Stormwater Ordinance

Knox County, TN Stormwater Management Manual: Volume 2

Whole Manual (pdf)

Chapter 1 Introduction (pdf)

Chapter 1 Addressing Stormwater Management Needs (pdf)

1.1 Impacts of Development and Stormwater Runoff
- 1.1.1 Development Changes Land and Runoff
- 1.1.2 Changes to Stream
- 1.1.3 Changes to Stream Geometry
- 1.1.4 Impacts to Aquatic Habitat
- 1.1.5 Water Quality Impacts
- 1.1.6 Stormwater Hotspots
- 1.1.7 Effects on Ponds, Lakes and Reservoirs
1.2 Addressing Stormwater Impacts
1.3 Comprehensive Stormwater Management Planning
1.4 Minimum Stormwater Management Standards
1.5 Stormwater Quality Treatment Rationale
- 1.5.1 Regulatory Overview
- 1.5.2 Attaining the Water Quality Standard

Chapter 2 Criteria for Stormwater Design (pdf)

2.1 Integrated Site Design Approach
- 2.1.1 Introduction
- 2.1.2 General Design Policies and Guidance
2.2 Stormwater Quality Management
- 2.2.1 General Requirements and Policies
- 2.2.2 Percent TSS Removal Values for Structural BMPs
- 2.2.3 Calculation of WQv and %TSS Removal
- 2.2.4 Calculation of %TSS Removal for BMPs in Parallel
- 2.2.5 Calculation of %TSS Removal for BMPs in Series
- 2.2.6 Calculation of %TSS Removal for Flow-through Situations
- 2.2.7 The Measurement and Calculation of Percent Imperviousness
- 2.2.8 Reducing the WQv
2.3 Channel Protection (CPv)
- 2.3.1 Background
- 2.3.2 Design Criteria and Policies
2.4 Stormwater Quantity Management
- 2.4.1 Overbank Flood Protection Criteria (Qp25)
- 2.4.2 Extreme Flood Protection (Qp100)
- 2.4.3 Downstream Impact Analysis
2.5 Stormwater Conveyance Design
- 2.5.1 General Criteria
- 2.5.2 Pipe Systems
- 2.5.3 Roadway Culverts
- 2.5.4 Open Channels
- 2.5.5 Outlet Protection
- 2.5.6 Gutters and Inlets
2.6 Bridge Requirements

Chapter 3 Stormwater Hydrology (pdf)

3.1 Introduction to Hydrologic Methods
- 3.1.1 Symbols and Definitions
- 3.1.2 Rainfall Estimation
- 3.1.3 Rational Method
- 3.1.4 Regression Methods
- 3.1.5 SCS Hydrologic Method
- 3.1.6 Clark Unit Hydrograph
- 3.1.7 Water Quality Calculations
- 3.1.8 Water Balance Calculations
- 3.1.9 Calculating Downstream Impacts (the Ten Percent Rule)
3.2 Storage Design
- 3.2.1 General Storage Concepts
- 3.2.2 Symbols and Definitions
- 3.2.3 Flood Protection Storage Design Procedures
- 3.2.4 Preliminary Detection Calculations
- 3.2.5 Estimation of the Channel Protection Volume
3.3 Outlet Structures
- 3.3.1 Symbols and Definitions
- 3.3.2 Primary Outlets
- 3.3.3 The Design of Extended Detention Outlets
- 3.3.4 The Design of Channel Protection Outlets
- 3.3.5 Multi-Stage Outlet Design
- 3.3.6 Trash Rack and Safety Grates
- 3.3.7 Secondary Outlets

Chapter 4 Design and Maintenance of Structural BMPs

4.1 Design Standards Policy
4.2 BMP Description and Selection Information

(Section 4.1 and 4.2 are part of one document. Please click on section 4.1 above to access this section)
- 4.2.1 General Application BMPs
- 4.2.2 Limited Application BMPs
- 4.2.3 Pollutant Removal Capabilities
- 4.2.4 Screening Process for General Application BMPs
- 4.2.5 Limited Application BMP Screening Process
- 4.2.6 Off-Line Versus On-Line Structural BMPs
- 4.2.7 Using Structural Stormwater BMPs in Series
4.3 General Application Stormwater BMPs
4.4 Limited Application Stormwater BMPs

Chapter 5 Stormwater Credits and Better Site Design Practices (pdf)

5.1 Introduction
5.2 Water Quality Volume (WQv) Credits
- 5.2.1 Introduction
- 5.2.2 Site Planning Using Stormwater Site Design Credits
- 5.2.3 General Policies for WQv Credits
- 5.2.4 Credit #1: Natural Area Preservation
- 5.2.5 Credit #2: Managed Open Space Preservation
- 5.2.6 Credit #3: Stream and Vegetated Buffers
- 5.2.7 Credit #4: Use of Vegetated Channels
- 5.2.8 Credit #5: Impervious Area Disconnection
- 5.2.9 Credit #6: Environmentally Sensitive Large Lot Neighborhoods
5.3 Better Site Design Practices
- 5.3.1 Overview
- 5.3.2 Incorporating Better Site Design Practices into Site Design Process
- 5.3.3 Discussion of Better Site Design Practices
- 5.3.4 Conservation of Natural Features and Resources
- 5.3.5 Low Impact Site Design Techniques
- 5.3.6 Reduction of Impervious Cover
- 5.3.7 Using Natural Features for Stormwater Management
- 5.3.8 Better Site Design Examples

