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17-105489-Preliminary TIR-04-02-2020-V13Woodbridge Business Park Preliminary Technical Information Report March 31, 2020 Prepared for Federal Way Campus, LLC 11100 Santa Monica Blvd., Suite 850 Los Angeles, CA, 90025 (310) 261 - 4382 Submitted by ESM Consulting Engineers, LLC 33400 8th Avenue S, Suite 205 Federal Way, WA 98003 253.838.6113 tel 253.838.7104 fax www.esmcivil.com Table of Contents Section 1. Project Overview Section 2. Conditions and Requirements Summary Section 3. Off-Site Analysis Section 4. Flow Control & Water Quality Facility Analysis and Design Section 5. Conveyance System Analysis and Design Section 6. Special Reports and Studies Section 7. Other Permits Section 8. ESC Analysis and Design Section 9. Bond Quantities, Facility Summaries, & Declaration of Covenant Section 10. Operations and Maintenance Manual List of Figures 1.1 Vicinity Map 1.2 Existing Site Conditions 1.3 Proposed Site Conditions 1.4 Soils Map 3.1 Site Topography 3.2 Downstream Analysis Flow Path Appendix A Developed Basin Map B Hydrology Model Output \\esm8\engr\esm-jobs\1886\001\016-0016\document\rprt-001.docx 1. Project Overview The purpose of this report is to encapsulate the documents and analysis required by the Drainage Review in the 2016 King County Surface Water Design Manual (SWDM). Existing Site: The proposed Greenline Business Park project site is located in the NE and SE quarters of Section 16, Township 21 North, Range 04 East, W.M. in the City of Federal Way, WA. More specifically, the project site is located on the west side of Weyerhaeuser Way S between S 336th Street & S 323rd Street. The project will include 4 parcels on approximately 146 acres (162104-9030, 162104-9013, 162104-9056, and 152104-9178) zoned as CP-1 and will be developed in accordance with the applicable City of Federal Way code. Additionally, the property is subject to the Concomitant Pre-Annexation Zoning Agreement dated August 23, 1994. See Figure 1.1 for a vicinity map and Figure 1.2 for a visual representation of the existing site conditions. Existing Site Hydrology: The existing site is partially developed with a commercial building and associated parking lots, outbuildings, paved driveways, and landscaped areas. The remainder of the site is predominantly forest with some pasture. The property slopes gently to the south and east at 0 - 8%. Stormwater runoff generally drains south to S 336th Street and into the existing stormwater drainage system. A portion of the site drains to the Weyerhaeuser Way S and is estimated to outfall to North Lake. The site is located in the Hylebos Creek drainage basin (WRIA number: 10). See Section 3 for more information. Proposed Site Improvements: The proposed development includes the demolition of existing parking lots, clearing, grading, and the construction of 3 new commercial buildings with parking lots, access roads, utility services, and stormwater facilities on approximately 75.16 acres as well as the associated frontage improvements along Weyerhaeuser Way S. Figure 1.3 illustrates the Proposed Site Conditions and Section 4 describes in more detail the proposed developed areas. Proposed Site Hydrology: The proposed onsite stormwater conveyance system will collect and convey runoff from the developed project site to the stormwater drainage system in the Right-of-Way (ROW) of S 336th Street and Weyerhaeuser Way S. The developed project site will drain to the south and east boundaries of the site, discharging to the Weyerhaeuser Pond and North Lake respectively, which are the natural discharge locations for the site. See Sections 4 and 5 of this report for more information. Stormwater Runoff Mitigation Standard: As detailed in the pre-application meeting notes, the proposed development will comply with Level 2 Flow Control, Basic and Enhanced Water Quality Treatment per the SWDM. See Section 4 for more information. Soils on the Project Site: The Soils Map and Geotechnical Engineering Report indicate the soils onsite include Alderwood gravely sandy loam, 0 - 8% slopes. See Figure 1.4 and the Geotechnical Engineering Report included under separate cover for more information. Flow Control BMP’s: All applicable Flow Control BMP’s are listed and explained in Section 4 of this report. µ ΗΜΣ∆ Θ Ρ Σ ≅ Σ ∆ 4 ς∆ Ξ ∆ Θ Γ ≅ ∆ Τ Ρ ∆ Θ ς ≅ Ξ Ρ ς∆Ξ∆ΘΓ≅∆ΤΡ∆Θ ς ≅ Ξ Ρ Ρ 2 2 5 Σ Γ Ρ Σ Θ ∆ ∆ Σ DRAWING:JOB NO.DATE:DRAWN:SHEET OF(425) 297-9900(253) 838-6113www.esmcivil.comLand PlanningLandscape ArchitectureLand SurveyingProject ManagementPublic WorksCivil EngineeringΚ Κ ΒΕδχδθκ ςξ+ ς≅ 87//2223// 7σγ ≅υδ Ρ+ Ρτησδ 1/4Β Ν Μ Ρ Τ Κ Σ Η Μ Φ ∆ Μ Φ Η Μ ∆ ∆ Θ ΡFEDERAL WAYEVERETT\\\\esm8\\engr\\ESM-JOBS\\1886\\001\\016-0010\\exhibits\\EN-03.dwg1/3/2020 4:29 PMPlotted:File:Plotted By: Tony AblemanΕ∆Χ∆Θ≅Κ ς≅Ξ Β≅ΛΟΤΡ+ ΚΚΒςΝΝΧΑΘΗΧΦ∆ ΑΤΡΗΜ∆ΡΡ Ο≅ΘϑEXISTING CONDITIONS1886-001-016-0010EN-03JJH10/07/20161 1 ΡΒ≅Κ∆9 0! < 0 2//& 150 300 \pxqc;EXISTING BUILDING ΕΗΦΤΘ∆ 0−1 S 336TH STWEYERHAEUSER WAY S.nSCALE: 1" = 100'C O N S U L T I N G E N G I N E E R SL L C Federal Way, WA 98003 33400 8th Ave S, Suite 205FEDERAL WAY CAMPUS, LLC WOODBRIDGE BUSINESS PARKFIG 1.311INTERSTATE 5POND 2 DETENTIONPOND 1DETENTIONPOND 3DETENTIONPOND 4DETENTIONPOND 5DETENTIONLEGEND BUILDING "1"±606,000 SFFF=VARIES442.37-448.87BUILDING "2"±240,900 SFFF=VARIES420.00-424.75FUTUREBUILDING "3"±125,700 SFFF=VARIES422.00-424.5EXISTINGWTCBUILDINGFF=437.00 Soil Map—King County Area, Washington (95 Acre Short Plat) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/6/2016 Page 1 of 352391005239200523930052394005239500523960052397005239800523990052400005239100523920052393005239400523950052396005239700523980052399005240000552600552700552800552900553000553100553200553300553400553500553600553700553800553900554000 552600 552700 552800 552900 553000 553100 553200 553300 553400 553500 553600 553700 553800 553900 554000 47° 18' 41'' N 122° 18' 18'' W47° 18' 41'' N122° 17' 7'' W47° 18' 10'' N 122° 18' 18'' W47° 18' 10'' N 122° 17' 7'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 300 600 1200 1800 Feet 0 100 200 400 600 Meters Map Scale: 1:6,840 if printed on A landscape (11" x 8.5") sheet. Warning: Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 11, Sep 14, 2015 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 8, 2014—Jul 15, 2014 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—King County Area, Washington (95 Acre Short Plat) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/6/2016 Page 2 of 3 Map Unit Legend King County Area, Washington (WA633) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AgB Alderwood gravelly sandy loam, 0 to 8 percent slopes 104.7 99.6% AgC Alderwood gravelly sandy loam, 8 to 15 percent slopes 0.4 0.4% Totals for Area of Interest 105.1 100.0% Soil Map—King County Area, Washington 95 Acre Short Plat Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/6/2016 Page 3 of 3 2. Conditions and Requirements Summary Review of the 9 Core Requirements and 5 Special Requirements This section describes how the project will meet the SWDM Core and Special Requirements. Core Requirement No. 1 Discharge at the Natural Location Stormwater runoff generated from the developed project site is estimated to drain south and east to the S 336th Street and Weyerhaeuser Way S, respectively. Thence runoff is conveyed to North Lake and to Stream AC, which continues south to the Weyerhaeuser Pond. Both are the natural discharge locations for the site. Core Requirement No. 2 Off-site Analysis The off-site and downstream analyses are documented in Section 3 of this report. Core Requirement No. 3 Flow Control Level 2 Flow Control is required per the pre-application meeting notes for this project, which will be met by proposed detention ponds and storage in the existing Weyerhaeuser Pond. See Section 4 of this report for more information. Core Requirement No. 4 Conveyance System Stormwater conveyance will be provided for the proposed and existing conveyance systems per Section 5 of the SWDM. Calculations will be provided in the final TIR. Core Requirement No. 5 Erosion and Sediment Control Erosion and sediment controls to prevent the transport of sediment from the project site to downstream drainage facilities, water resources, and adjacent properties will be provided on the construction plans. Core Requirement No. 6 Maintenance and Operations The Operations and Maintenance manual will be included with the final TIR. Core Requirement No. 7 Financial Guarantees and Liability All drainage facilities constructed or modified for projects will comply with the financial guarantee requirements as provided in the King County Bond Quantities Worksheet. Bond Quantities will be provided in the final TIR. Core Requirement No. 8 Water Quality Basic and Enhanced Water Quality Treatment is required per the pre-application meeting notes and will be provided as described in Section 4. Core Requirement No. 9 Flow Control BMP’s All applicable Flow Control BMP’s are listed and discussed in Section 4 of this report. Special Requirement No. 1 Other Adopted Area-Specific Requirements There are no master drainage plans, basin plans, salmon conservation plans, stormwater compliance plans, flood hazard reduction plan updates, or shared facility drainage plans for this project. Special Requirement No. 1 does not apply. Special Requirement No. 2 Flood Hazard Area Delineation The developed project site location is not in a 100-year floodplain. Special Requirement No. 2 does not apply. Special Requirement No. 3 Flood Protection Facilities The developed project site is not protected by an existing flood protection facility. The proposed site improvements do not include the modification of an existing flood protection facility. Special Requirement No. 3 does not apply. Special Requirement No. 4 Source Control The project will follow the King County Stormwater Pollution Prevention Manual and King County Code 9.12 to identify and implement source controls as needed. Due to the proposed use of the project site, source control is not required; therefore, Special Requirement No. 4 does not apply. Special Requirement No. 5 Oil Control The proposed development is commercial and (according to the definition provided in the SWDM), portions of the project site qualify as a “high-use site” due to vehicle fleet size; therefore, Special Requirement No. 5 does apply. Implementation details regarding oil control will be provided in the final TIR. 3. Off-Site Analysis A Level 1 downstream analysis has been performed