Proposed Flood and Water Quality Protection Manual

The City of Lincoln, in coordination with the Lower Platte South Natural Resources District, is working on revising the Flood and Water Quality Protection Manual to make updates, clarifications and readability improvements. It is planned to be produced as a digital document with a common and consistent format. The Flood and Water Quality Protection Manual provides guidelines and criteria primarily for Stormwater standards, detention/retention facilities, open channels, closed drainage systems, Stormwater best management practices, erosion and sediment control and flood design criteria.

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Final Draft Flood and Water Quality Protection Manual

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Cover and Table of Contents (418 K)

• Cover Page
• Acronyms and Abbreviations
• Definitions
• Table of Contents
• Preamble

1.0 INTRODUCTION (146 K)

• 1.1 Purpose
• 1.2 Objectives
• 1.3 Universal Requirements for Stormwater Management
• 1.4 Criteria and Technical Requirements
  • 1.4.1 Minor Drainage System
  • 1.4.2 Major Drainage System
• 1.5 Highlighted Elements of this Flood and Water Quality Protection Manual
  • 1.5.1 Detention / Retention Facilities
  • 1.5.2 Streets
  • 1.5.3 Minimum Flood Corridors
  • 1.5.4 Floodplain Management
  • 1.5.5 NPDES Construction Site Activities
  • 1.5.6 Stormwater Quality
  • 1.5.7 Rainfall Data
  • 1.5.8 Freeboard

2.0 HYDROLOGY (458 K)

• 2.1 Introduction
• 2.2 Hydrologic Analysis Methods
• 2.3 Hydrologic Design Criteria
• 2.4 Rational Method
  • 2.4.1 Time of Concentration (Tc)
  • 2.4.2 Rainfall Intensity (I)
  • 2.4.3 Runoff Coefficient (C)
  • 2.4.4 Rational Method Limitations
• 2.5 Curve Number Method
  • 2.5.1 Direct Runoff (Q)
  • 2.5.2 Drainage Area
  • 2.5.3 Rainfall
  • 2.5.4 Time of Concentration
  • 2.5.5 Runoff Factor

3.0 STORM DRAINAGE (226 K)

• 3.1 Introduction
• 3.2 Pavement Drainage Design Factors
  • 3.2.1 Runoff Width (Spread) on Pavement
  • 3.2.2 Longitudinal Slope
  • 3.2.3 Cross Slope
  • 3.2.4 Curb and Gutter
  • 3.2.5 Roadside and Median Drainageways
  • 3.2.6 Bridge Decks
  • 3.2.7 Median/Barriers
  • 3.2.8 Gutter Flows
• 3.3 Storm Drain Inlets
  • 3.3.1 Introduction
  • 3.3.2 Storm Drain Inlet Design Criteria
  • 3.3.3 Manholes
  • 3.3.4 Grate Inlets
  • 3.3.5 Curb Inlets
• 3.4 Storm Drain Systems
  • 3.4.1 Introduction
  • 3.4.2 Design Criteria
  • 3.4.3 Design Procedures
  • 3.4.4 Capacity

4.0 CULVERTS (209 K)

• 4.1 Introduction
• 4.2 Design Criteria
  • 4.2.1 Flood Frequency
  • 4.2.2 Velocity Limitations
  • 4.2.3 Buoyancy Protection
  • 4.2.4 Length and Slope
  • 4.2.5 Debris Control
  • 4.2.6 Headwater and Other Limitations
  • 4.2.7 Tailwater Considerations
  • 4.2.8 Freeboard
  • 4.2.9 Culvert Inlets
  • 4.2.10 Inlets with Headwalls
  • 4.2.11 Wingwalls and Aprons
  • 4.2.12 Improved Inlets
  • 4.2.13 Manning’s n Values
  • 4.2.14 Culvert Skews
  • 4.2.15 Culvert Sizes
  • 4.2.16 Outlet Protection
  • 4.2.17 Permitting Considerations
  • 4.2.18 Safety Considerations
  • 4.2.19 Loading Requirements
• 4.3 Culvert Flow Controls
  • 4.3.1 Inlet Control
  • 4.3.2 Outlet Control
• 4.4 Design Procedures
• 4.5 Design of Improved Inlets
  • 4.5.1 Outlet Control
  • 4.5.2 Inlet Control
  • 4.5.3 Common Entrances
  • 4.5.4 Capacity Determinations
  • 4.5.5 Improved Inlets
• 4.6 Culvert Computer Programs
• 4.7 Construction, Safety, and Maintenance Considerations
  • 4.7.1 Scour and Sedimentation
  • 4.7.2 Maintenance

