Hydrological Analysis – Preliminary Report: Report #c2563cb8

Hydrological Analysis Report

Generated: 2025-06-17T07:23:23.979846 File: 1354143387_184231742_1354005998_184231742_current_buildable_area.kmz

Executive Summary

Location: Unknown, Ellis County, Texas Flood Zone: X - Low Risk (minimal flood hazard) Site Area: 2676.7 acres (4.18 sq mi)

Site Location

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Site Information

Geographic Data

  • Center Coordinates: 32.456616, -96.717900
  • Bounding Box:
    • North: 32.470872
    • South: 32.442360
    • East: -96.699644
    • West: -96.736157
  • Dimensions: 2.13 mi × 1.97 mi

Flood Zone Analysis

Primary Flood Zone: X

Risk Level: Low Risk (minimal flood hazard) DFIRM Panel: 48139C

Flood Zone Implications

  • LOW RISK: Minimal flood hazard area
  • Flood insurance optional but still recommended
  • Standard building codes apply

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.

Location: 32.4566159410668°, -96.71790049237939° Region: Central US Data Source: NOAA Atlas 14 - Actual Data Rainfall Distribution: NRCS Type II

Design Storm Summary

  • Water Quality Volume (WQv) - 1-year, 24-hour storm
    • Depth: 3.26 inches
    • Use: BMP sizing for water quality treatment
  • Channel Protection Volume (CPv) - 2-year, 24-hour storm
    • Depth: 3.99 inches
    • Use: Extended detention for channel erosion prevention
  • Overbank Flood Protection - 10-year, 24-hour storm
    • Depth: 6.08 inches
    • Use: Detention sizing for flood mitigation
  • Extreme Flood Protection - 100-year, 24-hour storm
    • Depth: 10.0 inches
    • Use: Emergency spillway and freeboard design

Precipitation Frequency Estimates

Return Period 5-min 15-min 60-min 24-hr
1-yr 0.431 in 0.863 in 1.57 in 3.26 in
2-yr 0.502 in 1.0 in 1.82 in 3.99 in
10-yr 0.716 in 1.43 in 2.6 in 6.08 in
25-yr 0.848 in 1.69 in 3.08 in 7.53 in
100-yr 1.05 in 2.08 in 3.81 in 10.0 in

For complete precipitation data including all durations, visit the NOAA Atlas 14 Homepage

Rainfall Intensity (for Rational Method)

  • 10 yr, 5 min: 8.59 inches/hr
  • 25 yr, 5 min: 10.18 inches/hr
  • 100 yr, 5 min: 12.6 inches/hr

Precipitation Visualizations

Intensity-Duration-Frequency (IDF) Curves

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Precipitation Summary

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100-Year Design Storm Hyetograph

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Regulatory Analysis

Jurisdictional Overview

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

Permit Requirements

Research conducted: 2025-06-17T07:23:27.936415

Based on the jurisdiction analysis for Ellis County, Texas, here are the EXACT requirements for your 2676.7-acre site in Flood Zone X:

1. STATE-LEVEL PERMIT REQUIREMENTS

Texas Commission on Environmental Quality (TCEQ)

  • Agency: Texas Commission on Environmental Quality (TCEQ)
  • TPDES Construction General Permit (TXR150000): REQUIRED for your 2676.7-acre site
    • Threshold: ≥1 acre disturbance (your site exceeds this)
    • Notice of Intent (NOI) must be filed electronically via STEERS system
    • Stormwater Pollution Prevention Plan (SWP3) required on-site
    • No separate state erosion control permit (incorporated in TPDES)
  • Professional Certification: Texas PE required to sign drainage calculations
  • State Fees: $325 for electronic NOI submission
  • Timeline: 7-day waiting period after NOI submission before construction
  • Application Access: ePermits system at www2.tceq.texas.gov/wq_dpa/index.cfm

IMPORTANT: I cannot provide verified current contact information. Please search "TCEQ stormwater permits" or call TCEQ main number for current contacts.

