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Hydraulics of runoff and loess loam deposition
Author(s) -
De Ploey J.
Publication year - 1984
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.3290090607
Subject(s) - loam , surface runoff , deposition (geology) , rill , hydrology (agriculture) , loess , froude number , geology , soil water , erosion , meltwater , soil science , environmental science , geotechnical engineering , geomorphology , sediment , snow , flow (mathematics) , mathematics , ecology , geometry , biology
On many more or less loamy soils, rill erosion is reported to start on slopes that are equal to or steeper than 2–3°; critical Froude numbers for the start of rill wash on these slopes vary between 2·0 and 3·0. This explains why colluvial deposition often occurs on slopes below 2–3°, when water spreads out at the downslope extremities of the rills. The critical hydraulic conditions for loess loam deposition were tested in the laboratory for slopes of 0·5° and 2°, applying unit‐discharges ( q ) up to 10 cm 2 /s. It appeared from these experiments that for afterflow, without raindrop impact, deposition starts for critical load concentrations ( c cr ) varying between several g/1 and about 60 g/l. Under rain c cr amounts to a minimum value of 100–125 g/l and it increases when the runoff film becomes thinner. Nevertheless, deposition in pluvial runoff is also possible, as was the case during the Weichselian, according to data from quarries in Belgium and in The Netherlands. A modified Kalinske equation is proposed for c cr prediction, with the introduction of a typical empirical coefficient C r and considering such factors as shear stress and mean particle size. Massive sedimentation may occur when it stops raining and afterflow starts, since c cr values are then much lower. It is shown from the Shields' diagram that loamy suspensions are more sensitive to sedimentation than sands in clear water.