Hydrological Analysis Report

Generated: 2025-09-08T14:02:55.719608
File: texas_wharton_20250908_140254.kml

Executive Summary

Location: Unknown, Wharton County, Texas
Flood Zone: AE - 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: 29.298462, -96.107424
• Bounding Box:
• North: 29.301327
• South: 29.295598
• East: -96.104139
• West: -96.110708
• Dimensions: 0.4 mi × 0.4 mi

Flood Zone Analysis

Primary Flood Zone: AE

Risk Level: High Risk - Special Flood Hazard Area (1% annual chance)
DFIRM Panel: 48481C

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=29.2985&lon=-96.1074

Location: 29.2984625°, -96.10742350000001°
Region: Southeast US
Data Source: NOAA Atlas 14 - Actual Data

Design Storm Summary

• Water Quality Volume (WQv) - 1-year, 24-hour storm
• Depth: 3.73 inches
• Use: BMP sizing for water quality treatment
• Channel Protection Volume (CPv) - 2-year, 24-hour storm
• Depth: 4.86 inches
• Use: Extended detention for channel erosion prevention
• Overbank Flood Protection - 10-year, 24-hour storm
• Depth: 8.02 inches
• Use: Detention sizing for flood mitigation
• Extreme Flood Protection - 100-year, 24-hour storm
• Depth: 14.7 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	0.501 in	0.795 in	1.01 in	1.43 in	1.89 in	2.32 in	2.56 in	2.97 in	3.34 in	3.73 in	4.15 in	4.49 in	5.6 in	6.25 in
2-yr	0.578 in	0.919 in	1.16 in	1.64 in	2.18 in	2.75 in	3.1 in	3.7 in	4.27 in	4.86 in	5.52 in	5.97 in	7.16 in	7.85 in
5-yr	0.706 in	1.12 in	1.41 in	1.99 in	2.66 in	3.44 in	3.94 in	4.79 in	5.61 in	6.48 in	7.44 in	8.08 in	9.51 in	10.3 in
10-yr	0.81 in	1.29 in	1.62 in	2.28 in	3.05 in	4.02 in	4.67 in	5.79 in	6.87 in	8.02 in	9.3 in	10.1 in	11.6 in	12.5 in
25-yr	0.953 in	1.52 in	1.9 in	2.66 in	3.59 in	4.85 in	5.72 in	7.25 in	8.76 in	10.3 in	12.1 in	13.1 in	14.8 in	15.7 in
50-yr	1.06 in	1.7 in	2.11 in	2.94 in	3.99 in	5.49 in	6.56 in	8.47 in	10.4 in	12.4 in	14.7 in	15.9 in	17.5 in	18.3 in
100-yr	1.17 in	1.87 in	2.32 in	3.23 in	4.4 in	6.18 in	7.49 in	9.82 in	12.2 in	14.7 in	17.5 in	18.8 in	20.3 in	21.1 in

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

Rainfall Intensity (for Rational Method)

• 10 yr, 5 min: 9.72 inches/hr
• 25 yr, 5 min: 11.44 inches/hr
• 100 yr, 5 min: 14.04 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: Texas
• County: Wharton
• City: Unincorporated area

Permit Requirements

Research conducted: 2025-09-08T14:02:56.310656

Based on the jurisdiction analysis for Wharton County, Texas, here are the EXACT requirements for your 100.0-acre site in Zone AE:

1. STATE-LEVEL PERMIT REQUIREMENTS

Texas Commission on Environmental Quality (TCEQ)

• Agency: Texas Commission on Environmental Quality
• Construction General Permit: TPDES Construction General Permit (TXR150000) - REQUIRED for 100-acre site
• Threshold: 1 acre or more of disturbance (your site exceeds this)
• Notice of Intent (NOI) must be filed electronically via STEERS system
• Stormwater Pollution Prevention Plan (SWP3) required on-site
• State Stormwater Management: Incorporated into Construction General Permit
• Erosion Control: Part of TXR150000 requirements
• Wetland Permits: No state wetland program; federal Section 404 applies
• Professional Requirements:
• PE required for certain hydraulic calculations
• No state RLD certification program
• State Fees: $325 for Construction General Permit NOI
• Timeline: 7-day waiting period after NOI submission
• Applications: Submit via STEERS at www2.tceq.texas.gov/steers/

IMPORTANT: I cannot provide verified current phone numbers or email addresses. Please search "TCEQ Region 12 Houston" for the regional office serving Wharton County.

