Hydrological Analysis Report

Generated: 2025-09-08T14:00:14.053008
File: california_imperial_20250908_140012.kml

Executive Summary

Location: Unknown, Imperial 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: 33.161991, -115.558451
• Bounding Box:
• North: 33.164855
• South: 33.159127
• East: -115.555029
• West: -115.561873
• 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: 06025C

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=33.1620&lon=-115.5585

Location: 33.161991°, -115.558451°
Region: Western US
Data Source: NOAA Atlas 14 - Actual Data

Design Storm Summary

• Water Quality Volume (WQv) - 1-year, 24-hour storm
• Depth: 0.634 inches
• Use: BMP sizing for water quality treatment
• Channel Protection Volume (CPv) - 2-year, 24-hour storm
• Depth: 0.951 inches
• Use: Extended detention for channel erosion prevention
• Overbank Flood Protection - 10-year, 24-hour storm
• Depth: 1.84 inches
• Use: Detention sizing for flood mitigation
• Extreme Flood Protection - 100-year, 24-hour storm
• Depth: 3.67 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	0.06 in	0.086 in	0.104 in	0.146 in	0.203 in	0.281 in	0.329 in	0.417 in	0.497 in	0.634 in	0.72 in	0.761 in	0.847 in	0.866 in
2-yr	0.095 in	0.136 in	0.164 in	0.23 in	0.319 in	0.424 in	0.488 in	0.612 in	0.735 in	0.951 in	1.09 in	1.16 in	1.28 in	1.32 in
5-yr	0.148 in	0.211 in	0.256 in	0.358 in	0.497 in	0.64 in	0.728 in	0.902 in	1.09 in	1.42 in	1.63 in	1.74 in	1.92 in	1.97 in
10-yr	0.197 in	0.282 in	0.342 in	0.478 in	0.664 in	0.84 in	0.949 in	1.17 in	1.41 in	1.84 in	2.12 in	2.25 in	2.49 in	2.55 in
25-yr	0.276 in	0.395 in	0.478 in	0.669 in	0.929 in	1.16 in	1.3 in	1.58 in	1.9 in	2.49 in	2.85 in	3.02 in	3.34 in	3.41 in
50-yr	0.347 in	0.497 in	0.601 in	0.84 in	1.17 in	1.44 in	1.6 in	1.94 in	2.33 in	3.04 in	3.48 in	3.68 in	4.05 in	4.14 in
100-yr	0.429 in	0.615 in	0.744 in	1.04 in	1.44 in	1.76 in	1.95 in	2.35 in	2.82 in	3.67 in	4.18 in	4.41 in	4.84 in	4.95 in

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

Rainfall Intensity (for Rational Method)

• 10 yr, 5 min: 2.36 inches/hr
• 25 yr, 5 min: 3.31 inches/hr
• 100 yr, 5 min: 5.15 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: Imperial
• City: Unincorporated area

Permit Requirements

Research conducted: 2025-09-08T14:00:14.630394

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

1. STATE-LEVEL PERMIT REQUIREMENTS

Primary State Environmental Agency:

• California State Water Resources Control Board (SWRCB)
• Regional Water Quality Control Board, Region 7 (Colorado River Basin)

Required State Permits for 100-acre Site:

1. Construction General Permit (CGP)

• REQUIRED: Site exceeds 1-acre threshold
• Order No. 2009-0009-DWQ as amended by 2010-0014-DWQ and 2012-0006-DWQ
• Risk Level Determination Required (likely Risk Level 2 based on size)
• Application: Through SMARTS online system
• Timeline: 14 days after NOI submission before commencing construction
• Fee: $3,744 (Risk Level 2) + $490 annual fee

1. 401 Water Quality Certification

• REQUIRED if impacting Waters of the State
• Application through Regional Board Region 7
• Timeline: 60-day review period

Professional Certifications Required:

• Qualified SWPPP Developer (QSD) - must prepare SWPPP
• Qualified SWPPP Practitioner (QSP) - must implement SWPPP
• Professional Engineer (PE) for drainage calculations

State Permit Applications:

• SMARTS System: https://smarts.waterboards.ca.gov
• Regional Board 7: 73-720 Fred Waring Drive, Suite 100, Palm Desert, CA 92260
• Phone: (760) 346-7491

2. LOCAL PERMIT REQUIREMENTS

Required Imperial County Permits:

1. Floodplain Development Permit

• REQUIRED: Site is in Zone A
• Form: Available at Public Works Department
• Imperial County Code Title 9, Division 14

1. Grading Permit

• REQUIRED: Exceeds 5,000 cubic yards or 5 acres
• Form Number: Contact Public Works for current form
• Imperial County Code Title 9, Division 16