for the site. Task 1: Study Area Definition and Maps The study area consists of the project site and 1/4 mile downstream flow path for runoff released from the existing site. See Figure 1.2 and Figure 3.2 for the Existing Site Conditions and Downstream Analysis Flow Path exhibits. Task 2: Resource Review Flow Control Map According to the pre-application meeting notes, the project is required to comply with Level 2 Flow Control criteria. Soil Survey Map Web Soil Survey maps the soils onsite include Alderwood gravely sandy loam, 0 - 8% slopes. Refer to the Geotechnical Engineering Report attached under separate cover for more detail. King County iMap According to iMap, the project site is NOT mapped in any of the following areas: - Landslide Hazard area - Coal Mine Hazard Areas - Erosion Hazard area - 100 Year Floodplains - Critical Aquifer Recharge Area - Seismic Hazard area King County iMap and the Pre-Application Conference Notes The project site has the following areas mapped onsite and nearby: - Streams & Wetlands See Figure 3.1 for more information regarding the environmental hazards near the project site. Road Drainage Problems None noted Wetlands Inventory According to iMap, the Critical Areas Review, and the 1990 King County Wetlands Inventory Notebooks there are no recorded wetlands on the existing project site. However, the wetland biologist has located onsite wetland areas and there are wetland areas downstream of the developed project site. See Figure 1.2 for Existing Site Conditions and the wetland report for more information. Migrating River Study None noted Downstream Drainage Complaints According to iMap, there are no relevant downstream drainage complaints within the scope of this project. Task 3: Field Inspection (Level 1 Inspection) A Level 1 Downstream Analysis was completed by ESM Consulting Engineers, LLC in the early afternoon on October 5, 2016, when it was sunny and 65°F. During the inspection it was found that the project site has no apparent upstream offsite areas draining to the property. Stormwater runoff from the existing site’s lawn, vegetated areas, roof, roads, access ways, and parking lot is estimated to flow across the property to the south and east boundaries of the site and drain to the public ROW. From there, stormwater runoff south of the site’s existing south entrance is collected in the gutter along the west side of Weyerhaeuser Way S and continues south to S 336th Street. The runoff is conveyed in a piped system or via roadside ditch in the area near the roundabout. Once past the roundabout, the runoff crosses under S 336th Street in two 12 inch diameter concrete culverts and continues to the Weyerhaeuser Pond via established drainage paths. Stormwater runoff north of the site’s existing south entrance is estimated to be collected in a road side ditch and conveyed east under Weyerhaeuser Way S to North Lake via two culvert pipes. There did not appear to be any flooding issues over any of the roadways adjacent to, and downstream of, the project site. See Figure 3.2 Downstream Analysis Flowpath for further information and the approximate existing basin area draining to North Lake. The site was revisited around noon on January 18, 2017, when it was heavily raining. Following the flow of stormwater south of S 336th Street, stormwater was routed in a drainage ditch with no apparent restrictions on its way to the Weyerhaeuser Pond. The flow increased significantly once it was joined with the outflow from North Lake. At that point it appeared that the capacity of the drainage ditch was increased sufficiently to convey the stormwater runoff. Task 4: Drainage Description and Problem Descriptions According to iMap, the project site is in the Hylebos Creek (King County WRIA number: 10) drainage basin. Hylebos Creek is located approximately 0.3 miles to the west of the project and separated by I-5. No drainage problems are known to exist in the site’s present condition. There is an existing Sphagnum Bog located adjacent to the northwest corner of the project site (parcel 215465-0170). However, it is not part of the existing or developed drainage basin, and no associated drainage problems are known. Task 5: Mitigation of Existing or Potential Problems No existing or potential problems were observed with the existing drainage system within the scope of the downstream analysis. Therefore, no further mitigation is proposed. - Date: 10/7/2016 Notes: The information included on this map h as been compiled by King County sta ff from a varie ty of sources and is subject tochange without notice. King County makes no representations or warrantie s, express or implied, as to accuracy,completeness, timeliness, or rights to the use of such information. This document is not inten ded for use as a surveyproduct. King County shall not be liab le for any general, special, indirect, incidental, or consequential damages including,but not limited to, lost revenues or lost p rofits resulting from the use or misuse of the information contained on this map.Any sale of this map or information on th is map is prohibited except by written permission of King County. Le gend Parcels Bonde d Commercial -MF Commercial -SF Construction DOT FM D Region al Residential Drain age comp lai nts Potential land slidehazard a rea s (2016,see explan ation--->) Potential stee p slop ehazard a rea s (2016,see explan ation--->) Erosion haza rd (199 0SAO) Sei smic h azard (1 990SAO) Coal mi ne h azar d(19 90 SAO) cl ass 1 cl ass 2 perennia l cl ass 2 salmo nid cl ass 3 uncla ssified Wetland (1990 S AO ) Sensitive area noticeon title - Date: 10/5/2016 Notes: The information included on this map has been compiled by King County staff from a variety of sources and is subject tochange without notice. King County makes no representations or warranties, express or implied, as to accuracy,completeness, timeliness, or rights to the use of such information. This document is not intended for use as a surveyproduct. King County shall not be liable for any general, special, indirect, incidental, or consequential damages including,but not limited to, lost revenues or lost profits resulting from the use or misuse of the information contained on this map.Any sale of this map or information on this map is prohibited except by written permission of King County. Legend Parcels Streams Point 1: Looking south, east (across the road), and at the culvert inlet. Stormwater collected in the roadside ditch is conveyed to this culvert on the west side of Weyerhaeuser Way SW where it crosses the road and continues east to North Lake. Culvert Point 2: Looking south on the west side of Weyerhaeuser Way SW Water from the site that flows to Weyerhaeuser Way SW is routed to this culvert via roadside ditch and continues east. Looking north on the east side of Weyerhaeuser Way SW Point 3: Looking north on the west side of Weyerhaeuser Way SW. Stormwater runoff south of the south entrance to the existing site is collected by this roadside ditch. Point 3: Looking south on the west side of Weyerhaeuser Way SW. From the ditch, stormwater enters the existing stormwater conveyance system in this culvert. Point 3: Looking south toward the roundabout. Stormwater runoff not collect further north is collected by this ditch along the south boundary of the site and drains to Point 4. Point 4: Looking south at the inlet of the pipes crossing S 336th Street. Point 5: Looking west on the south side of S 336th Street where the stormwater runoff from the project site crosses and drains to Weyerhaeuser Pond. 4. Flow Control & Water Quality Facility Analysis and Design Existing Site Hydrology: The existing site is partially developed with a commercial building and associated parking lots, outbuildings, paved driveways, and landscaped areas. The remainder of the site is predominantly forest with some pasture. The property slopes gently to the south and east at 0 - 8%. Stormwater runoff generally drains south to the S 336th Street public ROW and into the existing stormwater drainage system. A small portion of the site drains east to the Weyerhaeuser Way S and is estimated to outfall to North Lake. The site is located in the Hylebos Creek drainage basin (WRIA number: 10). See Section 3 for more information. Due to the topography of the project site, the existing 5 onsite basins shown in Figure 1.3 drain to the south and east borders, which are the Points of Compliance. From there, stormwater runoff is conveyed to North Lake (Basin 1) and Weyerhaeuser Pond (Basins 2- 5). As required by the SWDM, the existing basins have been modeled as pre-developed forested, and the areas are described in Table 4.0 below (totaling 75.16 acres). Table 4.0 Land Use ( Acres ) Basin 1 Basin 2 (incl. Bypass) Basin 3 Basin 4 Basin 5 (incl. Bypass) C, Forest 13.14 41.19 4.53 5.72 10.58 Developed Site Hydrology: The developed Basins 1-5 (totaling 75.16 acres) are generally described below, shown in Table 4.1, and illustrated on the Developed Basin Map in Appendix A. Basin 1 The proposed drainage Basin 1 consists of 13.14 acres of developed area. This area discharges in the same direction as the existing 24-acre drainage basin that drains to the wetlands and associated buffers on the east side of Weyerhaeuser Way S and continues to North Lake, which is the natural discharge location for the basin. The developed area includes the eastern portion of the proposed Building 1, associated standard parking and landscaped areas, and the proposed Pond 1 area. Basin 2 The proposed drainage Basin 2 consists of 40.83 acres of developed area. This area discharges to the wetlands and associated buffers on the east side of Interstate 5 and continues to Stream AC, which continues south to the Weyerhaeuser Pond, which is the natural discharge location for the basin. The developed area includes the western portion of the proposed Building 1, associated truck and standard parking lot areas, relocated Tech Center parking lot areas, landscaped parking lot areas, and the proposed Pond 2 area. A small 0.36-acre portion of Basin 2 drains directly to Weyerhaeuser Way S and will bypass Pond 2, which has been modeled as bypass in WWHM. Basin 3 The proposed drainage Basin 3 consists of 4.53 acres of developed area. This area discharges to Stream AC, which continues south to the Weyerhaeuser Pond, which is the natural discharge location for the basin. The developed area includes Building 3 clean roof runoff as well as the proposed Pond 3 area. Basin 4 The proposed drainage Basin 4 consists