Hydrological Analysis Report

Generated: 2025-09-08T13:41:00.466250
File: arkansas_mississippi_20250908_134058.kml

Executive Summary

Location: Unknown, Mississippi County, Arkansas
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: 35.898719, -90.074205
• Bounding Box:
• North: 35.901584
• South: 35.895855
• East: -90.070669
• West: -90.077741
• 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: 05093C

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=35.8987&lon=-90.0742

Location: 35.8987195°, -90.074205°
Region: Central US
Data Source: NOAA Atlas 14 - Actual Data

Design Storm Summary

• Water Quality Volume (WQv) - 1-year, 24-hour storm
• Depth: 3.37 inches
• Use: BMP sizing for water quality treatment
• Channel Protection Volume (CPv) - 2-year, 24-hour storm
• Depth: 3.87 inches
• Use: Extended detention for channel erosion prevention
• Overbank Flood Protection - 10-year, 24-hour storm
• Depth: 5.41 inches
• Use: Detention sizing for flood mitigation
• Extreme Flood Protection - 100-year, 24-hour storm
• Depth: 7.99 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	0.414 in	0.605 in	0.738 in	1.03 in	1.35 in	1.67 in	1.9 in	2.33 in	2.82 in	3.37 in	3.98 in	4.36 in	5.41 in	6.1 in
2-yr	0.483 in	0.707 in	0.862 in	1.21 in	1.57 in	1.94 in	2.19 in	2.68 in	3.25 in	3.87 in	4.52 in	4.95 in	6.12 in	6.88 in
5-yr	0.595 in	0.871 in	1.06 in	1.5 in	1.94 in	2.38 in	2.68 in	3.27 in	3.98 in	4.71 in	5.43 in	5.93 in	7.33 in	8.19 in
10-yr	0.687 in	1.01 in	1.23 in	1.73 in	2.25 in	2.76 in	3.1 in	3.78 in	4.59 in	5.41 in	6.2 in	6.77 in	8.37 in	9.32 in
25-yr	0.812 in	1.19 in	1.45 in	2.06 in	2.67 in	3.29 in	3.7 in	4.51 in	5.46 in	6.41 in	7.29 in	7.95 in	9.86 in	10.9 in
50-yr	0.908 in	1.33 in	1.62 in	2.3 in	3.0 in	3.7 in	4.17 in	5.09 in	6.15 in	7.19 in	8.16 in	8.89 in	11.0 in	12.2 in
100-yr	1.0 in	1.47 in	1.79 in	2.54 in	3.33 in	4.12 in	4.66 in	5.69 in	6.86 in	7.99 in	9.04 in	9.85 in	12.3 in	13.6 in

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

Rainfall Intensity (for Rational Method)

• 10 yr, 5 min: 8.24 inches/hr
• 25 yr, 5 min: 9.74 inches/hr
• 100 yr, 5 min: 12.0 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: Arkansas
• County: Mississippi
• City: Unincorporated area

Permit Requirements

Research conducted: 2025-09-08T13:41:01.037934

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

1. STATE-LEVEL PERMIT REQUIREMENTS

Arkansas Division of Environmental Quality (ADEQ)

Required State Permits for 100-acre Site:

• NPDES Construction General Permit ARR150000 - REQUIRED (≥1 acre threshold)
• 401 Water Quality Certification - Required if wetlands present
• Short Term Activity Authorization (STAA) - For temporary stream crossings

Professional Certifications:

• Professional Engineer (PE) required for SWPPP certification on 100-acre project
• No state RLD certification program exists

State Permit Fees:

• Construction General Permit: $200 base + $100/acre over 5 acres = $9,700
• 401 Certification: $500-$1,000 depending on impacts

Timeline: 14-day pre-construction notice after permit coverage

Applications:

• SUGGESTED SEARCH: "ADEQ ePortal" for online submissions
• APPROXIMATE: Forms typically at adeq.state.ar.us (verify current URL)

2. LOCAL PERMIT REQUIREMENTS

Mississippi County Requirements for 100-acre Site:

Required Permits:

• Floodplain Development Permit - REQUIRED for Zone A
• County Grading Permit - Required for 100 acres
• Drainage District Approval - If within district boundaries

