EXH0051017658

• Proposedmitigationperiod: Aug 1 - Oct 31. This periodcapturesall 7-day lowflow eventsin theexistingrecordwithexceptionof threeoutliersinNov & Dec. • MitigationFlow - propose1991 as targetyear in post project conditions, I:e,".,ause 1991 flowsare closestsurrogateto the 2-year event withinpost projectconditior_s. Use of 1991 as targetyear resultsin a mitigationflow rate of 0.10 cfs. A mitiga:;:.n flowrate of 0.10 coversall stormswithinthe2-year return frequency. • Methodologyforderivingtargetflowrate: • Clear descriptionshouldbe providedcf methodologyused to determinetarget flowfor the 4-year modeledperiod - For both Miller& Walker watersheds,methodused to determinetarget flowwill be comparedwithalternatemethodthatwouldinitiatepost-projectconditicns:..'.r the4-year periodwithinfofrompre-projectrecord- provideas crosschec;_ • Comparisonof gaugedata & modelresultsrequestedto substantiatecalibration. AR 017658 c.,,,oc_-,,.,-,,,,.oc,,._.,,,.,,,,,.,._,. FiNAL n 07;I_G1 .".;ge 1 of 3 401 Permit Decision-Making, Sea-Tac Airport Third Runway Floyd & Smdet 1.¢. July 16, 2001 Reserve Storaqe Vaults • Vault sizes designed to provide g2-day release of 0 10 cfs • Proposing 14 ac-ft vault volume • Requires 62 days of fi!lingprior to Aug 1 based ¢n worst year in record • 5 vaults provided in Miller Basin for thisaggregate storage and flow rate • Drawings updating vault sizing will be provided in the low flow report - may not be updated in the final SMP • It was agreed that Port would propose a date in winter in the operations plan when the vaults would be closed for filling, so that filling will not occur in the spring just before release • Vault size is conservative enough that significant water will be remaining in vaults on Oct 31, which will continue to be released to the stream until empty or…

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Call to order – Roll Call – Quorum Established – Land Acknowledgement We would like to acknowledge that our Agency operates in four present-day counties, which are the traditional lands of the Coast Salish people, past and present. This acknowledgement does not take the place of authentic relationships with indigenous communities in our jurisdiction and [...]