Nienow, P. W. and Sharp, M. and Willis, I. C. (1996)
Sampling-rate effects on the properties of dye breakthrough curves from glaciers
- Cite key
- Journal of Glaciology
- Dye-tracer techniques are widely used to infer the character of subglacial drainage systems. Quantitative analysis of dye breakthrough curves focuses on the determination of the water throughflow velocity (u), the dispersion coefficient (D) and the dispersivity parameter (d = D/u). Together, these parameters describe the rate of passage of tracer through the drainage system and the extent of which the dye could becomes spread out during passage. They have been used to infer the nature of flow conditions within a drainage system and temporal changes in system morphology. Estimates of all three parameters, however, are dependent upon the sampling interval at which measurements of the dye concentration used to define breakthrough curves are made. For a given breakthrough curve, the dispersion coefficient increases with the sampling interval, while the throughflow velocity shows no systematic variation. As a result, the dispersivity also tends to increase with the sampling interval. Investigations of the sensitivity of parameter estimates to the sampling interval reveal that reliable estimates can be obtained only if the sampling interval is less that 1/16 of the time from dye injection to peak dye concentration. As a general guide, we suggest that, ideally, quantitative anlyses of dye breakthrough curves should therefore be conducted only when this criterion can be met.