Town of Prescott Valley

Uniform Drainage Policies and Standards Manual

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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, Pima County

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Jurisdiction level

City

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State

Arizona

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Last revised date

2025-02-10

“WEST Consultants, Inc. 10 10-Feb-25”
page 21

Relationship to state manual

independent

“The hydrology for the Town is based on the methods in the Drainage Design Manual for Yavapai County (Yavapai County, 2015).”
Section 6.3, page 69

Design Criteria

Design storm return periods (years)

2-year, 10-year, 25-year, 50-year, 100-year

“Post-development peak discharges may not exceed pre-development peak discharges for the 2-, 10-, and 100-year storm events for the design of detention basins.”
Standard 6.9.3, page 164

Water quality volume method

First flush: retain or treat the first 0.5 inches of direct runoff from a storm event; green infrastructure/LID in Appendix B may meet requirements if equivalent volume and performance are achieved.

“The minimum level of control for new development at which stormwater pollution prevention practices must be put in place is called the “first flush.” This consists of retaining or treating the first 0.5 inches of direct runoff from a storm event.”
Policy 3.5.6, page 29

Peak flow calculation method(s)

Hierarchy: Town Master Drainage Plan, ADMS/ADMPs, or approved flood insurance studies; then adjacent property drainage plans; otherwise procedures in this Manual (Section 6.3), Rational Method for peak discharges (areas ≤160 acres, Tc ≤60 min), Unit hydrograph method via HEC-HMS with 24-hour frequency storm (PFDS/Table 6-3); Green and Ampt rainfall losses for HMS

“The following is the preferred order of hierarchy for obtaining peak discharges and runoff volumes”
Policy 3.4.1, page 28

Hydrologic/hydraulic software

HEC-HMS (most recent version), HEC-RAS (most recent version), HY-8 (most recent version), EPA-SWMM (most recent version), FLO-2D (most recent version, or as approved by FEMA for an FIS study), XP Storm (most recent version, or as approved by FEMA for an FIS study)

“1D Hydrology – HEC-HMS (most recent version) 1D Hydraulics – HEC-RAS (most recent version), HY-8 (most recent version), and EPA-SWMM (most recent version)”
Section 6.12, page 175

Approved BMP categories

Best Management Practices (BMP), green infrastructure, low impact development, stormwater harvesting basins, sediment traps, curb openings, stormwater pollution prevention practices meeting first flush

“Stormwater Pollution Prevention is to be addressed through the use of Best Management Practices (BMP) to the maximum extent practicable”
Policy 3.5.5, page 29