EXH2003029170

Thismeetingwas scheduledas a follow up meetingto the Low Flow meetingof April25. The purposeof themeetingwas to: 1) describe the proposed process forward to address Ecology's concern regarding extrapolationof onemodelingsectionacrossthe lengthof theembankmentto determine embankmentseepage; 2) confirmthat the revisedHSPF modelingapproachas determinedat the 4/25 meeting is consistentwithrevisionsproposedabove; 3) determineprocessand scheduleexpectations. EMBANKMENT SEEPAGE CALCULATIONS Ecologyhas expressedconcernregardingthe representativenessof the techniqueused in the low flow documentin which one modelingsectionwas extrapolatedacross the length of the embankmentto determineembankmentseepage. To addressthis concem, embankmentseepage calculationswillbe revisedas follows: • The embankmentwillbe segmentedinto25-foot square cells,and an average depth calculatedfor each cell. The Hydrusmodel will be run on each of these 25-foot squarecellsof fillat theiraccuratedepths. ECYO0007390 C: _Temp_LowF'lowTech Mtg050901 FINAL. doccbo5/_8/ol FINAL DRAFT Page 1 of 4 AR 029170 401 Permit Decision-Making, Sea-Tac Airport Third Runway Floyd & SnJdcrI,,_ May 9, 2001 • The Hydrusresultsin aggregatewillprovidea more accuratecalculationof inputto the drainlayerat the base of the embankment. Ecologyconcursthat thisapproach addresses D. Garland's concern re: representativeness of the embankment seepage modelingapproach. Utilizationof this revised approachas described in thesemeetingminuteswilleliminatethe need to performa comparativeanalysis of revisedresultscomparedto the resultsof the previouscoarsermodelingapproach. REVISED HSPF MODELLING APPROACH, RELATIONSHIP TO EMBANKMENT SEEPAGE CALCULATIONS Three componentswillbe aggregatedto evaluatepotentialprojectimpactsto low streamflow: 1) EmbankmentseepagecalculationsusingHydrus-Slicemodelingtechnique 2) HSPF basin modeling, adjusted to coordinate with embankment seepage calculations 3) Considerationof non-hydrologicaffects. The followingapproachwasdeterminedatthismeeting: 1. Embankmentseepagemodelingwillbe re-run- • Three modelingsegmentswillbe used: one representativeof the embankmentfill in theWalkerbasin,one representativeof the northernportionof fill in the Miller basin; and one representativeof the southern,deeper portionof embankmentfill in the Millerbasin. • The Hydrus work in these modelingsegments will utilize the 25-foot square cell approach…

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PSCAA Advisory Council Meeting Agenda
Add to CalendarMWednesday Mar 11, 9:00am - 11:35am
1904 3rd Avenue, Suite 105, Seattle, WA 98101
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 [...]