University of California, San Diego
IN-36: Stormwater Modeling

The campus retains runoff on-site using LID practices and green infrastructure to the 85th percentile. We use the County Hydrology Manual and the California Phase II LID sizing tool to calculate the sizing that will be needed for either volume-based treatment BMPs or flow-based treatment BMPs. Calculations must be done by a registered Civil Engineer and must meet the criteria described below: 

1. Storm Water BMP Requirements 

• All projects that create or replace more than 2,500 SF are required to complete the flow chart and “Post-Construction Stormwater Management Checklist” in the campus storm water title sheets and obtain approval from UCSD Civil Engineers as well as Environment Health & Safety staff during the planning phase, Design Development phase, Construction Document phase.  

2. Quantify the runoff reduction and the “site design” LID BMPs using the California Phase II LIDS sizing tool (https://www.owp.csus.edu/LIDTool/) and show that post-construction water balance is achieved. If balancing is not possible, see 3) below. 

3) “Treatment Control” BMPs are only required if the Site Design BMPs above cannot fully meet Permit requirements. 

• Quantify and include any attachments as needed. 

• Design shall be based on the Flow-Based or Volume-Based criteria specified in Section F.5.g.2.b (Numeric Sizing Criteria) of the Phase II Small MS4 Permit. 

• Bioretention facilities are preferred, however alternative treatment BMPs can be used if proper documentation and supporting calculations prepared by a Registered Civil Engineer are provided. 

• An Operations and Maintenance Plan (O&M) for each Post-Construction BMP must be included. 

• Sources for additional guidance on the design of post-construction BMP and LID measures are listed below: 

County of San Diego Best Management Practices Design Manual: 

https://www.sandiegocounty.gov/content/sdc/dpw/watersheds/DevelopmentandConstruction/BMP_Design_Manual.html 

County of San Diego LID Handbook: 

http://www.sandiegocounty.gov/content/dam/sdc/dpw/WATERSHED_PROTECTION_PROGRAM/susmppdf/lid_handbook_2014sm.pdf 
 

California Stormwater Quality Association (CASQA) Southern California LID Manual: https://www.casqa.org/resources/california-lid-gi/socal-lid-manual 

 
Design of all post-construction BMP shall meet stormwater permit requirements (Section F.5.g of the Phase II Permit and the Construction General Permit as applicable); be consistent with UC San Diego’s current Stormwater Management Plan (SWMP) at http://www-ehs.ucsd.edu, and conform to the stormwater treatment standards of the time, as listed in the County of San Diego BMP Design Manual.