1. Definition & Purpose
- The primary purpose of drainage is to keep water away from the trail and to remove surface water from the trail to prevent damage to it.
- An effective drainage system will significantly reduce the amount of maintenance required and prevent the trail from changing from its initial character and build specfication.
- If the drainage system does not function properly erosion scars may become severe and the trails surface will change considerably, usually to the detriment of the trail.
Trail Flow vs Sheet Flow
- Trail Flow is water landing and running down the trail tread causing damage as it follows the line of the trail down the hill.
- Sheet Flow is water running down the slope of the hill. When you create a bench cut, the water flow will then enter your trail tread.
What affects drainage and your choice of water management technique?
- Soil and materials used in the trail construction (see section)
- The natural habitat that the trail is in will affect the amount of water. For example, a trail built through a forest will be impacted by the type of trees, the density of trees and the size of the trees.
- The amount of rainfall, the type of rainfall (eg frequent mild rainfall or heavy storms) and seasonal events (eg snow melt in Spring).
- It is also worth considering the long term plans for the environment the trail is within. For example, if a forest is due to be felled, and the trail retained, this will significantly heighten the water table and additional drainage may need to be constructed.
Stream Crossing vs Drainage Techniques
- Many stream crossings will use drainage techniques. Larger flows of water, even if these are episodic (eg snow melt or heavy storm), may require a bridge or wooden feature. See “bridges and wooden features template”.
2. Key Considerations
2.1 Typical techniques
2.2 Key Aspects
Figure 1: Illustration of a grade reversal done right or wrong
Photo 1-2: Drainage systems on a berm and portion of trail, Source: DIRTT
4. Additional reading & Media
- About – Trailism. (2020, April 13). https://trailism.com/
- Course 302. Drainage Crossings. (03.2011). https://www.pcta.org/wp-content/uploads/2012/11/302_Drainage_Crossings_v0311.pdf?x20165
- Drainage Structures. (n.d.). Www.Parks.ca.Gov. https://www.parks.ca.gov/pages/1324/files/Chapter%2014%20-%20Drainage%20Structures.FINAL.01.17.19.pdf
- Surface water control. (n.d.). Www.Fs.Fed.Us. Retrieved July 22, 2021, from https://www.fs.fed.us/eng/pubs/pdfpubs/pdf00232839/pdf00232839dpi72pt02.pdf
- Sustainable ATV Trails. (2021). https://www.fs.fed.us/t-d/atv_trails_site/index.html
- Wetland Trail Design and Construction. (2007). https://www.fhwa.dot.gov/environment/recreational_trails/publications/fs_publications/07232804/toc.cfm