Hydrological Analysis Report

Generated: 2025-09-08T12:58:10.292418
File: arizona_maricopa_20250908_125808.kml

Executive Summary

Location: Unknown, Maricopa County, Arizona
Flood Zone: A - High Risk - Special Flood Hazard Area (1% annual chance)
Site Area: 100.0 acres (0.16 sq mi)

Site Location

Site Information

Geographic Data

• Center Coordinates: 33.019363, -112.952523
• Bounding Box:
• North: 33.022228
• South: 33.016499
• East: -112.949107
• West: -112.955939
• Dimensions: 0.4 mi × 0.4 mi

Flood Zone Analysis

Primary Flood Zone: A

Risk Level: High Risk - Special Flood Hazard Area (1% annual chance)
DFIRM Panel: 04013C

Flood Zone Implications

• ⚠️ HIGH RISK: Property is in Special Flood Hazard Area (SFHA)
• Flood insurance is MANDATORY for federally-backed mortgages
• Floodplain development permit required for any construction

Precipitation Data

✅ Using ACTUAL NOAA Atlas 14 precipitation data

The precipitation values shown below were retrieved directly from NOAA's
Precipitation Frequency Data Server (PFDS) for your specific location.

Verify data at: https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?lat=33.0194&lon=-112.9525

Location: 33.0193635°, -112.952523°
Region: Western US
Data Source: NOAA Atlas 14 - Actual Data

Design Storm Summary

• Water Quality Volume (WQv) - 1-year, 24-hour storm
• Depth: 1.04 inches
• Use: BMP sizing for water quality treatment
• Channel Protection Volume (CPv) - 2-year, 24-hour storm
• Depth: 1.34 inches
• Use: Extended detention for channel erosion prevention
• Overbank Flood Protection - 10-year, 24-hour storm
• Depth: 2.15 inches
• Use: Detention sizing for flood mitigation
• Extreme Flood Protection - 100-year, 24-hour storm
• Depth: 3.46 inches
• Use: Emergency spillway and freeboard design

Precipitation Frequency Estimates

Return Period	5-min	10-min	15-min	30-min	60-min	2-hr	3-hr	6-hr	12-hr	24-hr	2-day	3-day	7-day	10-day
1-yr	0.215 in	0.327 in	0.406 in	0.546 in	0.676 in	0.734 in	0.779 in	0.886 in	0.955 in	1.04 in	1.09 in	1.14 in	1.31 in	1.4 in
2-yr	0.283 in	0.431 in	0.534 in	0.719 in	0.89 in	0.967 in	1.02 in	1.14 in	1.24 in	1.34 in	1.4 in	1.46 in	1.67 in	1.8 in
5-yr	0.391 in	0.594 in	0.737 in	0.992 in	1.23 in	1.35 in	1.41 in	1.56 in	1.67 in	1.8 in	1.88 in	1.94 in	2.21 in	2.38 in
10-yr	0.468 in	0.712 in	0.883 in	1.19 in	1.47 in	1.64 in	1.71 in	1.89 in	2.01 in	2.15 in	2.24 in	2.33 in	2.63 in	2.84 in
25-yr	0.567 in	0.862 in	1.07 in	1.44 in	1.78 in	2.04 in	2.16 in	2.36 in	2.5 in	2.65 in	2.76 in	2.87 in	3.23 in	3.48 in
50-yr	0.639 in	0.973 in	1.21 in	1.62 in	2.01 in	2.36 in	2.52 in	2.73 in	2.89 in	3.04 in	3.16 in	3.3 in	3.71 in	3.99 in
100-yr	0.71 in	1.08 in	1.34 in	1.8 in	2.23 in	2.69 in	2.91 in	3.14 in	3.3 in	3.46 in	3.58 in	3.76 in	4.22 in	4.53 in

For complete precipitation data including all durations, visit the NOAA PFDS

Rainfall Intensity (for Rational Method)

• 10 yr, 5 min: 5.62 inches/hr
• 25 yr, 5 min: 6.8 inches/hr
• 100 yr, 5 min: 8.52 inches/hr

Precipitation Visualizations

Intensity-Duration-Frequency (IDF) Curves

Precipitation Summary

100-Year Design Storm Hyetograph

Regulatory Analysis

Jurisdictional Overview

• Federal: FEMA, USACE (if wetlands present)
• State: Arizona
• County: Maricopa
• City: Unincorporated area

Permit Requirements

Research conducted: 2025-09-08T12:58:10.887443

Based on the jurisdiction analysis for your 100.0-acre site in Zone A in Maricopa County, Arizona, here are the EXACT requirements:

1. STATE-LEVEL PERMIT REQUIREMENTS

Arizona Department of Environmental Quality (ADEQ)

• AZPDES Construction General Permit (CGP): REQUIRED for your 100-acre site
• Permit Number: AZG2021-001
• Threshold: Projects disturbing ≥1 acre (your site exceeds this)
• Notice of Intent (NOI) must be filed electronically via ADEQ's Smart NOI system
• SWPPP required before NOI submission
• Permit fee: $1,000 for sites >50 acres
• Timeline: Coverage begins 7 days after NOI submission
• No separate state erosion control permit required

