Road Erosion, Sediment Delivery, and Consequence in the Simonette Watershed West-Central Alberta
Creators: Fath, Kenneth Jared
Publisher: name: University of Alberta Library
Year: 2022

<p>Gravel and dirt resource roads in the Alberta foothills are critical economic infrastructure, used to explore for, manage, and extract natural resources from this region. Resource roads are also known to add sediment to nearby streams and rivers, causing habitat stress for fish. Understanding road erosion and sediment delivery processes, and how road sediment moves through the stream network is therefore crucial to reducing habitat damage from these roads. The environment of west-central Alberta contains several features which make it susceptible to road erosion and sediment delivery problems: abundant glacial silt and clay deposits, seasonal freeze and thaw cycles, heavy industrial traffic, and a precipitation regime dominated by summer storms. This thesis examines factors and processes controlling road erosion and sediment delivery processes in the Simonette watershed, a 5400 km2 watershed that spans the foothills and boreal plains regions in west-central Alberta. An understanding of these processes was used to develop and evaluate road impact indicators and test them against physical measures of stream condition. This research thus provides baseline data on road erosion, sediment delivery, stream condition, and appropriate indicators of impact that may be used by future watershed assessors in prioritizing and remediating areas of problematic sediment contribution in west-central Alberta foothills watersheds. It was initially hypothesized that sedimentation, and infiltration rates would be strongly determined by mapped surficial geology on site, with significant differences between fine-textured (glaciolacustrine), sandy (glaciofluvial, aeolian), and mixed (morainal) sites. Higher-traffic roads were also expected to generate higher amounts of sediment than lower-traffic roads. The main hypothesis regarding sediment deposition was that the size and extent of road sediment discharge plumes was controlled by the ability of the ground to absorb the discharge generated in the road area. The relationship between contributing area of sediment plumes, and runout area would be related to different infiltration rates in the road and plume area, and precipitation intensity. Road sediment delivery impacts in streams were expected in stream features that promoted settlement of finer sediment, such as pools and areas of flow into the streambed.<br>
The strongest driver of erosion in the Simonette watershed was how efficient road segments were at producing runoff from rain events. There was some evidence that surficial geology and traffic influenced sedimentation rate: the highest producing site was a high-traffic road in silty morainal deposits, and the lowest-producing site was a well-drained, sandy, low-traffic road. Both sites were also on end members of a continuum of hydrological responses for the studied road segments: sites with better-drained soils produced less sediment than sites with poorly-drained soils. Overall, sedimentation rates from these Alberta study roads were moderate to high compared to studies of other dirt roads in North America. Potential connectivity of road segments was also driven by hydrology: strong geometric relationships existed between flow-generating areas in the road network, and flow-absorbing areas downslope of road drain points. The area of road sediment plumes was strongly correlated with the product of road-related contributing area and slope, and the length of road plumes was correlated with road-related contributing area. Road erosion and consequence models calibrated to the findings of the erosion and deposition studies in the Simonette watershed were tested for their effectiveness in predicting instream sedimentation pressure. Proportion of clay and silt in streambed gravel matrix was positively related to the number or density of upstream road crossings and with estimated sedimentation pressure from a hydrologically-based road model. Overall, road hydrology was found to be the single best predictor of sedimentation rate and delivery potential to streams. Stream impacts in the region were not well-correlated with the commonly-used metric of road density, but instead with road crossings. This study supports a growing body of literature that suggests that that the use of basic hydrological models is effective in predicting and assessing road sedimentation risk.</p>