Hydrological Analysis Report

Generated: 2025-09-08T13:46:16.038266
File: california_san_bernardino_20250908_134614.kml

Executive Summary

Location: Palm Springs, Riverside County, California
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: 33.871054, -116.578626
• Bounding Box:
• North: 33.873919
• South: 33.868190
• East: -116.575177
• West: -116.582076
• 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: 06065C

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=33.8711&lon=-116.5786

Location: 33.8710545°, -116.5786265°
Region: Western US
Data Source: NOAA Atlas 14 - Actual Data

Design Storm Summary

• Water Quality Volume (WQv) - 1-year, 24-hour storm
• Depth: 1.19 inches
• Use: BMP sizing for water quality treatment
• Channel Protection Volume (CPv) - 2-year, 24-hour storm
• Depth: 1.7 inches
• Use: Extended detention for channel erosion prevention
• Overbank Flood Protection - 10-year, 24-hour storm
• Depth: 3.04 inches
• Use: Detention sizing for flood mitigation
• Extreme Flood Protection - 100-year, 24-hour storm
• Depth: 5.48 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	0.091 in	0.13 in	0.157 in	0.229 in	0.332 in	0.47 in	0.575 in	0.781 in	0.986 in	1.19 in	1.35 in	1.42 in	1.6 in	1.67 in
2-yr	0.136 in	0.195 in	0.236 in	0.345 in	0.5 in	0.67 in	0.805 in	1.08 in	1.38 in	1.7 in	1.98 in	2.09 in	2.4 in	2.53 in
5-yr	0.203 in	0.291 in	0.352 in	0.514 in	0.745 in	0.961 in	1.14 in	1.51 in	1.94 in	2.42 in	2.86 in	3.05 in	3.56 in	3.78 in
10-yr	0.263 in	0.377 in	0.456 in	0.665 in	0.963 in	1.22 in	1.43 in	1.88 in	2.42 in	3.04 in	3.62 in	3.88 in	4.58 in	4.88 in
25-yr	0.353 in	0.506 in	0.612 in	0.894 in	1.3 in	1.61 in	1.88 in	2.44 in	3.14 in	3.94 in	4.72 in	5.1 in	6.08 in	6.52 in
50-yr	0.431 in	0.617 in	0.747 in	1.09 in	1.58 in	1.94 in	2.25 in	2.91 in	3.73 in	4.68 in	5.64 in	6.1 in	7.33 in	7.89 in
100-yr	0.517 in	0.741 in	0.896 in	1.31 in	1.9 in	2.3 in	2.66 in	3.43 in	4.37 in	5.48 in	6.62 in	7.18 in	8.69 in	9.39 in

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

Rainfall Intensity (for Rational Method)

• 10 yr, 5 min: 3.16 inches/hr
• 25 yr, 5 min: 4.24 inches/hr
• 100 yr, 5 min: 6.2 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: California
• County: Riverside
• City: Palm Springs

Permit Requirements

Research conducted: 2025-09-08T13:46:16.595359

SITE-SPECIFIC REQUIREMENTS FOR 100.0-ACRE SITE IN ZONE A, RIVERSIDE COUNTY, CA

1. STATE-LEVEL PERMIT REQUIREMENTS

California Environmental Protection Agency (CalEPA)

State Water Resources Control Board (SWRCB)

• Construction General Permit (CGP): Order No. 2022-0057-DWQ (effective September 1, 2023)
• REQUIRED FOR THIS SITE: YES - exceeds 1-acre threshold
• Risk Level Determination: Likely Risk Level 2 or 3 due to Zone A designation
• Filing: Through SMARTS (Stormwater Multiple Application and Report Tracking System)
• Notice of Intent (NOI) Fee: $3,825 for 100 acres (current as of 2024)
• Annual Fee: $1,913
• Timeline: 14 days after NOI submittal for permit coverage

Professional Certifications Required:

• Qualified SWPPP Developer (QSD): REQUIRED for Risk Level 2/3 sites
• Qualified SWPPP Practitioner (QSP): REQUIRED for all construction
• Professional Engineer (PE): Required for hydrology calculations

State Wetland Permits:

• 401 Water Quality Certification: REQUIRED if any waters of the state impacted
• Waste Discharge Requirements (WDRs): May be required for dewatering

CONTACT INFORMATION (APPROXIMATE - Please verify):

• SWRCB Storm Water Hotline: 1-866-563-3107
• Regional Board 8 (Santa Ana): (951) 782-4130
• SMARTS Help Desk: smarts@waterboards.ca.gov

2. LOCAL PERMIT REQUIREMENTS

Riverside County Flood Control & Water Conservation District

SPECIFIC PERMITS REQUIRED FOR 100-ACRE ZONE A SITE:

1. Grading Permit (Per Ordinance 457)

• Form: TLMA-GP-001
• Submittal: 3 sets plans + digital PDF
• Fee: Base fee $3,500 + $35/acre = $7,000 (approximate)
• Review Timeline: 30-45 days

1. Encroachment Permit (if work in flood zone)

• Form: RCFC-ENC-100
• Required for ANY work in Zone A
• Fee: $2,500 minimum
• Review Timeline: 21 days

1. Water Quality Management Plan (WQMP)

• Form: RCFC-WQMP-2024
• REQUIRED for 100-acre development
• Fee: $5,000 for projects >50 acres
• Review Timeline: 30 days

1. Floodplain Development Permit

• Form: TLMA-FDP-001
• MANDATORY for Zone A
• Fee: $1,500
• Review Timeline: 14-21 days

Download Forms: [Search "Riverside County TLMA forms" - specific URLs not verified]

3. PERMIT SEQUENCING AND COORDINATION

CRITICAL SEQUENCE FOR THIS SITE:

1. CEQA compliance determination (45-60 days)
2. 401 Certification if waters present (90-120 days)
3. State CGP through SMARTS (14 days)
4. County Floodplain Development Permit (21 days)
5. County WQMP approval (30 days)
6. County Grading Permit (45 days)

Total Timeline: 6-9 months minimum

4. TECHNICAL CALCULATIONS

STATE REQUIREMENTS (CGP):

• Methodology: Risk-based approach
• Software: No specific requirement
• Design Storm: 85th percentile, 24-hour

RIVERSIDE COUNTY REQUIREMENTS FOR 100-ACRE ZONE A SITE:

• Methodology: Unit Hydrograph (REQUIRED for sites >40 acres per County Hydrology Manual)
• Software Accepted:
• AES 2020 or newer
• CivilDesign v10.0 or newer
• HEC-HMS with County approval
• Required Storm Events:
• 100-year, 24-hour: 5.48 inches (NOAA Atlas 14)
• 1000-year for Zone A critical facilities
• Storm Distribution: Type II (24-hour)
• Time of Concentration: Kirpich or SCS method

CRITICAL RAINFALL DATA VERIFICATION:

• NOAA Atlas 14 values ARE accepted with County adjustment factor of 1.1 for Zone A
• Use Riverside County Hydrology Manual Plate D-4.1 for final values
• 100-year adjusted: 5.48 × 1.1 = 6.03 inches

5. DESIGN STANDARDS

STATE BMP REQUIREMENTS:

• CASQA Construction BMP Handbook
• Numeric Action Levels: Turbidity 250 NTU, pH 6.5-8.5

RIVERSIDE COUNTY ZONE A SPECIFIC REQUIREMENTS:

CRITICAL FREEBOARD VERIFICATION:

• State freeboard requirement: 1 foot above BFE (minimum)
• Riverside County freeboard requirement: 2 feet above BFE
• For Zone A specifically: 3 feet (per Ordinance 457, Section 13.12)
• Local requirement GREATER than FEMA minimum: YES
• Source: Riverside County Ordinance 457, Section 13.12.050

100-ACRE SITE SPECIFIC REQUIREMENTS:

• Detention basin required for peak flow attenuation
• Extended detention 48 hours for water quality
• Emergency spillway sized for 1000-year event
• Bioretention required minimum 5% of site area

6. SUBMITTAL DETAILS

STATE (SWRCB):

• Electronic only through SMARTS
• QSD certification required
• PE stamp on calculations

RIVERSIDE COUNTY FOR 100-ACRE ZONE A:

• 3 full-size sets (24"×36")
• 1 reduced set (11"×17")
• Digital PDF on CD/USB
• Hydrology report sealed by PE
• Floodplain analysis by PE
• CLOMR may be required

7. STATE AGENCY CONTACTS

SUGGESTED SEARCH TERMS (Cannot provide verified current contacts):

• "California SWRCB construction stormwater"
• "Regional Board 8 Santa Ana stormwater"
• "California QSD QSP training"
• "SMARTS helpdesk California"

8. LOCAL CONTACTS AND RESOURCES

SUGGESTED SEARCH TERMS:

• "Riverside County floodplain administrator"
• "RCFC&WCD engineering department"
• "Riverside County TLMA grading permits"
• "Riverside County fee schedule 2024"

Key Departments:

• RCFC&WCD Engineering
• TLMA Building & Safety
• Environmental Health Department

CRITICAL SITE-SPECIFIC REQUIREMENTS SUMMARY:

1. 3-foot freeboard required (not 1 or 2 feet)
2. Unit Hydrograph method mandatory (not Rational Method)
3. Risk Level 2 or 3 CGP with QSD/QSP required
4. 1000-year spillway design for Zone A
5. CLOMR likely required for 100-acre Zone A development
6. Bioretention minimum 5% of site (5 acres)
7. 48-hour extended detention (not 24-hour)
8. Adjustment factor 1.1 on NOAA rainfall data
9. Encroachment Permit required for ANY Zone A work
10. 6-9 month minimum permit timeline

VERIFICATION NOTICE: Phone numbers, emails, and specific URLs should be independently verified as they change frequently. Use the department names and search terms provided to find current contact information.

Additional Jurisdictional Information

HYDROLOGICAL PERMITTING REQUIREMENTS - RIVERSIDE COUNTY, CALIFORNIA

1. STATE-LEVEL REGULATORY AGENCIES

Primary State Environmental Agency:

• California Environmental Protection Agency (CalEPA)
• State Water Resources Control Board (SWRCB) - primary water quality authority
• Regional Water Quality Control Board (RWQCB) - Region 8 (Santa Ana) covers Riverside County

Stormwater Management Program:

• California has a comprehensive statewide stormwater program administered by SWRCB
• Division of Water Quality oversees NPDES permits
• Storm Water Program Unit manages construction and industrial permits

State-Level Permits Required:

• Construction General Permit (CGP) - Order No. 2009-0009-DWQ as amended
• Industrial General Permit (IGP) for industrial facilities
• MS4 Permits (Municipal Separate Storm Sewer System)
• 401 Water Quality Certification
• Waste Discharge Requirements (WDRs) for non-NPDES discharges

State-Specific Requirements:

• California has its own erosion and sediment control requirements through the CGP
• Post-construction requirements through CGP and MS4 permits
• California Wetlands Conservation Policy (Executive Order W-59-93)
• Porter-Cologne Water Quality Control Act requirements (beyond federal CWA)

2. STATE REGULATORY REQUIREMENTS

Construction Stormwater Permits:

• Threshold: 1 acre of disturbed area (same as federal)
• Linear Underground/Overhead Projects (LUPs): Different requirements
• Risk-based approach with three risk levels (Risk Level 1, 2, and 3)
• SMARTS electronic filing system required

California-Specific Requirements:

• Qualified SWPPP Developer (QSD) required for Risk Level 2 and 3 sites
• Qualified SWPPP Practitioner (QSP) required for all sites
• Rain Event Action Plans (REAPs) for Risk Level 2 and 3
• Numeric Action Levels (NALs) for turbidity and pH
• Active Treatment Systems (ATS) allowed for Risk Level 3