1. Building Permits (for any structures)

• Imperial County Building Department

Submittal Requirements:

• 3 sets of plans (24"x36" minimum)
• Digital submittal in PDF format
• Engineer's calculations sealed by California PE
• SWPPP copy
• Drainage study

Current Fees (verify with County):

• Floodplain Development Permit: ~$500-1,000
• Grading Permit: Based on volume, expect $5,000+
• Plan Check Fees: Additional percentage of permit fees

Review Timeline:

• Initial review: 30 days
• Resubmittal reviews: 14 days

3. PERMIT SEQUENCING AND COORDINATION

Required Sequence:

1. CEQA compliance determination
2. State CGP through SMARTS (concurrent with local)
3. County Floodplain Development Permit
4. County Grading Permit
5. Building Permits (if applicable)
6. IID Encroachment Permit (if near IID facilities)

Coordination:

• No combined application process
• County reviews state SWPPP compliance
• Total timeline: 60-90 days minimum

4. TECHNICAL CALCULATIONS

State Requirements:

• Water Quality Volume: 85th percentile, 24-hour storm
• Use CASQA BMP Sizing Calculator or equivalent

Imperial County Requirements:

• Design Storm: 100-year event for major drainage
• Method: Rational Method acceptable for 100 acres
• Software: HEC-HMS, HEC-RAS accepted
• Time of Concentration: SCS Method

CRITICAL RAINFALL DATA VERIFICATION:

• NOAA Atlas 14 values ARE accepted by Imperial County
• 100-year, 24-hour: 3.67 inches (CONFIRMED)
• Use Type I storm distribution
• No local adjustment factors required

Runoff Coefficients:

• Undeveloped desert: 0.10-0.30
• Developed areas: Per County Standards Table

5. DESIGN STANDARDS

State BMP Requirements:

• CASQA BMP Handbooks (current edition)
• Post-construction BMPs required
• LID prioritization mandatory

CRITICAL FREEBOARD REQUIREMENTS:

• State requirement: 1 foot minimum above BFE
• Imperial County requirement: 2 feet above BFE
• For Zone A specifically: 2 feet (County exceeds FEMA)
• County requirement is GREATER than FEMA minimum: YES
• Source: Imperial County Code Title 9, Division 14, Section 9.14.060

Detention Requirements:

• Post-development discharge ≤ pre-development
• Retention preferred due to limited outfalls
• Emergency spillway required

Foundation Requirements:

• Elevation Certificate required
• Lowest floor 2 feet above BFE
• FEMA Elevation Certificate by licensed surveyor

6. SUBMITTAL DETAILS

State Submittal:

• Electronic only through SMARTS
• PE certification required
• QSD signature on SWPPP

County Submittal:

• Plan sheets in order: Cover, Existing Conditions, Grading, Drainage, Erosion Control, Details
• PE wet stamp and signature
• Digital PDF required
• Calculations in 8.5"x11" format

7. STATE AGENCY CONTACTS

IMPORTANT: Contact information should be verified as it may change

State Water Resources Control Board:

• Main: (916) 341-5250
• Website: www.waterboards.ca.gov

Regional Board 7 (Colorado River Basin):

• SUGGESTED CONTACT: (760) 346-7491
• Address: 73-720 Fred Waring Drive, Suite 100, Palm Desert, CA 92260
• VERIFY current stormwater program manager

8. LOCAL CONTACTS AND RESOURCES

IMPORTANT: Verify all contact information as it changes frequently

Imperial County Public Works:

• SUGGESTED: (442) 265-1818
• Floodplain Administrator: Contact Public Works for current person
• Address: 155 South 11th Street, El Centro, CA 92243

Imperial County Planning & Development Services:

• SUGGESTED: (442) 265-1736
• Website: www.icpds.com

Imperial Irrigation District:

• Engineering: (760) 339-9228
• Encroachment Permits: Engineering Department

CRITICAL VERIFICATION NEEDED:

• All phone numbers and emails should be verified before use
• Fee schedules change annually
• Contact names change with staff turnover

Key Resources:

• Imperial County website: www.co.imperial.ca.us
• Search "Floodplain Development Permit" for current forms
• Search "Grading Ordinance" for current standards

Additional Jurisdictional Information

HYDROLOGICAL PERMITTING REQUIREMENTS - IMPERIAL 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, Region 7 (Colorado River Basin) - covers Imperial County

Stormwater Management Program:

• California has a comprehensive statewide stormwater program administered by SWRCB
• National Pollutant Discharge Elimination System (NPDES) program delegated to California

