CHAPTER 5 STORMWATER DRAINAGE SYSTEM DESIGN

1 Volume 2 (Technical Handbook) Georgia STORMWATER Management Manual 5-1 CHAPTER 5 STORMWATER DRAINAGE SYSTEM DESIGN Table of Contents SECTION STORMWATER DRAINAGE DESIGN OVERVIEW STORMWATER DRAINAGE SYSTEM DESIGN ..5-1 Introduction ..5-1 DRAINAGE SYSTEM Components ..5-1 Checklist for DRAINAGE Planning and DESIGN ..5-2 Key Issues in STORMWATER DRAINAGE DESIGN ..5-2 Introduction ..5-2 General DRAINAGE DESIGN Considerations ..5-3 Street and Roadway Gutters ..5-3 Inlets and Drains ..5-4 Storm Drain Pipe Systems (Storm Sewers) ..5-4 Culverts ..5-4 Open Channels ..5-5 Energy Dissipators ..5-5 DESIGN Storm Recommendations ..5-6 SECTION MINOR DRAINAGE SYSTEM DESIGN Overview ..5-1 Introduction ..5-1 General Criteria ..5-1 Symbols and Definitions.

2 5-2 Street and Roadway Gutters ..5-2 Formula ..5-3 Nomograph ..5-3 Manning's n Table ..5-3 Uniform Cross Slope ..5-3 Composite Gutter Sections ..5-4 Examples ..5-9 STORMWATER Inlets ..5-10 Grate Inlets DESIGN ..5-10 Grate Inlets on Grade ..5-10 Grate Inlets in Sag ..5-15 Curb Inlet DESIGN ..5-17 Curb Inlets on Grade ..5-17 Curb Inlets in Sump ..5-21 Combination Inlets ..5-25 On Grade ..5-25 Commented [A1]: Renumbering of the TOC will be completed with the 100% version 5-2 Georgia STORMWATER Management Manual Volume 2 (Technical Handbook) In Sump ..5-25 Storm Drain Pipe Systems ..5-26 Introduction ..5-26 General DESIGN Procedure ..5-26 DESIGN Criteria ..5-26 Capacity Calculations ..5-28 Nomographs and Table ..5-28 Hydraulic Grade Lines.

3 5-29 Minimum Grade ..5-36 Storm Drain Storage ..5-36 SECTION CULVERT DESIGN Overview ..5-1 Symbols and Definitions ..5-1 DESIGN Criteria ..5-2 Frequency Flood ..5-2 Velocity Limitations ..5-2 Buoyancy Protection ..5-2 Length and Slope ..5-2 Debris Control ..5-2 Headwater Limitations ..5-2 Tailwater Considerations ..5-3 Storage ..5-3 Culvert Inlets ..5-4 Inlets with Headwalls ..5-4 Wingwalls and Aprons ..5-4 Improved Inlets ..5-4 Material Selection ..5-4 Culvert Skews ..5-4 Culvert Sizes ..5-4 Weep Holes ..5-4 Outlet Protection ..5-6 Erosion and Sediment Control ..5-6 Environmental Considerations ..5-6 DESIGN Procedures ..5-7 Inlet and Outlet Control ..5-7 Procedures ..5-7 Nomographs ..5-7 DESIGN Procedure.

4 5-10 Performance Curves - Roadway Overtopping ..5-10 Storage Routing ..5-11 Culvert DESIGN Example ..5-13 Introduction ..5-13 Example ..5-13 Example Data ..5-13 Computations ..5-13 Volume 2 (Technical Handbook) Georgia STORMWATER Management Manual 5-3 DESIGN Procedures for Beveled-Edged Inlets ..5-16 Introduction ..5-16 DESIGN Figures ..5-16 DESIGN Procedure ..5-16 DESIGN Figure Limits ..5-16 Multibarrel Installations ..5-17 Skewed Inlets ..5-17 Flood Routing and Culvert DESIGN ..5-17 Introduction ..5-17 DESIGN Procedure ..5-18 Culvert DESIGN Charts and Nomographs .. SECTION OPEN CHANNEL DESIGN Overview ..5-1 Introduction ..5-1 Open Channel Types ..5-1 Symbols and Definitions ..5-2 DESIGN Criteria ..5-3 General Criteria.

5 5-3 Velocity Limitations ..5-3 Manning s n Values ..5-3 Uniform Flow Calculations ..5-5 DESIGN Manning s Equations ..5-5 Geometric Relationships ..5-5 Direct Solutions ..5-5 Trial and Error Solutions ..5-14 Critical Flow Calculations ..5-16 Background ..5-16 Semi-Empirical Equations ..5-16 Vegetative DESIGN ..5-19 Introduction ..5-19 DESIGN Stability ..5-19 DESIGN Capacity ..5-20 Riprap DESIGN ..5-22 Assumptions ..5-22 Procedure ..5-22 Uniform Flow - Example Gradually Varied Flow ..5-30 Rectangular, Triangular and Trapezoidal Open Channel DESIGN Figures ..5-30 Introduction ..5-30 Description of Figures ..5-30 Instructions for Rectangular and Trapezoidal Figures ..5-31 Grassed Channel Figures ..5-36 Description of Figures.