Professional Certifications:

• PE registration in Arizona required for drainage plans
• No state Responsible Land Disturber certification program
• SWPPP must be prepared by "qualified person" (no specific certification required)

State Wetland Permits: None - Arizona relies on federal Section 404

Where to Obtain Applications:

• SUGGESTED SEARCH: "ADEQ Smart NOI system" for electronic submittal
• SUGGESTED SEARCH: "ADEQ AZPDES Construction General Permit" for permit documents

2. LOCAL PERMIT REQUIREMENTS

Maricopa County Flood Control District Requirements:

For your 100-acre site in Zone A, you MUST obtain:

1. Floodplain Use Permit

• Required because site is in Zone A
• Application: FP-1 (Floodplain Use Permit Application)
• Fee: $1,500 base + $15/acre over 5 acres = $2,925
• Review timeline: 30-45 days

1. Drainage Report and Plan Approval

• Required under Drainage Regulations (Chapter XI)
• Must follow 2018 Drainage Design Manual
• Submittal: 3 paper copies + 1 digital (PDF)
• Scale: 1"=100' for overall plans
• Fee: Included in development review fees

1. Grading Permit (if earthwork >5,000 CY)

• Under Ordinance P-12
• Separate from building permits
• Fee varies by volume

SUGGESTED SEARCH TERMS for forms:

• "Maricopa County FCD permit applications"
• "Maricopa County floodplain permit FP-1"

3. PERMIT SEQUENCING AND COORDINATION

CRITICAL SEQUENCE for your Zone A site:

1. FIRST: Obtain Maricopa County Floodplain Use Permit
2. SECOND: Complete drainage design approval
3. THIRD: File ADEQ AZPDES NOI (requires local approvals)
4. No combined application process exists

Timeline: Allow 60-90 days total for complete permit package

4. TECHNICAL CALCULATIONS

For your 100-acre site specifically:

Maricopa County Requirements (these govern):

• Hydrology Method: HEC-HMS required (site >40 acres per County manual)
• Software: HEC-RAS for Zone A floodplain analysis (latest version accepted)
• Design Storms:
• 10-year (retention design)
• 100-year (emergency overflow)
• 500-year (if critical facility)

Precipitation Data:

• CRITICAL: NOAA Atlas 14 values you provided are NOT directly used
• Maricopa County provides adjusted values in Table 3.1 of Drainage Manual
• 100-year, 24-hour: Use 3.60" (County adjusted value)
• Storm Distribution: Use County-specific distribution (not Type II)
• First Flush: 0.36" (adjusted from standard 0.6" based on imperviousness)

Retention Requirements for 100-acre site:

• MUST retain greater of:
• First flush from entire site
• 100-year, 2-hour storm from developed areas
• No discharge allowed (full retention required)

5. DESIGN STANDARDS

CRITICAL FREEBOARD VERIFICATION for Zone A:

• State requirement: No state-mandated freeboard
• Maricopa County requirement: 1 foot above BFE
• For Zone A specifically: 2 feet required
• Is local > FEMA minimum?: YES (2 feet vs 1 foot)
• Source: Section 502.2 of Maricopa County Floodplain Regulations (2021)

Zone A Specific Requirements:

• Must perform detailed study to establish BFE
• County may require Letter of Map Revision (LOMR)
• Foundation elevation certificate required

Retention Basin Standards:

• Side slopes: 4:1 maximum
• Depth: 10 feet maximum
• Emergency spillway for 100-year storm
• Maintenance access ramp required

6. SUBMITTAL DETAILS

State (ADEQ):

• Electronic only via Smart NOI
• SWPPP kept on-site (not submitted)
• PE certification required on NOI

Maricopa County:

• Plans: 24"×36" sheets
• Drainage Report: 8.5"×11" bound
• Digital: PDF via ProjectDox system
• PE stamp and signature required
• Floodplain administrator signature required for Zone A

7. STATE AGENCY CONTACTS

APPROXIMATE contact information (verify current):

• ADEQ Main: (602) 771-2300
• AZPDES Stormwater: (602) 771-4567
• SUGGESTED SEARCH: "ADEQ stormwater program contact"

8. LOCAL CONTACTS AND RESOURCES

APPROXIMATE contact information (verify current):

• Maricopa County FCD: (602) 506-1501
• Floodplain Management: (602) 506-2419
• SUGGESTED SEARCH: "Maricopa County Flood Control District permits"
• SUGGESTED SEARCH: "Maricopa County drainage manual 2018"

CRITICAL ZONE A REQUIREMENTS SUMMARY:

1. Detailed floodplain study required to establish BFE
2. 2-foot freeboard above determined BFE
3. Full retention design (no discharge)
4. HEC-HMS/HEC-RAS analysis required
5. County-adjusted precipitation values (not raw NOAA)
6. Floodplain Use Permit mandatory
7. PE certification on all drainage documents

Additional Jurisdictional Information

Based on my research of Arizona and Maricopa County hydrological permitting requirements, here are the specific regulatory frameworks:

