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Some Slope and Water Relations Affecting the Movement of Soil Particles
Author(s) -
Lutz J. F.,
Hargrove B. D.
Publication year - 1944
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1944.036159950008000c0022x
Subject(s) - agricultural experiment station , agriculture , library science , south carolina , geography , hydrology (agriculture) , political science , archaeology , engineering , public administration , computer science , geotechnical engineering
D the past 10 years considerable information has been accumulated on runoff and soil losses under various field conditions and many of the factors .affecting runoff and erosion have been studied. One factor of considerable importance is the slope of the land. It is generally true that, other conditions being •equal, runoff increases logarithmically with increases in slope, the greatest increases being on slopes below 2 or 3%. Erosion increases rapidly with increases in .slope, but the nature of the increase varies widely even when other conditions are apparently constant. For •example, Duley and Hays (7) found that erosion increased with slope up to i%, decreased between i and 3%, and then increased again: In many of the •data reported by Diseker and Yoder (6) greater soil losses occurred on lesser slopes. Copley, et al. ('4) in .studying row grades on tobacco soils found that less soil was carried on a grade of 18 inches per 100 feet •of row than on the 12or 24-inch grades. Obviously, slope affects water velocity and velocity .affects the size of particle which can be carried. Thus, soil texture would be an important factor determining the amount of erosion on any given slope and soil conservation practices should be based on more definite information about the specific effects of slope on •water velocity and the effects of water velocity on losses from soils of various textures. A number of investigators have stated rather definite relations between water velocity and size of parti•cles carried. Among the earlier work is that of Leslie (10) in 1823, of Hopkins (9) in 1844, and of Airy .and Law in 1885, cited by Gilbert (8), all of whom deduced the law that, "The moving force of a current, •estimated by the volume or weight of the masses of .any proposed form which it is capable of moving varies as the sixth power of the velocity." Deacon (5) in 1883 and Bennett (3) concluded that the moving force varied as the fifth power of velocity. These relations refer only to the size of particle and not .to the total amount of material moved. . Ayres (i) calculated that the velocity of flowing water is doubled by increasing the slope four times :and both he and Bennett agree that doubling the •velocity increases by 32 times the amount of material •of a given size that can be carried. Pirsson and Schu•chert (n), Dubuat, cited by Bennett (3, page 116), .•and Baver (2) gave figures on the water velocity •necessary to move particles of given sizes. However, in all of these the specific size of particle, the slope, depth of water or nature of surface was not given. Probably the most comprehensive study designed to measure debris movement was made by Gilbert (8) who took into account width and velocity of stream, size and density of particles, and slope. However, the minimum depth of water used was o.i foot which cannot be interpreted in terms of the forces active in initiating the movement of an individual soil particle in the erosion process. It was the purpose of this investigation to determine more definitely the 'effect of slope on water velocity and the effect of water velocity on the size of soil particles carried using shallow flow simulating sheet erosion conditions. As the work progressed it became quite evident that depth of water is equally as important as velocity.