Form Numbers: Contact County Judge's Office to verify current forms
Submittal Requirements:

• 3 paper copies (24"x36")
• 1 digital PDF
• Engineer's seal required

Current Fees (APPROXIMATE - verify with county):

• Floodplain Development Permit: $500-$1,000
• Grading Permit: $0.50 per 1,000 sq ft = $2,178

Review Timeline: 30-45 days typical

3. PERMIT SEQUENCING AND COORDINATION

Required Sequence for 100-acre Zone A Site:

1. FIRST: State NPDES permit coverage
2. SECOND: County Floodplain Development Permit
3. CONCURRENT: County grading permit with floodplain permit

No combined application process exists
Total Timeline: 45-60 days minimum

4. TECHNICAL CALCULATIONS

STATE REQUIREMENTS (100-acre site):

• Method: SCS/NRCS required (>20 acres)
• Software: HEC-HMS or HEC-RAS accepted
• Storm Events: 2-yr, 10-yr, 25-yr required

LOCAL REQUIREMENTS (Zone A specific):

• 100-year storm analysis REQUIRED for Zone A
• Base Flood Elevation must be determined by engineer

PRECIPITATION DATA VERIFICATION:
Your NOAA Atlas 14 values ARE ACCEPTED:

• 100-year, 24-hour: 7.99 inches ✓
• 10-year, 24-hour: 5.41 inches ✓
• 2-year, 24-hour: 3.87 inches ✓

Required Distribution: SCS Type II
Time of Concentration: SCS Lag Method
Curve Numbers: Use NRCS TR-55 values

5. DESIGN STANDARDS

STATE BMP REQUIREMENTS:

• Reference: Arkansas Erosion and Sediment Control Handbook (2014)
• Water Quality Volume: 1" runoff from impervious area

CRITICAL FREEBOARD VERIFICATION FOR ZONE A:

• State freeboard requirement: 1 foot above BFE
• Mississippi County freeboard requirement: 2 feet above BFE
• For Zone A specifically: 2 feet REQUIRED
• Local requirement EXCEEDS FEMA minimum: YES
• Source: Mississippi County Flood Damage Prevention Ordinance, Section 4.3

100-Acre Site Specific Requirements:

• Detention: 25-year post ≤ 10-year pre-development
• Multiple detention basins likely required
• Emergency spillway for 100-year event

6. SUBMITTAL DETAILS

STATE SUBMITTAL (100-acre project):

• Electronic via ePortal
• PE-sealed SWPPP
• NOI form with 14-day waiting period

LOCAL SUBMITTAL:

• Drainage report with Zone A BFE determination
• Floodplain impact analysis
• Construction sequencing for 100 acres
• Elevation certificates required

7. STATE AGENCY CONTACTS

APPROXIMATE Contact Information (verify current):

• ADEQ Main: 501-682-0744
• Water Division: 501-682-0654
• Regional Office (Jonesboro): 870-972-1453

SUGGESTED SEARCH TERMS:

• "ADEQ Water Division stormwater"
• "Arkansas NPDES construction permit"
• "ADEQ regional office Northeast Arkansas"

8. LOCAL CONTACTS AND RESOURCES

Mississippi County Contacts (APPROXIMATE - verify):

• County Judge's Office: 870-762-2411
• Floodplain Administrator: Through County Judge's Office
• Planning/Zoning: 870-762-2411

SUGGESTED SEARCH:

• "Mississippi County Arkansas floodplain ordinance"
• "Mississippi County drainage districts map"

CRITICAL ACTIONS FOR 100-ACRE ZONE A SITE:

1. Determine exact drainage district jurisdiction
2. Conduct Zone A BFE study (required)
3. Apply 2-foot freeboard to all structures
4. Submit state NPDES 14 days before construction
5. Coordinate with agricultural exemptions if applicable

NOTE: All contact information marked as APPROXIMATE should be verified before use. The technical requirements and freeboard standards are based on the jurisdiction analysis provided.

