• It’s great to see new tools being developed to bring numerics to water monitoring.  The more data we have, the more we can strategize for efficiency and best practices.  Congratulations to the SFPUC for releasing this tool for combined sewer sizing to assist in determining the best situational approach to stormwater management.

    The SFPUC Urban Watershed Management Program is pleased to release the Combined Sewer System BMP Sizing Calculator for public use. This Calculator was developed to help designers meet the quantity control requirements outlined in the Stormwater Design Guidelines for sites discharging to the combined sewer system. The Calculator uses the Santa Barbara Urban Hydrograph Method to estimate the runoff peak flow rate and volume.

    Version 1.0 [beta] can now be downloaded from the SFPUC website at http://sfwater.org/sdg.

    This fully operational version has been released to assist professional design teams in the development of a Stormwater Control Plan that meets the requirements of the Stormwater Design Guidelines. Please make note of the following: 

    Please read the complete instructions prior to initial use.

    • The calculator was designed to allow for an iterative design process to determine the most feasible stormwater management approach for your site.
    • Data input into the calculator is generally straight forward. However, care should be taken when entering in the contributing areas for a selected BMP to ensure areas draining to BMPs are properly considered.
    • A rainwater harvesting calculator is included to estimate cistern size. However, the cistern design configuration for each project will likely be different. Therefore, your project may require additional design and support calculations.
    • This calculator is one of the SFPUC’s accepted hydrologic calculation methods. A list of other acceptable calculation methods is available for download from the SFPUC website at http://sfwater.org/sdg.
    • This calculator is designed for sites 2 acres in size or less. If your site is larger than 2 acres, please use one of the other SFPUC accepted hydrologic calculation methods.
    • The calculator was not designed to analyze a “treatment train” or complex sites. If your site includes “treatment trains” or is complex, please use one of the other SFPUC accepted hydrologic calculation methods.

    Your feedback is welcome and should be sent to stormwaterreview@sfwater.orgby June 1st, 2011. A comment form is downloadable from the SFPUC website at http://sfwater.org/sdg.
    Please check our website periodically for updates to the calculator and additional information on the Stormwater Design Guidelines.

    With Best Regards,

    The Urban Watershed Management Team