Chapter 6 Water Quality Buffers (pdf)

6.1 Introduction
6.2 Applicability
- 6.2.1 Community Waters Definition
6.3 Buffer Zones and Widths
- 6.3.1 Zones
- 6.3.2 Widths
- 6.3.3 Width Requirements for Steep Slopes
6.4 Vegetation and Enhancement Requirements
- 6.4.1 Inner Zone (Streams and Wetlands)
- 6.4.2 Outer Zone (Streams and Ponds/Lakes)
- 6.4.3 Non-native and Invasive Vegetation
- 6.4.4 Buffer Enhancement Requirements
6.5 Water Quality Buffer Averaging
- 6.5.1 Requirements and Policies
- 6.5.2 Areas Where Buffer Averaging is Prohibited
- 6.5.3 Example Calculation
6.6 Use of Buffer Areas
- 6.6.1 Prohibited Uses
- 6.6.2 Allowable Uses in the Inner Zone
- 6.6.3 Allowable Uses in the Outer Zone
6.7 Allowable Disturbances
- 6.7.1 Inner Zone
- 6.7.2 Outer Zone
6.8 Protection of Water Quality Buffers
- 6.8.1 During Construction
- 6.8.2 After Construction
- 6.8.3 Signage
6.9 Level Spreaders
6.10 Conflicts with State Requirements

Chapter 7 Stormwater Drainage Design (pdf)

7.1 Stormwater Drainage System Design
- 7.1.1 Drainage System Components
- 7.1.2 Checklist for Drainage Planning and Design
- 7.1.3 General Drainage Design Standards
7.2 Storm Drain Pipe Systems
- 7.2.1 Design Standards and Considerations
- 7.2.2 General Design Procedure
- 7.2.3 Capacity Calculations
- 7.2.4 Hydraulic Grade Lines
- 7.2.5 Minimum Grade
7.3 Culvert Design
- 7.3.1 Symbols and Definitions
- 7.3.2 Design Standards and Considerations
- 7.3.3 Design Procedures
- 7.3.4 Culvert Design Example
- 7.3.5 Design Procedures for Beveled-Edged Inlets
- 7.3.6 Flood Routing and Culvert Design
7.4 Open Channel Design
- 7.4.1 Open Channel Types
- 7.4.2 Symbols and Definitions
- 7.4.3 Design Standards and Considerations
- 7.4.4 Manning’s “n” Values
- 7.4.5 Uniform Flow Calculations
- 7.4.6 Critical Flow Calculations
- 7.4.7 Vegetative Design
- 7.4.8 Riprap Design for Lining Open Channels
- 7.4.9 Gradually Varied Flow
- 7.4.10 Rectangular, Triangular, and Trapezoidal Open Channel Design
7.5 Energy Dissipation Design
- 7.5.1 Overview
- 7.5.2 Symbols and Definitions
- 7.5.3 Design Guidelines
- 7.5.4 Riprap Aprons
- 7.5.5 Riprap Basins
- 7.5.6 Baffled Outlets
- 7.5.7 Level Spreaders
7.6 Minor Drainage System Design
- 7.6.1 Introduction and General Criteria
- 7.6.2 Symbols and Definitions
- 7.6.3 Street and Roadway Gutters
- 7.6.4 Stormwater Inlets
- 7.6.5 Grate Inlet Design
- 7.6.6 Curb Inlet Design
- 7.6.7 Combination Inlets
7.7 Bridge Hydraulics
- 7.7.1 Bridge Hydraulics Concepts
- 7.7.2 Computer Applications

Chapter 8 Floodplain and Sinkholes (pdf)

8.1 Introduction
8.2 Applicable Federal Regulations
- 8.2.1 National Flood Insurance Program
- 8.2.2 Community Rating System
8.3 Local Floodplain Management Tools
- 8.3.1 FEMA Flood Insurance Studies
- 8.3.2 Knox County Engineering Floodplain Mapping
- 8.3.3 Stormwater Master Plans
8.4 Floodplain Management Regulations
- 8.4.1 Summary of Ordinance Requirements for Development in Floodplains
- 8.4.2 Requirements for Land Use and Land Disturbance
- 8.4.3 Requirements for Engineering Studies
- 8.4.4 Requirements for Construction in Floodplains
8.5 Regulations for Development in Sinkhole Areas
- 8.5.1 Background
- 8.5.2 Regulations and Policies

Chapter 9 Construction Site Stormwater Management (pdf)

9.1 TN Construction General Permit
9.2 General Principles
9.3 Regulations and Policies
- 9.3.1 General
- 9.3.2 Protection of Water Quality Buffers
- 9.3.3 Stabilization of Disturbed Areas
- 9.3.4 Off-Site Sedimentation
- 9.3.5 Construction Sequencing
- 9.3.6 Structural Controls
- 9.3.7 Special Requirements Priority Construction Activities
- 9.3.8 Cut and Fill Slopes
- 9.3.9 Construction Exits
- 9.3.10 Good Housekeeping Practices
9.4 Erosion Prevention and Sediment Control Plans
- 9.4.1 Plan Modifications
9.5 Deficient Performance
9.6 Inspections and Maintenance
9.7 Small Lot EPSC Plans