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Drifting & Wind Blown Sand Managing Risk to Infrastructure Projects By: J. Wayne Boulton (M.Sc.), Senior Consultant, Principal (wayne.boulton@rwdi.com) Duncan Phillips (Ph.D., P.Eng.), Senior Consultant, Principal (duncan.phillips@rwdi.com)

Drifting and blowing sand is a natural phenomenon that occurs throughout the world’s deserts. Wind driven sand is in constant flux as it adapts to achieve an equilibrium state with the wind. Because of this constant state of change, blowing and drifting sand poses a significant risk to infrastructure and transportation projects.

In the rail industry, drifting and blowing sand poses numerous risks, including: •

drifting dunes and route blockages;

ballast contamination; and,

fouling of electrical systems and jamming of switch / gear boxes.

RWDI has a long history of assessing and mitigating snow drifting issues for the architectural, master planning, and building science communities. Coupled with our experience assessing and mitigating wind-blown dust from waste and material stockpiles for industrial facilities, RWDI is in a unique position to assess blowing and drifting sand.

Analysing wind blown sand and generating mitigation strategies requires a multi-faceted approach that includes meteorology, the physics of sand entrainment and transport, sand dune dynamics, computational fluid dynamics (CFD), and wind engineering.

RWDI has assembled a multi-disciplinary team to assess the risk of wind blown sand at local and regional levels.

Sand transporting wind map of the UAE

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Drifting & Wind Blown Sand Techniques Employed by RWDI RWDI's approach is to use a science based methodology to assess sand migration. While a comprehensive review covering all the technical activities below can achieve a better solution, screening analyses in any of the disciplines can help to understand the phenomena and lead to some mitigation options. Field Surveys & Consultation

Risk Maps / Indices and Mitigation Options

On-site assessments are carried out by RWDI’s wind / geomorphology experts to determine local conditions and influencing factors, collect surface sand samples for geomorphic analysis, and explore potential mitigation options.

Results are superimposed onto maps and transport corridors to develop more site-specific hazard maps. Local surface conditions, sand dune typology, elevation changes, etc. are also taken into account.

Geomorphic Analyses

CFD models are used to assess mitigation options at the track level, such as: porous fences; Sand samples are analysed for grain size cross-sectional shape; surface armoring; etc. distribution as well as particle and bulk density. CFD models can also be used to assess These data are used to assess sand transport and changes to local wind flow patterns as a result of deposition rates. larger scale cut and fill applications. Wind Tunnel Testing Specialized wind tunnel facilities are used to quantify the minimum wind speed required to initiate particle entrainment and sand flux (rate of sand movement) for a given material. Meteorological Modelling CFD Simulation results of wind over a railway track bed mitigation strategy

A severe challenge in assessing blowing sand risks is the lack of robust and accurate meteorological data sets. These data need to have high spatial resolution and cover a sufficient length of record. These data sets are even more rare in remote, desert areas. RWDI uses state of the art meteorological modelling techniques to generate 3-D wind fields over data sparse regions. Model outputs are used to develop climate models and wind statistics, including the frequency and magnitude of high wind events. Coupled with wind tunnel results this information can be used to estimate the frequency and magnitude of sand that becomes airborne and net sand drift patterns.

Sand migration risk map

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Resources

Results w w w .r w di .com


Drifting and Wind Blown Sand