Mike Tuke’s

TRANSPORT OF SEDIMENT

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Transportation of sediment Modes of transportation D Use a tennis ball to demonstrate traction, saltation and suspension. Modes of water transportation D or A P 5 min To illustrate traction, suspension, solution and flotation put a table spoon of poorly sorted sediment, a small twig and some salt crystals into a 1 litre plastic beaker and then add 200ml water. Stir rapidly using ruler but avoid touching the sediment. Students note different modes of transport and have to explain what has happened to the salt crystals.  Sometimes saltation is also visible. Use only a very little very fine material otherwise it clouds out the movement of the coarser grains. To use as a demonstration use a flat bottomed basin 30cm in diameter. Hjulstrom's diagram of erosion and deposition   Pa I 15 min Students plot data and try to explain why clay requires a higher velocity to erode than sand.  Minimum velocity for transportation  A P 3 min per sample Students use callipers or grain size card to measure median diameter of a variety of pebbles, grit, sand and silt. They then use Hjulstrom's chart to work out the minimum water velocity for the transportation of each. Falling grains 1 D or A P 20 min To show how the speed of fall varies between air and water and the shape, size and density of the grains use four 2 litre cylinders. Cylinder A is empty, cylinders B, C, and D are filled with water 1) Students drop a teaspoon of poorly sorted sediment into cylinder A and then into B. Students compare the speed of fall and note that in A they all the sediment arrives at the bottom at once whereas in cylinder B the largest arrive first.   2) Students drop a few grains of the same size of galena and of quartz at the same time into cylinder C. 3) Students drop a grain of quartz and a grain of mica of the same weight at the same time into cylinder D. Falling grains E P F 1 hour To measure the speed of fall of grains of different sizes, densities and shapes students drop steel or glass balls of varying sizes into a 150cm column of water and record the time it takes to fall. One can also use fimo discs to compare their fall with spheres of the same weight. Hydrodynamic lift  D or A I 5min This idea is to demonstrate the hydrodynamic “lift” acting on the grains resting on the river bed. First students blow over a piece of A4 paper as in diagram, the paper rises up. Then they blow over the top of a ping pong ball which should also rise up. This should be related to Bernoulli’s principle, aircraft lift, and water speed at the boundary layer. The ping pong balls are treaded onto thin wires on wooden blocks as in photo.   To demonstrate laminar and turbulent flow D or A I 5 min Students describe the pattern made by water falling in a thin stream from a tap into a kitchen sink without the plug in.  As a demonstration allow water to fall on a horizontal glass sheet over a sink.     Ocean currents D Fill a clear tank with water and place a block of ice made from water dyed blue on a shelf at one end and a lamp above the tank at the other end. As the ice melts a blue streak descends and spreads out over the bottom and a circular current will develop. The effect of shape on ease of transportation D or E P F 15min A 2m flat bottomed piece of guttering has 1cm pebbles glued to its inside bottom surface. A variety of shapes (cubes, spheres, ovals, discs, rollers and pyramids) made from fimo (see appendix) are put at the top end and a jug of water poured quickly into the guttering.      Factors controlling traction   TE Students are asked to imagine a pebble on the stream bed and to work out what factors determine whether it will roll or not  (size, shape, density, roughness of bottom, speed of water, viscosity of water, other grains hitting it). Which grains move  D Make a pile of very poorly sorted sediment with a crater in the middle on a large gently sloping tray with a hole with a hole in the lower end. Place it over a sink.  Fill the crater with water until it bursts. Students have to explain the distribution of grain sizes. Transport by wind  D or A P 10 min Take a piece of lining wallpaper 120cm by 50 cm. and make a channel by folding up 10cm on each of the long edges. Make a line across the channel every 5cm along its length and write on each line its distance from the end.  Place poorly sorted sand on the 5cm mark. Hold a hair drier on the 0 mark and turn it on.  Notice the distribution of the different grain sizes.  Do the same with sand and galena sand of the same size.  Do the same with a sand grain and a mica flake each weighting the same (0.1g). Transport by wind  E P F 15 min As above but with trays in a channel to catch the sediment so the measurements can be quantative.   Turbidity currents D To demonstrate a turbidity current pour milk into the end of a transparent tank full of water. Scree slopes    E P F 40 min Students drop pebbles onto a curved rough surface to see whether small or large pebbles travel furthest down slope.   Delta formation D Coloured water enters into the edge of a clear tray through a narrow mouth so that the pattern of water movement at the mouth of a delta can be seen both in plan and section. The water flowing in can be made lighter or heavier in density than the water in the tray by varying the temperature or salinity. The use of sediment laden water will show the pattern of sediment build up around the mouth.  Walther's Law and lateral accretion in deltas  A I F 15min Students are provided with several pieces of paper, each represents the deposits that form in one time interval. They stick these onto paper to show lateral accretion, diachronous beds and Walther's Law.  Rounding   D To show the effect of rounding by abrasion place an angular pebble and a slightly smaller well rounded pebble on the overhead projector or use larger samples to show directly to the students. Placing pebbles in order of roundness A P 5 min Students place pebbles with different degrees of roundness in order of increasing roundness. Rounding of grains   P 10 min Take 4 pieces of soft limestone, sketch one and then shake them in a plastic container or cardboard tube for 5 min. Remove and sketch one lump. This can be made more quantative by weighing before and after each shake of 1 minute's duration, ignoring the dust and small fragments. Plot the weight against number of shakes. Jurassic limestone is best. Alternatively use sugar cubes. Desert Sand E P F 15 min This activity demonstrates the greater degree of rounding achieved by wind transport than water transport. Take 8 pieces of soft limestone (not chalk) each about 25g. Divide the limestone into two groups of 4 each. Weigh each group. Put one group into a plastic container and the second into another but fill the latter with water. Shake both with equal intensity for five minutes.  Weigh each group after drying and note any changes in shape.  The group shaken in air will show some rounding, those in water will not. Pebble history A I 15 min for 5 samples Students are given a variety of pebbles which have been both broken and rounded, sometimes several times. They must work out the order of rounding and breaking.