705 80TH ST SW 2018-01-02 MF Import

OL PUBLIC WORKS REVIEW MEMORANDUM TO: Kirk Brooks FROM: Jane Zimmerman DATE: February 18, 1999 SUBJECT: Drainage Calci lations/Requirements, Everett Post Office, 80" Street I don't agree with the input parameters for the calculation of time of concentration and existing flows, p: rticularly the curve number for the pervious surface, the slope, and roughness coefficient for travel time calculation. The majority of the site is 2% slope or less, the site is roughly graded (it isn't uniform and it has surface pockets and ridges in non -compacted soils) and the site vegetation is brushy except for a portion of the site which has been cleared and graveled for truck parking. The truck parking area is mostly level, the underlying soils do not appear to have been compacted and are rutted, and the gravel is relatively deep and loose. The volume of dead storage in each cell must be calculated and stated. The calculations should show, at least, the bottom area and elevation of each cell. the dead storage elevation, and the surface area at the dead storage elevation for each cell. A map, which shows the subbasin areas used in the computer calculations must be provided - the map on page 11 does not appear to be consistent with the subbasin used in the computer calculation. City standards requite the application of a correction factor to the calculated detention volumes (please see section 1-3.2.2.2 of the City's stormwater manual).