of 5.72 acres of developed area. This area discharges to Stream AC, which continues south to the Weyerhaeuser Pond, which is the natural discharge location for the basin. The developed area includes truck and standard parking lot areas associated with Building 3, landscaped parking lot areas and the proposed Pond 4 area. Basin 5 The proposed drainage Basin 5 consists of 9.96 acres of developed area. This area discharges to Stream AC, which continues south to the Weyerhaeuser Pond, which is the natural discharge location for the basin. The developed area includes Building 2, associated truck and standard parking lot areas, landscaped parking lot areas, and the proposed Pond 5 area. A small 0.62-acre portion of Basin 5 drains directly to Weyerhaeuser Way S and will bypass Pond 5, which has been modeled as bypass in WWHM. Table 4.1 Land Use (Acres) Basin 1 Basin 2 Basin 3 Basin 4 Basin 5 Total Dev Dev By pass Dev Dev Dev By pass Lawn 2.75 7.15 0.00 1.50 1.33 1.53 0.20 14.46 Road 5.50 19.16 0.36 0.14 4.39 2.90 0.42 32.87 Roof 4.89 14.52 0.00 2.89 0.00 5.53 0.00 27.83 Basin Total 13.14 40.83 0.36 4.53 5.72 9.96 0.62 75.16 The frontage improvements along the majority of both sides of Weyerhaeuser Way S consist of approximately 5.5 acres of ROW dedication, 2.4 acres of asphalt pavement, 1.7 acres of sidewalk, and 1.4 acres of landscaping. The northern portion of the existing roadway and associated frontage improvements discharges in the same direction as the existing 24-acre drainage basin that drains to the wetlands and associated buffers on the east side of Weyerhaeuser Way S and continues to North Lake. The remaining portion of the existing roadway and associated frontage improvements flows southeast to the Weyerhaeuser Pond, which is the natural discharge location for the basin. Per Section 1.1.2.5 of the SWDM, the project is not an Urban Planned Development (UPD). Additionally, the project proposes 32.87 acres of road area, 27.83 acres of roof area, and 4.1 acres of impervious frontage area (2.4 ac asphalt pavement + 1.7 ac sidewalk), which totals 64.8 acres of impervious area. Subtracting 10.84 acres of replaced impervious area and 7.75 acres of existing impervious area to remain equals 46.21 acres of new impervious area, which is less than 50 acres and is not in a critical aquifer recharge area. Therefore, large project drainage review is not required. Performance Standards: Stormwater systems onsite are to be designed to mitigate runoff generated from the project per the requirements of the SWDM, specifically the Level 2 Flow Control standards per the Pre-application meeting notes for this project. The existing building and areas to remain will be retrofitted to meet the Level 2 Flow Control standard. The facility size is required to be determined by an approved hydrology model per the SWDM. Flow Control System: The approved hydrology model used to size the detention portion of Ponds 1-5 was the Western Washington Hydrology Model (WWHM) version 2012. The default sizing from that software complies with the Level 2 Flow Control standards. As modeled in WWHM, Basins 2 and 5 mitigated developed flows include flows bypassing the stormwater facilities. The pre-developed and developed project site mitigated flow rates are given in Table 4.2 and comply with the Level 2 Flow Control standards. The estimated volumes required and provided are given in Table 4.3. The WWHM output is provided in Appendix B. Table 4.2 Peak Flows (cfs) Basin 1 Basin 2 Basin 3 Basin 4 Basin 5 Return Period Pre Dev Mit Pre Dev Mit Pre Dev Mit Pre Dev Mit Pre Dev Mit 2 Year 0.386 0.243 1.211 0.800 0.133 0.083 0.168 0.097 0.331 0.839 5 Year 0.607 0.374 1.902 1.214 0.209 0.127 0.264 0.148 0.489 1.579 10 Year 0.732 0.476 2.294 1.545 0.252 0.161 0.318 0.188 0.589 2.291 25 Year 0.864 0.626 2.708 2.034 0.298 0.210 0.376 0.246 0.696 3.520 50 Year 0.946 0.754 2.965 2.454 0.326 0.251 0.412 0.295 0.762 4.731 100 Year 1.016 0.895 3.183 2.925 0.350 0.297 0.442 0.349 0.818 6.250 Table 4.3 Stormwater Detention Volume (acre-feet) Pond 1 Pond 2 Pond 3 Pond 4 Pond 5 Required 5.12 16.36 1.54 2.32 4.88* Provided 5.78 19.33 1.77 2.65 1.45 Additional Safety Factor 13% 18% 15% 14% N/A *3.43 acre-feet to Weyerhaeuser Pond The Weyerhaeuser Pond’s headworks were modified and approved in July of 2004 to increase the live storage by 200,000 cubic feet (4.59 acre-feet). The pond’s weir was adjusted to obtain this additional live storage. This project preliminarily proposes to discharge 3.43 acre-feet of additional live storage from Pond 5 to the Weyerhaeuser Pond, to use the available additional live storage. Flow control for the proposed frontage improvements will be provided in relocated roadside swales, matching the drainage flow paths for the existing pavement, with additional detention capacity in the Weyerhaeuser Pond. Detailed flow control analysis will be completed with the final frontage improvement plans, which will also require relocating existing utility infrastructure, extending existing culverts, as well as new pavement channelization. Water Quality System: The approved hydrology model used to size the Ponds 1-5 was WWHM version 2012. A Modular Wetlands System (MWS) or approved equivalent precedes Basin 1’s detention. Due to the MWS’s internal bypass system, WWHM’s offline water quality flow rate was used to size the unit. An MWS is downstream of Basin 2, 4, and 5’s detention and was sized with the 2-year mitigated flow rate. Basin 3 only consists of non-pollution generating or “clean” roof runoff from Building 3 and therefore does not require water quality treatment. The MWS meets the Enhanced Water Quality Treatment standards in Section 1.2.8 of the SWDM. The eastern portion of Building 1 in Basin 1, the western portion of Building 1 in Basin 2, and Building 2 in Basin 5’s roof runoff are considered non-pollution generating or “clean”, thus does not require water quality treatment, and will be conveyed directly into their respective detention Ponds 1, 2, and 5. The roof material to be used on the proposed Buildings 1, 2, and 3 will be TOP and is considered to be non-leaching which complies with the requirements specified in Section 1.2.8 of the SWDM. Oil control is required for the parking lot areas, Further details for oil control will be provided in the final TIR. The required treatment rates are given in Table 4.4. The WWHM output is provided in Appendix B. Further details on the Modular Wetlands System will be provided in the final TIR. Table 4.4 Water Quality Flow Rate (cfs) Basin 1 Basin 2 Basin 3 Basin 4 Basin 5 Required 0.494* 0.800 N/A 0.097 0.839 *Basin 1’s MWS precedes detention and therefore is sized with WWHM’s offline WQ flow rate Water quality for the asphalt pavement portion of the proposed frontage improvements will be provided in relocated roadside swales, matching the drainage flow paths for the existing pavement. Detailed flow control analysis will be completed with the final frontage improvement plans, which will also require relocating existing utility infrastructure, extending existing culverts, as well as new pavement channelization. Flow Control BMPs Flow control BMPs have been preliminarily evaluated for the project site as outlined in the SWDM under Section 1.2.9.2.2 – Large Lot BMP Requirements. These BMP’s are described below in the required order, with feasibility determined and the portion of applicable area credited as mitigated, which should be no less than 10% of the total site area – 7.52 acres. Full Dispersion There are multiple native vegetated areas surrounding the project site that will be left undisturbed. The areas on the east side of the project site are not large enough to accommodate a minimum flowpath of 100 feet in length. The areas on the west side of the project site consist mostly of wetlands, streams and associated buffers and are not feasible for full dispersion. The areas on the north side of the project site are upstream, thus also not feasible for full dispersion. In summary, Full Dispersion is deemed to be infeasible for this project site. Full Infiltration The Geotechnical Engineering Report states that “…there is very limited infiltration potential at this site. Because of these factors we recommend that stormwater detention be used for site development.” Because of this recommendation, Full Infiltration (specified in Section C.2.2.2.1) minimum requirements cannot be met; hence, Full Infiltration is infeasible for this project site. Limited Infiltration Limited Infiltration (specified in Section C.2.3) has the same minimum design requirements as Full Infiltration. Since Full Infiltration has been deemed infeasible, Limited Infiltration is also infeasible for this project site. Bioretention Bioretention (specified in Section C2.6) may be feasible, using raingardens pending further geotechnical field investigation (to be completed with final design). Permeable Pavement, Permeable Pavement (specified in Section C2.7) may be feasible for the onsite and frontage non-pollution generating impervious concrete sidewalk, pending further geotechnical field investigation (to be completed with final design). Basic Dispersion As discussed above for Full Dispersion, the native vegetated areas deemed to be infeasible for Basic Dispersion. If the impervious area credited as mitigated is less than the threshold specified in Flow Control BMPs above, then (according to Section 1.2.9.2.2.5 of the SWDM) a fee in lieu must be paid OR one or more the following BMPs must be implemented to achieve compliance: Reduced Impervious Surface Credit This project is larger than 250,000 square feet (Section C.2.9.2), cannot use wheel strip driveways (Section C.2.9.3) due to the proposed parking layout, cannot implement a minimum disturbance foundation (Section C.2.9.4) due to the building type, and open grid decking over pervious surface (Section C.2.9.5) is not applicable. Therefore, minimum design requirement #1 (specified in Section C.2.9.1) cannot be met; hence, the Reduced Impervious Surface Credit cannot be claimed for the proposed site improvements. Native Growth Retention Credit The minimum design requirement that any area of target impervious surface credited as mitigated by this credit must be directed to vegetated pervious areas on the site or discharged through a perforated pipe connection in accordance with Section C.2.11. While it is not feasible to direct stormwater runoff to those surfaces due to the elevation difference of the applicable vegetated pervious areas, the