As a Ph.D. student at the University of Washington, my research focuses on the erosion of unpaved forest roads in western Washington.
The erosion of high-traffic, near stream (HTNS) forest roads is a large source of sediment in nearby streams. The fine-grained sediment generated by and transported from forest roads can adversely affect water quality and aquatic resources in logging-adjacent watersheds. Because of this, a project has been designed to help efficiently and effectively mitigate this sediment generation and transport from HTNS road segments. The project design includes the collection of extensive field data in western Washington, as well as the development of a process-based model. This project is funded by the Washington Department of Natural Resources (WADNR) and is a collaborative effort among members of WADNR, Catchment Aquatic Ecology (CAE), Rayonier, the United States Forest Service (USFS), and the Watershed Dynamics Research Group at the University of Washington. The project consists of three main parts: the Major Experiment; the Parameterization Experiments; and the Modeling.
The Major Experiment is designed to measure annual sediment load and quantify how forest road best management practices (BMP) that are put in place affect that sediment load. We have 78 field sites, 39 of each in two lithologies. Each site consists of an 80 meter segment of road partitioned off by steel troughs and cross-drain culverts and is equipped with a sediment tub, a tipping bucket, and a suspended solids tank. Four pilot sites were installed in November 2018, and data collection at those sites is ongoing. The remaining 72 were installed in Summer 2019. Data collection and site maintenance is ongoing.
The Parameterization Experiments are designed to help answer six critical questions posed in our study design that are not necessarily answerable by the Major Experiment alone. Additionally, some of these experiments are being used to parameterize the model. We have six Parameterization Experiments planned: Ditch Line Hydraulics; Sediment Trap Efficiency; Road Micro-Topography Evolution; Short-Time-Scale Interactions; Cost Versus Maintenance Survey; and GRAIP/WARSEM Delivery Analyses. The Road Micro-Topography Evolution experiment is underway, and the Short-Time-Scale Interactions experiment will begin in January 2021.
The Modeling component of this project is designed to create a model to accurately represent the sediment yield from HTNS roads, as well as the effects that select BMP have on that sediment yield.
We are currently developing a spatially-lumped model in Python that focuses on three main traffic-induced sediment production processes, as well as a component that focuses on sediment transport away from the road prism. Spatially lumping the model and focusing on four main processes simplifies model parameters and helps get at the question of what’s actually happening on these roads.
Future iterations of the model will be ported into Landlab, a Python-based Earth surface processes modeling toolkit. The model in Landlab will be spatially distributed and will allow for more processes to be modeled on a finer scale.