2. LOCAL PERMIT REQUIREMENTS

Wharton County Requirements

• Floodplain Development Permit - REQUIRED for Zone AE
• Form: Contact Wharton County Engineer's Office for current application
• Submittal: Typically 3 paper copies + 1 digital
• Scale: 1"=100' or larger for site plans
• Fees: Contact County Engineer for current fee schedule
• Review Timeline: Typically 2-4 weeks

VERIFICATION NEEDED: Contact Wharton County Engineer's Office directly for:

• Current permit application forms
• 2024/2025 fee schedule
• Exact submittal requirements

3. PERMIT SEQUENCING AND COORDINATION

1. First: Obtain Wharton County Floodplain Development Permit
2. Second: File TCEQ TPDES NOI (at least 7 days before construction)
3. No combined application - separate submissions required
4. Total Timeline: 3-5 weeks minimum for complete permit package

4. TECHNICAL CALCULATIONS

State Requirements (TCEQ):

• Methodology: No specific state methodology mandated
• Software: No specific software required by state
• Storm Events:
• 2-year for temporary erosion controls
• 25-year for permanent BMPs

Local Requirements (Wharton County):

• Methodology: Unit hydrograph method REQUIRED for 100-acre site (exceeds 200-acre threshold for Rational Method)
• Software: HEC-RAS commonly accepted for floodplain analysis
• Storm Events:
• 100-year storm for detention design (Zone AE requirement)
• Pre-development vs post-development comparison required

Precipitation Data:

CRITICAL VERIFICATION NEEDED:

• NOAA Atlas 14 values provided (100-year, 24-hour: 14.7 inches) should be verified with County Engineer
• Ask specifically: "Does Wharton County accept NOAA Atlas 14 values or require local IDF curves?"
• Storm distribution: Verify if Type II or Type III required

5. DESIGN STANDARDS

State BMP Standards:

• Reference: TCEQ RG-348 (technical guidance)
• No mandatory state BMP manual

Local Standards for 100-Acre Site in Zone AE:

• CRITICAL FREEBOARD REQUIREMENT:
• Wharton County: 1 foot above Base Flood Elevation (per Flood Damage Prevention Order)
• This meets FEMA minimum for Zone AE
• VERIFICATION NEEDED: Confirm current freeboard requirement with County Engineer
• Detention: 100-year post-development release rate ≤ pre-development rate
• Foundation Requirements: Elevation Certificate required for structures in Zone AE
• Fill Requirements: Compensatory storage may be required in Zone AE

6. SUBMITTAL DETAILS

State (TCEQ):

• Electronic submittal via STEERS
• PE certification required for certain elements
• SWP3 kept on-site, not submitted

Local (Wharton County):

• Plan sheets typically include:

1. Cover sheet with project data
2. Existing conditions/topography
3. Proposed grading plan
4. Drainage area map
5. Hydraulic calculations
6. Erosion control plan
7. Details and specifications

• PE seal required on drainage plans
• Digital format: PDF typical, verify current requirements

7. STATE AGENCY CONTACTS

SUGGESTED SEARCH TERMS (I cannot provide verified current contact info):

• "TCEQ Region 12 Houston office"
• "TCEQ stormwater permits contact"
• "Texas floodplain management program"

8. LOCAL CONTACTS AND RESOURCES

SUGGESTED SEARCH TERMS:

• "Wharton County Engineer's Office"
• "Wharton County floodplain administrator"
• "Wharton County development permits"

CRITICAL ACTIONS FOR YOUR 100-ACRE ZONE AE SITE:

1. Contact Wharton County Engineer immediately to verify:

• Current freeboard requirement for Zone AE
• Acceptance of NOAA Atlas 14 precipitation data
• Specific application forms and fees
• Compensatory storage requirements for fill in Zone AE

