Lane, S.N. (1997)

The reconstruction of bed material yield and supply histories in gravel-bed streams

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This paper details a basic method for estimation of both bed material yield and supply rates for a glaciated catchment. Recent research has illustrated the potential of morphological methods for the estimation of bed material transport rates, but also raised important methodological issues, notably regarding the requisite spatio-temporal resolution of morphological data and the need for either information on upstream sediment supply or assumptions about typical distances of particle movement during transport. Both of the latter have proved problematic. This paper provides an additional means of estimating bed material transport rates and yields through the combination of a simple process-based relationship with morphological information. For a short reach of gravel-bed stream, in a glaciated catchment with a characteristic diurnal discharge hydrograph, a strong positive relationship was found between the volume of water passing through the reach and the volume of erosion in the reach, for points early on the rising limb of the hydrograph. This relationship broke down later in the hydrograph, notably after the discharge peak, associated with the advent of sediment supply from upstream. Thus, early in the hydrograph, this relationship provides an indication of the capacity of this reach to move sediment, either locally eroded material or sediment supplied from upstream, and this paper applies this relationship to a six week discharge hydrograph to predict the potential transport volumes. From these predictions, it calculates the minimum volume of bed material that must have been supplied to the reach from upstream, per hour, to maintain its observed elevation. The results are used to illustrate and discuss some of the problems associated with the use of morphological information for the estimation of bed material transfer rates.