6 5-36 Instructions for Grassed Channel Figures ..5-36 Open Channel DESIGN Figures .. Triangular Channel Nomograph .. Grassed Channel DESIGN Figures .. SECTION ENERGY DISSIPATION DESIGN Overview ..5-1 5-4 Georgia STORMWATER Management Manual Volume 2 (Technical Handbook) Introduction ..5-1 General Criteria ..5-1 Recommended Energy Dissipators ..5-1 Symbols and Definitions ..5-2 DESIGN Guidelines ..5-2 Riprap Aprons ..5-5 Description ..5-5 DESIGN Procedure ..5-5 DESIGN Considerations ..5-9 Example Designs ..5-9 Riprap Basins ..5-10 Description ..5-10 Basin Features ..5-10 DESIGN Procedure ..5-10 DESIGN Considerations ..5-16 Example Designs ..5-16 Baffled Description ..5-21 DESIGN Procedure ..5-21 Example DESIGN .

7 5-23 References ..5-24 Volume 2 (Technical Handbook) Georgia STORMWATER Management Manual 5-5 List of Tables Symbols and Definitions .. Manning s n Values for Street and Pavement Gutters .. Grate Debris Handling Efficiencies .. Symbols and Definitions .. Inlet Coefficients .. Manning s n Values .. Symbols and Definitions .. Maximum Velocities for Comparing Lining Materials .. Maximum Velocities for Vegetative Channel Linings .. Manning s Roughness Coefficients (n) for Artificial Channels .. Uniform Flow Values of Roughness Coefficient n .. Classification of Vegetal Covers as to Degrees of Retardance .. Critical Depth Equations for Uniform Flow in Selected Channel Cross Symbols and Definitions .. List of Figures Alternate Roadway Section without Gutters .. Compound Channel .. Flow in Triangular Gutter Sections.

8 Ratio of Frontal Flow to Total Gutter Flow .. Flow in Composite Gutter Sections .. Grate Inlet Frontal Flow Interception Efficiency .. Grate Inlet Side Flow Interception Efficiency .. Grate Inlet Capacity in Sag Conditions .. Curb-Opening and Slotted Drain Inlet Length for Total Interception .. Curb-Opening and Slotted Drain Inlet Interception Efficiency .. Depressed Curb-Opening Inlet Capacity in Sump Locations .. Curb-Opening Inlet Capacity in Sump Locations .. Curb-Opening Inlet Orifice Capacity for Inclined and Vertical Orifice Throats .. Storm Drain SYSTEM Computation Form .. Nomograph for Solution of Manning s Formula for Flow in Storm Sewers .. Nomograph for Computing Required Size of Circular Drain, Flowing Full (n = or ) .. Concrete Pipe Flow Nomograph .. Values of Various Elements of Circular Section for Various Depths of Flow.

9 Hydraulic Grade Line Computation Form .. Culvert Flow Conditions .. Headwater Depth for Concrete Pipe Culvert with Inlet Control .. Head for Concrete Pipe Culverts Flowing Full .. Discharge Coefficients for Roadway Overtopping .. Culvert DESIGN Calculation Form .. Manning s n Values for Vegetated Channels .. Nomograph for the Solution of Manning s Equation .. Solution of Manning s Equation for Trapezoidal Channels .. Trapezoidal Channel Capacity Chart .. Open Channel Geometric Relationships for Various Cross Sections .. Protection Length, Lp, Downstream of Channel Bend .. Riprap Lining Bend Correction Coefficient .. Riprap Lining Specific Weight Correction Coefficient .. Riprap Lining d30 Stone Size Function of Mean Velocity and Depth .. [A2]: Renumbering of the Tables List will be completed with the 100% version Commented [A3]: Renumbering of the Figures List will be completed with the 100% version 5-6 Georgia STORMWATER Management Manual Volume 2 (Technical Handbook) Riprap Lining Thickness Adjustment for d85/d15 = to.

10 Example Nomograph #1 .. Example Nomograph #2 .. Example Nomograph #3 .. Example Nomograph #4 .. Example Nomograph #5 .. Unnumbered Figures Section (Open Channel DESIGN Figures) .. Unnumbered Figures Section (Triangular Channel Nomograph) .. Unnumbered Figures Section (Grassed Channel DESIGN Figures) .. Riprap Size for Use Downstream of Energy Dissipator .. DESIGN of Riprap Apron under Minimum Tailwater Conditions .. DESIGN of Riprap Apron under Maximum Tailwater Conditions .. Riprap Apron .. Details of Riprap Outlet Basin .. Dimensionless Rating Curves for the Outlets of Rectangular Culverts on Horizontal and Mild Slopes .. Dimensionless Rating Curve for the Outlets of Circular Culverts on Horizontal and Mild Slopes .. Relative Depth of Scour Hole Versus Froude Number at Brink of Culvert with Relative Size of Riprap as a Third Variable.