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.

2 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 ..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.

3 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.

4 5-26 Capacity Calculations ..5-28 Nomographs and Table ..5-28 Hydraulic Grade Lines ..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 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 ..5-10 Performance Curves - Roadway Overtopping ..5-10 Storage Routing ..5-11 Culvert DESIGN Example.

6 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.

7 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 ..5-3 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.

8 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.

9 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.

10 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 ..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.