FLOOD05322

• County: Statewide
• Basin: Statewide
• Title: Evaluating Scour at Bridges
• Date: 1/1/1993
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

CHAPTER 4 - ESTIMATING SCOUR AT BRIDGES ",.""""""",.,."",.".",,;. 25

4,1 lN1RODUCTION, , " , ., , , '" '" ., , , " , "" " . .. , ",., , ." ." " , , ,. .. ", 25
4.2 SPECIFIC DESIGN APPROACH . , , , , . , . . . , , . , , , , , . , , , , , . , , . , , , , ,. , . , . . , . , . ., 25

4.3 DETAILED PROCEDURES """"".".""",.""."."..""...,..",. 25

4.3.1 Step I: Determine Scour Analysis Variables, , " , , .', " , " ,., , " , .., .". , " 25
4,3,2 Step 2: Analysis of Long-Term Bed Elevation Change . , , , ,'. , . , , , . , , , , . , . . , . ,. 27
4.3.3 Step 3: Evaluate the Scour Analysis Method , , , , , , , , , , , . , , , . , , , , , . . , . , , ., ., 27
4.3.4 Step 4: Compute the Magnitude of Contraction Scour, , , . , , . , , , , . , . . , , . , , , . , " 28
4,3,5 Step 5: Compute the Magnitude of Local Scour at Piers "".""..."".",.., 33
4,3,6 Step 6: Local Scour at Abutments ."."."",.".",..".".,.".,..'" 45
4,3,7 Step 7: Plot Total Scour Depths and Evaluate Design, , , , , , , , , , , , , , , . , , , , . . , " 49

4.4 SCOUR EXAMPLE PROBLEMS", " " ., "", " . , " , " , " . , , , " , " , " , ,. " " 51

4.4.1 General Description of Problem, , , , , , , , , , , , , , , , , , . , , , , . . . , , , , , . , , . . , , ,. 51
4.4,2 Step I: Determine Scour Analysis Variables ".."",.""."""".. '.'.," 52
4.4.3 Step 2: Analyze Long-Term Bed Elevation Changes, , , , . . , " , , , , , . . , . ", ,; , " 59
4.4.4 Step 3: Evaluate the Scour Analysis Method ". , , , , , , , . , . , , , , , , ; , , , , . . , , , " 59
4.4.5 Step 4A: Compute the Magnitude of Contraction Scour (Main Channel) ,.,.".,.", 60
4,4,6 Step 4B: Compute the Contraction Scour for Left Overbank, , . , , " , . , , . , . , ,; , , . ,. 63
4.4,7 Step 5: Compute the Magnitude of Locill Scour at Piers ",.,..".",..".",., 63
4.4,8 Step 6A: Compute the Magnitude of Local Scour at Left Abutment. . . , , " , , , , , , , .. 65
4.4.9 Step 6B: Compute the Magnitude of Local Scour at Right Abutment , , , , . , , , , , , , . " 67
4.4,10 Step 7: Plot Total Scour Depth and Evaluate Design ".".",."".,."".", 67
4,4,11 Complete General Design Procedure, , , , , , , , , , , , , , " , , , , , , , " , , . , , , , . . , " 69

4,5 SCOUR ANALYSIS FOR TIDAL AREAS ,.,..",.",."."."""",.,.",:", 69

4,5,1 Introduction, . , , . , , , . , , , , , , , . . , , , , , , , , , , , , , , , . . , . , . , , , , , , . , , , , , ; " 69
4,5,2 Overview of Tidal Processes ,.,..",."""""""""."",."""" 70

4.5,3 Level I Analysis .""."""""""""",.""""""".".".. 75
4.5.4 Level 2 Analysis ,."""""..,."""""."""""""..""". 79
4,5.5 Level 3 Analysis """",.""""".,...,.."""",.".,.,.."" 88
4,5.6 Example Problem Number I ,.""""".,.""."""""",'.""". 88
4.5.7 Example Problem Number 2 ,.."""",.",.,.""""""""".,.,. 93

CHAPTER 5 - EV ALUA T1NG lHE VULNERABILITY OF EXISTING BRIDGES TO

SCOUR """""..",.,..""""".""""""""",.""., 97

5,1 INTRODUCTION, , , , , , , , , . , , , , . , , , . , , , , , , , , , , . , , , , , , , , , , , , . , , , , , . , . ; , " 97
5,2 lHE EVALUATION PROCESS """.""""",..,."""'.",'."."",,. 97
5,3 CONDUCTING SCOUR EVALUATION STUDIES, , , , , . , , . . , , , , , , , , , , , , , , . , , " " 100
5.4 WORST-CASE ANALYSIS """",."""".,..".."""""""",.", 100

5.4,1 Water-Surface Elevations, . , , . , . , , , , , , , , . , . , . , , , , , , , , . , , , , , , , , , , , , . ,. 100
5.4,2 Long-Term Aggradation or Degradation, , , , . . , , , . , , . , , , , . . , , , , , , , , , , , , , .' 101
5.4.3 Planform Changes """""""""."""..""..""""""", 101

5.4.4 Contraction Scour, , . , , , , , , . , , , , , , , , , . , , , , , , . . , , . , . , , , , , , , , , , , , , , " 101
5.4,5 Local Pier Scour ,..'"",."""",.""."."""""",.""", 101
5.4,6 Local Abutment Scour ""..""""""""."""""""",."" 101

5,5 DOCUMENTING BRIDGE SCOUR ASSESSMENTS ".",.",.""."""""", 10]

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