For streets without curbs and gutters, roadside ditches are key to maintaining roadway drainage, which is important to ensuring the long life of the roadway by:
- Preventing erosion of the roadway
- Preventing saturation of the sub base
- Preventing damage to roadway structure
Roadside ditches should be cleaned on a regular basis to prevent them from silting up and forcing water back onto the travel way surface or into the subbase material of the pavement structure.
- In sections of the travel way where runoff drains directly onto shoulders, water may collect along the edge of the travel way. Water on a portion of the roadway can result in drivers losing control of their vehicle, particularly when braking in an emergency. This can happen when the inside tires are in contact with the roadway surface and the braking ability of the outside tires is hindered by the water.
- Water can pond on the outside edge of the travel way surface when debris, particularly aggregate and soil on turf shoulders, builds up. As debris accumulates on the shoulder, it raises the level of the edge and eventually hinders run-off from flowing into side ditches. Edge drop-offs and shoulder scour are often caused when water is trapped at the pavement edge by the build-up of debris and vegetation growth.
- Maintaining culverts and roadside ditches is important to ensure water does not pond along the ditch or in the culverts, which are conditions that are prime for mosquito breeding. In addition, in ditches and culverts where obstructions exist due to excessive siltation or debris, the conveyance capacity of the ditch is hindered, which can lead to upstream flooding of adjacent properties and potential overtopping of the roadway.