5.0 OPEN CHANNELS (288 K)

• 5.1 Introduction
• 5.2 Hydraulic Terms
  • 5.2.1 Steady and Unsteady State Flow
  • 5.2.2 Uniform Flow and Normal Depth
  • 5.2.3 Critical Flow
  • 5.2.4 Gradually Varied Flow
  • 5.2.5 Rapidly Varied Flow
• 5.3 General Open Channel Design Criteria
  • 5.3.1 Return Period Design Criteria
  • 5.3.2 Flood Limits Determination
  • 5.3.3 Velocity Limitations
  • 5.3.4 Channel Transitions
  • 5.3.5 Construction and Maintenance Considerations
  • 5.3.6 Freeboard
• 5.4 Channel Types
  • 5.4.1 Natural Channels
  • 5.4.2 Grass-Lined Channels (Constructed Channel)
  • 5.4.3 Wetland Bottom Channels (Constructed Channel)
  • 5.4.4 Rock-lined Channels (Constructed Channel)
  • 5.4.5 Concrete Channels (Constructed Channel)
• 5.5 Grade Control Structures
  • 5.5.1 Check Structures
  • 5.5.2 Drop Structures, Chutes, and Flumes
  • 5.5.3 Grade Control Design Guidance
• 5.6 Streambank Protection
  • 5.6.1 Rock Riprap
  • 5.6.2 Wire-enclosed Rock (Gabions)
  • 5.6.3 Pre-Cast Concrete Blocks
  • 5.6.4 Grouted Rock
  • 5.6.5 Bioengineering Methods

6.0 DETENTION / RETENTION FACILITIES (147 K)

• 6.1 Introduction
• 6.2 Ownership and Maintenance
• 6.3 Design Criteria
  • 6.3.1 Discharge Rates
  • 6.3.2 Storage Volumes
  • 6.3.3 Grading and Depth Requirements
  • 6.3.4 Outlet Works
  • 6.3.5 Location and Downstream/Upstream Analysis
  • 6.3.6 Construction and Maintenance Considerations
• 6.4 Nebraska Safety of Dams and Reservoirs Act
  • 6.4.1 Classification
  • 6.4.2 New Dams

7.0 ENERGY DISSIPATION (735 K)

• 7.1 Introduction
• 7.2 Riprap Apron
  • 7.2.1 Design Procedures for Riprap Apron
  • 7.2.2 Outletting to a Channel
  • 7.2.3 Depth of Riprap
• 7.3 Energy Dissipation Basin
  • 7.3.1 Design Procedures for Energy Dissipation Basins
• 7.4 Submittals

8.0 POST-CONSTRUCTION BEST MANAGEMENT PRACTICES (162 K)

• 8.1 Introduction
  • 8.1.1 Clean Water Act Requirements
  • 8.1.2 General Planning and Design Guidelines
  • 8.1.3 Ownership and Maintenance of BMPs
  • 8.1.4 Type of BMPs
• 8.2 Design Criteria
  • 8.2.1 General Criteria
  • 8.2.2 New Development Standard Criteria
  • 8.2.3 Redevelopment Standard Criteria
  • 8.2.4 Water Quality Control Volume
  • 8.2.5 Release Rates
  • 8.2.6 Storage Volume
  • 8.2.7 Infiltration
  • 8.2.8 Grading and Depth Requirements
  • 8.2.9 Outlet Works
  • 8.2.10 Location and Downstream Analysis
• 8.3 Other Items
  • 8.3.1 Exemptions
  • 8.3.2 Waivers
  • 8.3.3 Approved Alternatives
  • 8.3.4 Credit Policy
• 8.4 Stormwater Management Plan and Maintenance Agreement
  • 8.4.1 Introduction
  • 8.4.2 Maintenance Responsibility for BMPs