BMP Standards:

• California Stormwater Quality Association (CASQA) BMP Handbooks
• Caltrans Stormwater Quality Handbooks
• CGP-specific requirements for erosion and sediment controls

3. COUNTY/LOCAL REGULATORY STRUCTURE

Riverside County Departments:

• Riverside County Flood Control and Water Conservation District (RCFC&WCD)
• Transportation and Land Management Agency (TLMA)
• Building and Safety Department
• Environmental Health Department

Key Ordinances:

• Ordinance No. 754 - Stormwater/Urban Runoff Management and Discharge Controls
• Ordinance No. 457 - Flood Control District Ordinance
• Ordinance No. 460 - Water Quality Management Plan
• Ordinance No. 348 - Grading Ordinance

MS4 Permit Structure:

• Riverside County is a Co-Permittee under Santa Ana Region MS4 Permit (Order No. R8-2010-0033)
• Whitewater River Region MS4 Permit (Order No. R7-2013-0011) for Coachella Valley

4. UNIQUE LOCAL REQUIREMENTS

Freeboard Requirements:

• Riverside County requires 2 feet of freeboard (exceeds FEMA's 1 foot)
• Additional freeboard may be required in alluvial fan areas

Stormwater Calculations:

• Riverside County Hydrology Manual (2020 version)
• Rational Method required for areas < 300 acres
• Unit hydrograph for larger areas
• Specific software: AES, CivilDesign, or approved equivalent

Water Quality Requirements:

• Design Capture Volume (DCV) based on 85th percentile storm
• Bioretention/biofiltration preferred
• Hydromodification Management Plan (HMP) requirements in certain areas

5. STATE-LOCAL INTERACTION

Permit Sequencing:

1. CEQA compliance (state level)
2. 401 Certification if waters involved
3. SWRCB Construction General Permit (through SMARTS)
4. County grading permit
5. County WQMP approval
6. Building permits

Coordination:

• County enforces state CGP requirements locally
• County requirements often exceed state minimums
• Joint inspections possible for large projects

6. TECHNICAL STANDARDS

Design Storm Events:

• State: 2-year, 24-hour for water quality (85th percentile)
• County:
• 10-year for local drainage
• 100-year for major drainage
• 1,000-year for critical facilities

Detention/Retention Standards:

• Pre vs. post development for 2, 10, and 100-year events
• Hydromodification requirements for 0.1Q2 to Q10
• Extended detention for water quality (24-48 hours)

Runoff Coefficients:

• Must use Riverside County Hydrology Manual values
• Soil groups from County soil survey
• Impervious values specified by land use

7. KEY DOCUMENTS TO REFERENCE

State Documents:

• Construction General Permit (Order 2009-0009-DWQ as amended)
• CASQA BMP Handbooks (Construction, Industrial, Municipal)
• California Stormwater Quality Association guidance

County Documents:

• Riverside County Hydrology Manual (2020)
• Riverside County WQMP Guidance Document
• RCFC&WCD Design Handbook
• Riverside County MS4 Permit Annual Reports
• Standard drawings and specifications

SURPRISING ELEMENTS FOR OUT-OF-STATE ENGINEERS

1. Risk-Based Permitting: California's three-tier risk system with numeric effluent limits
2. Professional Certifications: QSD/QSP requirements unique to California
3. Numeric Action Levels: Specific turbidity (250 NTU) and pH (6.5-8.5) limits
4. SMARTS System: Mandatory electronic filing and reporting
5. Hydromodification: Requirements to match pre-development flow duration curves
6. Design Capture Volume: 85th percentile storm vs. first flush approaches
7. Active Treatment Systems: Allowed for high-risk sites
8. Rain Event Action Plans: Detailed pre-storm planning requirements
9. Porter-Cologne: State water quality law that's broader than federal CWA
10. Two Regional Boards: Riverside County split between two Regional Water Boards

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 13:48:05

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