1. Prepare for TCEQ TPDES permit:

• Register for STEERS account
• Prepare SWP3 document
• Budget $325 for state permit fee

1. Design considerations specific to your site:

• Use unit hydrograph method (required for 100 acres)
• Design for 100-year storm event
• Ensure 1-foot freeboard minimum above BFE
• Plan for potential compensatory storage if placing fill

Additional Jurisdictional Information

Based on my research of hydrological permitting requirements for Wharton County, Texas:

1. STATE-LEVEL REGULATORY AGENCIES

• Primary state environmental agency: Texas Commission on Environmental Quality (TCEQ)
• Stormwater management: TCEQ Water Quality Division handles the Texas Pollutant Discharge Elimination System (TPDES)
• State-level permits required:
• TPDES Construction General Permit (TXR150000) for construction activities
• TPDES Multi-Sector General Permit for industrial facilities
• TPDES Municipal Separate Storm Sewer System (MS4) permits
• Erosion and sediment control: Incorporated into TPDES Construction General Permit requirements
• State wetland program: No state-specific wetland protection 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: Yes, TPDES Construction General Permit required
• Disturbed area threshold: 1 acre or more (same as federal)
• BMP standards: Technical guidance in TCEQ's "Complying with the Edwards Aquifer Rules" (RG-348) serves as statewide reference
• Freeboard requirements: No state-mandated freeboard beyond local requirements
• Post-construction requirements: Required through TPDES permits for MS4 communities
• Professional certifications: No state-specific Responsible Land Disturber certification; Professional Engineer (PE) required for certain submissions

3. COUNTY/LOCAL REGULATORY STRUCTURE

• Wharton County:
• Wharton County Engineer's Office handles floodplain development permits
• No separate stormwater management district
• City of Wharton (if applicable):
• Public Works Department handles drainage issues
• May have separate requirements from county
• Key ordinances:
• Wharton County Flood Damage Prevention Order
• Local subdivision regulations

4. UNIQUE LOCAL REQUIREMENTS

• Freeboard: Wharton County typically requires 1 foot of freeboard above Base Flood Elevation
• Calculation methods: Rational Method for areas under 200 acres; unit hydrograph methods for larger areas
• Software: No specific software mandated, but HEC-RAS commonly accepted for floodplain analysis
• Design standards: County may reference TxDOT Hydraulic Design Manual for roadway drainage

5. STATE-LOCAL INTERACTION

• Permit sequence:

1. Local floodplain development permit typically obtained first
2. TPDES Notice of Intent (NOI) filed before construction begins

• Joint applications: No joint application process; separate submissions required
• Local vs. state: Local requirements often exceed state minimums for drainage design

6. TECHNICAL STANDARDS

State Requirements:

• 2-year storm for temporary erosion controls
• 25-year storm for permanent BMPs

Local Requirements:

• 10-year storm for residential streets
• 25-year storm for collector streets
• 100-year storm for detention design
• Runoff coefficients per local standards or TxDOT manual
• Pre- vs. post-development runoff rates must not increase

7. KEY DOCUMENTS TO REFERENCE

State Documents:

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

Local Documents:

• Wharton County Flood Damage Prevention Order
• Wharton County Subdivision Regulations
• Local drainage criteria (if published)
• Floodplain Development Permit Application
• County fee schedule

WHAT WOULD SURPRISE AN OUT-OF-STATE ENGINEER:

1. No state-level stormwater management act - Unlike states with comprehensive stormwater laws, Texas relies primarily on TPDES implementation
2. Limited state design standards - No statewide stormwater BMP manual; local jurisdictions have significant discretion
3. No state wetland program - Texas is one of few states without state-level wetland regulations
4. County-level authority - In unincorporated areas, counties have limited regulatory authority compared to other states
5. Edwards Aquifer rules - While not applicable to Wharton County, the Edwards Aquifer rules create a unique regional regulatory framework in other parts of Texas

Note: Specific requirements should be verified with Wharton County Engineer's Office and TCEQ, as regulations may have been updated.

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 14:04:13

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