head Diversion Canal seepage ET Deep Percolation Ignore for now other components: precipitation and soil moisture Return flows

  5. Water budget summary as percent of average diversion for Twin Falls Canal:

  6. Water Budget Schematic Known Values Canal Head Diversion Canal seepage ET Deep Percolation Return flows

  7. Water budget approach using satellite imagery based ET can be used to establishes apparent project efficiencies: Apparent project efficiency = 41% Apparent project efficiency can be used in adjustment process of average annual irrigation need

  8. Development of an average annual irrigation need: • “Predictions of need should be based on an average year of need, subject to adjustment up or down depending upon the particular water conditions for the irrigation season”Recommended Order at 49 • Adjustment can be made using the measured in-season ET from satellite imagery and project efficiency • Propose using 2006 irrigation diversions as the average annual irrigation need, or baseline demand: • Adjust for above normal winter/spring rains in 2006 • Normal Heise gage runoff and adequate storage supply • ET values generated with Landsat data available

  9. Correct 2006 diversion for soil moisture excess using ETIdaho data (in progress)

  10. Heise gage runoff volume

  11. Regional weather data

  12. Twin Falls growing season precipitation

  13. Twin Falls Canal Company annual diversions 97% of average

  14. Summary of Baseline Demands for Surface Water Coalition members based on 2006 irrigation diversion with upward correction for average soil moisture NOTE: PRELIMINARY, UNCHECKED DATA

  15. Summary of Baseline Demands for Surface Water Coalition members, comparison to historic average diversions (cont.) NOTE: PRELIMINARY, UNCHECKED DATA

  16. Hearing Officer Recommendation: • The concept of a baseline is that it is adjustable as weather conditions or practices change, and that those adjustments will occur in an orderly, understood protocolRecommended Order at 51 IDWR Proposed Protocol: • Each SWC canal begins season with reasonable in-season demand equal to adjusted 2006 diversions, and called baseline demand (BD).

  17. IDWR Proposed Protocol • Determine crop water needs (CWN) during season using Landsat generated ET: • CWN = (ET – PEFF) * Area where PEFF = effective precipitation Area = canal company total irrigated area • Calculate revised reasonable in-season demand (RISD) as season progresses: • RISD = CWN÷ Ep where Ep = project efficiency

  18. SUMMARY • Replace minimum full supply with the reasonable in-season demand, with baseline equal to 2006 SWC diversions, adjusted upward for beginning season soil moisture • In-season adjustments made relative to 2006 crop water needs using Landsat generated ET and effective precipitation • Baseline year for reasonable in-season demand will be amended in the future to reflect current average conditions

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