9.0 EROSION AND SEDIMENT CONTROL PROCEDURES (1.81 M)

• 9.1 Introduction
  • 9.1.1 Fundamentals of the Erosion Process
  • 9.1.2 Erosion Types
  • 9.1.3 Factors Influencing Soil Erosion
• 9.2 Stormwater Pollution Prevention Plan Requirements for Construction Activity
  • 9.2.1 Construction Stormwater Permitting
  • 9.2.2 Summary of Required SWPPP Items for Construction Activities
  • 9.2.3 General Information for Construction Activity SWPPPs
  • 9.2.4 General Requirements for Construction Activity SWPPPs
  • 9.2.5 SWPPP Objectives
  • 9.2.6 SWPPP Development – Site Assessment and Planning
  • 9.2.7 Requirements for the Building Phase of Development
  • 9.2.8 SWPPP Erosion and Sediment Control Requirements
  • 9.2.9 Good Housekeeping BMPs
  • 9.2.10 SWPPP Inspection, Maintenance, and Enforcement Procedures
• 9.3 Best Management Practice (BMP) Selection
  • 9.3.1 Vegetated Buffer/Filter Strip BMP Designs
  • 9.3.2 Silt Fence
  • 9.3.3 Wattle Barriers
  • 9.3.4 Compost Berms
  • 9.3.5 Storm Drain Inlet Protection
  • 9.3.6 Outlet Protection
  • 9.3.7 Protection (Transition) Mat
  • 9.3.8 Temporary Diversions
  • 9.3.9 Check Dams
  • 9.3.10 Construction Entrance
  • 9.3.11 Temporary Culvert Stream Crossing
  • 9.3.12 Temporary Sediment Trap
  • 9.3.13 Temporary Sediment Basin
  • 9.3.14 Temporary Seeding
  • 9.3.15 Permanent Seeding
  • 9.3.16 Hydroseeding / Hydromulching
  • 9.3.17 Slope Tracking
  • 9.3.18 Mulching
  • 9.3.19 Rolled Erosion Control Products
  • 9.3.20 Safety Fence
  • 9.3.21 Dust Control
  • 9.3.22 Other Best Management Practices

10.0 FLOODPLAIN MANAGEMENT (186 K)

• 10.1 Introduction
• 10.2 No Net Rise and No Net Fill / Compensatory Storage
  • 10.2.1 No Net Rise
  • 10.2.2 No Net Fill / Compensatory Storage
  • 10.2.3 No Net Fill in the Existing Urban Area
  • 10.2.4 Exceptions to No Net Fill and No Net Rise Criteria
  • 10.2.5 Minimum Federal Standards
• 10.3 Minimum Flood Corridor in New Growth Areas
  • 10.3.1 Sequencing Criteria for Minimum Flood Corridors
  • 10.3.2 Mitigation
• 10.4 Stream Crossings
  • 10.4.1 Mitigation
• 10.5 Information Required

References (113 K)