perforated pipe connection will be provided to the roof downspouts for the three proposed buildings. Out of the total parcel area (146 acres), the undisturbed native vegetation area of 56.9 acres mitigates for 16.26 acres of impervious area, which is equivalent to 22% of the total project site area (75.16 acres) and 27% of the total impervious area (60.70 acres). The native vegetated area used for this credit requires specific covenants, per SWDM, and these requirements have been preliminarily compared with the Weyerhaeuser Company Concomitant Pre-Annexation Zoning Agreement (CZA). The requirements in the SWDM appear to not conflict with the CZA, therefore, native growth retention appears to be feasible for the project site and will be confirmed with final design. Soil Amendment Minimum Requirement #6 All new pervious surfaces will be amended per Section 1.2.9.2.2.6 of the SWDM to satisfy the requirements specified therein (notes will be added on the final landscape plans). Roof Downspout Minimum Requirement #7 All roof downspouts will be shown on the final construction plans to connect to the storm system via Perforated Pipe Connection (as specified in Section C.2.11 of the SWDM). In summary, the project site will implement the following flow control BMPs, if determined feasible during final design: Bioretention and Permeable Pavement for the project site and frontage improvements, pending further geotechnical field investigation. If the impervious area credited as mitigated is not sufficient, a fee in lieu will be paid, or the Native Growth Retention Credit will be implemented. Additionally, the project will amend soils and use perforated pipe connections for downspouts. 5. Conveyance System Analysis and Design Onsite Conveyance System: Runoff from the developed project site will be collected by the onsite conveyance system. The proposed stormwater drainage system is composed of catch basin structures with pipes. The proposed stormwater drainage system will be designed to convey the 25-year peak flow rate generated by the developed tributary basin as required by the SWDM. The system will contain the 100-year flow within the catch basins without any backwater issues. A conveyance and backwater analysis will be completed to verify the capacity of the critical pipes in the system with the final TIR. Outlet Conveyance System: The proposed detention Pond 1 will discharge pre-developed forested stormwater runoff to the existing wetland buffers and continues to North Lake for an estimated maximum 100 year flow of 0.818 cfs, which is less than the 100 year flow of 1.87 cfs for the estimated 24 acre forested basin that currently drains in the same direction. The proposed detention Ponds 2 – 4 will match pre-developed conditions and discharge pre- developed forested stormwater runoff to Stream AC, which continues south to the Weyerhaeuser Pond for a combined 100 year discharged flow rate of 3.571 cfs. Furthermore, the existing forested and pasture areas that flow to Stream AC amount to approximately 14 acres and an associated 100-year flow rate of 1.581 cfs. In addition, Pond 5 will discharge 3.43 acre-feet of additional live storage to Weyerhaeuser Pond, to use the available additional live storage, which results in a 100-year discharged flow rate of 6.250 cfs. The total stormwater runoff to this location is 11.402 cfs (3.571 + 1.581 + 6.250), which is less than the existing culverts preliminary calculated flow capacity of 12.84 cfs, using a Manning’s n of 0.013. Conveyance and backwater calculations will be provided with the final TIR. 6. Special Reports and Studies The Critical Areas Report and Conceptual Mitigation Plan by Talasaea Consultants, Inc, (dated September 20, 2017) are included under separate cover. The Geotechnical Engineering Report by GeoEngineers, (dated September 19, 2017) is included under separate cover. 7. Other Permits Building and NPDES permits will be required for this project, together with permits for utility connections. These will be applied for and provided at a later date. 8. ESC Analysis and Design The Erosion and Sedimentation Control calculations will be provided with the final TIR. 9. Bond Quantities, Facility Summaries, and Declaration of Covenant The Bond Quantities worksheet will be provided with the final TIR. The Facilities Summaries and Declaration of Covenant will be evaluated with final design to determine if applicable. 10. Operations and Maintenance The Operations and Maintenance manual will be provided with the final TIR. Appendix A Developed Basin Map S 336TH STWEYERHAEUSER WAY S.nSCALE: 1" = 100'C O N S U L T I N G E N G I N E E R SL L C Federal Way, WA 98003 33400 8th Ave S, Suite 205FEDERAL WAY CAMPUS, LLC WOODBRIDGE BUSINESS PARKFIG. 1.311INTERSTATE 5BUILDING "1"±606,000 SFFF=VARIES442.37-448.87BUILDING "2"±240,900 SFFF=VARIES420.00-424.75FUTUREBUILDING "3"±125,700 SFFF=VARIES422.00-424.5EXISTINGWTCBUILDINGFF=437.00 Appendix B Hydrology Model Output WWHM2012 PROJECT REPORT General Model Information Project Name: Basin 1 Site Name: Site Address: City: Report Date: Gage:Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 1.000 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 13.14 Pervious Total 13.14 Impervious Land Use acre Impervious Total 0 Basin Total 13.14 Element Flows To:Surface Interflow Groundwater Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 2.75 Pervious Total 2.75 Impervious Land Use acre ROADS FLAT 5.5 ROOF TOPS FLAT 4.89 Impervious Total 10.39 Basin Total 13.14 Element Flows To:Surface Interflow GroundwaterPond 1 Pond 1 Mitigated Routing Pond 1 Bottom Length:220.00 ft.Bottom Width:220.00 ft.Depth:6 ft.Volume at riser head: 5.1223 acre-feet.Side slope 1:4 To 1Side slope 2:4 To 1Side slope 3:4 To 1Side slope 4:4 To 1Discharge StructureRiser Height:4 ft.Riser Diameter:18 in.Orifice 1 Diameter: 2.125 in. Elevation:0 ft.Orifice 2 Diameter: 2 in. Elevation:2.3 ft.Orifice 3 Diameter: 2.875 in. Elevation:2.7 ft.Element Flows To:Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs)0.0000 1.111 0.000 0.000 0.0000.0667 1.116 0.074 0.031 0.0000.1333 1.121 0.148 0.044 0.0000.2000 1.127 0.223 0.054 0.0000.2667 1.132 0.299 0.063 0.0000.3333 1.138 0.374 0.070 0.0000.4000 1.143 0.450 0.077 0.0000.4667 1.149 0.527 0.083 0.0000.5333 1.154 0.604 0.089 0.0000.6000 1.160 0.681 0.094 0.0000.6667 1.165 0.758 0.100 0.0000.7333 1.171 0.836 0.104 0.0000.8000 1.176 0.915 0.109 0.0000.8667 1.182 0.993 0.114 0.0000.9333 1.187 1.072 0.118 0.0001.0000 1.193 1.152 0.122 0.0001.0667 1.199 1.231 0.126 0.0001.1333 1.204 1.311 0.130 0.0001.2000 1.210 1.392 0.134 0.0001.2667 1.215 1.473 0.137 0.0001.3333 1.221 1.554 0.141 0.0001.4000 1.227 1.636 0.145 0.0001.4667 1.232 1.718 0.148 0.0001.5333 1.238 1.800 0.151 0.0001.6000 1.244 1.883 0.155 0.0001.6667 1.249 1.966 0.158 0.0001.7333 1.255 2.049 0.161 0.0001.8000 1.261 2.133 0.164 0.0001.8667 1.267 2.218 0.167 0.0001.9333 1.272 2.302 0.170 0.0002.0000 1.278 2.387 0.173 0.0002.0667 1.284 2.473 0.176 0.0002.1333 1.290 2.559 0.179 0.000 2.2000 1.296 2.645 0.181 0.0002.2667 1.301 2.731 0.184 0.0002.3333 1.307 2.818 0.207 0.0002.4000 1.313 2.906 0.224 0.0002.4667 1.319 2.993 0.236 0.0002.5333 1.325 3.082 0.247 0.0002.6000 1.331 3.170 0.257 0.0002.6667 1.337 3.259 0.265 0.0002.7333 1.343 3.348 0.315 0.0002.8000 1.348 3.438 0.352 0.0002.8667 1.354 3.528 0.380 0.0002.9333 1.360 3.619 0.404 0.0003.0000 1.366 3.710 0.425 0.0003.0667 1.372 3.801 0.445 0.0003.1333 1.378 3.893 0.463 0.0003.2000 1.384 3.985 0.480 0.0003.2667 1.390 4.077 0.497 0.0003.3333 1.396 4.170 0.512 0.0003.4000 1.402 4.264 0.527 0.0003.4667 1.408 4.357 0.541 0.0003.5333 1.415 4.452 0.555 0.0003.6000 1.421 4.546 0.569 0.0003.6667 1.427 4.641 0.582 0.0003.7333 1.433 4.736 0.594 0.0003.8000 1.439 4.832 0.607 0.0003.8667 1.445 4.928 0.619 0.0003.9333 1.451 5.025 0.630 0.0004.0000 1.457 5.122 0.642 0.0004.0667 1.464 5.219 0.927 0.0004.1333 1.470 5.317 1.436 0.0004.2000 1.476 5.415 2.079 0.0004.2667 1.482 5.514 2.809 0.0004.3333 1.488 5.613 3.579 0.0004.4000 1.495 5.712 4.339 0.0004.4667 1.501 5.812 5.042 0.0004.5333 1.507 5.913 5.651 0.0004.6000 1.513 6.013 6.137 0.0004.6667 1.520 6.114 6.500 0.0004.7333 1.526 6.216 6.769 0.0004.8000 1.532 6.318 7.103 0.0004.8667 1.539 6.420 7.371 0.0004.9333 1.545 6.523 7.629 0.0005.0000 1.551 6.626 7.879 0.0005.0667 1.558 6.730 8.120 0.0005.1333 1.564 6.834 8.354 0.0005.2000 1.571 6.939 8.582 0.0005.2667 1.577 7.044 8.803 0.0005.3333 1.583 7.149 9.019 0.0005.4000 1.590 7.255 9.229 0.0005.4667 1.596 7.361 9.435 0.0005.5333 1.603 7.468 9.636 0.0005.6000 1.609 7.575 9.833 0.0005.6667 1.616 7.682 10.02 0.0005.7333 1.622 7.790 10.21 0.0005.8000 1.629 7.899 10.40 0.0005.8667 1.635 8.008 10.58 0.0005.9333 1.642 8.117 10.76 0.0006.0000 1.648 8.227 10.93 0.000 6.0667 1.655 8.337 11.11 0.000 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1Total Pervious Area: 13.14Total Impervious Area: 0 Mitigated Landuse Totals for POC #1Total Pervious Area: 2.75Total Impervious Area: 10.39 Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1Return Period Flow(cfs)2 year 0.3863275 year 0.60674210 year 0.73165425 year 0.86398850 year 0.945877100 year 1.015527 Flow Frequency Return Periods for Mitigated. POC #1Return Period Flow(cfs)2 year 0.2433695 year 0.37365410 year 0.47642125 year 0.62643150 year 0.753729100 year 0.895134 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1Year Predeveloped Mitigated1949 0.379 0.1651950 0.473 0.2451951 0.851 0.5721952 0.268 0.1491953 0.217 0.2271954 0.333 0.1751955 0.531 0.1711956 0.422 0.4081957 0.341 0.1751958 0.384 0.211 1959 0.329 0.1671960 0.575 0.4901961 0.325 0.2881962 0.202 0.1511963 0.277 0.1981964 0.365 0.2581965 0.261 0.3621966 0.251 0.1801967 0.525 0.2431968 0.328 0.1791969 0.321 0.1761970 0.264 0.2161971 0.283 0.1931972 0.634 0.5001973 0.288 0.3481974 0.312 0.1841975 0.423 0.1681976 0.306 0.1791977 0.036 0.1551978 0.268 0.2401979 0.162 0.1401980 0.600 0.5161981 0.240 0.1821982 0.461 0.4331983 0.414 0.1821984 0.255 0.1521985 0.152 0.1601986 0.670 0.2501987 0.592 0.4631988 0.234 0.1701989 0.152 0.1581990 1.238 0.4991991 0.746 0.4931992 0.288 0.2371993 0.300 0.1511994 0.101 0.1361995 0.430 0.2831996 0.905 0.5531997 0.757 0.5571998 0.171 0.1521999 0.710 0.5022000 0.299 0.2402001 0.054 0.1292002 0.327 0.2752003 0.418 0.1752004 0.541 0.5692005 0.388 0.1762006 0.457 0.4102007 0.919 0.7502008 1.186 0.5292009 0.582 0.357 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1Rank Predeveloped Mitigated11.2384 0.750321.1858 0.571730.9192 0.5689 4 0.9052 0.557250.8507 