May 15, 2000 1

SOUTH CAROLINA DEPARTMENT OF TRANSPORTATION

REQUIREMENTS FOR

HYDRAULIC DESIGN STUDIES

May 15, 2000

Prepared by William H. Hulbert

May 15, 2000 2

INDEX

Section No. Subject Page No. Introduction 5 PART 1: Requirements for Hydraulic Design of Bridges 5

and Bridge Sized Culverts 1 Analysis Procedures 6 1.1 Design Criteria 7 1.1.1 Design Frequencies 7 1.1.2 FloodwayFloodplain Requirements 7 1.1.3 Flow Velocities 8 1.1.4 Bridge Scour 8 1.1.5 Design Freeboard 8 1.1.5.1 Freeboard for Riverine Bridges 8 1.1.5.2 Freeboard for Tidal Bridges 9 1.1.5.3 Freeboard for Bridges over Lakes and Reservoirs 9 1.1.5.4 Freeboard for Road Subgrades 9 1.1.6 Bridge Abutment Protection 9 1.1.7 Guide Banks 9 1.1.8 Bridge Sized Culverts 9 1.2 Level 1: Qualitative and Geomorphic Analysis 9 1.2.1 Level 1 Procedure 10 Step 1 Stream Characteristics 10 Step 2 Land Use Changes 10 Step 3 Overall Stability 10 Step 4 Lateral Stability 10 Step 5 Vertical Stability 11 Step 6 Debris Potential 12 Step 7 Stream Response 13 1.2.2 Fast Track Bridge Investigation 13 1.3 Level 2: Basic Engineering Analysis 14 1.3.1 Level 2 Procedures for Riverine Bridges 14 Step 1 Flood History and Hydrology 14 A. Flood History 14 B. Bridge Site Scour History 15 C. Hydrology 15 D. Develop Comparative Data 16 Step 2 Evaluate Hydraulic Conditions 17 A. Evaluate Field Conditions 17 1. Comparative Bridge Sites 17 2. Job Site Inspection 17 B. Hydraulic Analysis 18 Step 3 Bed and Bank Material 22 Step 4 Evaluate Watershed Sediment Yield 22 Step 5 Incipient Motion Analysis 22

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Section No. Subject Page No. Step 6 Evaluate Armoring Potential 22 Step 7 Evaluating Rating Curve Shifts 23 Step 8 Design Bridge 23 Step 9 Scour Analysis 24 Step 10 Risk Assessment 26 1.3.2 Level 2 Procedures for Tidal Bridges 26 1.3.2.1 Establish Minimum Bridge Grades 27 1.3.2.2 Historic Storm and Site Data 28 1.3.2.3 Develop the Tidal Hydrograph 28 1.3.2.4 Tidal Hydraulic Analysis and Scour Analysis 29 1.3.2.5 Culverts in Tidal Streams 30 1.4 Level 3 Analysis 31 1.5 Information to Be Shown on Plans 31 1.5.1 For Riverine Bridges 31 1.5.2 For Riverine Culverts 32 1.5.3 For Tidal Bridges 33 1.5.4 For Tidal Culverts 33 1.6.1 Sample Title Page 34 1.6.2 Comparative Data Sheet 35 1.6.3 Site Inspection Form 36 1.6.3.1 Site Characteristics 37 1.6.3.2 Mannings n ValuesChannel 37 1.6.3.3 Mannings n Values for Overbank Areas 38 1.6.4 Comparative Bridge Site Inspection Form 40 1.6.5 Risk Assessment 41 Figure No. 1 Level 1 Flow Chart 43 Figure No. 2 Level 2 Flow Chart 44 Figure No. 3 Geomorphic Factors 45 2. PART 2: Requirements For Roadway Drainage 46 2.1 Analysis Procedures 46 2.2 Design Criteria 46 2.2.1 Cross-Lines 46 2.2.2 Storm Drains and Roadside Ditches 46 2.2.3 Inlet Spacing 46 2.2.4 Minimum Ditch and Pipe Grades 47 2.2.5 Minimum Pipe Size 47 2.2.6 Minimum Cover for Pipes 47 2.2.7 Precast Manholes 47 2.2.8 Storm Drain Systems 47 2.2.9 Outlet Protection for Culverts 48 2.2.10 Drainage Outfalls and Stormwater Management 48 2.2.10.1 Outfalls in Flood Hazard Areas 48 2.2.10.2 Drainage Regulation Violations by Others 48

