Pima County

Design Standards for Stormwater Detention and Retention

CountyArizonahighNoCitations verified

Other manuals in Arizona: Arizona Department of Transportation (ADOT), City of Chandler, City of Flagstaff, City of Mesa, City of Phoenix, City of Scottsdale, City of Tucson, City of Yuma, Maricopa County / Flood Control District of Maricopa County, Town of Prescott Valley

Document Metadata

Jurisdiction level

County

“runoff detention and retention systems are required for development in Pima County... management regulations throughout the jurisdictions of Pima County”
Section 1.1

State

Arizona

“Design and Floodplain Management in Tucson, Arizona; or c. Other methods accepted by the Floodplain Administrator. 2. When flow crosses a sidewalk or other paved pedestrian pathway, a scupper or other conveyance to prohibit overtopping of the 10-year design discharge shall be”
pp. 44–45

Version / edition

First Edition June 2014; Chapter 6 revised February 2015

“First Edition June 2014... Chapter 6 Revised to Include Benefits of Multiple-Use Basins February 2015”
Revisions

Adoption / effective date

2014-06

“First Edition June 2014”
Revisions / Cover

Last revised date

2015-02

“Chapter 6 Revised to Include Benefits of Multiple-Use Basins February 2015”
Revisions

Relationship to state manual

independent

“Supplement to Title 16, Chapter 16.48, Runoff Detention Systems Floodplain and Erosion Hazard Management Ordinance”
Cover

Design Criteria

Design storm return periods (years)

2-year, 10-year, 100-year

“New development located within a Balanced Basin must provide sufficient detention to reduce the post-developed 2-, 10- and 100-year peak discharge rates to the pre-developed rates.”
Section 1.2

Water quality volume method

First-flush retention: capture and retain runoff from 0.5 inch of rainfall on newly disturbed or impervious areas (85th percentile storm). Required volumes by land type from SCS Curve Number method (e.g., 1440 ft³/ac impervious on lower-permeability areas; 1815 ft³/ac on mapped riparian/higher-permeability areas).

“First-flush retention is defined as the capturing and retaining of the stormwater runoff volume from 0.5 inch of rainfall on all newly disturbed or impervious areas for new development or redevelopment”
Section 1.5, Page 5

Peak flow calculation method(s)

PC-Hydro, Pima County Technical Policy TECH-015 (Acceptable Methods for Determining Peak Discharges), Pima County Technical Policy TECH-018 (Acceptable Model Parameterization), City of Tucson Standards Manual for Drainage Design and Floodplain Management (where applicable), HEC-HMS (basin routing)

“The pre-developed conditions peak discharge rates for each return period shall be established using the modeling methods described in the District's Technical Policy, TECH-015, Acceptable Methods for Determining Peak Discharges, and Technical Policy, TECH-018”
Section 3.2.1, Page 21

Hydrologic/hydraulic software

PC-Hydro, PC-LID spreadsheet, HEC-HMS (Version 3.3 or higher acceptable for basin routing)

“Volumes of each basin were calculated using the PC-LID spreadsheet.”
Section 2.2 Example, Page 12

Approved BMP categories

Detention Basins, Stormwater Harvesting Basins, Roadside Stormwater Harvesting Basins, Bioretention Basins, Retention within Detention Basins, Pervious Pavements (porous gravel, concrete grid, PICP, pervious concrete), Dry Wells, Low Impact Development (LID) Practices

“Design Standards for Stormwater Detention and Retention for Pima County 53 6. To allow for inspection and maintenance, LID practices shall be legally and physically accessible. 7. Upon completion of construction of all LID practices, an As-built Certification s”
p. 65