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Stormwater Detention-Retention

The District used to regulate stormwater detention/retention through the Stormwater Detention/Retention Manual developed in coordination with the City of Tucson. The District has recently revised this manual, as discussed below. The revision was adopted by the Board of Supervisors on December 15, 2015.

Stormwater Detention/Retention Manual Revision

The Pima County Regional Flood Control District has prepared the manual: Design Standards for Stormwater Detention and Retention (Manual) to supersede the Pima County/City of Tucson Stormwater Detention/Retention Manual. The Manual contains some substantive changes, including replacement of the threshold retention requirement with a first flush retention requirement (retaining the first 0.5 inches of rainfall), introduction of the use of integrated site planning and other Low Impact Development practices, description of acceptable methodology for hydrologic and hydraulic analysis, more specific design standards, and a description of  inspection and maintenance responsibilities for detention and retention facilities.

The June 2014 version of the Manual, including appendices, was adopted by the Flood Control District Advisory Committee on June 17, 2014.  Prior to adoption by the Committee, the District performed a literature review, prepared an initial draft, and completed a significant stakeholder process, where a substantive discussion occurred with the development community and engineering professionals.  The Manual has been written to be applicable to both incorporated and unincorporated jurisdictions of Pima County.

The following outlines some of the chronology of the preparation of the Standards:

  • Literature review completed, and first draft provided for stakeholder review is dated 9/19/2012.
  • Substantive comments by the Flood Control District Advisory Committee were documented in a spreadsheet, FCDAC Comments and Responses, February 2013.
  • Second draft of Design Standards for Stormwater Detention for Pima County-FCDAC Draft, in response to FCDAC comments provided March 2013.
  • Substantive stakeholder comments on Chapter 4 received in April , 2013.
  • All comments on Chapter 4 of the Manual, detention basin construction standard, addressed on June 2013. Immediate use of this Chapter was approved via Technical Policy by the Chief Engineer, effective August 1, 2013. Substantive comments on water harvesting and other LID practices, inspection and maintenance responsibilities and submittal content were completed by stakeholders and the FCDAC Technical Committee in December, 2014.
  • Increased outreach to water resources groups, transportation and zoning staff, and sustainability partnerships culminated in a third (May 2014) draft responding to stakeholder, FCDAC, and outreach comments.
  • Final draft of Manual, June 2014, with minor editing and format changes, approved by FCDAC on June 17, 2014. 
  • Chapter 6 revised to include the benefits of multi-use basins in February 2015.
  • Final revisions to applicability completed in November, 2015. This version submitted to Board for approval.

The version adopted by the Advisory Committee is available for viewing below, along with previous drafts.