Relations between dune morphology, air flow, and sediment flux on reversing dunes, Silver Peak, Nevada

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ABSTRACT

Relations between wind speed, sediment flux and dune morphology were measured for two reversing dunes situated in the south-western part of the Silver Peak dunefield in Clayton Valley, west-central Nevada. The larger dune was 120 m in length with a height of 12.5 m and the smaller dune 80 m long and 6 m high. Both dunes were sharp crested, aligned approximately E-W perpendicular to the dominant wind direction, and had slightly concave stoss profiles. Twenty-seven rotating cup anemometers were placed (0.3 m elevation) along N-S transects on each of the dunes. At each anemometer site a passive wedge-shaped sediment trap was used to measure sediment flux. Amplification of wind speed was observed towards the crest on the stoss side of both dunes with speed-up factors (ucrest/Ubase) ranging from 1·50–3·19, with a corresponding increase in sediment flux by 1–2 orders of magnitude. In general, the ratio of crest flux to base flux (qc/qt,) increased with increasing incident basal wind speed on both dunes. Direct measurements of the stoss slope variation in sediment flux relative to the dune crest are in good agreement with Owen's transport model. Friction speed (u) was approximated from near surface (0·3 m) point wind speed. Although not all assumptions of the Owen model are upheld, the modified model performance is sufficiently robust to predict short-term variation in stoss sediment flux on the study dunes.

Improved models that adequately account for variation in sediment flux under changing air flow and transport conditions are necessary for the prediction of longterm evolution of dunes. In this regard, further progress in model development will require increased understanding of the spatial and temporal variability of airflow and the short term response of sediment flux to these flow conditions.

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