0.552860.7567 0.529470.7457 0.516380.7096 0.502090.6696 0.5000100.6335 0.4993110.6004 0.4926120.5923 0.4900130.5822 0.4632140.5752 0.4329150.5407 0.4100160.5309 0.4082170.5253 0.3621180.4732 0.3566190.4615 0.3482200.4574 0.2878210.4295 0.2832220.4232 0.2753230.4225 0.2583240.4176 0.2504250.4138 0.2455260.3879 0.2428270.3841 0.2404280.3795 0.2396290.3649 0.2370300.3409 0.2273310.3330 0.2163320.3295 0.2109330.3277 0.1978340.3273 0.1926350.3245 0.1836360.3206 0.1824370.3123 0.1822380.3060 0.1804390.2995 0.1792400.2987 0.1788410.2878 0.1762420.2876 0.1758430.2827 0.1754440.2772 0.1752450.2685 0.1751460.2681 0.1711470.2644 0.1698480.2613 0.1679490.2554 0.1668500.2512 0.1649510.2400 0.1598520.2337 0.1584530.2168 0.1552540.2019 0.1523550.1712 0.1520560.1622 0.1508570.1525 0.1508580.1516 0.1494590.1007 0.1397600.0536 0.1363610.0364 0.1289 Duration Flows The Facility PASSED Flow(cfs) Predev Mit Percentage Pass/Fail0.1932 17590 15137 86 Pass0.2008 16292 14292 87 Pass0.2084 15015 13417 89 Pass0.2160 13975 12309 88 Pass0.2236 12887 11242 87 Pass0.2312 11828 9965 84 Pass0.2388 10983 8949 81 Pass0.2464 10149 7940 78 Pass0.2540 9467 7116 75 Pass0.2616 8782 5918 67 Pass0.2692 8162 5172 63 Pass0.2768 7653 4960 64 Pass0.2844 7086 4761 67 Pass0.2920 6588 4579 69 Pass0.2996 6175 4483 72 Pass0.3072 5784 4363 75 Pass0.3148 5467 4244 77 Pass0.3224 5120 4092 79 Pass0.3300 4808 3936 81 Pass0.3376 4547 3805 83 Pass0.3452 4259 3630 85 Pass0.3528 4042 3476 85 Pass0.3604 3799 3315 87 Pass0.3680 3546 3187 89 Pass0.3756 3356 3078 91 Pass0.3832 3140 2952 94 Pass0.3908 2971 2804 94 Pass0.3984 2791 2639 94 Pass0.4061 2599 2490 95 Pass0.4137 2455 2329 94 Pass0.4213 2310 2160 93 Pass0.4289 2175 2038 93 Pass0.4365 2033 1879 92 Pass0.4441 1898 1755 92 Pass0.4517 1798 1652 91 Pass0.4593 1694 1533 90 Pass0.4669 1601 1392 86 Pass0.4745 1488 1246 83 Pass0.4821 1381 1114 80 Pass0.4897 1299 985 75 Pass0.4973 1225 836 68 Pass0.5049 1160 729 62 Pass0.5125 1098 645 58 Pass0.5201 1048 516 49 Pass0.5277 999 427 42 Pass0.5353 930 366 39 Pass0.5429 889 333 37 Pass0.5505 841 283 33 Pass0.5581 789 224 28 Pass0.5657 745 184 24 Pass0.5733 714 144 20 Pass0.5809 673 138 20 Pass0.5885 634 131 20 Pass 0.5961 596 124 20 Pass0.6037 569 119 20 Pass0.6113 540 110 20 Pass0.6189 501 103 20 Pass0.6265 475 70 14 Pass0.6341 435 47 10 Pass0.6418 403 32 7 Pass0.6494 370 29 7 Pass0.6570 350 27 7 Pass0.6646 324 26 8 Pass0.6722 296 23 7 Pass0.6798 275 22 8 Pass0.6874 256 21 8 Pass0.6950 237 19 8 Pass0.7026 218 15 6 Pass0.7102 197 10 5 Pass0.7178 182 10 5 Pass0.7254 158 8 5 Pass0.7330 146 6 4 Pass0.7406 130 4 3 Pass0.7482 119 2 1 Pass0.7558 110 0 0 Pass0.7634 97 0 0 Pass0.7710 91 0 0 Pass0.7786 82 0 0 Pass0.7862 76 0 0 Pass0.7938 69 0 0 Pass0.8014 61 0 0 Pass0.8090 54 0 0 Pass0.8166 48 0 0 Pass0.8242 41 0 0 Pass0.8318 38 0 0 Pass0.8394 33 0 0 Pass0.8470 27 0 0 Pass0.8546 22 0 0 Pass0.8622 21 0 0 Pass0.8698 20 0 0 Pass0.8774 19 0 0 Pass0.8851 17 0 0 Pass0.8927 14 0 0 Pass0.9003 12 0 0 Pass0.9079 9 0 0 Pass0.9155 4 0 0 Pass0.9231 3 0 0 Pass0.9307 3 0 0 Pass0.9383 3 0 0 Pass0.9459 3 0 0 Pass Water Quality Water Quality BMP Flow and Volume for POC #1On-line facility volume: 0.7607 acre-feetOn-line facility target flow: 0.8791 cfs.Adjusted for 15 min: 0.8791 cfs.Off-line facility target flow: 0.4935 cfs.Adjusted for 15 min: 0.4935 cfs. Appendix Predeveloped Schematic Mitigated Schematic General Model Information Project Name: Basin 2 Site Name: Site Address: City: Report Date: Gage:Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 1.000 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Landuse Basin Data Predeveloped Land Use Basin 2 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 41.19 Pervious Total 41.19 Impervious Land Use acre Impervious Total 0 Basin Total 41.19 Element Flows To:Surface Interflow Groundwater Mitigated Land Use Basin 2 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 7.15 Pervious Total 7.15 Impervious Land Use acre ROADS FLAT 19.16 ROOF TOPS FLAT 14.52 Impervious Total 33.68 Basin Total 40.83 Element Flows To:Surface Interflow GroundwaterPond 2 Pond 2 Basin 2 Bypass Bypass:Yes GroundWater:No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre ROADS FLAT 0.36 Impervious Total 0.36 Basin Total 0.36 Element Flows To:Surface Interflow Groundwater Mitigated Routing Pond 2 Bottom Length:305.00 ft.Bottom Width:300.00 ft.Depth:9 ft.Volume at riser head: 16.3580 acre-feet.Side slope 1:2 To 1Side slope 2:2 To 1Side slope 3:2 To 1Side slope 4:2 To 1Discharge StructureRiser Height:7 ft.Riser Diameter:18 in.Orifice 1 Diameter: 3.3 in. Elevation:0 ft.Orifice 2 Diameter: 3 in. Elevation:4 ft.Orifice 3 Diameter: 4.5 in. Elevation:4.7 ft.Element Flows To:Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs)0.0000 2.100 0.000 0.000 0.0000.1000 2.106 0.210 0.093 0.0000.2000 2.111 0.421 0.132 0.0000.3000 2.117 0.632 0.161 0.0000.4000 2.122 0.844 0.186 0.0000.5000 2.128 1.057 0.209 0.0000.6000 2.134 1.270 0.228 0.0000.7000 2.139 1.484 0.247 0.0000.8000 2.145 1.698 0.264 0.0000.9000 2.150 1.913 0.280 0.0001.0000 2.156 2.128 0.295 0.0001.1000 2.162 2.344 0.309 0.0001.2000 2.167 2.560 0.323 0.0001.3000 2.173 2.777 0.336 0.0001.4000 2.179 2.995 0.349 0.0001.5000 2.184 3.213 0.361 0.0001.6000 2.190 3.432 0.373 0.0001.7000 2.196 3.651 0.385 0.0001.8000 2.201 3.871 0.396 0.0001.9000 2.207 4.092 0.407 0.0002.0000 2.213 4.313 0.417 0.0002.1000 2.218 4.534 0.428 0.0002.2000 2.224 4.757 0.438 0.0002.3000 2.230 4.979 0.448 0.0002.4000 2.236 5.203 0.457 0.0002.5000 2.241 5.426 0.467 0.0002.6000 2.247 5.651 0.476 0.0002.7000 2.253 5.876 0.485 0.0002.8000 2.259 6.102 0.494 0.0002.9000 2.264 6.328 0.503 0.0003.0000 2.270 6.555 0.511 0.0003.1000 2.276 6.782 0.520 0.0003.2000 2.282 7.010 0.528 0.000 3.3000 2.287 7.238 0.536 0.0003.4000 2.293 7.467 0.544 0.0003.5000 2.299 7.697 0.552 0.0003.6000 2.305 7.927 0.560 0.0003.7000 2.311 8.158 0.568 0.0003.8000 2.317 8.389 0.576 0.0003.9000 2.322 8.621 0.583 0.0004.0000 2.328 8.854 0.591 0.0004.1000 2.334 9.087 0.675 0.0004.2000 2.340 9.321 0.714 0.0004.3000 2.346 9.555 0.746 0.0004.4000 2.352 9.790 0.774 0.0004.5000 2.358 10.02 0.799 0.0004.6000 2.363 10.26 0.823 0.0004.7000 2.369 10.49 0.845 0.0004.8000 2.375 10.73 1.039 0.0004.9000 2.381 10.97 1.131 0.0005.0000 2.387 11.21 1.206 0.0005.1000 2.393 11.45 1.271 0.0005.2000 2.399 11.69 1.330 0.0005.3000 2.405 11.93 1.384 0.0005.4000 2.411 12.17 1.435 0.0005.5000 2.417 12.41 1.483 0.0005.6000 2.423 12.65 1.529 0.0005.7000 2.429 12.89 1.573 0.0005.8000 2.435 13.14 1.615 0.0005.9000 2.441 13.38 1.656 0.0006.0000 2.447 13.63 1.695 0.0006.1000 2.453 13.87 1.734 0.0006.2000 2.459 14.12 1.771 0.0006.3000 2.465 14.36 1.807 0.0006.4000 2.471 14.61 1.842 0.0006.5000 2.477 14.86 1.876 0.0006.6000 2.483 15.10 1.910 0.0006.7000 2.489 15.35 1.943 0.0006.8000 2.495 15.60 1.975 0.0006.9000 2.501 15.85 2.007 0.0007.0000 2.507 16.10 2.038 0.0007.1000 2.513 16.35 2.570 0.0007.2000 2.519 16.61 3.503 0.0007.3000 2.525 16.86 4.629 0.0007.4000 2.531 17.11 5.789 0.0007.5000 2.537 17.36 6.824 0.0007.6000 2.544 17.62 7.615 0.0007.7000 2.550 17.87 8.134 0.0007.8000 2.556 18.13 8.607 0.0007.9000 2.562 18.38 9.018 0.0008.0000 2.568 18.64 9.409 0.0008.1000 2.574 18.90 9.781 0.0008.2000 2.580 19.16 10.13 0.0008.3000 2.587 19.41 10.48 0.0008.4000 2.593 19.67 10.81 0.0008.5000 2.599 19.93 11.13 0.0008.6000 2.605 20.19 11.44 0.0008.7000 2.611 20.45 11.74 0.0008.8000 2.617 20.71 12.03 0.0008.9000 2.624 20.98 12.31 0.0009.0000 2.630 21.24 12.59 0.000 9.1000 2.636 21.50 12.86 0.000 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1Total Pervious Area: 41.19Total Impervious Area: 0 Mitigated Landuse Totals for POC #1Total Pervious Area: 7.15Total Impervious Area: 34.04 Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1Return Period Flow(cfs)2 year 1.2110215 year 1.90195510 year 2.29351925 year 2.70834750 year 2.965044100 year 3.183376 Flow Frequency Return Periods for Mitigated. POC #1Return Period Flow(cfs)2 year 0.7998245 year 1.21419910 year 1.54526125 year 2.03435150 year 2.454219100 year 2.925264 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1Year Predeveloped Mitigated1949 1.190 0.5471950 1.483 0.7911951 2.667 1.8551952 0.840 0.5091953 0.680 0.7241954 1.044 0.5801955 1.664 0.5811956 1.324 1.3061957 1.069 0.5891958 1.204 0.659 1959 1.033 0.5811960 1.803 1.5911961 1.017 0.9001962 0.633 0.4951963 0.869 0.6281964 1.144 0.8311965 0.819 1.1581966 0.787 0.6031967 1.647 0.7751968 1.027 0.6051969 1.005 0.5801970 0.829 0.6721971 0.886 0.6381972 1.986 1.6151973 0.902 1.1111974 0.979 0.6161975 1.327 0.6111976 0.959 0.5831977 0.114 0.5651978 0.842 0.7731979 0.508 0.4581980 1.882 1.6621981 0.752 0.5941982 1.447 1.4211983 1.297 0.6021984 0.801 0.5311985 0.475 0.5521986 2.099 0.8291987 1.857 1.5081988 0.733 0.5941989 0.478 0.5461990 3.882 1.6041991 2.337 1.6071992 0.901 0.7531993 0.939 0.4981994 0.316 0.4721995 1.346 0.8601996 2.838 1.7901997 2.372 1.7951998 0.537 0.5631999 2.224 1.6242000 0.936 0.7722001 0.168 0.5112002 1.026 0.8622003 1.309 0.5892004 1.695 1.8642005 1.216 0.6002006 1.434 1.3192007 2.882 2.7302008 3.717 1.7242009 1.825 1.161 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1Rank Predeveloped Mitigated13.8820 2.730323.7171 1.864332.8815 1.8547 4 2.8376 1.795052.6668 1.789962.3721 1.724072.3374 1.661782.2244 1.624092.0990 1.6150101.9859 1.6068111.8821 1.6039121.8567 1.5913131.8251 1.5077141.8032 1.4209151.6949 1.3185161.6643 1.3061171.6467 1.1614181.4833 1.1580191.4467 1.1113201.4339 0.8999211.3464 0.8621221.3266 0.8603231.3243 0.8311241.3090 0.8291251.2970 0.7908261.2159 0.7746271.2040 0.7733281.1896 0.7721291.1439 0.7532301.0687 0.7237311.0437 0.6718321.0328 0.6587331.0272 0.6385341.0261 0.6278351.0173 0.6160361.0049 0.6110370.9791 0.6051380.9591 0.6026390.9390 0.6020400.9363 0.6001410.9021 0.5943420.9015 0.5937430.8863 0.5894440.8690 0.5889450.8415 0.5832460.8404 0.5810470.8287 0.5808480.8190 0.5797490.8006 0.5795500.7874 0.5649510.7522 0.5631520.7327 0.5520530.6797 0.5471540.6330 0.5456550.5366 0.5311560.5085 0.5114570.4780 0.5090580.4751 0.4977590.3155 0.4948600.1679 0.4722610.1142 0.4576 Duration Flows The Facility PASSED Flow(cfs) Predev Mit Percentage Pass/Fail0.6055 17590 14801 84 Pass0.6293 16181 13779 85 Pass0.6532 14970 13013 86 Pass0.6770 13849 12299 88 Pass0.7008 12842 11231 87 Pass0.7247 11834 10121 85 Pass0.7485 10910 8992 82 Pass0.7723 10123 8008 79 Pass0.7962 9385 7133 76 Pass0.8200 8729 6064 69 Pass0.8438 8166 4999 61 Pass0.8677 7610 4571 60 Pass0.8915 7073 4460 63 Pass0.9153 6592 4365 66 Pass0.9392 6149 4282 69 Pass0.9630 5775 4209 72 