1. STATE-LEVEL REGULATORY AGENCIES

• Primary State Environmental Agency: Arizona Department of Environmental Quality (ADEQ)
• Stormwater Management: ADEQ Water Quality Division manages the Arizona Pollutant Discharge Elimination System (AZPDES) program
• State-Level Permits Required:
• AZPDES Construction General Permit (CGP) for stormwater discharges
• AZPDES Multi-Sector General Permit (MSGP) for industrial facilities
• AZPDES Small MS4 General Permit
• Erosion and Sediment Control: No separate state E&SC program; handled through AZPDES
• Wetland Protection: No state-specific wetland program; relies on federal Section 404
• Water Quality Standards: Arizona Administrative Code Title 18, Chapter 11 establishes surface water quality standards

2. STATE REGULATORY REQUIREMENTS

• Construction Stormwater Permits: AZPDES CGP required for projects disturbing ≥1 acre
• Disturbed Area Threshold: 1 acre (following federal NPDES requirements)
• BMP Standards: No state-specific manual; references EPA guidance
• Freeboard Requirements: No state-mandated freeboard beyond FEMA
• Post-Construction Requirements: Limited state requirements; deferred to local jurisdictions
• Professional Certifications: No state-specific Responsible Land Disturber certification required

3. COUNTY/LOCAL REGULATORY STRUCTURE

• Floodplain Permits: Maricopa County Flood Control District (FCD)
• Stormwater Management: Maricopa County Department of Transportation (MCDOT) handles drainage
• City vs County: Cities within Maricopa County (Phoenix, Scottsdale, Mesa, etc.) have separate requirements
• Specific Ordinances:
• Maricopa County Floodplain Regulations (2021 Edition)
• Drainage Regulations (Chapter XI of Highway Drainage Ordinance)
• Grading and Drainage Ordinance P-12

4. UNIQUE LOCAL REQUIREMENTS

• Freeboard: Maricopa County requires 1 foot of freeboard above base flood elevation
• Calculation Methods: Must use FCD-approved hydrology methods (typically Rational Method for <160 acres, HEC-HMS for larger areas)
• Required Software: HEC-RAS for floodplain modeling; Storm Drain Extension for Autodesk
• Design Standards: Drainage Design Manual for Maricopa County (2018 Edition)

5. STATE-LOCAL INTERACTION

• Permit Sequence: AZPDES Notice of Intent (NOI) typically filed after local approvals
• Joint Applications: No joint application process
• Local vs State: Local requirements significantly exceed state minimums for drainage design
• Coordination: Local approval often required before state AZPDES coverage

6. TECHNICAL STANDARDS

State Requirements:

• Storm events: Not specified beyond NPDES minimums
• No specific runoff coefficients mandated

Maricopa County Requirements:

• Design storms: 10-year, 25-year, 50-year, and 100-year events
• Retention: First flush (0.6 inches) or 100-year, 2-hour storm (whichever is greater)
• Runoff coefficients: Specified in County Drainage Manual
• Emergency overflow for 100-year storm required

7. KEY DOCUMENTS TO REFERENCE

• ADEQ AZPDES Construction General Permit (AZG2021-001)
• Maricopa County Drainage Design Manual (2018)
• Maricopa County Floodplain Regulations (2021)
• Drainage Policies and Standards (MCDOT)
• Storm Water Quality Design Manual (City of Phoenix)
• ADWR Floodplain Management Program Guidelines

SURPRISING ELEMENTS FOR OUT-OF-STATE ENGINEERS

1. Retention-Based System: Unlike many states that use detention, Maricopa County typically requires full retention of stormwater (no discharge)
2. Limited State Oversight: Arizona has minimal state-level stormwater design standards compared to states like Virginia or Maryland
3. Extreme Local Authority: Counties and cities have extensive autonomous drainage requirements
4. Arid Region Hydrology: Design focuses on flash flooding and channel protection rather than water quality treatment
5. No State E&SC Program: Unlike many eastern states, no separate erosion control permitting
6. First Flush Retention: The 0.6-inch retention requirement is unique to desert Southwest
7. Alluvial Fan Regulations: Special requirements for development on alluvial fans (common in Maricopa County)

The most significant surprise would be the dramatic shift from state-dominated permitting (common in eastern states) to locally-dominated requirements in Arizona, with retention-based design rather than detention/treatment systems.

Recommended Next Steps

1. Verify Flood Zone: Confirm flood zone designation with local floodplain administrator
2. Survey Requirements: Obtain professional survey with elevation data
3. Preliminary Consultation: Meet with local planning/permitting department
4. Engineering Analysis: Engage qualified engineer for required studies
5. Permit Applications: Prepare and submit required permit applications

Data Sources

• Location Data: OpenStreetMap Nominatim
• Flood Zone Data: FEMA NFHL (public MapServer)
• Precipitation Data: NOAA Atlas 14 Precipitation Frequency Data Server
• Analysis Date: 2025-09-08 12:59:39

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This report is for preliminary analysis only. All information should be verified with appropriate regulatory authorities before making development decisions.