Chapter 1: Roads

ROADWAY SURFACE AND SHOULDER EROSION

Introduction

Problem: 

Road surface and shoulder erosion caused by water flowing over the top of the roadway, due to low roadway elevation or inadequate drainage structure capacity.

Mitigation Objective: 

Harden the top of the roadway or divert floodwater from the top of the roadway to prevent erosion of the road surface and shoulder.

C.1.  Increase Roadway Elevation

Increase the roadway elevation by adding suitable fill material to raise the roadway surface above the design flood elevation.

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Effectiveness:

Very effective in areas where the flood elevations are above the roadway surface for a short distance.

Prevents future damage and keeps the roadway in service during flood events.

Limitations:

May not be justified if frequent flood elevations are too high above the roadway.

May increase upstream flood elevation and create a damming effect.

Should be used in conjunction with embankment slope protection measures.

Considerations:

C.2. Construct Shoulder Protection

To protect the road shoulder from erosion, pave downstream shoulder with asphalt concrete pavement, concrete, riprap, or other appropriate revetments.

Effectiveness:

Very effective when drainage structure capacity cannot be increased to prevent overtopping.

Limitations:

The treatment must be compatible with the soil type and roadway conditions.

Asphalt concrete may have a limited life on slopes.

May have adverse impacts on riparian areas.  Willows and other plantings can be staked within the shoulder protection.

Considerations:

C.3  Increase Capacity of Drainage Structure

(Link to 2.A.4)