HomeMy WebLinkAboutARCH-0161-2019 Prelim Hydrology Summary1413 Monterey St.
San Luis Obispo, CA 93401
www.ashleyvance.com
SAN LUIS OBISPO • SANTA BARBARA • LOS ANGELES • OAKLAND • BEND
Memorandum Page 1 of 1
Date: 4/27/2020
To: Hal Hannula
City of San Luis Obispo
Public Works Department
Project: French Hospital
Job #: 181067 and 181474
Subject: Preliminary Stormwater Control Plan Hydrology Analysis
Comments:
This Project is part of the build out of French Hospital and will include the addition of a new parking deck and a new
medical facility building, and will include the regrading of parking lots.
The new improvements will drain to an existing onsite stormwater basin that was designed to attenuate the peak
runoff rate for the full build out of the hospital.
This site will result in over 22,000 square feet of impervious surface and as a result is subject to performance
requirements 1 through 4, however this site is located in WMZ 3 and is not required to retain the 95 th event.
Performance requirement 1 will be met through the use of pervious pavers to reduce impervious surface onsite.
Performance requirement 2 requires that the site treats the runoff from the 85th percentile storm. This will be met
through the use of pervious pavers as well as treatment planters. Downspouts will outlet to raised planters. These
planters will consist of 6” of ponding depth, over 2’ of planting soil over 1’ of gravel. These planters will have an
underdrain that will remove the treated runoff and direct it to the onsite basin.
Parking stalls will be constructed of pervious pavers. These pavers will have a gravel section beneath them that will
store the runoff in the void space, allowing the runoff directed to them from the drive aisles to percolate back into the
native ground, these areas will not have an underdrain and the gravel will be sized to store the 85th percentile volume.
This project is exempt from Performance requirement 3 due to its location in WMZ 3.
Performance requirement 4 is already addressed through the use of the existing stormwater basin.
As this project moves forward, exhibits showing each DMA, and the BMP they drain to will be shown. Calculations
sizing each BMP will be included.
Regards,
Kathleen Allwine, PE.
(805) 545-0010 x.165