Reducing Uncertainties in Snow Fence Design: Development of Methods for Estimation of Snow Drifting and the Snow Relocation Coefficient - TR760

(2020) Reducing Uncertainties in Snow Fence Design: Development of Methods for Estimation of Snow Drifting and the Snow Relocation Coefficient - TR760. Transportation, Department of

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Abstract

Blowing and drifting of snow is a major concern for transportation safety and road maintenance. Mitigation of snow drift on roadways is often achieved by installing temporary or permanent snow fences along the road segments affected by snow drift. Robust design of snow fences is critical for road safety and for maintaining clear and open roads during the winter season in the US Midwest, as well as for other states affected by large snow events. Reducing accumulation of snow on roadways also decreases the need for associated repairs due to damage caused to roads. The design of snow fences relies on empirical relations that do not necessarily apply to the U S Midwest. Majors changes are related to the accurate estimation of the snow relocation coefficient (SRC), a critical parameter for sizing snow fences and determining the required easement for snow storage. Currently, IDOT snow fence designers use a default value of SRC despite conditions vary widely across the state and from where SRC has been determined empirically. Estimation of SRC requires quantification of the snowfall and snowdrift fluxes at sites where snow fences are installed. The lack of available, reliable data to estimate the local value of SRC results in an inefficient and possibly inadequate design of the snow fence. The research described in this report addresses two critical questions related to snow fence design: 1) What is the seasonal snow relocation coefficient for Iowa? and, 2) What is the seasonal storage capacity of snow fences when accounting for successive storms and ablation between snow events? Estimation of the SRC in the field is a challenging problem as it requires accurate quantification of snowfall and snowdrift fluxes at the site where the snow fence is installed. Therefore, we first developed methods for accurate estimation of snowfall and snow drifting fluxes, building on prior research efforts. The methods include monitoring techniques designed to continuously acquire data without supervision as well as detailed field collection efforts, typically after major snowstorm events. A range of intrusive monitoring methods (i.e., direct snow depth measurements, topographic surveys of snow deposit profiles, and snow density measurements) and non-intrusive methods were used for quantification of meteorological conditions at snow fence installations and tracking changes in snow deposits during and between snowstorm events. The results of the study conducted at three snow fence sites suggest that the SRC estimates are significantly lower than the default value of 0.5, currently used for snow fence design. The study also found that additional storage capacity is available during the winter season due to ablation, comprised of compaction, sublimation or evaporation, and melting between storm events. The outcomes of the two-year project confirmed the reliability of the developed monitoring methods as well as the consistency of the results for the three experimental sites investigated during the study.