9909 2ND AVE W 2018-08-01 - Laserfiche WebLink

DEVELOPED CONDITIONS The City Lights Project proposes to build 27 single-family homes on the 3.73-acre site. However,only 2.23 acres of the lot will be developed due to the wetland located on the east side of the property. Approximately 600-feet of paved private roadway, 25-feet wide including curb, gutter and sidewalk will be constructed to provide access to the homes. The proposed private roadway will take access from 1st Ave SW. Two detention vaults are proposed to mitigate the increased storm water runoff from the developed impervious surfaces. Storm water runoff will be released from the detention vaults at pre-developed rates of 50%of the 2-year storm and 100%of the 10 and 100-year storm events. The vaults are designed and sized using the following parameters: • The developed contributing basin is the site area designated for development plus the frontage improvements (see basin map in appendix). All areas not identified as impervious are assumed to be in lawns and landscaping. • Detention calculations are based on an assumption of pre-development 2"d growth forested conditions over the entire site. • The detention vault is sized per D.O.E.'s 2001 guidelines to provide storage for runoff from a 100-year design storm. The outlet structure will release stormwater at rates not exceeding the pre-development peak runoff rates of one-half the 2-year,the 10-year and 100-year,24-hour design storms events. The"Stormshed"program Santa Barbara Unit Hydrograph(SBUH)method and Type 1A rainfall distribution was used to calculate runoff amounts and model the detention pond. The first proposed detention vault(Vault 1) will be located near the north east corner of the area to be developed,beneath an asphalt driveway. It will have a control structure designed to release peak runoff at pre-developed runoff rates of 50% of the 2-year and 100%of the 10-year and 100- year storm events. The control structure will be located outside the vault and will be accessible from the proposed private driveway accessing the site. Vault 1 is composed of two chambers. Stormwater entering the vault goes into the first chamber sized to provide sediment treatment for the stormwater. From the first chamber the water exits the vault and is filtered by a single Contech Catchbasin Stormfilter. Stormwater then enters the second vault chamber from the filter and is detained until it can be released at pre-developed rates. The storm filter will provide water treatment for Basin 1 only. The table below summarizes the design for Vault 1. 5