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Section No. Subject Page No. 2.2.10.3 Basic Design Requirements 48 2.2.10.4 Stormwater Management for C Projects 50 2.2.11 Sediment and Erosion Control 50 2.2.12 Hydraulic Analysis 51 2.2.12.1 Rational Method 51 2.2.12.2 The SCS TR-55 Method 51 2.2.12.3 USGS Regression Equations 51 2.2.12.4 USGS Urban Peak-Discharge Frequency Method 52 2.2.12.5 Log Pearson Type III 52 2.2.12.6 Hydrograph Methods 52 2.3 Hydrologic and Hydraulic Design for Stormwater Management 52 Step 1 Scoping Review 52 Step 2 Gathering data 53 Step 3 Preliminary Drainage Design 53 Step 4 Field Inspection 53 Step 5 Complete Drainage Design 54 Step 6 Design Cross-Line Drainage 56 A. Determine Basic Data Need for Design 56 B. Compute Design Discharge 56 C. Develop Rating Curve for Stream Channel 57 D. Design Culvert 57 E. Exceptions to Normal Designs 58 F. Culvert as Stormwater Management Control Structure 58 G. Information to be Shown on Plans for Cross Line 58 Structures Step 7 Prepare Design Study Report 59 2.4 Sediment and Erosion Control 60 2.4.1 Criteria 60 2.4.2 Sediment Barriers 60 2.4.2.1 Silt Fence 60 2.4.2.2 Hay Bales 61 2.4.3 Ditch Protection 61 2.4.3.1 Ditch Checks 60 2.4.3.2 Temporary Linings 61 2.4.3.3 Sediment Dams 61 2.4.3.4 Sediment Traps or Inlet Filters 61 2.4.4 Sediment Ponds or Basins 61 2.4.5 Detention Ponds 62 2.5 Title Sheet 63

References 64

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SOUTH CAROLINA DEPARTMENT OF TRANSPORTATION

REQUIREMENTS FOR HYDRAULIC DESIGN STUDIES Introduction This document delineates the requirements for hydraulic design studies performed for the South Carolina Department of Transportation (SCDOT). Its purpose is to give guidance to Departmental staff and to consultants performing design work for the Department in the preparation of construction plans. Before the hydraulic design engineer performs a design study utilizing this guideline, he should be thoroughly familiar with the more detailed coverage of the different design procedures given in the manuals in the reference list. Compliance with these procedures will insure that the requirements in the following laws and regulations will be adhered to.

Federal Highway Administration's Federal-Aid Policy Guide, 23 CRF 650A, December 1, 1991, Transmittal 1, "Bridges, Structures, and Hydraulics",

The Federal Emergency Management Agency Regulations, 44 CFR Ch.1, The Environmental Protection Agency's (EPA) Regulations 40 CFR Parts

9, 122, 123, and 124 National Pollution Discharge Elimination System (NPDES) as administered under general permit by the South Carolina Department of Health and Environmental Control (DHEC),

The State Stormwater and Sediment and Erosion Control regulations administered by DHEC, 26 S. C. Code Ann. Regs. 72-405 (Supp.1995) et seq.

Departmental policy, South Carolina State Water Law.

The requirements are presented in two parts. The first part is for bridges and bridge-sized culverts (culverts greater than or equal to 20 feet in width along the highway centerline). In Part 1, references to bridges include bridge-sized culverts unless it is obvious that a bridge structure is being addressed or the information is directed specifically to culverts. Part 2 is for roadway drainage and culverts less than twenty feet wide. The second part also includes the guidelines established to insure compliance with the NPDES permit requirements and the State Stormwater Management and Sediment and Erosion Control Act.

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PART 1: REQUIREMENTS FOR HYDRAULIC DESIGN OF

BRIDGES AND BRIDGE-SIZED CULVERTS

1. Analysis Procedures Bridges and bridge-sized culverts shall be de