How Does Sediment End Up in a Creek?
Restoring streams and fish habitat often means working on the land

How does sediment end up in a creek? Restoring streams and fish habitat often means working on the land, rather than in water. The reality is water comes to the streams from the land and what’s happening in the stream is a reflection of what’s happening on the surrounding landscape.

What happens to a drop of rain that falls onto the land is really important to a fish. If the rain soaks into the spongy ground, it helps to recharge the water table, or the water stored underground, and it will later emerge as groundwater inputs into a stream. This is good! The earth is acting as a filter so that the water is clean and cold by the time it enters the stream. These groundwater upwellings are especially important for trout, as they tend to spawn in these areas. Groundwater also helps to maintain consistent and reliable streamflow and temperature, which is also great for fish and other critters.

When rain hits a hard surface (like pavement and rooftops in urban areas, or dirt roads and trails in less developed areas), it does not have a chance to soak into the ground but rather follows the path of least resistance downhill over the surface. As more and more rainwater flows downhill along the hard surface, it picks up momentum and starts to erode exposed soils. The eroded soils then get picked up by the moving water and continue to flow downhill. Sometimes, this sediment-laden water may end up in a vegetated forest where the water can soak into the soil–but oftentimes, it flows directly into a watercourse. This is how straight lines (AKA linear features) of bare ground (like trails) act as sediment chutes during rainfall or snowmelt. And too much sediment can be bad for fish.

Certainly, not all roads and trails are bad! Thankfully, we humans are pretty clever at coming up with solutions to problems. Ditches, berms, cross drains, and culverts are all engineering tools that can direct water off trails and into softer, more absorbent undisturbed soils. Adding gravel to roads and designing and locating them properly also helps to prevent sediment delivery. The problem is that we don’t always know where these problems are, and we don’t always have the means to fix them all.

Over the past few years, TUC has been using a tool called READI (Road Erosion And Delivery Index) to help us find where the worst of the worst sediment sources are in a watershed. This tool has been developed by FRI Research and Alberta Agriculture and Forestry, and it helps us be more strategic in planning and carrying out restoration works. We can’t fix everything everywhere, so we need to make sure we are being effective and efficient by targeting the worst sites first.

We know that all roads/trails can produce sediment, but not all roads/trails deliver sediment to watercourses. The model predicts where these sediment delivery points are, based on existing datasets of linear features and streams on the landscape, along with other analytical tools. Basically, the output is a map of the watershed with a whole bunch of points where the model predicts a potential sediment source exists. We use the map to plan our field visits, then we put our boots on and visit these sites in real life to determine if there is an issue–and if so, what we can do to fix it. We use apps on our smartphones to record data at each site. In 2019 and 2020, TUC partnered with Alberta Environment and Parks (AEP) and Cows and Fish to assess over 200 sites using a “blitz” approach in the Tay River watershed. Afterward, we exported the data and photos taken in the field and came up with our own restoration prioritization based on the issues observed, and whether restoration at a specific site will help us meet our goals of watershed resiliency and Bull Trout recovery.

Cost, logistics, and land use are also taken into consideration. For example, if the issue is located on a motorized recreation trail, we must consider the use and value of that trail, and the restoration options available to us. Is the trail part of a well-used loop, or does it lead to nowhere? Can the trail be improved, or should it be decommissioned? Is there another trail that leads to the same place? Will fixing this issue make a difference, or should we focus efforts elsewhere in the watershed? These conversations and decisions are especially challenging on vacant public land (land that is not part of Public Land Use Zones or Provincial Parks and does not have designated trail systems).

In 2021, TUC is working with partners to use these assessment and prioritization tools in the Waiparous Creek watershed, thanks to funding and partnership with Alberta Environment and Parks and the Habitat Stewardship Program for Species and Risk.

Posted by: Trout Unlimited Canada on October 1, 2021.
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