EXH0581023792

Notes on HSPF Modeling of Miller, Walker and Des Moines Creeks: Linkages between HSPF and Hydrus/Slice The land surface surrounding the new runways and taxiways at Seatac is_modeled as outwash grass, a type of pervious land segment (PERLAND). The active runoff flowpaths for outwash grass are surface rtmoffand groundwater, interflow is not modeled. Surface runoff is small and has previously been neglected. The only significant active flowpath is groundwater. The impervious surfaces of the new runways and taxiways_ modeled as an HSPF impervious land segment (IMP/.,AND). Surface runoff from _therunways and taxiways flows into swalcs where infiltration into the fill will occur. T_.isinfiltration can be added to the percolation below the root zone (AGWI) found by modeling the land surrounding the new runways and taxiways as out'wash grass with a DEE_FR parameter of zero. Any surface runoff from the pervious land should be accounted f_r and sent to the proper flowpath. ercolationfromtheperviouslandbelowthe1"oozoneand_ffltrationof surfacerunoff from the impervious land are input to Hydrus. This inflow tq Hydras accounts for actual evaptranspiration fi'om the pervious land and actual evaporation from impervious surfaces. The Hydrus inflows move vertically and are attenu?ted and delayed by amounts approximately proportional to the depth of the flU before it rFaches a cell in the Slice model. l The Slice model handles lateral flow toward the toe of the n_v fill in the drain layer and in the soils that overlie the Vashon till, and calculates flux through the Vashon till into underlying Vashon advance soils. The Slice model…

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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 [...]