Pass0.9868 5443 4117 75 Pass1.0107 5108 4019 78 Pass1.0345 4812 3936 81 Pass1.0584 4528 3811 84 Pass1.0822 4254 3670 86 Pass1.1060 4017 3495 87 Pass1.1299 3794 3371 88 Pass1.1537 3553 3232 90 Pass1.1775 3341 3108 93 Pass1.2014 3138 2973 94 Pass1.2252 2952 2853 96 Pass1.2490 2785 2710 97 Pass1.2729 2603 2571 98 Pass1.2967 2449 2445 99 Pass1.3205 2308 2257 97 Pass1.3444 2162 2124 98 Pass1.3682 2026 1988 98 Pass1.3920 1898 1855 97 Pass1.4159 1790 1734 96 Pass1.4397 1690 1595 94 Pass1.4635 1590 1484 93 Pass1.4874 1483 1379 92 Pass1.5112 1380 1241 89 Pass1.5350 1292 1131 87 Pass1.5589 1223 1013 82 Pass1.5827 1155 897 77 Pass1.6065 1098 758 69 Pass1.6304 1048 664 63 Pass1.6542 997 545 54 Pass1.6780 930 464 49 Pass1.7019 884 398 45 Pass1.7257 838 346 41 Pass1.7495 789 311 39 Pass1.7734 743 272 36 Pass1.7972 713 229 32 Pass1.8210 668 195 29 Pass1.8449 633 158 24 Pass 1.8687 596 132 22 Pass1.8925 567 126 22 Pass1.9164 539 120 22 Pass1.9402 497 113 22 Pass1.9640 473 107 22 Pass1.9879 436 93 21 Pass2.0117 401 62 15 Pass2.0355 368 47 12 Pass2.0594 348 42 12 Pass2.0832 323 38 11 Pass2.1070 296 36 12 Pass2.1309 273 35 12 Pass2.1547 256 34 13 Pass2.1785 235 34 14 Pass2.2024 217 33 15 Pass2.2262 195 32 16 Pass2.2500 180 31 17 Pass2.2739 158 31 19 Pass2.2977 145 30 20 Pass2.3215 129 29 22 Pass2.3454 119 27 22 Pass2.3692 109 22 20 Pass2.3930 97 18 18 Pass2.4169 91 17 18 Pass2.4407 82 17 20 Pass2.4645 76 16 21 Pass2.4884 69 15 21 Pass2.5122 61 14 22 Pass2.5360 54 13 24 Pass2.5599 48 11 22 Pass2.5837 41 10 24 Pass2.6075 38 8 21 Pass2.6314 33 7 21 Pass2.6552 27 7 25 Pass2.6790 22 5 22 Pass2.7029 21 5 23 Pass2.7267 20 1 5 Pass2.7505 19 0 0 Pass2.7744 17 0 0 Pass2.7982 14 0 0 Pass2.8220 12 0 0 Pass2.8459 9 0 0 Pass2.8697 4 0 0 Pass2.8935 3 0 0 Pass2.9174 3 0 0 Pass2.9412 3 0 0 Pass2.9650 3 0 0 Pass Appendix Predeveloped Schematic Mitigated Schematic General Model Information Project Name: Basin 3 Site Name: Site Address: City: Report Date: Gage:Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 1.000 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Landuse Basin Data Predeveloped Land Use Basin 3 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 4.53 Pervious Total 4.53 Impervious Land Use acre Impervious Total 0 Basin Total 4.53 Element Flows To:Surface Interflow Groundwater Mitigated Land Use Basin 3 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 1.5 Pervious Total 1.5 Impervious Land Use acre ROADS FLAT 0.14 ROOF TOPS FLAT 2.89 Impervious Total 3.03 Basin Total 4.53 Element Flows To:Surface Interflow GroundwaterPond 3 Pond 3 Mitigated Routing Pond 3 Bottom Length:175.00 ft.Bottom Width:175.00 ft.Depth:3 ft.Volume at riser head: 1.5386 acre-feet.Side slope 1:4 To 1Side slope 2:4 To 1Side slope 3:4 To 1Side slope 4:4 To 1Discharge StructureRiser Height:2 ft.Riser Diameter:18 in.Orifice 1 Diameter: 1.5 in. Elevation:0 ft.Orifice 2 Diameter: 1.25 in. Elevation:1.1 ft.Orifice 3 Diameter: 2 in. Elevation:1.33 ft.Element Flows To:Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs)0.0000 0.703 0.000 0.000 0.0000.0333 0.705 0.023 0.011 0.0000.0667 0.707 0.047 0.015 0.0000.1000 0.709 0.070 0.019 0.0000.1333 0.711 0.094 0.022 0.0000.1667 0.713 0.118 0.024 0.0000.2000 0.716 0.141 0.027 0.0000.2333 0.718 0.165 0.029 0.0000.2667 0.720 0.189 0.031 0.0000.3000 0.722 0.213 0.033 0.0000.3333 0.724 0.237 0.035 0.0000.3667 0.726 0.262 0.037 0.0000.4000 0.729 0.286 0.038 0.0000.4333 0.731 0.310 0.040 0.0000.4667 0.733 0.335 0.041 0.0000.5000 0.735 0.359 0.043 0.0000.5333 0.737 0.384 0.044 0.0000.5667 0.739 0.408 0.046 0.0000.6000 0.742 0.433 0.047 0.0000.6333 0.744 0.458 0.048 0.0000.6667 0.746 0.483 0.049 0.0000.7000 0.748 0.508 0.051 0.0000.7333 0.751 0.533 0.052 0.0000.7667 0.753 0.558 0.053 0.0000.8000 0.755 0.583 0.054 0.0000.8333 0.757 0.608 0.055 0.0000.8667 0.759 0.633 0.056 0.0000.9000 0.762 0.659 0.057 0.0000.9333 0.764 0.684 0.059 0.0000.9667 0.766 0.710 0.060 0.0001.0000 0.768 0.735 0.061 0.0001.0333 0.771 0.761 0.062 0.0001.0667 0.773 0.787 0.063 0.000 1.1000 0.775 0.812 0.064 0.0001.1333 0.777 0.838 0.072 0.0001.1667 0.780 0.864 0.076 0.0001.2000 0.782 0.890 0.080 0.0001.2333 0.784 0.916 0.083 0.0001.2667 0.786 0.943 0.086 0.0001.3000 0.789 0.969 0.088 0.0001.3333 0.791 0.995 0.097 0.0001.3667 0.793 1.022 0.114 0.0001.4000 0.795 1.048 0.124 0.0001.4333 0.798 1.075 0.132 0.0001.4667 0.800 1.101 0.139 0.0001.5000 0.802 1.128 0.146 0.0001.5333 0.805 1.155 0.152 0.0001.5667 0.807 1.182 0.158 0.0001.6000 0.809 1.209 0.163 0.0001.6333 0.812 1.236 0.168 0.0001.6667 0.814 1.263 0.173 0.0001.7000 0.816 1.290 0.178 0.0001.7333 0.818 1.317 0.183 0.0001.7667 0.821 1.345 0.187 0.0001.8000 0.823 1.372 0.191 0.0001.8333 0.825 1.400 0.196 0.0001.8667 0.828 1.427 0.200 0.0001.9000 0.830 1.455 0.204 0.0001.9333 0.832 1.482 0.207 0.0001.9667 0.835 1.510 0.211 0.0002.0000 0.837 1.538 0.215 0.0002.0333 0.839 1.566 0.315 0.0002.0667 0.842 1.594 0.496 0.0002.1000 0.844 1.622 0.728 0.0002.1333 0.846 1.650 1.001 0.0002.1667 0.849 1.679 1.307 0.0002.2000 0.851 1.707 1.640 0.0002.2333 0.853 1.735 1.995 0.0002.2667 0.856 1.764 2.366 0.0002.3000 0.858 1.793 2.747 0.0002.3333 0.861 1.821 3.131 0.0002.3667 0.863 1.850 3.513 0.0002.4000 0.865 1.879 3.887 0.0002.4333 0.868 1.908 4.247 0.0002.4667 0.870 1.937 4.587 0.0002.5000 0.872 1.966 4.903 0.0002.5333 0.875 1.995 5.191 0.0002.5667 0.877 2.024 5.448 0.0002.6000 0.880 2.053 5.673 0.0002.6333 0.882 2.083 5.867 0.0002.6667 0.884 2.112 6.032 0.0002.7000 0.887 2.142 6.173 0.0002.7333 0.889 2.171 6.297 0.0002.7667 0.892 2.201 6.491 0.0002.8000 0.894 2.231 6.627 0.0002.8333 0.897 2.261 6.760 0.0002.8667 0.899 2.291 6.891 0.0002.9000 0.901 2.321 7.019 0.0002.9333 0.904 2.351 7.145 0.0002.9667 0.906 2.381 7.269 0.0003.0000 0.909 2.411 7.391 0.000 3.0333 0.911 2.442 7.510 0.000 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1Total Pervious Area: 4.53Total Impervious Area: 0 Mitigated Landuse Totals for POC #1Total Pervious Area: 1.5Total Impervious Area: 3.03 Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1Return Period Flow(cfs)2 year 0.1331865 year 0.20917310 year 0.25223725 year 0.29785950 year 0.32609100 year 0.350102 Flow Frequency Return Periods for Mitigated. POC #1Return Period Flow(cfs)2 year 0.083275 year 0.12662210 year 0.16056925 year 0.20983450 year 0.251428100 year 0.297447 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1Year Predeveloped Mitigated1949 0.131 0.0571950 0.163 0.0831951 0.293 0.1931952 0.092 0.0521953 0.075 0.0731954 0.115 0.0621955 0.183 0.0601956 0.146 0.1331957 0.118 0.0621958 0.132 0.076 1959 0.114 0.0571960 0.198 0.1681961 0.112 0.0941962 0.070 0.0511963 0.096 0.0661964 0.126 0.0841965 0.090 0.1221966 0.087 0.0621967 0.181 0.0801968 0.113 0.0621969 0.111 0.0611970 0.091 0.0741971 0.097 0.0711972 0.218 0.1671973 0.099 0.1151974 0.108 0.0711975 0.146 0.0581976 0.105 0.0631977 0.013 0.0521978 0.093 0.0821979 0.056 0.0481980 0.207 0.1761981 0.083 0.0641982 0.159 0.1421983 0.143 0.0681984 0.088 0.0531985 0.052 0.0551986 0.231 0.0861987 0.204 0.1551988 0.081 0.0581989 0.053 0.0541990 0.427 0.1741991 0.257 0.1581992 0.099 0.0831993 0.103 0.0521994 0.035 0.0471995 0.148 0.0891996 0.312 0.1891997 0.261 0.1921998 0.059 0.0521999 0.245 0.1662000 0.103 0.0812001 0.018 0.0442002 0.113 0.0962003 0.144 0.0612004 0.186 0.1882005 0.134 0.0622006 0.158 0.1342007 0.317 0.2682008 0.409 0.1832009 0.201 0.118 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1Rank Predeveloped Mitigated10.4269 0.268520.4088 0.193230.3169 0.1922 4 0.3121 0.188750.2933 0.187660.2609 0.183470.2571 0.175680.2446 0.173590.2308 0.1684100.2184 0.1667110.2070 0.1658120.2042 0.1584130.2007 0.1554140.1983 0.1420150.1864 0.1336160.1830 0.1325170.1811 0.1225180.1631 0.1179190.1591 0.1149200.1577 0.0960210.1481 0.0937220.1459 0.0891230.1456 0.0862240.1440 0.0841250.1426 0.0833260.1337 0.0829270.1324 0.0824280.1308 0.0810290.1258 0.0805300.1175 0.0763310.1148 0.0737320.1136 0.0729330.1130 0.0709340.1128 0.0706350.1119 0.0680360.1105 0.0661370.1077 0.0636380.1055 0.0626390.1033 0.0622400.1030 0.0622410.0992 0.0620420.0991 0.0619430.0975 0.0617440.0956 0.0610450.0925 0.0606460.0924 0.0600470.0911 0.0583480.0901 0.0577490.0881 0.0571500.0866 0.0571510.0827 0.0551520.0806 0.0544530.0747 0.0526540.0696 0.0524550.0590 0.0522560.0559 0.0522570.0526 0.0516580.0523 0.0514590.0347 0.0480600.0185 0.0467610.0126 0.0436 Duration Flows The Facility PASSED Flow(cfs) Predev Mit Percentage Pass/Fail0.0666 17547 15411 87 Pass0.0692 16164 14617 90 Pass0.0718 14964 13937 93 Pass0.0745 13851 12853 92 Pass0.0771 12814 11618 90 Pass0.0797 11811 10271 86 Pass0.0823 10898 8932 81 Pass0.0849 10119 7822 77 Pass0.0876 9383 6543 69 Pass0.0902 8729 5728 65 Pass0.0928 8143 5351 65 Pass0.0954 7593 4994 65 Pass0.0980 7060 4729 66 Pass0.1007 6594 4584 69 Pass0.1033 6160 4442 72 Pass0.1059 5777 4323 74 Pass0.1085 5435 4179 76 Pass0.1112 5106 4032 78 Pass0.1138 4815 3895 80 Pass0.1164 4532 3713 81 Pass0.1190 4254 3561 83 Pass0.1216 4019 3437 85 Pass0.1243 3788 3307 87 Pass0.1269 3553 3161 88 Pass0.1295 3337 3037 91 Pass0.1321 3138 2909 92 Pass0.1347 2954 2761 93 Pass0.1374 2789 2624 94 Pass0.1400 2603 2473 95 Pass0.1426 2447 2299 93 Pass0.1452 2306 2169 94 Pass0.1478 2162 2039 94 Pass0.1505 2028 1904 93 Pass0.1531 1903 1754 92 Pass0.1557 1790 1597 89 Pass0.1583 1689 1451 85 Pass0.1610 1590 1337 84 Pass0.1636 1483 1184 79 Pass0.1662 1383 1032 74 Pass0.1688 1292 905 70 Pass0.1714 1221 826 67 Pass0.1741 1155 731 63 Pass0.1767 1098 615 56 Pass0.1793 1048 513 48 Pass0.1819 997 408 40 Pass0.1845 930 328 35 Pass0.1872 884 254 28 Pass0.1898 839 199 23 Pass0.1924 789 162 20 Pass0.1950 743 144 19 Pass0.1977 713 136 19 Pass0.2003 670 129 19 Pass0.2029 633 122 19 Pass 0.2055 595 114 19 Pass0.2081 566 107 18 Pass0.2108 539 92 17 Pass0.2134 497 48 9 Pass0.2160 473 33 6 Pass0.2186 434 32 7 Pass0.2212 400 31 7 Pass0.2239 368 31 8 Pass0.2265 348 29 8 Pass0.2291 323 29 8 Pass0.2317 296 28 9 Pass0.2343 272 27 9 Pass0.2370 256 27 10 Pass0.2396 235 24 10 Pass0.2422 217 22 10 Pass0.2448 195 21 10 Pass0.2475 180 19 10 Pass0.2501 158 17 10 Pass0.2527 145 10 6 Pass0.2553 129 10 7 Pass0.2579 119 8 6 Pass0.2606 109 8 7 Pass0.2632 97 6 6 Pass0.2658 91 4 4 Pass0.2684 82 1 1 Pass0.2710 76 0 0 Pass0.2737 69 0 0 Pass0.2763 61 0 0 Pass0.2789 54 0 0 Pass0.2815 48 0 0 Pass0.2842 41 0 0 Pass0.2868 38 0 0 Pass0.2894 33 0 0 Pass0.2920 27 0 0 Pass0.2946 22 0 0 Pass0.2973 21 0 0 Pass0.2999 20 0 0 Pass0.3025 19 0 0 Pass0.3051 17 0 0 Pass0.3077 14 0 0 Pass0.3104 12 0 0 Pass0.3130 9 0 0 Pass0.3156 4 0 0 Pass0.3182 3 0 0 Pass0.3208 3 