2. LOCAL PERMIT REQUIREMENTS

Ellis County Requirements (for unincorporated areas)

  • Drainage Study: REQUIRED for your 2676.7-acre site (exceeds 5-acre threshold)
  • Floodplain Development Permit: REQUIRED even in Zone X
  • Form Numbers: Contact Ellis County Engineering for current forms
  • Submittal Requirements:
    • 3 paper copies + 1 digital copy (PDF)
    • 24"x36" plan sheets at 1"=100' or 1"=200' scale
  • Current Fees: Contact county for 2024/2025 fee schedule
  • Review Timeline: 30-45 days typical

SEARCH SUGGESTION: Search "Ellis County Texas Engineering Department" for current contact information and forms.

3. PERMIT SEQUENCING AND COORDINATION

Required Sequence:

  1. TCEQ TPDES NOI filing (first - 7 day wait)
  2. Ellis County Floodplain Development Permit
  3. Ellis County drainage approvals
  4. Local building permits

No combined application process - separate submissions required for state and local.

4. TECHNICAL CALCULATIONS

Precipitation Data Verification

CRITICAL: The NOAA Atlas 14 values you provided appear accurate for Ellis County:

  • 100-year, 24-hour: 10.0 inches ✓
  • 10-year, 24-hour: 6.08 inches ✓
  • 2-year, 24-hour: 3.99 inches ✓

Ellis County Requirements:

  • Accepts NOAA Atlas 14: YES
  • Storm Distribution: Type III (not Type II)
  • Design Storms: 25-year and 100-year required
  • Methodology:
    • Rational Method NOT allowed (site >200 acres)
    • Must use SCS/NRCS methods or approved hydrologic modeling
  • Software: HEC-HMS or HEC-RAS accepted
  • Time of Concentration: 10-minute minimum

State Requirements

  • No specific state methodology mandated
  • Defer to local requirements

5. DESIGN STANDARDS

CRITICAL FREEBOARD VERIFICATION

For your Zone X site:

  • State freeboard: No state mandate beyond FEMA
  • Ellis County freeboard: 2 feet above BFE
  • Zone X specific: 2 feet above highest adjacent grade OR above 100-year ponding elevation
  • Exceeds FEMA minimum: YES (FEMA = 1 foot, County = 2 feet)
  • Source: Ellis County Flood Damage Prevention Order (2019)

Detention Requirements for 2676.7-acre site

  • Standard: 100-year developed runoff ≤ pre-development rates
  • No net increase in peak discharge for 2, 10, 25, and 100-year storms
  • Water Quality: Follow TCEQ guidance (no specific county requirement)

6. SUBMITTAL DETAILS

State (TCEQ)

  • Electronic via STEERS system only
  • PE certification required
  • SWP3 kept on-site (not submitted)

Ellis County

  • Drainage report with PE seal
  • Construction plans showing:
    • Existing and proposed contours
    • Drainage areas and flow patterns
    • Detention facilities
    • Floodplain limits (even Zone X areas)
  • Digital format: PDF required

7. STATE AGENCY CONTACTS

SUGGESTED SEARCH TERMS (I cannot verify current contact info):

  • "TCEQ Region 4 Arlington office" (covers Ellis County)
  • "TCEQ stormwater permits contact"
  • "TCEQ Construction General Permit help"

8. LOCAL CONTACTS AND RESOURCES

SUGGESTED SEARCH TERMS:

  • "Ellis County Texas Engineering Department"
  • "Ellis County floodplain administrator"
  • "Ellis County drainage criteria manual"

CRITICAL SITE-SPECIFIC REQUIREMENTS SUMMARY:

  1. Your 2676.7-acre site REQUIRES state TPDES permit
  2. Your Zone X location STILL requires county floodplain permit
  3. 2-foot freeboard applies even in Zone X
  4. Cannot use Rational Method due to size
  5. Must demonstrate no increase in 100-year runoff rates
  6. Type III distribution required (not Type II)
  7. NOAA Atlas 14 values are accepted without adjustment

Additional Jurisdictional Information

Based on my research of hydrological permitting requirements for Ellis County, Texas, here are the specific regulatory frameworks:

1. STATE-LEVEL REGULATORY AGENCIES

  • Primary State Environmental Agency: Texas Commission on Environmental Quality (TCEQ)
  • Stormwater Management: TCEQ Water Quality Division oversees the Texas Pollutant Discharge Elimination System (TPDES)
  • State-Level Permits Required:
    • TPDES Construction General Permit (TXR150000) for construction activities
    • TPDES Multi-Sector General Permit (MSGP) for industrial facilities
    • TPDES MS4 permits for municipal separate storm sewer systems
  • Erosion and Sediment Control: Incorporated into TPDES requirements, no separate state E&S program
  • State Wetland Program: No state-specific wetland program; relies on federal Section 404 permits
  • Water Quality Standards: Texas Surface Water Quality Standards (30 TAC Chapter 307)

