Topographical Heterogeneity (aka Rough and Loose)
Tools we use to address sedimentation during our restoration projects

It may seem like a lot of our work in Alberta involves restoration relating to off-highway vehicle trails. In fact, some of our biggest projects in recent years have involved trail reclamation and stream crossing repair.

So what does this trail reclamation look like? We know that oftentimes these trails act as sediment chutes, delivering high amounts of sediment into the creeks during precipitation and snowmelt events, which degrades the aquatic habitat. This is because water cannot penetrate through the compacted soils of a trail, so it runs over the bare ground instead. The flat surface of the ground allows the moving water to pick up speed quickly. As speeds increase, more and more sediment is also dragged into the flow of the water, until it is all deposited into the creek. Plant roots are also unable to penetrate compacted soils or cannot establish where disturbance is continuous (like being driven over regularly) so there is nothing to help reduce water speed or help hold soils in place.

Sometimes the solution is to close or re-route a problematic trail segment. In 2020, we closed a few trail segments in the Waiparous Creek watershed. Since this area falls within a Public Land Use Zone, there is a designated trail system in effect. However, despite the established trail system, sometimes legacy trails continue to be used, or new trails start to appear. When users see that undesignated trails are being used by others, they are more likely to drive down those segments as well. Signage can be installed to indicate motorized access is not permitted on a trail, however, that is not always effective as, without adequate enforcement, signs and barricades are often ignored or intentionally destroyed. In that case, it takes more of an engineering approach to not only make the trail impassible but also to aid in the ecological recovery process. While some natural recovery may occur just by preventing continued motorized use, it is very difficult for plants to establish in heavily compacted soils and full recovery can take decades.

Rough and loose is a reclamation technique where an excavator is used to dig holes and create mounds in the soil. It can also be done by hand if the reclamation feature is small, or the site is not accessible by heavy machinery or vehicles. This creates “topographic heterogeneity” which basically means the surface of the ground is changed from flat and compacted to rough and loose with lots of high and low points.

A common misconception about rough and loose is that it damages the environment. However, rough and loose treatments are actually one of the most effective methods of addressing soil erosion and compaction and kick-starting natural recovery. The loosened soil provides ideal conditions for bioengineering techniques like live staking, and promotion of new native vegetation growth. Additionally, loose soils hold water much better than compacted soils, so during precipitation and snowmelt events, more water is retained in the soil instead of draining directly into the creeks. Rough and loose treatments also create habitat heterogeneity. A water gradient is created, with the wettest soils at the bottom of holes, and the driest soils at the top of mounds. Each mound has its own little north and south-facing slopes, which offer different light and wind regimes. This variety of micro-habitats encourages a diverse array of plants to establish on the site, which increases the resiliency of the habitat. To protect the exposed soils from raindrop erosion, woody debris and leaf litter can be strewn across the site, mimicking what the habitat might look like after a natural disturbance. After rough and loose treatments, sites normally recover in less than 10 years.

Posted by: Trout Unlimited Canada on October 4, 2021.
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