The Hjulström curve, named after

Filip Hjulström Henning Filip Hjulström (6 October 1902 – 26 March 1982) was a Swedish geographer. Hjulström was professor of geography at Uppsala University from 1944, and in 1949, when the subject of geography was split, he became professor of Physical ...

(1902–1982), is a graph used by

hydrologists Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...

and geologists to determine whether a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...

will

erode Erode () is a city in the Indian state of Tamil Nadu. Erode is the seventh largest urban agglomeration in the state, after Chennai, Coimbatore, Madurai, Tiruchirapalli, Tiruppur and Salem. It is also the administrative headquarters of the ...

transport Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land ( rail and road), water, cable, pipelin ...

, or deposit sediment. It was originally published in his doctoral thesis "Studies of the morphological activity of rivers as illustrated by the River Fyris.Hjulstrom, F. (1935). Studies of the morphological activity of rivers as illustrated by the River Fyris, Bulletin. Geological Institute Upsalsa, 25, 221-527." in 1935. The graph takes sediment particle size and water velocity into account.Sediment transportation
Last accessed 26 Dec 2011. The upper curve shows the critical erosion velocity in cm/s as a function of particle size in mm, while the lower curve shows the deposition velocity as a function of particle size. Note that the axes are logarithmic. The plot shows several key concepts about the relationships between erosion, transportation, and deposition. For particle sizes where friction is the dominating force preventing erosion, the curves follow each other closely and the required velocity increases with particle size. However, for cohesive sediment, mostly

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...

but also

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...

, the ''erosion'' velocity increases with decreasing

grain size Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which ...

, as the cohesive forces are relatively more important when the particles get smaller. The critical velocity for deposition, on the other hand, depends on the settling velocity, and that decreases with decreasing grainsize. The Hjulström curve shows that sand particles of a size around 0.1 mm require the lowest stream velocity to erode. The curve was expanded by Åke Sundborg in 1956. He significantly improved the level of detail in the cohesive part of the diagram, and added lines for different modes of transportation.Hjulström's Diagram

Idaho State University , mottoeng = " The truth will set you free" , established = , former_names = Academy of Idaho(1901–1915)Idaho Technical Institute(1915–1927) University of Idaho—Southern Branch(1927–1947)Idaho Sta ...

. Last accessed 26 Dec 2011. The result is called the ''Sundborg diagram'', or the ''Hjulström-Sundborg Diagram'', in the academic literature. This curve dates back to early 20th century research on river geomorphology and has no more than a historical value nowadays, although its simplicity is still attractive. Among the drawbacks of this curve are that it does not take the water depth into account and more importantly, that it does not show that sedimentation is caused by flow velocity ''deceleration'' and erosion is caused by flow ''acceleration''. The dimensionless Shields Diagram, in combination with the Shields formula is now unanimously accepted for initiation of sediment motion in rivers. Much work was done on river sediment transport formulae in the second half of the 20th century and that work should be used preferably to Hjulström's curve.

References

Hydrology Geomorphology Curves Geography Geological techniques 1935 in science {{hydrology-stub

See also

References