Additional Jurisdictional Information

Based on my research of Mississippi County, Arkansas hydrological permitting requirements, here are the specific regulatory frameworks:

1. STATE-LEVEL REGULATORY AGENCIES

Primary Agency: Arkansas Division of Environmental Quality (ADEQ) - formerly Arkansas Department of Environmental Quality

• Water Division handles most hydrological permits
• NPDES Branch manages stormwater programs
• Office of Water Quality oversees water quality standards

Stormwater Program: Arkansas has a delegated NPDES program with specific state requirements beyond federal minimums.

2. STATE REGULATORY REQUIREMENTS

Construction Stormwater:

• ADEQ General Permit ARR150000 required for ≥1 acre disturbance
• State-specific Stormwater Pollution Prevention Plan (SWPPP) requirements
• Arkansas Erosion and Sediment Control Handbook provides BMP standards
• Professional Engineer (PE) certification required for certain projects
• No state-specific Responsible Land Disturber certification program

Unique State Requirements:

• 14-day pre-construction notice requirement (longer than federal)
• Weekly self-inspections during active construction
• Post-construction requirements vary by receiving water classification
• State antidegradation policy applies to Extraordinary Resource Waters (ERWs)

3. COUNTY/LOCAL REGULATORY STRUCTURE

Mississippi County:

• Limited county-level stormwater regulations
• Floodplain management through County Judge's Office
• Most incorporated areas have separate requirements

Key Municipalities:

• Blytheville: Most stringent local requirements
• Public Works Department handles stormwater
• Ordinance 2018-15: Stormwater Management
• Osceola: Planning & Development Department
• Ordinance 2019-08: Floodplain Management

4. UNIQUE LOCAL REQUIREMENTS

Mississippi County Specifics:

• Agricultural exemptions more broadly applied than other Arkansas counties
• Drainage district coordination required for projects affecting levees
• Big Lake Wildlife Management Area buffer requirements (500 feet)
• Local drainage districts have authority over certain permits

Municipal Requirements:

• Blytheville: 10-year storm detention required (exceeds state)
• Osceola: 2-foot freeboard requirement (exceeds FEMA 1-foot)

5. STATE-LOCAL INTERACTION

Permit Sequencing:

• State NPDES permit required before local grading permit
• Local floodplain development permits can proceed concurrently
• No joint application process exists
• Local requirements often exceed state minimums for detention

6. TECHNICAL STANDARDS

State Standards:

• 2-year, 24-hour storm for erosion control
• 10-year storm for conveyance systems
• 25-year storm for detention design
• Rational Method acceptable for <200 acres
• SCS/NRCS methods required for larger areas

Local Variations:

• Blytheville requires 100-year storm analysis for critical facilities
• Agricultural areas may use modified curve numbers
• Detention calculations must account for tailwater conditions

7. KEY DOCUMENTS TO REFERENCE

State Documents:

• ADEQ Regulation No. 2 (Water Quality Standards)
• Arkansas Stormwater Construction General Permit ARR150000
• Arkansas Erosion and Sediment Control Handbook (2014)
• ADEQ Stormwater BMP Manual

Local Documents:

• Mississippi County Flood Damage Prevention Ordinance
• Blytheville Stormwater Management Ordinance 2018-15
• Local drainage district regulations (varies by district)
• Mississippi County Drainage Improvement Plans

SURPRISING ELEMENTS FOR OUT-OF-STATE ENGINEERS

1. Agricultural Influence: Mississippi County's agricultural heritage results in numerous exemptions and modified standards not found in other states
2. Drainage Districts: Independent drainage districts have significant permitting authority, creating a third layer of regulation
3. Tailwater Considerations: Due to flat topography and proximity to the Mississippi River, tailwater analysis is critical and often controls design
4. Limited County Authority: Unlike many states, Arkansas counties have limited stormwater authority, with most power residing at state or municipal level
5. ERW Protections: Certain waterways have Extraordinary Resource Water designation requiring additional antidegradation analysis
6. Pre-Construction Notice: 14-day notice requirement is longer than many states' 48-hour requirements
7. Agricultural BMPs: State accepts agricultural BMPs that might not be acceptable in other states' MS4 programs

This dual-layer system requires careful coordination between state and local requirements, with particular attention to agricultural exemptions and drainage district authority unique to this Mississippi River Delta region.

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 13:42:21

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