INDETERMINACY IN AEOLIAN SEDIMENT TRANSPORT ACROSS BEACHES

Conventional models of aeolian transport relate sediment flux to shear velocity, among several other relevant factors such as grain size, gr ain density, and air density. Application of these predictive models t o natural systems has yielded mixed results. Analysis of data from fie ld experiments designed to provide simultaneous measurements of wind s peed and sediment flux across beaches underscores the limitations of t hese models, especially when surface conditions are variable over spac e and time. Accurate predictions of aeolian sediment flux may never be universally realized because conventional parameterizations of the pr oblem are indeterminate. Indeterminacy arises because the number of un knowns exceeds, by more than one, the number of available equations, a nd this analytical constraint is inextricably bound to empirical aspec ts of the problem. It is not immediately apparent what the relevant fu ndamental variables are, how they might be linked in a system of equat ions, nor how the inherent uncertainty in their specification, measure ment, and spatio-temporal character might be surmounted. In particular , it is becoming more evident that the indiscriminant use of shear vel ocity, as a surrogate for a spatially and temporally variable shear-st ress field, in sediment-transport equations is problematic and an over simplification of a complex process-response system. Accepting indeter minacy implies accepting uncertainty, and this suggests developing com plementary research strategies that explore and quantify natural-syste m variability.