Detachment and transportation of loose sediments by raindrop splash. Part I. The calculation of absolute data on detachability and tranportability

Laboratory experiments on sediments ejected by splash consisted of two parts: quantities ejected and mean projected distances were measured. Since the splash tray was 100 cm long and 20 cm wide, and since both measurements were made on a receiving screen of one square metre, it was obvious that only part of the translocated sediment was caught. It was subject to serious doubt that the measured distances were representative for all sediment translocated. If it is stated that the ejected sediment is distributed according to an exponential function, around any point of impact located on the tray, and if by definition tray and rainfall are perfectly homogeneous, the ratio of the true to the measured distance, and the ratio of the caught to the translocated sediment, are only a function of the exponent of the "real" function. The apparent distance, being also a function of this exponent, is thus the only factor needed to solve the two questions. Hence, all empirical data were transformed into true data. © 1981.status: publishe

Detachment and transportation of loose sediments by raindrop splash. Part II. Detachability and transportability measurements

Laboratory experiments with simulated rainfall and using a recently developed weighing technique were conducted in order to obtain information on the detachability and transportability of 9 loose sediments as a time-dependent phenomenon. The effect of three different initial states on these two erodibility parameters was also studied. During a rain erosion experiment, detachability was significantly influenced by surface water content changes while transportability was not. Both erodibility parameters decreased as soon as a surface water film developed. After transforming the measurements into absolute data, using the nomogram developed in part I, the effect of grain size on detachment and transportation was studied. The relation between resistance to detachment by raindrop impact and grain size was very similar to the relation between resistance to detachment by turbulent runoff or wind and grain size. The lowest resistance was found for a fine sandy sediment. Transportability was negatively related to grain size, and this relation could be represented by a power function. For the same range of sediments detachability variations were more important than variations in transportability. For the coarse sediments, transportation by raindrop impact was a selective process. Finally, the data obtained in this and other studies were combined in order to make a rough estimate of the net downslope splash erosion unit discharge on a bare slope. © 1981.status: publishe

Splash and discontinuous runoff as creators of fine sandy lag deposits with Kalahari sands

Earlier field experiments have shown that the sandy dome-shaped hills south of Kinshasa are denuded by the combined action of splash and discontinous runoff. The sandy cover of a typical hill becomes progressively finer downhill where the slope is steeper. Laboratory experiments on similar sands demonstrate that splash has a preference for the coarse modal fraction. Simulated disturbed rough laminar runoff exports slightly coarser sands than does splash, even over gentle slopes where the regime is subcritical. But splash leaves the grains over 0.6 mm while discontinuous run-off selects even these for rapid transportation. Study of the transportation rates of both mechanisms conclusively demonstrates that splash creates a coarse lag on the summital sections of the Amba hill but that discontinuous runoff leaves a progressively finer residue, which is being transported, as the slope becomes steeper. Silt is also protected from erosion but it is not known to what extent the creation of a filtration pavement is responsible for this. The critical grain-size limit, below which the relative concentration increased, is 0.215 mm, both in the field and in the laboratory. This critical limit is some-what finer than the median grain-size of the Kalahari sands covering the hilltops and also of the fabricated bimodal sands. © 1977.status: publishe

Manipulating the data: Teaching and NAPLAN in the control society

High-stakes testing is changing what it means to be a ‘good teacher’ in the contemporary school. This paper uses Deleuze and Guattari’s ideas on the control society and dividuation in the context of NAPLAN testing in Australia to suggest that the database generates new understandings of the ‘good teacher’. Media reports are used to look at how teachers are responding to the high-stakes database through manipulating the data. This paper argues that manipulating the data is a regrettable, but logical, response to manifestations of teaching where only the data counts