0 0 Pass0.3235 3 0 0 Pass0.3261 3 0 0 Pass Appendix Predeveloped Schematic Mitigated Schematic General Model Information Project Name: Basin 4 Site Name: Site Address: City: Report Date: Gage:Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 1.000 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Landuse Basin Data Predeveloped Land Use Basin 4 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 5.72 Pervious Total 5.72 Impervious Land Use acre Impervious Total 0 Basin Total 5.72 Element Flows To:Surface Interflow Groundwater Mitigated Land Use Basin 4 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 1.33 Pervious Total 1.33 Impervious Land Use acre ROADS FLAT 4.39 Impervious Total 4.39 Basin Total 5.72 Element Flows To:Surface Interflow GroundwaterPond 4 Pond 4 Mitigated Routing Pond 4 Bottom Length:70.00 ft.Bottom Width:75.00 ft.Depth:12 ft.Volume at riser head: 2.3151 acre-feet.Side slope 1:2 To 1Side slope 2:2 To 1Side slope 3:2 To 1Side slope 4:2 To 1Discharge StructureRiser Height:11 ft.Riser Diameter:18 in.Orifice 1 Diameter: 1 in. Elevation:0 ft.Orifice 2 Diameter: 1 in. Elevation:7 ft.Orifice 3 Diameter: 1.5 in. Elevation:8 ft.Element Flows To:Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs)0.0000 0.120 0.000 0.000 0.0000.1333 0.122 0.016 0.009 0.0000.2667 0.124 0.032 0.014 0.0000.4000 0.125 0.049 0.017 0.0000.5333 0.127 0.066 0.019 0.0000.6667 0.129 0.083 0.022 0.0000.8000 0.131 0.100 0.024 0.0000.9333 0.133 0.118 0.026 0.0001.0667 0.135 0.136 0.028 0.0001.2000 0.137 0.154 0.029 0.0001.3333 0.138 0.172 0.031 0.0001.4667 0.140 0.191 0.032 0.0001.6000 0.142 0.210 0.034 0.0001.7333 0.144 0.229 0.035 0.0001.8667 0.146 0.249 0.037 0.0002.0000 0.148 0.268 0.038 0.0002.1333 0.150 0.288 0.039 0.0002.2667 0.152 0.308 0.040 0.0002.4000 0.154 0.329 0.042 0.0002.5333 0.156 0.350 0.043 0.0002.6667 0.158 0.371 0.044 0.0002.8000 0.160 0.392 0.045 0.0002.9333 0.162 0.413 0.046 0.0003.0667 0.164 0.435 0.047 0.0003.2000 0.166 0.457 0.048 0.0003.3333 0.169 0.480 0.049 0.0003.4667 0.171 0.502 0.050 0.0003.6000 0.173 0.525 0.051 0.0003.7333 0.175 0.549 0.052 0.0003.8667 0.177 0.572 0.053 0.0004.0000 0.179 0.596 0.054 0.0004.1333 0.181 0.620 0.055 0.0004.2667 0.184 0.644 0.056 0.000 4.4000 0.186 0.669 0.056 0.0004.5333 0.188 0.694 0.057 0.0004.6667 0.190 0.719 0.058 0.0004.8000 0.192 0.745 0.059 0.0004.9333 0.195 0.771 0.060 0.0005.0667 0.197 0.797 0.061 0.0005.2000 0.199 0.824 0.061 0.0005.3333 0.202 0.850 0.062 0.0005.4667 0.204 0.877 0.063 0.0005.6000 0.206 0.905 0.064 0.0005.7333 0.208 0.932 0.065 0.0005.8667 0.211 0.960 0.065 0.0006.0000 0.213 0.989 0.066 0.0006.1333 0.216 1.017 0.067 0.0006.2667 0.218 1.046 0.067 0.0006.4000 0.220 1.076 0.068 0.0006.5333 0.223 1.105 0.069 0.0006.6667 0.225 1.135 0.070 0.0006.8000 0.228 1.165 0.070 0.0006.9333 0.230 1.196 0.071 0.0007.0667 0.233 1.227 0.079 0.0007.2000 0.235 1.258 0.085 0.0007.3333 0.237 1.290 0.089 0.0007.4667 0.240 1.322 0.092 0.0007.6000 0.242 1.354 0.095 0.0007.7333 0.245 1.386 0.098 0.0007.8667 0.248 1.419 0.101 0.0008.0000 0.250 1.453 0.103 0.0008.1333 0.253 1.486 0.128 0.0008.2667 0.255 1.520 0.140 0.0008.4000 0.258 1.554 0.149 0.0008.5333 0.260 1.589 0.157 0.0008.6667 0.263 1.624 0.164 0.0008.8000 0.266 1.659 0.171 0.0008.9333 0.268 1.695 0.177 0.0009.0667 0.271 1.731 0.183 0.0009.2000 0.274 1.767 0.189 0.0009.3333 0.276 1.804 0.194 0.0009.4667 0.279 1.841 0.200 0.0009.6000 0.282 1.878 0.205 0.0009.7333 0.284 1.916 0.209 0.0009.8667 0.287 1.954 0.214 0.00010.000 0.290 1.993 0.219 0.00010.133 0.293 2.032 0.223 0.00010.267 0.295 2.071 0.227 0.00010.400 0.298 2.111 0.232 0.00010.533 0.301 2.151 0.236 0.00010.667 0.304 2.191 0.240 0.00010.800 0.307 2.232 0.244 0.00010.933 0.310 2.273 0.248 0.00011.067 0.312 2.315 0.525 0.00011.200 0.315 2.357 1.660 0.00011.333 0.318 2.399 3.141 0.00011.467 0.321 2.442 4.589 0.00011.600 0.324 2.485 5.667 0.00011.733 0.327 2.528 6.284 0.00011.867 0.330 2.572 6.870 0.00012.000 0.333 2.616 7.363 0.000 12.133 0.336 2.661 7.824 0.000 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1Total Pervious Area: 5.72Total Impervious Area: 0 Mitigated Landuse Totals for POC #1Total Pervious Area: 1.33Total Impervious Area: 4.39 Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1Return Period Flow(cfs)2 year 0.1681735 year 0.26412210 year 0.31849825 year 0.37610450 year 0.411752100 year 0.442071 Flow Frequency Return Periods for Mitigated. POC #1Return Period Flow(cfs)2 year 0.0972235 year 0.14806610 year 0.18792425 year 0.24582150 year 0.294743100 year 0.348903 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1Year Predeveloped Mitigated1949 0.165 0.0661950 0.206 0.0981951 0.370 0.2241952 0.117 0.0611953 0.094 0.0961954 0.145 0.0691955 0.231 0.0671956 0.184 0.1761957 0.148 0.0691958 0.167 0.083 1959 0.143 0.0671960 0.250 0.1891961 0.141 0.1251962 0.088 0.0611963 0.121 0.0871964 0.159 0.1061965 0.114 0.1511966 0.109 0.0741967 0.229 0.0981968 0.143 0.0701969 0.140 0.0701970 0.115 0.0941971 0.123 0.0751972 0.276 0.2021973 0.125 0.1481974 0.136 0.0771975 0.184 0.0661976 0.133 0.0701977 0.016 0.0611978 0.117 0.0961979 0.071 0.0561980 0.261 0.2071981 0.104 0.0731982 0.201 0.1651983 0.180 0.0721984 0.111 0.0611985 0.066 0.0631986 0.291 0.0941987 0.258 0.1771988 0.102 0.0671989 0.066 0.0631990 0.539 0.1931991 0.325 0.1991992 0.125 0.0951993 0.130 0.0601994 0.044 0.0551995 0.187 0.1291996 0.394 0.2171997 0.329 0.2221998 0.075 0.0621999 0.309 0.2002000 0.130 0.0922001 0.023 0.0522002 0.142 0.1012003 0.182 0.0692004 0.235 0.2162005 0.169 0.0692006 0.199 0.1702007 0.400 0.2482008 0.516 0.2032009 0.253 0.135 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1Rank Predeveloped Mitigated10.5391 0.248020.5162 0.224430.4002 0.2225 4 0.3941 0.216850.3703 0.215660.3294 0.207070.3246 0.203380.3089 0.202290.2915 0.1996100.2758 0.1991110.2614 0.1932120.2578 0.1892130.2534 0.1771140.2504 0.1756150.2354 0.1701160.2311 0.1653170.2287 0.1514180.2060 0.1478190.2009 0.1355200.1991 0.1291210.1870 0.1253220.1842 0.1060230.1839 0.1006240.1818 0.0984250.1801 0.0976260.1688 0.0964270.1672 0.0958280.1652 0.0950290.1588 0.0941300.1484 0.0936310.1449 0.0925320.1434 0.0874330.1426 0.0834340.1425 0.0768350.1413 0.0751360.1396 0.0742370.1360 0.0733380.1332 0.0717390.1304 0.0702400.1300 0.0702410.1253 0.0696420.1252 0.0688430.1231 0.0688440.1207 0.0686450.1169 0.0685460.1167 0.0675470.1151 0.0673480.1137 0.0667490.1112 0.0660500.1093 0.0659510.1045 0.0631520.1017 0.0627530.0944 0.0623540.0879 0.0615550.0745 0.0610560.0706 0.0610570.0664 0.0605580.0660 0.0604590.0438 0.0564600.0233 0.0552610.0159 0.0521 Duration Flows The Facility PASSED Flow(cfs) Predev Mit Percentage Pass/Fail0.0841 17603 16416 93 Pass0.0874 16322 14869 91 Pass0.0907 15207 13107 86 Pass0.0940 13854 10658 76 Pass0.0973 12908 9129 70 Pass0.1006 11982 7845 65 Pass0.1039 11148 6498 58 Pass0.1073 10166 5944 58 Pass0.1106 9492 5781 60 Pass0.1139 8891 5645 63 Pass0.1172 8177 5463 66 Pass0.1205 7676 5330 69 Pass0.1238 7180 5221 72 Pass0.1271 6596 5078 76 Pass0.1304 6194 4915 79 Pass0.1337 5850 4699 80 Pass0.1370 5435 4417 81 Pass0.1404 5142 4233 82 Pass0.1437 4866 4019 82 Pass0.1470 4605 3833 83 Pass0.1503 4271 3561 83 Pass0.1536 4051 3401 83 Pass0.1569 3850 3253 84 Pass0.1602 3557 2992 84 Pass0.1635 3371 2789 82 Pass0.1668 3181 2605 81 Pass0.1701 2954 2359 79 Pass0.1734 2802 2201 78 Pass0.1768 2637 2045 77 Pass0.1801 2449 1862 76 Pass0.1834 2321 1733 74 Pass0.1867 2182 1588 72 Pass0.1900 2069 1422 68 Pass0.1933 1911 1215 63 Pass0.1966 1807 1048 57 Pass0.1999 1720 841 48 Pass0.2032 1597 677 42 Pass0.2065 1497 571 38 Pass0.2099 1397 481 34 Pass0.2132 1295 378 29 Pass0.2165 1230 266 21 Pass0.2198 1174 226 19 Pass0.2231 1098 178 16 Pass0.2264 1055 154 14 Pass0.2297 1006 146 14 Pass0.2330 930 132 14 Pass0.2363 889 124 13 Pass0.2396 846 114 13 Pass0.2430 798 103 12 Pass0.2463 745 33 4 Pass0.2496 720 0 0 Pass0.2529 680 0 0 Pass0.2562 634 0 0 Pass 0.2595 601 0 0 Pass0.2628 574 0 0 Pass0.2661 540 0 0 Pass0.2694 502 0 0 Pass0.2727 477 0 0 Pass0.2761 434 0 0 Pass0.2794 404 0 0 Pass0.2827 377 0 0 Pass0.2860 353 0 0 Pass0.2893 325 0 0 Pass0.2926 301 0 0 Pass0.2959 281 0 0 Pass0.2992 257 0 0 Pass0.3025 239 0 0 Pass0.3058 219 0 0 Pass0.3091 198 0 0 Pass0.3125 182 0 0 Pass0.3158 159 0 0 Pass0.3191 145 0 0 Pass0.3224 131 0 0 Pass0.3257 120 0 0 Pass0.3290 109 0 0 Pass0.3323 97 0 0 Pass0.3356 93 0 0 Pass0.3389 87 0 0 Pass0.3422 76 0 0 Pass0.3456 69 0 0 Pass0.3489 63 0 0 Pass0.3522 55 0 0 Pass0.3555 48 0 0 Pass0.3588 43 0 0 Pass0.3621 38 0 0 Pass0.3654 33 0 0 Pass0.3687 29 0 0 Pass0.3720 22 0 0 Pass0.3753 21 0 0 Pass0.3787 20 0 0 Pass0.3820 19 0 0 Pass0.3853 17 0 0 Pass0.3886 14 0 0 Pass0.3919 13 0 0 Pass0.3952 9 0 0 Pass0.3985 4 0 0 Pass0.4018 3 0 0 Pass0.4051 3 0 0 Pass0.4084 3 0 0 Pass0.4118 3 0 0 Pass Appendix Predeveloped Schematic Mitigated Schematic General Model Information Project Name: Basin 5 Site Name: Site Address: City: Report Date: Gage:Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 1.000 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Landuse Basin Data Predeveloped Land Use Basin 5 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 10.58 Pervious Total 10.58 Impervious Land Use acre Impervious Total 0 Basin Total 10.58 Element Flows To:Surface Interflow Groundwater Mitigated Land Use Basin 5 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 1.53 Pervious Total 1.53 Impervious Land Use acre ROADS FLAT 2.9 ROOF TOPS FLAT 5.53 Impervious Total 8.43 Basin Total 9.96 Element Flows To:Surface Interflow GroundwaterPond 5 Pond 5 Basin 5 Bypass Bypass:Yes GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.2 Pervious Total 0.2 Impervious Land Use acre ROADS FLAT 0.42 Impervious Total 0.42 Basin Total 0.62 Element Flows To:Surface Interflow Groundwater Mitigated Routing Pond 5 Bottom Length:90.00 ft.Bottom Width:89.00 ft.Depth:9 ft.Volume at riser head: 1.4553 acre-feet.Side slope 1:2 To 1Side slope 2:2 To 1Side slope 3:2 To 1Side slope 4:2 To 1Discharge StructureRiser Height:6 ft.Riser Diameter:18 in.Orifice 1 Diameter: 1.5 in. Elevation:0 ft.Orifice 2 Diameter: 2.5 in. Elevation:3.25 ft.Orifice 3 Diameter: 3 in. Elevation:4 ft.Element Flows To:Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs)0.0000 0.183 0.000 0.000 0.0000.1000 0.185 0.018 0.019 0.0000.2000 0.187 0.037 0.027 0.0000.3000 0.188 0.055 0.033 0.0000.4000 0.190 0.074 0.038 0.0000.5000 0.192 0.094 0.043 0.0000.6000 0.193 0.113 0.047 0.0000.7000 0.195 0.132 0.051 0.0000.8000 0.197 0.152 0.054 0.0000.9000 0.199 0.172 0.057 0.0001.0000 0.200 0.192 0.061 0.0001.1000 0.202 