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. t 2. DRAINAGE INFORMATION SUMMARY FORM Project: Thompson Short Plat PFN: SP11-001 Engineer: Omega Engineeing, Inc. 2717 Rockefeller Ave Total site area: 1.07 acres Everett, WA 98201 Offsite area: 0.00 acres Attention: Joseph Smeby, P.E. Disturbed area: 0.73 acres Applicant: Omega Engineeing, Inc. 2717 Rockefeller Ave Everett, WA 98201 Attention: Joseph Smeby, P.E. Number of lots/Units: 3 Drainage Basin Information Basin A Basin B Basin C Private.Road Roof 1 & 2 On-site Developed Area 0.12 acres 0.10 acres 0.51 acres Types of storage proposed Perv. Pave. Inf. Trench N/A Approximate total storage volume N/A 462 cf N/A Soil Types Type B Soils Type B Soils Type B Soils Basin Data Post-developed run-off rates: 2-year 0.003 cfs 0.003 cfs 0.04 cfs 10-year 0.008 cfs 0.008 cfs 0.08 cfs 100-year 0.017 cfs 0.016 cfs 0.14 cfs Post-developed run-off rates: 2-year 0.00 cfs 0.00 cfs 0.03 cfs 10-year 0.00 cfs 0.00 cfs 0.07 cfs 100-year 0.00 cfs 0.00 cfs 0.12 cfs Description of drainage plan: This project consists of one on-site basin broken into three basins for the purpose of analysis. Basin A includes the pervious pavement for the private road and the majority of the Lot 3 driveway. This basin is fully infiltrated and is therefore considered non-effective impervious surface. Basin B includes the roofs on lots 1 &2. This basin infiltrates 100-percent of the runoff from both roofs in a common infiltration trench located on the property line between both structures. This area is also fully infiltrated and is considered non-effective impervious surfaces. Basin C includes the remainder of the site on lots 1-3. The runoff from the driveways on lots 1 &2 along with 18-feet of driveway on lot 3 and all of the roof area on lot 3 and the site landscaping will be dispersed using transition zones or level spreader. Therefore, the impervious areas for Basin C are considered effective impervious surfaces and total 4,625 sf. Runoff from the dispersed surfaces flows west over existing soils and vegetation prior to leaving the site. Proposed design standards and criteria: See Figure 3—Developed Drainage Basin Map. The design for this project will meet or exceed the requirements of the City of Everett 2010DM. This requires the calculation of the site runoff characteristics along with the sizing of all drainage facilities to be done using a continuous runoff model and for this project the WWHM3 was used. Thompson Short Plat 11-012 May 2011 Page 4