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Swan Falls Average Daily Flow Measurement Report

Progress report presented by Sean Vincent on March 12, 2012, for the Snake River Measurement Technical Committee. Goals include determining average daily flow, addressing measurement issues, and assisting in management responses.

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Swan Falls Average Daily Flow Measurement Report

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  1. Progress Report Snake River Measurement Technical Committee Presented by Sean Vincent March 12, 2012

  2. Representation • State of Idaho • Idaho Power Company • USGS • Consultants • City of Pocatello • IGWA

  3. Goals • Facilitate determination of “average daily flow” as defined in paragraph 7 of the 1984 Agreement • Based on “actual flow conditions” (¶ 7B)  must factor out reservoir operations since IPCO reservoirs not strictly run-of-river • Also factor out IPCO leased/acquired/owned releases (¶ 7E) • Currently unable to determine “actual flow conditions” (Dreher) • Transparency • Advise/inform policymakers re: technical issues (measurement uncertainty, significance of fluctuations, etc.) • Assist with development of management responses/triggers

  4. Subject to I.R.E. 408Swan Falls Agreement Paragraph 7B

  5. Capacity (acre-feet) Reservoir

  6. Actual Flow Conditions • Write equation Flowactual = FlowMurphy – IPCOowned/leased + ΔS/Δtreservoir1 + ΔS/Δtreservoir2 + … where, ΔS/Δtreservoir_x = Inflowreservoir_x – Outflowreservoir_x orΔS/Δtreservoir_xαΔstage = (volumestage2 – volumestage1)/(t2-t1) • For each reservoir, measure stage and/or identify and quantify inflow and outflow terms • Inflows • Snake River, tributaries, agricultural return flows, precipitation, river and reservoir gains • Outflows • canals, diversions, reservoir evaporation, river and reservoir losses • Perform accounting (lag, shape, and sum)

  7. Measurement Issues • Aquatic growth • Backwater effects • Location of river/reservoir interface not well defined • Wide range of flows (max at Murphy = 47,300 cfs) • Wind effects on reservoir stage

  8. Work to Date • Pre-committee work • Dreher report • Workshops on flow measurement 5/14/2009 and 6/11/2009 • Reconnaissance field work (IPCO, USGS, IDWR) • Identify diversions, identify and evaluate suitability of potential gaging locations • Project outline (IPCO) • Committee meetings on 1/24/12 and 2/28/12 • Review previous work • Compile data  IDWR web site (http://www.idwr.idaho.gov/News/Issues/SwanFalls/swan_falls_agreement.htm) • Develop questions for policy group

  9. Work Remaining • Finalize project scope of work • Execute the work • Evaluate methods for quantifying impacts of reservoir operations • Conduct seepage survey(s) (near minimum flows) • Quantify reservoir inflow and outflow terms • Establish gages and, if necessary, modify existing gages • Evaluate measurement uncertainty • Develop accounting and forecasting tools as required

  10. Concerns • Schedule • Water District 02 diversion measurements ~ 2 years out • Lead time for locating and installing gages • Seepage survey likely will be delayed another year • Public perception • Avoid potential appearance of bias • Accuracy of Snake River gages • Snake River near Murphy (13172500) rated “Good” by USGS in 2001  95% of daily values within 10% of the true

  11. Snake River Bonefish

  12. Questions?

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