0.212 0.064 0.0001.2000 0.204 0.232 0.066 0.0001.3000 0.205 0.253 0.069 0.0001.4000 0.207 0.273 0.072 0.0001.5000 0.209 0.294 0.074 0.0001.6000 0.211 0.315 0.077 0.0001.7000 0.212 0.337 0.079 0.0001.8000 0.214 0.358 0.081 0.0001.9000 0.216 0.379 0.084 0.0002.0000 0.218 0.401 0.086 0.0002.1000 0.220 0.423 0.088 0.0002.2000 0.221 0.445 0.090 0.0002.3000 0.223 0.467 0.092 0.0002.4000 0.225 0.490 0.094 0.0002.5000 0.227 0.513 0.096 0.0002.6000 0.229 0.535 0.098 0.0002.7000 0.230 0.558 0.100 0.0002.8000 0.232 0.582 0.102 0.0002.9000 0.234 0.605 0.104 0.0003.0000 0.236 0.628 0.105 0.0003.1000 0.238 0.652 0.107 0.0003.2000 0.240 0.676 0.109 0.000 3.3000 0.242 0.700 0.148 0.0003.4000 0.244 0.725 0.178 0.0003.5000 0.245 0.749 0.199 0.0003.6000 0.247 0.774 0.216 0.0003.7000 0.249 0.799 0.231 0.0003.8000 0.251 0.824 0.244 0.0003.9000 0.253 0.849 0.257 0.0004.0000 0.255 0.874 0.269 0.0004.1000 0.257 0.900 0.357 0.0004.2000 0.259 0.926 0.399 0.0004.3000 0.261 0.952 0.434 0.0004.4000 0.263 0.978 0.464 0.0004.5000 0.265 1.005 0.491 0.0004.6000 0.267 1.031 0.517 0.0004.7000 0.269 1.058 0.540 0.0004.8000 0.271 1.085 0.563 0.0004.9000 0.273 1.112 0.584 0.0005.0000 0.275 1.140 0.605 0.0005.1000 0.277 1.167 0.624 0.0005.2000 0.279 1.195 0.643 0.0005.3000 0.281 1.223 0.661 0.0005.4000 0.283 1.251 0.679 0.0005.5000 0.285 1.280 0.696 0.0005.6000 0.287 1.309 0.713 0.0005.7000 0.289 1.337 0.729 0.0005.8000 0.291 1.366 0.745 0.0005.9000 0.293 1.396 0.761 0.0006.0000 0.295 1.425 0.776 0.0006.1000 0.297 1.455 1.293 0.0006.2000 0.299 1.485 2.210 0.0006.3000 0.302 1.515 3.321 0.0006.4000 0.304 1.545 4.466 0.0006.5000 0.306 1.576 5.486 0.0006.6000 0.308 1.606 6.262 0.0006.7000 0.310 1.637 6.766 0.0006.8000 0.312 1.668 7.226 0.0006.9000 0.314 1.700 7.623 0.0007.0000 0.316 1.731 7.999 0.0007.1000 0.319 1.763 8.358 0.0007.2000 0.321 1.795 8.700 0.0007.3000 0.323 1.828 9.030 0.0007.4000 0.325 1.860 9.347 0.0007.5000 0.327 1.893 9.653 0.0007.6000 0.330 1.926 9.949 0.0007.7000 0.332 1.959 10.23 0.0007.8000 0.334 1.992 10.51 0.0007.9000 0.336 2.026 10.78 0.0008.0000 0.338 2.059 11.05 0.0008.1000 0.341 2.093 11.31 0.0008.2000 0.343 2.128 11.56 0.0008.3000 0.345 2.162 11.81 0.0008.4000 0.347 2.197 12.05 0.0008.5000 0.350 2.232 12.29 0.0008.6000 0.352 2.267 12.52 0.0008.7000 0.354 2.302 12.75 0.0008.8000 0.357 2.338 12.97 0.0008.9000 0.359 2.373 13.19 0.0009.0000 0.361 2.409 13.41 0.000 9.1000 0.363 2.446 13.62 0.000 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1Total Pervious Area: 10.58Total Impervious Area: 0 Mitigated Landuse Totals for POC #1Total Pervious Area: 1.73Total Impervious Area: 8.85 Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1Return Period Flow(cfs)2 year 0.3110615 year 0.48853310 year 0.5891125 year 0.69566250 year 0.761597100 year 0.817677 Flow Frequency Return Periods for Mitigated. POC #1Return Period Flow(cfs)2 year 0.8386945 year 1.57868710 year 2.29056725 year 3.51950650 year 4.730733100 year 6.250035 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1Year Predeveloped Mitigated1949 0.306 0.6541950 0.381 0.7681951 0.685 1.7421952 0.216 0.4081953 0.175 0.6001954 0.268 0.5941955 0.427 0.8371956 0.340 0.7501957 0.275 0.7621958 0.309 0.754 1959 0.265 0.6811960 0.463 2.2581961 0.261 0.7421962 0.163 0.2761963 0.223 0.6661964 0.294 0.5491965 0.210 0.6831966 0.202 0.5001967 0.423 0.7631968 0.264 0.6641969 0.258 0.6521970 0.213 0.5081971 0.228 0.7501972 0.510 0.9551973 0.232 0.6521974 0.251 0.5871975 0.341 0.7911976 0.246 0.6291977 0.029 0.5491978 0.216 0.5871979 0.131 0.3711980 0.483 1.2721981 0.193 0.5951982 0.372 4.1411983 0.333 0.7351984 0.206 0.5391985 0.122 0.5831986 0.539 2.3591987 0.477 2.4091988 0.188 0.5421989 0.123 0.5391990 0.997 3.8841991 0.600 2.9551992 0.232 0.5741993 0.241 0.5541994 0.081 0.3061995 0.346 0.7771996 0.729 2.6301997 0.609 2.0521998 0.138 0.7051999 0.571 2.0832000 0.241 0.7192001 0.043 0.4372002 0.264 2.1612003 0.336 0.6172004 0.435 4.3762005 0.312 0.7372006 0.368 0.7872007 0.740 3.6872008 0.955 4.5862009 0.469 2.137 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1Rank Predeveloped Mitigated10.9971 4.585820.9548 4.375830.7401 4.1412 4 0.7289 3.884050.6850 3.686660.6093 2.955270.6004 2.630180.5714 2.409390.5392 2.3590100.5101 2.2581110.4834 2.1609120.4769 2.1367130.4688 2.0828140.4632 2.0520150.4353 1.7421160.4275 1.2723170.4230 0.9547180.3810 0.8367190.3716 0.7914200.3683 0.7871210.3458 0.7766220.3408 0.7676230.3402 0.7633240.3362 0.7615250.3331 0.7536260.3123 0.7499270.3093 0.7496280.3056 0.7425290.2938 0.7368300.2745 0.7351310.2681 0.7193320.2653 0.7052330.2638 0.6830340.2635 0.6806350.2613 0.6661360.2581 0.6635370.2515 0.6538380.2464 0.6520390.2412 0.6516400.2405 0.6286410.2317 0.6172420.2316 0.6005430.2276 0.5954440.2232 0.5944450.2162 0.5869460.2159 0.5865470.2129 0.5831480.2104 0.5743490.2056 0.5540500.2023 0.5491510.1932 0.5489520.1882 0.5420530.1746 0.5392540.1626 0.5392550.1378 0.5079560.1306 0.4995570.1228 0.4374580.1220 0.4081590.0810 0.3706600.0431 0.3056610.0293 0.2757 Duration Flows Flow(cfs) Predev Mit Percentage Pass/Fail0.1555 17695 58135 328 Fail0.1617 16303 55953 343 Fail0.1678 15111 53878 356 Fail0.1739 13999 52039 371 Fail0.1800 12814 50007 390 Fail0.1861 11828 48146 407 Fail0.1923 10934 46200 422 Fail0.1984 10158 44275 435 Fail0.2045 9435 42286 448 Fail0.2106 8799 40211 456 Fail0.2167 8220 38222 464 Fail0.2229 7670 36297 473 Fail0.2290 7133 34286 480 Fail0.2351 6594 32040 485 Fail0.2412 6162 30094 488 Fail0.2474 5792 28126 485 Fail0.2535 5456 26180 479 Fail0.2596 5142 24212 470 Fail0.2657 4836 22415 463 Fail0.2718 4562 20679 453 Fail0.2780 4291 19278 449 Fail0.2841 4019 18163 451 Fail0.2902 3794 17526 461 Fail0.2963 3557 16985 477 Fail0.3025 3354 16525 492 Fail0.3086 3151 16129 511 Fail0.3147 2971 15798 531 Fail0.3208 2800 15475 552 Fail0.3269 2620 15212 580 Fail0.3331 2449 14917 609 Fail0.3392 2310 14666 634 Fail0.3453 2165 14444 667 Fail0.3514 2035 14245 700 Fail0.3576 1910 14035 734 Fail0.3637 1798 13815 768 Fail0.3698 1710 13575 793 Fail0.3759 1605 13300 828 Fail0.3820 1483 12951 873 Fail0.3882 1382 12639 914 Fail0.3943 1293 12354 955 Fail0.4004 1225 12065 984 Fail0.4065 1159 11762 1014 Fail0.4126 1102 11469 1040 Fail0.4188 1055 11176 1059 Fail0.4249 1004 10870 1082 Fail0.4310 930 10534 1132 Fail0.4371 884 10241 1158 Fail0.4433 839 9954 1186 Fail0.4494 790 9672 1224 Fail0.4555 745 9388 1260 Fail0.4616 719 9148 1272 Fail0.4677 673 8902 1322 Fail0.4739 634 8618 1359 Fail0.4800 601 8337 1387 Fail 0.4861 566 8027 1418 Fail0.4922 540 7777 1440 Fail0.4984 498 7492 1504 Fail0.5045 475 7223 1520 Fail0.5106 440 6977 1585 Fail0.5167 404 6718 1662 Fail0.5228 374 6459 1727 Fail0.5290 351 6179 1760 Fail0.5351 323 5905 1828 Fail0.5412 296 5696 1924 Fail0.5473 274 5501 2007 Fail0.5535 257 5304 2063 Fail0.5596 236 5127 2172 Fail0.5657 218 4954 2272 Fail0.5718 201 4783 2379 Fail0.5779 183 4611 2519 Fail0.5841 158 4432 2805 Fail0.5902 145 4278 2950 Fail0.5963 130 4134 3180 Fail0.6024 119 4013 3372 Fail0.6085 110 3878 3525 Fail0.6147 97 3762 3878 Fail0.6208 93 3645 3919 Fail0.6269 85 3521 4142 Fail0.6330 76 3375 4440 Fail0.6392 69 3238 4692 Fail0.6453 61 3095 5073 Fail0.6514 55 2954 5370 Fail0.6575 48 2843 5922 Fail0.6636 42 2704 6438 Fail0.6698 38 2590 6815 Fail0.6759 33 2468 7478 Fail0.6820 27 2344 8681 Fail0.6881 22 2220 10090 Fail0.6943 21 2115 10071 Fail0.7004 20 2014 10070 Fail0.7065 19 1910 10052 Fail0.7126 17 1829 10758 Fail0.7187 14 1742 12442 Fail0.7249 12 1661 13841 Fail0.7310 9 1588 17644 Fail0.7371 4 1502 37550 Fail0.7432 3 1435 47833 Fail0.7494 3 1372 45733 Fail0.7555 3 1312 43733 Fail0.7616 3 1254 41800 Fail The development has an increase in flow durationsfrom 1/2 Predeveloped 2 year flow to the 2 year flowor more than a 10% increase from the 2 year to the 50year flow.The development has an increase in flow durations formore than 50% of the flows for the range of theduration analysis. Appendix Predeveloped Schematic Mitigated Schematic General Model Information Project Name: Forest and Meadow Site Name: Site Address: City: Report Date: Gage:Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 1.000 Version Date:2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Land Use Forest and Meadow Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 7.56 C, Pasture, Flat 6.18 Pervious Total 13.74 Impervious Land Use acre Impervious Total 0 Basin Total 13.74 Element Flows To:Surface Interflow Groundwater Analysis Results POC 1 Landuse Totals for POC #1Total Pervious Area: 13.74Total Impervious Area: 0 Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Land Use. POC #1Return Period Flow(cfs)2 year 0.4328265 year 0.71822910 year 0.91987925 year 1.18247850 year 1.381222100 year 1.581181 General Model Information Project Name:24 Acre Basin Site Name: Site Address: City: Report Date: Gage:Seatac Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 1.000 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Land Use 24 Acre Basin Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 24.21 Pervious Total 24.21 Impervious Land Use acre Impervious Total 0 Basin Total 24.21 Element Flows To:Surface Interflow Groundwater Analysis Results POC 1 Landuse Totals for POC #1Total Pervious Area: 24.21Total Impervious Area: 0 Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Land Use. POC #1Return Period Flow(cfs)2 year 0.7117945 year 1.11790110 year 1.34804825 year 1.59186950 year 1.742746100 year 1.871074 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2019; All Rights Reserved. Clear Creek Solutions, Inc.6200 Capitol Blvd. Ste FOlympia, WA. 98501Toll Free 1(866)943-0304Local (360)943-0304 www.clearcreeksolutions.com Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.013 Channel Slope 0.03200 ft/ft Normal Depth 1.00 ft Diameter 1.00 ft Results Discharge 6.37 ft³/s Flow Area 0.79 ft² Wetted Perimeter 3.14 ft Hydraulic Radius 0.25 ft Top Width 0.00 ft Critical Depth 0.96 ft Percent Full 100.0 % Critical Slope 0.02798 ft/ft Velocity 8.11 ft/s Velocity Head 1.02 ft Specific Energy 2.02 ft Froude Number 0.00 Maximum Discharge 6.86 ft³/s Discharge Full 6.37 ft³/s Slope Full 0.03200 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % Normal Depth Over Rise 100.00 % Downstream Velocity Infinity ft/s 12" Culvert #1 9/15/2017 11:31:13 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page GVF Output Data Upstream Velocity Infinity ft/s Normal Depth 1.00 ft Critical Depth 0.96 ft Channel Slope 0.03200 ft/ft Critical Slope 0.02798 ft/ft 12" Culvert #1 9/15/2017 11:31:13 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of2Page