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-federal waters

Erosion and Sediment Control:

• Required through the Construction General Permit
• Must prepare and implement a Storm Water Pollution Prevention Plan (SWPPP)

State Wetland Protection:

• Porter-Cologne Water Quality Control Act provides broader protection than federal Clean Water Act
• Covers "Waters of the State" including isolated wetlands not covered federally

2. STATE REGULATORY REQUIREMENTS

Construction Stormwater Permits:

• Required for projects disturbing 1 acre or more
• Linear projects: 1 acre or more of disturbed area
• Risk-based approach with three risk levels (1, 2, and 3)

BMP Design Standards:

• California Stormwater Quality Association (CASQA) BMP Handbooks
• Caltrans Stormwater Quality Handbooks for transportation projects

Post-Construction Requirements:

• Mandatory post-construction stormwater management requirements
• Low Impact Development (LID) prioritization
• Hydromodification management requirements in some areas

Professional Certifications:

• Qualified SWPPP Developer (QSD)
• Qualified SWPPP Practitioner (QSP)
• Professional Engineer (PE) for certain designs

3. COUNTY/LOCAL REGULATORY STRUCTURE

Imperial County Departments:

• Imperial County Public Works Department - Floodplain Management
• Imperial County Planning & Development Services Department
• Imperial County Air Pollution Control District (dust control requirements)

Specific Ordinances:

• Imperial County Code Title 9, Division 14 - Floodplain Management Ordinance
• Imperial County Code Title 9, Division 16 - Grading Ordinance
• Imperial County Stormwater Management Plan (as MS4 permittee)

Imperial Irrigation District (IID):

• Major regional entity controlling water delivery and drainage
• Encroachment permits required for work near IID facilities

4. UNIQUE LOCAL REQUIREMENTS

Imperial County Specific Requirements:

• Desert environment considerations - emphasis on dust control
• Agricultural drainage considerations due to extensive farming
• Salton Sea proximity impacts for northern county projects
• IID coordination required for most drainage projects

Calculation Methods:

• Rational Method typically used for areas under 640 acres
• Must account for agricultural return flows
• Special considerations for New and Alamo Rivers

Design Standards:

• Imperial County Improvement Standards and Specifications
• Coordination with IID Drainage Design Manual

5. STATE-LOCAL INTERACTION

Permit Sequencing:

1. CEQA compliance (state level)
2. State Water Board permits (CGP, 401 Cert)
3. County grading and building permits
4. IID encroachment permits if applicable

Overlapping Requirements:

• County requirements generally meet or exceed state minimums
• Both require SWPPP implementation
• County enforces state water quality standards locally

6. TECHNICAL STANDARDS

State Requirements:

• 85th percentile, 24-hour storm for water quality treatment
• Risk Level 2 & 3 sites: additional numeric effluent limitations
• pH range: 6.5-8.5
• Turbidity limits based on risk level

Imperial County Standards:

• 100-year storm event for major drainage facilities
• 10-year storm for local drainage
• Special considerations for closed basin hydrology
• Retention/detention often required due to limited outfall options

Unique Considerations:

• High evaporation rates affect pond sizing
• Shallow groundwater in many areas
• High salinity considerations
• Seismic design requirements for retention structures

7. KEY DOCUMENTS TO REFERENCE

State Documents:

• Construction General Permit Order 2009-0009-DWQ
• CASQA BMP Handbooks
• SWRCB SMARTS database requirements

Local Documents:

• Imperial County Improvement Standards and Specifications
• Imperial County Floodplain Management Ordinance
• Imperial County MS4 Permit and SWMP
• IID Water Department Engineering Standards
• Imperial County CEQA Guidelines

SURPRISING ELEMENTS FOR OUT-OF-STATE ENGINEERS:

1. Dual Water Systems: The prominence of IID as a quasi-governmental entity controlling both irrigation water and drainage
2. Desert Hydrology: Extreme evaporation rates and rare but intense rainfall events
3. Agricultural Interface: Extensive tile drain systems and agricultural return flows affecting project drainage
4. Salton Sea Influence: Declining sea levels creating new drainage challenges
5. CEQA Process: California's additional environmental review beyond NEPA
6. Risk-Based Permitting: CGP's three-tier risk system unique to California
7. Waters of the State: Broader jurisdiction than federal Clean Water Act
8. Numeric Effluent Limitations: Specific turbidity limits for construction sites
9. QSD/QSP Requirements: Mandatory certifications for SWPPP preparers and implementers
10. Post-Construction Requirements: Extensive LID and hydromodification control requirements at state level

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 14:01:52

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