BRIDGESBRIDGES

Lan Zi Road, Lan Gao, China

Structural Capacity

Hydraulic Capacity

Safety

Scour ProtectionScour Protection

Failed during 6” Storm Failed during 6” Storm (50 Year Event)(50 Year Event)10 Killed10 Killed

New York- (1955- 1987)New York- (1955- 1987)150 Meters long- 5 Spans150 Meters long- 5 Spans

What is importantWhat is important

• Structural Capacity/Load • Hydraulic Capacity• Structure-Stream Compatibility/Adequate

Span• A Good Foundation• Scour Protection• Safety Features• Structure Inspection and Maintenance

LOW-WATER CROSSINGLOW-WATER CROSSING(FORDS, DRIFTS)(FORDS, DRIFTS)

Where to Use a Low-Water Crossing

• Flashy Flows/High Flow Fluctuation• Low Traffic Use• Delays are Acceptable/Non-critical Route• Broad/Flat Channels (Slightly Entrenched)• Debris Prone Channels• Grade Control Structures/Barriers• $$$-Least Expensive Alternative

Aspects of Low-Water Crossing Aspects of Low-Water Crossing DesignDesign

• **Structure-Site CompatibilityStructure-Site Compatibility• *Providing for Aquatic Organism Passage (AOP)*Providing for Aquatic Organism Passage (AOP)• Roadway and Site GeometryRoadway and Site Geometry• Site Hydrology-Design High and Low FlowsSite Hydrology-Design High and Low Flows• Hydraulic Design-Capacity, VelocitiesHydraulic Design-Capacity, Velocities• Scour and Bank ProtectionScour and Bank Protection• Driving Surface Structural DesignDriving Surface Structural Design• Traffic Control and SafetyTraffic Control and Safety• Materials SelectionMaterials Selection• BMPs for Erosion Control and Water QualityBMPs for Erosion Control and Water Quality

Structure-Site Compatibility

Providing for Aquatic Organism Passage

K. Clarkin

Problematic Designs

K.Clarkin

Roadway and Site GeometryRoadway and Site Geometry

Site Hydrology andSite Hydrology andHydraulic DesignHydraulic Design

Scour and Bank ProtectionScour and Bank Protection

Driving Surface Driving Surface Structural DesignStructural Design

K. Clarkin

Traffic Control and SafetyTraffic Control and Safety

USGS

Materials SelectionMaterials Selection

•Provide for AOP•Keep Stream Function

SUMMARY

•Design it Well!

TWarhol

http://fsweb.sdtdc.wo.fs.fed.us/pubs/pdf/LowWaterCrossings/

Roy Gu. 2003. Low water Crossing Study, FHWA, DTFH68-02-C-00024