Appendices

• Appendix A Structural Best Management Practice Descriptions (Appendices 8.1 and 8.2) (1.13 M)
  • Appendix 8.1 Structural Best Management Practice (BMP) Descriptions
    • Appendix 8.1.1 Bioretention (also Rain Garden, Porous Landscape Detention)
    • Appendix 8.1.2 Constructed Wetland Pond
    • Appendix 8.1.3 Extended Detention Basin
    • Appendix 8.1.4 Green Roof
    • Appendix 8.1.5 Permeable Pavement
      • Appendix 8.1.5.1 Permeable Interlocking Concrete Pavement (PICP)
      • Appendix 8.1.5.2 Concrete Grid Pavement
      • Appendix 8.1.5.5 Reinforced Grass
    • Appendix 8.1.6 Retention Pond
    • Appendix 8.3.7 Underground BMPs
    • Appendix 8.1.8 Grassed-Swales
    • Appendix 8.1.9 Buffer Areas
    • Appendix 8.1.10 Soil Conditioning
  • Appendix 8.2 Best Management Practice Maintenance
    • Appendix 8.2.1 Introduction
    • Appendix 8.2.2 Defining Maintenance Responsibility for Public and Private Facilities
    • Appendix 8.2.3 Developing a Maintenance Plan
    • Appendix 8.2.4 Bioretention Maintenance
    • Appendix 8.2.5 Constructed Wetland Maintenance
    • Appendix 8.2.6 Extended Detention Basin Maintenance
    • Appendix 8.2.7 Green Roof Maintenance
    • Appendix 8.2.8 Permeable Pavement Maintenance
    • Appendix 8.2.9 Retention Pond Maintenance
    • Appendix 8.2.10 Underground BMP Maintenance
    • Appendix 8.2.11 Grassed-Swales and Buffers Maintenance
    • Appendix 8.2.12 Soil Conditioning Maintenance
• Appendix B Water Quality Control Form (Appendix 8-3) (50 K)
• Appendix C Request for Waiver to Chapter 28.03 (Appendix 8.4) (47 K)
• Appendix D Request for Approved Alternative to Chapter 28.03 (Appendix 8.5) (48 K)
• Appendix E Stormwater Management Plan Maintenance Agreement and Easement (Appendix 8.6) (154 K)
• Appendix F Example Maintenance Inspection Form (Appendix 8.7) (110 K)

List of Figures

• Figure 2-1. NOAA Atlas 14 Intensity-Duration-Frequency Curves for Lincoln, Nebraska
• Figure 2-2. Graphic Data for the MSE3 Distribution
• Figure 7-1. Design of Riprap Apron Minimum Tailwater Conditions
• Figure 7-2. Design of Riprap Apron Maximum Tailwater Conditions
• Figure 7-3. Riprap Apron Schematic for Uncertain Tailwater Conditions
• Figure 7-4. Energy Dissipation Basin
• Figure 9-1. Process Chart
• Figure 9-2. Vegetated Filter / Buffer Strip
• Figure 9-3. Wattle Barrier Installation
• Figure 9-4. Compost Berm Detail
• Figure 9-5. Temporary Diversion Dike
• Figure 9-6. Rock Check Dams
• Figure 9-7. Temporary Culvert Crossing
• Figure 9-7. Temporary Sediment Trap
• Figure 9-7. Sediment Trap Embankment Diagram
• Figure 9-10. Principal Spillway with Rock Option
• Figure 9-11. Principal Spillway with Skimmer Option
• Figure 9-12. Emergency Spillway
• Figure 9-13. Hydroseed / Hydromulch / Polymer Application
• Figure 9-14. Slope Tracking / Contour Furrows
• Appendix Figure 8-1. Bioretention
• Appendix Figure 8-2. Constructed Wetland Pond
• Appendix Figure 8-3. Extended Detention Basin
• Appendix Figure 8-4. Permeable Pavement Systems
• Appendix Figure 8-5. Retention Pond - Plan and Cross Section

