Understanding the risk of unpaved roads on drinking water treatability by assessing sediment erosion across Canada
Creators: Hall, Jennifer
Publisher: name: University of Alberta Library
Year: 2023

<p>Forest harvesting, wildfire suppression, energy resource exploration, and recreation all require<br>
unpaved roads. As a result, many roads in drinking watersheds are potential sources of fine (&lt;63<br>
µm) sediment. Erosion of fine sediment threatens drinking water treatability as can be a source<br>
of increased nutrients and sediment, creating issues in reservoirs and treatment infrastructure.<br>
However, there is a lack of research regarding sediment yields and erosion models on unpaved<br>
roads in Canada. The objectives of this study were 1) to understand the variability and<br>
predominant factors that contribute to increased road erosion risk in Canadian drinking<br>
watersheds, 2) evaluate the Forest and Range Evaluation Program (FREP) used to categorize<br>
risk, 3) evaluate erosion and runoff dynamics from representative unpaved roads and trails within<br>
the Ghost and Elbow River Watershed, near Calgary, Alberta, and 4) to validate the runoff and<br>
sediment production predictions of the Road Erosion and Delivery Index (READI) model using<br>
UAV data and rainfall simulations on the representative road segments.<br>
The first two objectives were addressed in chapter 2 with 107 site surveys and 22 small-plot<br>
(1.5m 2 ) rainfall simulations. Unpaved road erosion risk was influenced by road surface<br>
conditions, road slope, and traffic. Furthermore, traffic and poor road surface conditions<br>
increased fine sediment yields. Risk was found to be highest in the Montane Cordillera which<br>
had poor road surfacing conditions, steep slopes, and high traffic. Rainfall simulations and the<br>
FREP model could not be directly compared because of sediment yield units, but when plot<br>
sediment yields were ranked from lest to highest sediment there was a positive linear<br>
relationship.<br>
The final 2 objectives were addressed in chapter 3 with 6 site surveys, 6 large (60-150m 2 ) and<br>
small rainfall (1.5m 2 ) simulations, and 5 UAV flights. Site surveys gave insight to road</p>

<p>3<br>
construction, road sweep samples provided details on available sediment, runoff and erosion<br>
rates were assessed from the rainfall simulations, and UAV flights produced digital surface<br>
models that gave an understanding to road roughness. Rainfall simulations showed that large and<br>
small plots preferentially (&gt;70%) eroded fine particles. The rainfall simulations erosion rates<br>
followed three patterns: a steady-state of erosion, an increasing rate of erosion, and a decreasing<br>
rate of erosion. Similarly, runoff followed three patterns; a gradual increase to a steady state,<br>
increase with no steady state, and a steady state throughout the simulation. Runoff started at<br>
different time intervals based on scale; large-scale experiments started between 8-16 minutes and<br>
small simulations started between 2-4 minutes. Lastly, the READI model did not accurately<br>
predict time-to-concentrations or sediment yields compared to rainfall simulations, expect when<br>
site specific roughness values from digital surface models and erosivity (K) values were applied.<br>
The assessment of road erosion is valuable for understanding the impacts of road management<br>
practices on water quality. In Canada, sediment yields predominantly consists of particles ≤ 63<br>
µm which poses a larger threat to drinking water treatability. Results showed fine sediment<br>
yields are related to traffic volume and road surface conditions. The Forest and Range Evaluation<br>
Program (FREP) and Road Erosion and Drainage Index (READI) models are tools to understand<br>
road erosion risk. These models assist in assessing sediment yields, providing useful insights for<br>
road managers. The appropriate method depends on the objectives and the available information<br>
to effectively address road erosion challenges.</p>