6. Drainage

This chapter will focus on one of the most important aspects of gravel road condition management, ie drainage.
In this chapter we will use plenty of material from the ROADEX Drainage elearning package. The idea is not to use cross references to avoid “jumping” from one package to another, but instead use the same figures and partly the same text but modified to fit the needs of gravel and forest roads.

6.1 General

This chapter will discuss the general aspects of drainage on gravel and forest roads and what is the general function of the drainage system. Some words will also be given about what is surface drainage (dewatering) and deep drainage

6.2 Drainage components

6.2.1.Road geometry, crossfall

General instructions about road crossfall and surface drainage and how it should be changed for ice conditions (5%=>3%). Also discussion about the geometry and ditches

6.2.2. Side ditches

Depth of the side ditches in different soil conditions. The width of the ditches and longitudinal gradient

6.2.3. Outlet ditches

Outlet ditches and their principles

6.2.4. Main road culverts

Main road culverts design principles in different soil and topography conditions, culvert types, environmental issues – especially when a watercourse with fish goes under the road

6.2.5. Special structures

Deep drains, infiltration wells etc

6.3. Drainage maintenance

6.3.1. General

This chapter will focus on the economic aspects of drainage maintenance of gravel and forest roads, ie why it is important to monitor and react if there are deficiencies in the drainage system. Also why drainage has to be kept in mind in winter maintenance.

6.3.2. Drainage condition monitoring

Introduction of the traditional (visual) and future drainage monitoring techniques (laser scanners, GPR)

6.3.3. Drainage maintenance operations

Description of techniques for surface drainage (crossfall) and deep drainage (ditch cleaning, culvert cleaning) maintenance operations. In addition special attention for winter maintenance and drainage (removing compacted snow, removing snow from road shoulders)