List of Tables

• Table 2-1. City of Lincoln Rainfall Amounts by Recurrence Interval and Percentiles
• Table 2-2. NOAA Atlas 14 Intensity-Duration-Frequency Table for Lincoln, Nebraska
• Table 2-3. Recommended Rational Method Coefficient of Runoff Values for Various Selected Land Uses
• Table 2-4. Recommended Rational Method Coefficient of Runoff for Pervious Surfaces (Unimproved Areas) by Selected Hydrologic Soil Groupings and Slope Ranges
• Table 2-5. Tabular Rainfall Distribution from NOAA Atlas 14
• Table 2-6. Roughness Coefficients (Manning’s n) for Sheet Flow
• Table 2-7. Runoff Curve Numbers – Urban Areas
• Table 2-8. Cultivated Agricultural Land
• Table 2-9. Other Agricultural Lands
• Table 2-10. Conversion from Average Antecedent Moisture Conditions to Dry and Wet Conditions
• Table 2-11. Rainfall Groups for Antecedent Soil Moisture Conditions during Growing and Dormant Seasons
• Table 2-12. Composite Curve Number Calculations
• Table 3-1. Allowable Maximum Encroachment for Minor Storms
• Table 3-2. Allowable Maximum Encroachment for Major Storms
• Table 3-3. Allowable Cross Street Flow
• Table 3-4. Manning’s n Values for Street and Pavement Gutters
• Table 3-5. Inlet Design
• Table 3-6. Pipe Sizing
• Table 4-1. Inlet Coefficients
• Table 4-2. Manning’s n values
• Table 5-1. Uniform Flow Values of Roughness Coefficient – n
• Table 5-2. Manning’s Roughness Coefficients for Grass-Lined Channels = n
• Table 7-1 Template Submittal Form
• Table 8-1. Water Quality Rainfall Amounts
• Table 9-1. Typical Land Slope and Distance for Silt Fence
• Table 9-2. Permissible Velocities for Grass- and Earth-lined Channels
• Table 9-3. Properties of Filter Cloth
• Table 9-4. General Guideline Pipe Diameter (inches) for Stream Crossings.*
• Table 9-5. Guidelines for Temporary Seeding
• Appendix Table 8-1. Filter Cloth Gradation
• Appendix Table 8-2.* Slotted Pipe Dimensions

List of Equations

• Equation 2.1    The Rational Method Equation (Q = CIA)
• Equation 2.2    Q = C_f CIA
• Equation 2.3    Q = (P – 0.2S)² / (P +0.8S)
• Equation 2.4    S = (1000 / CN) – 10
• Equation 2.5    T_t = L/(3600V)
• Equation 2.6    T_c = T_t1 + T_t2 + ... Tt_m
• Equation 2.7    T_t = [0.42 (nL)^0.8 / (P₂) ^0.5s^0.4]
• Equation 2.8    Unpaved (V = 16.1345(s)^0.5)
• Equation 2.9    Paved (V = 20.3282(s)^0.5)
• Equation 2.10    V = (1.486 r^2/3 s^1/2)/n )
• Equation 3.1    Q = [0.56 / n] Sx ^5/3 S^1/2 T^8/3
• Equation 3.2    Q_w = 3.0 Pd^1.5 (weir flow)
• Equation 3.3    Q_o = 0.67 A (2gd)^0.5 (orifice flow)
• Equation 3.4    Q_i = Q_g (1-(1-(E_L/(k Q_g^0.42 S^0.3)) (n S_e)^0.6)^1.8) (FHA, Circular 22)
• Equation 3.5    Q = [1.486 A R^2/3 S^1/2]/n
• Equation 3.6    Q = K S^1/2
• Equation 5.1    Q = 1.486 A R ^2/3 S ^1/2/n
• Equation 5.2    Fr = v / (gD)^0.5
• Equation 5.3    nc = (n₀p₀ + n_wp_w)/(p₀ + p_w)
• Equation 5.4    n = 0.0395 (d₅₀)^1/6
• Equation 5.5    VS^0.17/d₅₀^0.5(S_s – 1)^0.66 = 4.5
• Equation 8.1    WQCV = P x (0.05 + 0.009 x I) x A x 1/12
• Equation 9.1    V₁= 0.85 x A₁ x D₁ where:
• Equation 9.2    V₂= (A1 + A₂) / 2 x D₂ where:
• Appendix Equation 8.1    V = WQCV x 43,560 ft²/ac
• Appendix Equation 8.2    A = (V/86,400)/(0.6 x (64.4 x H/2)0.5)
• Appendix Equation 8.3    D = 24 x (A/π)0.5
• Appendix Equation 8.4    Vp ≥ 1.2 x (WQCV)
• Appendix Equation 8.5    Vel = Q100/A ≤ 2
• Appendix Equation 8.6    Vr= Por x ((D-1)/12) x Ap
• Appendix Equation 8.7    Vp ≥ 1.2 x (WQCV)
• Appendix Equation 8.8    A = (V/43,200)/(0.6 x (64.4*H/2)0.5)
• Appendix Equation 8.9    D = 24 x (A/π)0.5

Current Drainage Criteria Manual