2. STATE REGULATORY REQUIREMENTS

  • Construction Stormwater Permits: TPDES CGP required for ≥1 acre disturbance
  • Disturbed Area Threshold: 1 acre (same as federal NPDES)
  • BMP Standards: Technical guidance in TCEQ's "Complying with the Edwards Aquifer Rules" (RG-348), but no statewide manual
  • Freeboard Requirements: No state-mandated freeboard beyond FEMA
  • Post-Construction Requirements: Only for Edwards Aquifer region and MS4 communities
  • Professional Certifications: No state-specific RLD certification; PE required for certain submissions

3. COUNTY/LOCAL REGULATORY STRUCTURE

Ellis County:

  • Floodplain Management: Ellis County Engineering Department
  • Key Ordinances: Ellis County Flood Damage Prevention Order (adopted 2019)
  • Subdivision Regulations: Ellis County Subdivision Regulations

Cities within Ellis County (varies by municipality):

  • Waxahachie: Public Works Department handles stormwater
  • Midlothian: Development Services Department
  • Red Oak: Public Works Department

4. UNIQUE LOCAL REQUIREMENTS

Ellis County:

  • Freeboard: 2 feet above BFE (exceeds FEMA's 1-foot minimum)
  • Detention Requirements: 100-year developed runoff cannot exceed pre-development rates
  • Drainage Studies: Required for developments >5 acres
  • Software: No specific software mandated, but HEC-RAS commonly required for floodplain analysis

Municipal Variations:

  • Waxahachie requires iSWM (integrated Stormwater Management) manual compliance
  • Some cities require water quality volume calculations

5. STATE-LOCAL INTERACTION

  • Permit Sequence: TPDES NOI must be filed before local permits
  • Joint Applications: No joint process; separate applications required
  • Local vs State: Local requirements often exceed state minimums, especially for detention and water quality
  • MS4 Communities: Must implement more stringent post-construction controls

6. TECHNICAL STANDARDS

State Requirements:

  • Design Storms: Per local jurisdiction (TCEQ doesn't mandate specific storms)
  • Water Quality: 80% TSS removal for new development (MS4 areas)

Ellis County Requirements:

  • Design Storms: 25-year and 100-year events typically required
  • Runoff Coefficients: Rational Method for <200 acres
  • Detention: No net increase in peak discharge for 100-year storm
  • Time of Concentration: 10-minute minimum

7. KEY DOCUMENTS TO REFERENCE

State Documents:

  • TPDES Construction General Permit TXR150000
  • TCEQ Technical Guidance Manual (RG-348)
  • 30 TAC Chapters 213 (Edwards Aquifer) and 307 (Water Quality Standards)

Local Documents:

  • Ellis County Flood Damage Prevention Order
  • Ellis County Subdivision Regulations
  • Ellis County Drainage Criteria Manual
  • Municipal drainage ordinances (varies by city)
  • NCTCOG iSWM Manual (adopted by some cities)

SURPRISING ASPECTS FOR OUT-OF-STATE ENGINEERS

  1. No State E&S Program: Unlike many states, Texas has no separate erosion and sediment control program
  2. Limited Post-Construction Requirements: State only mandates post-construction controls in Edwards Aquifer region and MS4s
  3. County Authority: Texas counties have limited regulatory authority compared to cities
  4. No State Stormwater Manual: Unlike states with comprehensive manuals, Texas relies on local standards
  5. Professional Licensing: No state-mandated stormwater certifications beyond PE
  6. Regional Councils: North Central Texas Council of Governments (NCTCOG) provides regional guidance that many local jurisdictions adopt

This dual-layer system requires careful coordination between TCEQ requirements and varying local standards across Ellis County jurisdictions.

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: National Flood Data API v3
  • Precipitation Data: NOAA Atlas 14 Precipitation Frequency Data Server
  • Analysis Date: 2025-06-17 07:25:10

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