EXH1221049788

5808 Lake Washington Blvd. NE, Suite 200 Kirkland, Washington 98033-7350 December 2000 556-2912-001(48) AR 049789 TABLE OF CONTENTS Page 1. HYDROLOGIC IMPACTS AND MITIGATION .................................................................. 1 1.1 INTRODUCTION ........................................................................................................ 1 1.2 MODIFIC .ATIONS AND REFINEMENTS TO PROPOSED ACTION ................... 2 1.3 HYDROLOGIC IMPACTS AND MITIGATION ...................................................... 3 1.3.1 Flow Impacts .................................................................................................... 3 2. PATHWAYS AND INDICATORS ....................................................................................... 19 3. REFERENCES ........................................................................................................................ 22 LIST OF FIGURES Figure Miller, Walker, and Des Moines Creek Watersheds ................................................................ 5 Proposed Stormwater Detention Facilities for Master Plan Projects ....................................... 9 Flow Duration Curve for Miller Creek at SR509 ................................................................... 13 Flow Duration Curve for Walker Creek at South 12thStreet ................................................. 14 Flow Duration Curve for Des Moines Creek at South 200 thStreet ........................................ 15 LIST OF TABLES Table Summary of Miller, Walker, and Des Moines Creek drainage areas at STIA and change in impervious area between 1994 baseline and 2006 future conditions (acres) .......... 6 Summary of required detention facility volumes ................................................................... 10 Summary of flood peak flow frequency results for Miller/Walker Creek subbasins (all values are cubic feet per second) ............................................................................................ 16 Summary of flood peak flow frequency results for Des Moines Creek subbasins (all values are cubic feet per second) ............................................................................................ 17 Estimated Low Stream Flow Changes .................................................................................... 18 Effects of Master Plan Update improvements for STIA on relevant indicators in Miller Creek ............................................................................................................................ 19 Effects of Master Plan Update improvements for STIA on relevant indicators in Des Moines Creek ................................................................................................................... 19 Environmental baseline conditions in Des Moines Creek, near STIA ................................... 20…

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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 [...]