EXH0697026132

RE: Low Streamflow Analysis and Summer Low Flow Impact Offset Facility Proposal, Water Quality Certification # 1996-4-02325 (Amended, 1) Dear Ms. Kenny: The Port of Seattle is working to finalize the Low Streamflow Analysis and Summer Low Flow Impact Offset Facility Proposal required by the referenced Water Quality Certification for the Seattle-Tacoma International Airport Master Plan Update. In order to meet the 45-day schedule set forth in Section I. 1 of the certification, the report needs to be submitted to Ecology on or before November 5, 2001. While revising the HSPF/Hydrus/Slice models to implement the changes required in section I. 1.c.i of the certification, an error was discovered in how the data is transferred between the Slice and HSPF models. Specifically, the HSPF model has a default function that assumes the input is in daily units, and automatically converts the input to hourly units. When the output from the Slice modeling was transferred to HSPF, the modeler manually applied the conversion. Therefore, the conversion was applied twice, and the effect was that the modeled embankment flow was 1/24 of what it should have been. The results of this error are that the impacts to Miller and Walker Creeks were overestimated. The actual impacts to summer low flow will be less than previously thought, and the facilities proposed to offset the impacts can be reduced in size. It is important to note that the error is limited to data handling between the models. The basic modeling approach, the calibration, and the…

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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 [...]